Special Report: Special Report on the Ocean and Cryosphere in a Changing Climate
Ch 01

Framing and Context of the Report

1.5 Risk and Impacts Related to Ocean and Cryosphere Change
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1.6.1 Mitigation and Adaptation Options in the Ocean and Cryosphere
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1.7 Governance and Institutions
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1.8.1.4 Palaeoclimate Data
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1.8.2 Indigenous Knowledge and Local Knowledge
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1.10 Integrated Storyline of this Special Report
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1.10 Integrated Storyline of this Special Report
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Executive Summary

This special report assesses new knowledge since the IPCC 5th Assessment Report (AR5) and the Special Report on Global Warming of 1.5°C (SR15) on how the ocean and cryosphere have and are expected to change with ongoing global warming, the risks and opportunities these changes bring to ecosystems and people, and mitigation, adaptation and governance options for reducing future risks. Chapter 1 provides context on the importance of the ocean and cryosphere, and the framework for the assessments in subsequent chapters of the report.

All people on Earth depend directly or indirectly on the ocean and cryosphere. The fundamental roles of the ocean and cryosphere in the Earth system include the uptake and redistribution of anthropogenic carbon dioxide and heat by the ocean, as well as their crucial involvement of in the hydrological cycle. The cryosphere also amplifies climate changes through snow, ice and permafrost feedbacks. Services provided to people by the ocean and/or cryosphere include food and freshwater, renewable energy, health and wellbeing, cultural values, trade and transport. {1.1, 1.2, 1.5}

Sustainable development is at risk from emerging and intensifying ocean and cryosphere changes. Ocean and cryosphere changes interact with each of the United Nations Sustainable Development Goals (SDGs). Progress on climate action (SDG 13) would reduce risks to aspects of sustainable development that are fundamentally linked to the ocean and cryosphere and the services they provide (high confidence1). Progress on achieving the SDGs can contribute to reducing the exposure or vulnerabilities of people and communities to the risks of ocean and cryosphere change (medium confidence). {1.1}

Communities living in close connection with polar, mountain, and coastal environments are particularly exposed to the current and future hazards of ocean and cryosphere change. Coasts are home to approximately 28% of the global population, including around 11% living on land less than 10 m above sea level. Almost 10% of the global population lives in the Arctic or high mountain regions. People in these regions face the greatest exposure to ocean and cryosphere change, and poor and marginalised people here are particularly vulnerable to climate-related hazards and risks (very high confidence). The adaptive capacity of people, communities and nations is shaped by social, political, cultural, economic, technological, institutional, geographical and demographic factors. {1.1, 1.5, 1.6, Cross-Chapter Box 2 in Chapter 1}

Ocean and cryosphere changes are pervasive and observed from high mountains, to the polar regions, to coasts, and into the deep ocean. AR5 assessed that the ocean is warming (0 to 700 m: virtually certain; 700 to 2,000 m: likely), sea level is rising (high confidence), and ocean acidity is increasing (high confidence). Most glaciers are shrinking (high confidence), the Greenland and Antarctic ice sheets are losing mass (high confidence), sea ice extent in the Arctic is decreasing (very high confidence), Northern Hemisphere snow cover is decreasing (very high confidence), and permafrost temperatures are increasing (high confidence). Improvements since AR5 in observation systems, techniques, reconstructions and model developments, have advanced scientific characterisation and understanding of ocean and cryosphere change, including in previously identified areas of concern such as ice sheets and Atlantic Meridional Overturning Circulation (AMOC). {1.1, 1.4, 1.8.1}

Evidence and understanding of the human causes of climate warming, and of associated ocean and cryosphere changes, has increased over the past 30 years of IPCC assessments (very high confidence). Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels (SR15). Areas of concern in earlier IPCC reports, such as the expected acceleration of sea level rise, are now observed (high confidence). Evidence for expected slow-down of AMOC is emerging in sustained observations and from long-term palaeoclimate reconstructions (medium confidence), and may be related with anthropogenic forcing according to model simulations, although this remains to be properly attributed. Significant sea level rise contributions from Antarctic ice sheet mass loss (very high confidence), which earlier reports did not expect to manifest this century, are already being observed. {1.1, 1.4}

Ocean and cryosphere changes and risks by the end-of-century (2081-2100) will be larger under high greenhouse gas emission scenarios, compared with low emission scenarios (very high confidence). Projections and assessments of future climate, ocean and cryosphere changes in the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) are commonly based on coordinated climate model experiments from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced with Representative Concentration Pathways (RCPs) of future radiative forcing. Current emissions continue to grow at a rate consistent with a high emission future without effective climate change mitigation policies (referred to as RCP8.5). The SROCC assessment contrasts this high greenhouse gas emission future with a low greenhouse gas emission, high mitigation future (referred to as RCP2.6) that gives a two in three chance of limiting warming by the end of the century to less than 2oC above pre-industrial. {Cross-Chapter Box 1 in Chapter 1} 

Characteristics of ocean and cryosphere change include thresholds of abrupt change, long-term changes that cannot be avoided, and irreversibility (high confidence). Ocean warming, acidification and deoxygenation, ice sheet and glacier mass loss, and permafrost degradation are expected to be irreversible on time scales relevant to human societies and ecosystems. Long response times of decades to millennia mean that the ocean and cryosphere are committed to long-term change even after atmospheric greenhouse gas concentrations and radiative forcing stabilise (high confidence). Ice-melt or the thawing of permafrost involve thresholds (state changes) that allow for abrupt, nonlinear responses to ongoing climate warming (high confidence). These characteristics of ocean and cryosphere change pose risks and challenges to adaptation {1.1, Box 1.1, 1.3}.

Societies will be exposed, and challenged to adapt, to changes in the ocean and cryosphere even if current and future efforts to reduce greenhouse gas emissions keep global warming well below 2°C (very high confidence). Ocean and cryosphere-related mitigation and adaptation measures include options that address the causes of climate change, support biological and ecological adaptation, or enhance societal adaptation. Most ocean-based local mitigation and adaptation measures have limited effectiveness to mitigate climate change and reduce its consequences at the global scale, but are useful to implement because they address local risks, often have co-benefits such as biodiversity conservation, and have few adverse side effects. Effective mitigation at a global scale will reduce the need and cost of adaptation, and reduce the risks of surpassing limits to adaptation. Ocean-based carbon dioxide removal at the global scale has potentially large negative ecosystem consequences. {1.6.1, 1.6.2, Cross-Chapter Box 2 in Chapter 1}

The scale and cross-boundary dimensions of changes in the ocean and cryosphere challenge the ability of communities, cultures and nations to respond effectively within existing governance frameworks (high confidence). Profound economic and institutional transformations are needed if climate-resilient development is to be achieved (high confidence). Changes in the ocean and cryosphere, the ecosystem services that they provide, the drivers of those changes, and the risks to marine, coastal, polar and mountain ecosystems, occur on spatial and temporal scales that may not align within existing governance structures and practices (medium confidence). This report highlights the requirements for transformative governance, international and transboundary cooperation, and greater empowerment of local communities in the governance of the ocean, coasts, and cryosphere in a changing climate. {1.5, 1.7, Cross-Chapter Box 2 in Chapter 1, Cross-Chapter Box 3 in Chapter 1}

Robust assessments of ocean and cryosphere change, and the development of context-specific governance and response options, depend on utilising and strengthening all available knowledge systems (high confidence). Scientific knowledge from observations, models and syntheses provides global to local scale understandings of climate change (very high confidence). Indigenous knowledge (IK) and local knowledge (LK) provide context-specific and socio-culturally relevant understandings for effective responses and policies (medium confidence). Education and climate literacy enable climate action and adaptation (high confidence). {1.8, Cross-Chapter Box 4 in Chapter 1} Long-term sustained observations and continued modelling are critical for detecting, understanding and predicting ocean and cryosphere change, providing the knowledge to inform risk assessments and adaptation planning (high confidence). Knowledge gaps exist in scientific knowledge for important regions, parameters and processes of ocean and cryosphere change, including for physically plausible, high impact changes like high end sea level rise scenarios that would be costly if realised without effective adaptation planning and even then may exceed limits to

This special report assesses new knowledge since the IPCC 5th Assessment Report (AR5) and the Special Report on Global Warming of 1.5°C (SR15) on how the ocean and cryosphere have and are expected to change with ongoing global warming, the risks and opportunities these changes bring to ecosystems and people, and mitigation, adaptation and governance options for reducing future risks. Chapter 1 provides context on the importance of the ocean and cryosphere, and the framework for the assessments in subsequent chapters of the report.

All people on Earth depend directly or indirectly on the ocean and cryosphere. The fundamental roles of the ocean and cryosphere in the Earth system include the uptake and redistribution of anthropogenic carbon dioxide and heat by the ocean, as well as their crucial involvement of in the hydrological cycle. The cryosphere also amplifies climate changes through snow, ice and permafrost feedbacks. Services provided to people by the ocean and/or cryosphere include food and freshwater, renewable energy, health and wellbeing, cultural values, trade and transport. {1.1, 1.2, 1.5}

Sustainable development is at risk from emerging and intensifying ocean and cryosphere changes. Ocean and cryosphere changes interact with each of the United Nations Sustainable Development Goals (SDGs). Progress on climate action (SDG 13) would reduce risks to aspects of sustainable development that are fundamentally linked to the ocean and cryosphere and the services they provide (high confidence). Progress on achieving the SDGs can contribute to reducing the exposure or vulnerabilities of people and communities to the risks of ocean and cryosphere change (medium confidence). {1.1}

Communities living in close connection with polar, mountain, and coastal environments are particularly exposed to the current and future hazards of ocean and cryosphere change. Coasts are home to approximately 28% of the global population, including around 11% living on land less than 10 m above sea level. Almost 10% of the global population lives in the Arctic or high mountain regions. People in these regions face the greatest exposure to ocean and cryosphere change, and poor and marginalised people here are particularly vulnerable to climate-related hazards and risks (very high confidence). The adaptive capacity of people, communities and nations is shaped by social, political, cultural, economic, technological, institutional, geographical and demographic factors. {1.1, 1.5, 1.6, Cross-Chapter Box 2 in Chapter 1}

Ocean and cryosphere changes are pervasive and observed from high mountains, to the polar regions, to coasts, and into the deep ocean. AR5 assessed that the ocean is warming (0 to 700 m: virtually certain; 700 to 2,000 m: likely), sea level is rising (high confidence), and ocean acidity is increasing (high confidence). Most glaciers are shrinking (high confidence), the Greenland and Antarctic ice sheets are losing mass (high confidence), sea ice extent in the Arctic is decreasing (very high confidence), Northern Hemisphere snow cover is decreasing (very high confidence), and permafrost temperatures are increasing (high confidence). Improvements since AR5 in observation systems, techniques, reconstructions and model developments, have advanced scientific characterisation and understanding of ocean and cryosphere change, including in previously identified areas of concern such as ice sheets and Atlantic Meridional Overturning Circulation (AMOC). {1.1, 1.4, 1.8.1}

Evidence and understanding of the human causes of climate warming, and of associated ocean and cryosphere changes, has increased over the past 30 years of IPCC assessments (very high confidence). Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels (SR15). Areas of concern in earlier IPCC reports, such as the expected acceleration of sea level rise, are now observed (high confidence). Evidence for expected slow-down of AMOC is emerging in sustained observations and from long-term palaeoclimate reconstructions (medium confidence), and may be related with anthropogenic forcing according to model simulations, although this remains to be properly attributed. Significant sea level rise contributions from Antarctic ice sheet mass loss (very high confidence), which earlier reports did not expect to manifest this century, are already being observed. {1.1, 1.4}

Ocean and cryosphere changes and risks by the end-of-century (2081-2100) will be larger under high greenhouse gas emission scenarios, compared with low emission scenarios (very high confidence). Projections and assessments of future climate, ocean and cryosphere changes in the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) are commonly based on coordinated climate model experiments from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced with Representative Concentration Pathways (RCPs) of future radiative forcing. Current emissions continue to grow at a rate consistent with a high emission future without effective climate change mitigation policies (referred to as RCP8.5). The SROCC assessment contrasts this high greenhouse gas emission future with a low greenhouse gas emission, high mitigation future (referred to as RCP2.6) that gives a two in three chance of limiting warming by the end of the century to less than 2oC above pre-industrial. {Cross-Chapter Box 1 in Chapter 1} 

Characteristics of ocean and cryosphere change include thresholds of abrupt change, long-term changes that cannot be avoided, and irreversibility (high confidence). Ocean warming, acidification and deoxygenation, ice sheet and glacier mass loss, and permafrost degradation are expected to be irreversible on time scales relevant to human societies and ecosystems. Long response times of decades to millennia mean that the ocean

This special report assesses new knowledge since the IPCC 5th Assessment Report (AR5) and the Special Report on Global Warming of 1.5°C (SR15) on how the ocean and cryosphere have and are expected to change with ongoing global warming, the risks and opportunities these changes bring to ecosystems and people, and mitigation, adaptation and governance options for reducing future risks. Chapter 1 provides context on the importance of the ocean and cryosphere, and the framework for the assessments in subsequent chapters of the report.

All people on Earth depend directly or indirectly on the ocean and cryosphere. The fundamental roles of the ocean and cryosphere in the Earth system include the uptake and redistribution of anthropogenic carbon dioxide and heat by the ocean, as well as their crucial involvement of in the hydrological cycle. The cryosphere also amplifies climate changes through snow, ice and permafrost feedbacks. Services provided to people by the ocean and/or cryosphere include food and freshwater, renewable energy, health and wellbeing, cultural values, trade and transport. {1.1, 1.2, 1.5}

Sustainable development is at risk from emerging and intensifying ocean and cryosphere changes. Ocean and cryosphere changes interact with each of the United Nations Sustainable Development Goals (SDGs). Progress on climate action (SDG 13) would reduce risks to aspects of sustainable development that are fundamentally linked to the ocean and cryosphere and the services they provide (high confidence). Progress on achieving the SDGs can contribute to reducing the exposure or vulnerabilities of people and communities to the risks of ocean and cryosphere change (medium confidence). {1.1}

Communities living in close connection with polar, mountain, and coastal environments are particularly exposed to the current and future hazards of ocean and cryosphere change. Coasts are home to approximately 28% of the global population, including around 11% living on land less than 10 m above sea level. Almost 10% of the global population lives in the Arctic or high mountain regions. People in these regions face the greatest exposure to ocean and cryosphere change, and poor and marginalised people here are particularly vulnerable to climate-related hazards and risks (very high confidence). The adaptive capacity of people, communities and nations is shaped by social, political, cultural, economic, technological, institutional, geographical and demographic factors. {1.1, 1.5, 1.6, Cross-Chapter Box 2 in Chapter 1}

Ocean and cryosphere changes are pervasive and observed from high mountains, to the polar regions, to coasts, and into the deep ocean. AR5 assessed that the ocean is warming (0 to 700 m: virtually certain2; 700 to 2,000 m: likely), sea level is rising (high confidence), and ocean acidity is increasing (high confidence). Most glaciers are shrinking (high confidence), the Greenland and Antarctic ice sheets are losing mass (high confidence), sea ice extent in the Arctic is decreasing (very high confidence), Northern Hemisphere snow cover is decreasing (very high confidence), and permafrost temperatures are increasing (high confidence). Improvements since AR5 in observation systems, techniques, reconstructions and model developments, have advanced scientific characterisation and understanding of ocean and cryosphere change, including in previously identified areas of concern such as ice sheets and Atlantic Meridional Overturning Circulation (AMOC). {1.1, 1.4, 1.8.1}

Evidence and understanding of the human causes of climate warming, and of associated ocean and cryosphere changes, has increased over the past 30 years of IPCC assessments (very high confidence). Human activities are estimated to have caused approximately 1.0°C of global warming above pre-industrial levels (SR15). Areas of concern in earlier IPCC reports, such as the expected acceleration of sea level rise, are now observed (high confidence). Evidence for expected slow-down of AMOC is emerging in sustained observations and from long-term palaeoclimate reconstructions (medium confidence), and may be related with anthropogenic forcing according to model simulations, although this remains to be properly attributed. Significant sea level rise contributions from Antarctic ice sheet mass loss (very high confidence), which earlier reports did not expect to manifest this century, are already being observed. {1.1, 1.4}

Ocean and cryosphere changes and risks by the end-of-century (2081-2100) will be larger under high greenhouse gas emission scenarios, compared with low emission scenarios (very high confidence). Projections and assessments of future climate, ocean and cryosphere changes in the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) are commonly based on coordinated climate model experiments from the Coupled Model Intercomparison Project Phase 5 (CMIP5) forced with Representative Concentration Pathways (RCPs) of future radiative forcing. Current emissions continue to grow at a rate consistent with a high emission future without effective climate change mitigation policies (referred to as RCP8.5). The SROCC assessment contrasts this high greenhouse gas emission future with a low greenhouse gas emission, high mitigation future (referred to as RCP2.6) that gives a two in three chance of limiting warming by the end of the century to less than 2oC above pre-industrial. {Cross-Chapter Box 1 in Chapter 1} 

Characteristics of ocean and cryosphere change include thresholds of abrupt change, long-term changes that cannot be avoided, and irreversibility (high confidence). Ocean warming, acidification and deoxygenation, ice sheet and glacier mass loss, and permafrost degradation are expected to be irreversible on time scales relevant to human societies and ecosystems. Long response times of decades to millennia mean that the ocean and cryosphere are committed to long-term change even after atmospheric greenhouse gas concentrations and radiative forcing stabilise (high confidence). Ice-melt or the thawing of permafrost involve thresholds (state changes) that allow for abrupt, nonlinear responses to ongoing climate warming (high confidence). These characteristics of ocean and cryosphere change pose risks and challenges to adaptation {1.1, Box 1.1, 1.3}.

Societies will be exposed, and challenged to adapt, to changes in the ocean and cryosphere even if current and future efforts to reduce greenhouse gas emissions keep global warming well below 2°C (very high confidence). Ocean and cryosphere-related mitigation and adaptation measures include options that address the causes of climate change, support biological and ecological adaptation, or enhance societal adaptation. Most ocean-based local mitigation and adaptation measures have limited effectiveness to mitigate climate change and reduce its consequences at the global scale, but are useful to implement because they address local risks, often have co-benefits such as biodiversity conservation, and have few adverse side effects. Effective mitigation at a global scale will reduce the need and cost of adaptation, and reduce the risks of surpassing limits to adaptation. Ocean-based carbon dioxide removal at the global scale has potentially large negative ecosystem consequences. {1.6.1, 1.6.2, Cross-Chapter Box 2 in Chapter 1}

The scale and cross-boundary dimensions of changes in the ocean and cryosphere challenge the ability of communities, cultures and nations to respond effectively within existing governance frameworks (high confidence). Profound economic and institutional transformations are needed if climate-resilient development is to be achieved (high confidence). Changes in the ocean and cryosphere, the ecosystem services that they provide, the drivers of those changes, and the risks to marine, coastal, polar and mountain ecosystems, occur on spatial and temporal scales that may not align within existing governance structures and practices (medium confidence). This report highlights the requirements for transformative governance, international and transboundary cooperation, and greater empowerment of local communities in the governance of the ocean, coasts, and cryosphere in a changing climate. {1.5, 1.7, Cross-Chapter Box 2 in Chapter 1, Cross-Chapter Box 3 in Chapter 1} 

Robust assessments of ocean and cryosphere change, and the development of context-specific governance and response options, depend on utilising and strengthening all available knowledge systems (high confidence). Scientific knowledge from observations, models and syntheses provides global to local scale understandings of climate change (very high confidence). Indigenous knowledge (IK) and local knowledge (LK) provide context-specific and socio-culturally relevant understandings for effective responses and policies (medium confidence). Education and climate literacy enable climate action and adaptation (high confidence). {1.8, Cross-Chapter Box 4 in Chapter 1} 

Long-term sustained observations and continued modelling are critical for detecting, understanding and predicting ocean and cryosphere change, providing the knowledge to inform risk assessments and adaptation planning (high confidence). Knowledge gaps exist in scientific knowledge for important regions, parameters and processes of ocean and cryosphere change, including for physically plausible, high impact changes like high end sea level rise scenarios that would be costly if realised without effective adaptation planning and even then may exceed limits to adaptation. Means such as expert judgement, scenario building, and invoking multiple lines of evidence enable comprehensive risk assessments even in cases of uncertain future ocean and cryosphere changes. {1.8.1, 1.9.2; Cross-Chapter Box 5 in Chapter 1}and cryosphere are committed to long-term change even after atmospheric greenhouse gas concentrations and radiative forcing stabilise (high confidence). Ice-melt or the thawing of permafrost involve thresholds (state changes) that allow for abrupt, nonlinear responses to ongoing climate warming (high confidence). These characteristics of ocean and cryosphere change pose risks and challenges to adaptation {1.1, Box 1.1, 1.3}.

Societies will be exposed, and challenged to adapt, to changes in the ocean and cryosphere even if current and future efforts to reduce greenhouse gas emissions keep global warming well below 2°C (very high confidence). Ocean and cryosphere-related mitigation and adaptation measures include options that address the causes of climate change, support biological and ecological adaptation, or enhance societal adaptation. Most ocean-based local mitigation and adaptation measures have limited effectiveness to mitigate climate change and reduce its consequences at the global scale, but are useful to implement because they address local risks, often have co-benefits such as biodiversity conservation, and have few adverse side effects. Effective mitigation at a global scale will reduce the need and cost of adaptation, and reduce the risks of surpassing limits to adaptation. Ocean-based carbon dioxide removal at the global scale has potentially large negative ecosystem consequences. {1.6.1, 1.6.2, Cross-Chapter Box 2 in Chapter 1}

The scale and cross-boundary dimensions of changes in the ocean and cryosphere challenge the ability of communities, cultures and nations to respond effectively within existing governance frameworks (high confidence). Profound economic and institutional transformations are needed if climate-resilient development is to be achieved (high confidence). Changes in the ocean and cryosphere, the ecosystem services that they provide, the drivers of those changes, and the risks to marine, coastal, polar and mountain ecosystems, occur on spatial and temporal scales that may not align within existing governance structures and practices (medium confidence). This report highlights the requirements for transformative governance, international and transboundary cooperation, and greater empowerment of local communities in the governance of the ocean, coasts, and cryosphere in a changing climate. {1.5, 1.7, Cross-Chapter Box 2 in Chapter 1, Cross-Chapter Box 3 in Chapter 1} 

Robust assessments of ocean and cryosphere change, and the development of context-specific governance and response options, depend on utilising and strengthening all available knowledge systems (high confidence). Scientific knowledge from observations, models and syntheses provides global to local scale understandings of climate change (very high confidence). Indigenous knowledge (IK) and local knowledge (LK) provide context-specific and socio-culturally relevant understandings for effective responses and policies (medium confidence). Education and climate literacy enable climate action and adaptation (high confidence). {1.8, Cross-Chapter Box 4 in Chapter 1} 

Long-term sustained observations and continued modelling are critical for detecting, understanding and predicting ocean and cryosphere change, providing the knowledge to inform risk assessments and adaptation planning (high confidence). Knowledge gaps exist in scientific knowledge for important regions, parameters and processes of ocean and cryosphere change, including for physically plausible, high impact changes like high end sea level rise scenarios that would be costly if realised without effective adaptation planning and even then may exceed limits to adaptation. Means such as expert judgement, scenario building, and invoking multiple lines of evidence enable comprehensive risk assessments even in cases of uncertain future ocean and cryosphere changes. {1.8.1, 1.9.2; Cross-Chapter Box 5 in Chapter 1} adaptation. Means such as expert judgement, scenario building, and invoking multiple lines of evidence enable comprehensive risk assessments even in cases of uncertain future ocean and cryosphere changes. {1.8.1, 1.9.2; Cross-Chapter Box 5 in Chapter 1}

1. In this report, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, for example, medium confidence. For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see Section 1.9.2 and Figure 1.4 for more details).

2. In this report, the following terms have been used to indicate the assessed likelihood of an outcome or a result: Virtually certain 99–100% probability, Very likely 90–100%, Likely 66–100%, About as likely as not 33–66%, Unlikely 0–33%, Very unlikely 0–10%, and Exceptionally unlikely 0–1%. Additional terms (Extremely likely: 95–100%, More likely than not >50–100%, and Extremely unlikely 0–5%) may also be used when appropriate. Assessed likelihood is typeset in italics, for example, very likely (see Section 1.9.2 and Figure 1.4 for more details). This Report also uses the term ‘likely range’ to indicate that the assessed likelihood of an outcome lies within the 17–83% probability range.

1.1

Why this Special Report?

All people depend directly or indirectly on the ocean and cryosphere (see FAQ1.1). Coasts are the most densely populated areas on Earth. As of 2010, 28% of the global population (1.9 billion people) were living in areas less than 100 km from the coastline and less than 100 m above sea level, including 17 major cities which are each home to more than 5 million people (Kummu et al., 2016). Small Island Developing States are together home to around 65 million people (UN, 2015a). The low elevation coastal zone (land less than 10 m above sea level), where people and infrastructure are most exposed to coastal hazards, is currently home to around 11% of the global population (around 680 million people), and by 2050 the population in this zone is projected to grow to more than one billion under all Shared Socioeconomic Pathways (SSPs) (Section 4.3.3.2; Merkens et al., 2016; O’Neill et al., 2017). In 2010, approximately 4 million people lived in the Arctic (Section 3.5.1), and an increase of only 4% is projected for 2030 (Heleniak, 2014) compared to 1623% for the global population increase (O’Neill et al., 2017). Almost 10% of the global population (around 670 million people) lived in high mountain regions in 2010, and by 2050 the population in these regions is expected to grow to between 736844 million across the SSPs (Section 2.1). For people living in close contact with the ocean and cryosphere, these systems provide essential livelihoods, food security, well-being and cultural identity, but are also a source of hazards (Sections 1.5.1, 1.5.2). 

Even people living far from the ocean or cryosphere depend on these systems. Snow and glacier melt from high mountains helps to sustain the rivers that deliver water resources to downstream populations (Kaser et al., 2010; Sharma et al., 2019). In the Indus and Ganges river basins, for example, snow and glacier melt provides enough water to grow food crops to sustain a balanced diet for 38 million people, and supports the livelihoods of 129 million farmers (Biemans et al., 2019). The ocean and cryosphere regulate global climate and weather; the ocean is the primary source of rain and snowfall needed to sustain life on land, and uptake of heat and carbon into the ocean has so far limited the magnitude of anthropogenic warming experienced at the Earth’s surface (Section 1.2). The ocean’s biosphere is responsible for about half of the primary production on Earth, and around 17% of the non-grain protein in human diets is derived from the ocean (FAO, 2018). Communities far from the coast can also be exposed to changes in the ocean through extreme weather events. Ocean and cryosphere changes can result in differing consequences and benefits on local to global scales; for example, declining sea ice in the Arctic is allowing access to shorter international shipping routes but restricting traditional sea ice based travel for Arctic communities. 

Human activities are estimated to have so far caused approximately 1°C of global warming (0.8°C1.2°C likely range; above pre-industrial levels; IPCC, 2018). The IPCC Fifth Assessment Report (AR5) concluded that, ‘Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased’ (IPCC, 2013). Subsequently, Parties to the Paris Agreement aimed to strengthen the global response to the threats of climate change, including by ‘holding the increase in global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C’ (UNFCCC, 2015).

Pervasive ocean and cryosphere changes that are already being caused by human-induced climate change are observed from high mountains, to the polar regions, to coasts and into the deep reaches of the ocean. Changes by the end of this century are expected to be larger under high greenhouse gas emission futures compared with low-emission futures (Cross-Chapter Box 1 in Chapter 1), and inaction on reducing emissions will have large economic costs. If human impacts on the ocean continue unabated, declines in ocean health and services are projected to cost the global economy 428 billion USD yr-1 by 2050, and 1.979 trillion USD yr-1 by 2100. Alternatively, steps to reduce these impacts could save more than a trillion dollars USD yr-1 by 2100 (Ackerman, 2013). Similarly, sea level rise scenarios of 25 to 123 cm by 2100 without adaptation are expected to see 0.24.6% of the global population impacted by coastal flooding annually, with average annual losses amounting to 0.39.3% of global GDP. Investment in adaptation reduces by 2 to 3 orders of magnitude the number of people flooded and the losses caused (Hinkel et al., 2014).

The United Nations 2030 SDGs (UN, 2015b) are all connected to varying extents with the ocean and cryosphere (see FAQ1.2). Climate action (SDG 13) would limit future ocean and cryosphere changes (high confidence; Cross-Chapter Box 1 in Chapter 1, Figure 1.5, Chapter 2 to 6), and would reduce risks to SDGs that are fundamentally linked to the ocean and cryosphere, including life below water, and clean water and sanitation. (Sections 2.4, 4.4, 5.4; Szabo et al., 2016; LeBlanc et al., 2017; Singh et al., 2018; Visbeck, 2018; Wymann von Dach et al., 2018; Kulonen, Accepted). Other goals for sustainable development depend on the services the ocean and cryosphere provide or are impacted by ocean and cryosphere change; including, life on land, health and wellbeing, eradicating poverty and hunger, economic growth, clean energy, infrastructure, and sustainable cities and communities. Progress on the other SDGs (education, gender equality, reduced inequalities, responsible consumption, strong institutions, and partnerships for the goals) are important for reducing the vulnerability of people and communities to the risks of ocean and cryosphere changes (Section 1.5; 2.3), and for supporting mitigation and adaptation responses (Sections 1.6, 1.7 and 1.8.3; medium confidence). 

The characteristics of ocean and cryosphere change (Section 1.3) present particular challenges to climate-resilient development pathways (CRDPs). Ocean acidification and deoxygenation, ice sheet and glacier mass loss, and permafrost degradation are expected to be irreversible on time scales relevant to human societies and ecosystems (Lenton et al., 2008; Solomon et al., 2009; Frölicher and Joos, 2010; Cai et al., 2016; Kopp et al., 2016). Ocean and cryosphere changes also have the potential to worsen anthropogenic climate change, globally and regionally; for example, by additional greenhouse gas emissions released through permafrost thaw that would intensify anthropogenic climate change globally, or by increasing the absorption of solar radiation through snow and ice loss in the Arctic that is causing regional climate to warm at more than twice the global rate (AMAP, 2017; Steffen et al., 2018). Ocean and cryosphere changes place particular pressures on the adaptive capacities of cultures who maintain centuries to millennia-old relationships to the planet’s polar, mountain, and coastal environments, as well as on cities, states and nations whose territorial boundaries are being transformed by ongoing sea level rise (Gerrard and Wannier, 2013). The scale and cross-boundary dimensions of changes in the ocean and cryosphere challenge the ability of current local, regional and international governance structures to respond (Section 1.7). Profound economic and institutional transformations are needed if climate-resilient development is to be achieved, including ambitious mitigation efforts to avoid the risks of large-scale and abrupt ocean and cryosphere changes. 

The commissioning of this SROCC recognises the interconnected ways in which the ocean and cryosphere are expected to change in a warming climate. SROCC assesses new knowledge since AR5 and provides an integrated approach across IPCC working groups I and II, linking physical changes with their ecological and human impacts, and the strategies to respond and adapt to future risks. It is one of three special reports being produced by the IPCC during its Sixth Assessment Cycle (in addition to the three working groups’ main assessment reports). The concurrent IPCC Special Report on Climate Change and Land (due August 2019) links to SROCC where terrestrial environments and their habitability interact closely with the ocean or cryosphere, such as in mountain, Arctic, and coastal regions. SR15 concluded that human-induced warming will reach 1.5°C between 20302052 if it continues to increase at the current rate (high confidence), and that there are widespread benefits to human and natural systems of limiting warming to 1.5oC compared with 2oC or more (high confidence; IPCC, 2018). 

1.2

Role of the Ocean and Cryosphere in the Earth System

1.2.2

Interactions Between the Ocean and Cryosphere

The ocean and cryosphere are interconnected in a multitude of ways (Box 1.1, Figure 1). Evaporation from the ocean provides snowfall that builds and sustains the ice sheets and glaciers that store large amounts of frozen water on land (Section 4.2.1). The vast ice sheets in Antarctica and Greenland currently hold about 66 m of potential global sea level rise (Fretwell et al., 2013), although the loss of a large fraction of this potential would require millennia of ice sheet retreat. Ocean temperature and sea level affect ice sheet, glacier and ice shelf stability in places where the base of ice bodies are in direct contact with ocean water (Section 3.3.1). The nonlinear response of ice-melt to ocean temperature changes means that even slight increases in ocean temperature have the potential to rapidly melt and destabilise large sections of an ice sheet or ice shelf (Section 3.3.1.5).

The formation of sea ice leads to the production of dense ocean water that contributes to the deep ocean circulation (Section 3.3.3.2). Paleoclimate evidence and modelling indicates that releases of large amounts of glacier and ice sheet melt water into the surface ocean can disrupt deep overturning circulation of the ocean, causing global climate impacts (Knutti et al., 2004; Golledge et al., 2019). Ice sheet melt water in the Antarctic may cause changes in surface ocean salinity, stratification and circulation, that feedback to generate further ocean-driven melting of marine-based ice sheets (Golledge et al., 2019) and promote sea ice formation (Purich et al., 2018). The cryosphere and ocean further link through the movement of biogeochemical nutrients. For example, iron accumulated in sea ice during winter is released to the ocean during the spring and summer melt, helping to fuel ocean productivity in the seasonal sea ice zone (Tagliabue et al., 2017). Nutrient rich sediments delivered by glaciers further connect cryosphere processes to ocean productivity (Arrigo et al., 2017). 

1.2.1

Ocean and Cryosphere in Earth’s Energy, Water and Biogeochemical Cycles

The ocean and cryosphere play a key role in the Earth system. Powered by the Sun’s energy, large quantities of energy, water and biogeochemical elements (predominantly carbon, nitrogen, oxygen and hydrogen) are exchanged between all components of the Earth system, including between the ocean and cryosphere (Box 1.1, Figure 1). 

During an equilibrium (stable) climate state, the amount of incoming solar energy is balanced by an equal amount of outgoing radiation at the top of Earth’s atmosphere (Hansen et al., 2011). At the Earth’s surface energy from the Sun is transformed into various forms (heat, potential, latent, kinetic, and chemical), that drive weather systems in the atmosphere and currents in the ocean, fuel photosynthesis on land and in the ocean, and fundamentally determine the climate (Trenberth et al., 2014). The ocean has a large capacity to store and release heat, and the Earth’s energy budget can be effectively monitored through the heat content of the ocean on time scales longer than one year (Palmer and McNeall, 2014; von Schuckmann et al., 2016; Cheng et al., 2018). The large heat capacity of the ocean leads to different characteristics of the ocean response to external forcings compared with the atmosphere (Sections 1.3, 1.4). The reflective properties of snow and ice also play an important role in regulating climate via the albedo effect. Increased amounts of solar energy are absorbed when snow or ice are replaced by less reflective land or ocean surfaces, resulting in a climate change feedback responsible for amplified changes.

Water is exchanged between the ocean, atmosphere, land and cryosphere as part of the hydrological cycle driven by solar heating (Box 1.1, Figure 1; Trenberth et al., 2007; Lagerloef et al., 2010; Durack et al., 2016). Evaporation from the surface ocean is the main source of water in the atmosphere, which is moved back to the Earth’s surface as precipitation (Gimeno et al., 2012). The hydrological cycle is closed by the eventual return of water to the ocean by rivers, streams, and groundwater flow, and through ice discharge and melting of ice sheets and glaciers (Yu, 2018). Hydrological extremes related to the ocean include floods from extreme rainfall (including tropical cyclones) or ocean circulation-related droughts (Sections 6.3, 6.5), while cryosphere-related flooding can be caused by rapid snow melt and melt water discharge events (Sections 2.3, 3.4).

Ninety-two percent of the carbon on Earth that is not locked up in geological reservoirs (e.g., in sedimentary rocks or coal, oil and gas reservoirs) resides in the ocean (Sarmiento and Gruber, 2002). Most of this is in the form of dissolved inorganic carbon, some of which readily exchanges with CO2 in the overlying atmosphere. This represents a major control on atmospheric CO2 and makes the ocean and its carbon cycle one of the most important climate regulators in the Earth system, especially on time scales of a few hundred years and more (Sigman and Boyle, 2000; Berner and Kothavala, 2001). The ocean also contains as much organic carbon (mostly in the form of dissolved organic matter) as the total vegetation on land (Jiao et al., 2010; Hansell, 2013). Primary production in the ocean, which is as large as that on land (Field et al., 1998), fuels complex food-webs that provide essential food for people. 

Ocean circulation and mixing redistribute heat and carbon over large distances and depths (Delworth et al., 2017). The ocean moves heat laterally from the tropics towards polar regions (Rhines et al., 2008). Vertical redistribution of heat and carbon occurs where warm, low-density surface ocean waters transform into cool high-density waters that sink to deeper layers of the ocean (Talley, 2013), taking high carbon concentrations with them (Gruber et al., 2019). Driven by winds, ocean circulation also brings cold water up from deep layers (upwelling) in some regions, allowing heat, oxygen and carbon exchange between the deep ocean and the atmosphere (Oschlies et al., 2018; Shi et al., 2018) and fuelling biological production (Sarmiento and Gruber, 2006).

1.3

Time Scales, Thresholds and Detection of Ocean and Cryosphere Change

It takes hundreds of years to millennia for the entire deep ocean to turn over (Matsumoto, 2007; Gebbie and Huybers, 2012), while renewal of the large ice sheets requires many thousands of years (Huybrechts and de Wolde, 1999). Long response times mean that the deep ocean and the large ice sheets tend to lag behind in their response to the rapidly changing climate at Earth’s surface, and that they will continue to change even after radiative forcing stabilises (e.g., Golledge et al., 2015; Figure 1.1a). Such ‘committed’ changes mean that some ocean and cryosphere changes are essentially irreversible on time scales relevant to human societies (decades to centuries), even in the presence of immediate action to limit further global warming (e.g., Section 4.2.3.5). 

While some aspects of the ocean and cryosphere might respond in a linear (i.e., directly proportional) manner to a perturbation by some external forcing, this may change fundamentally when critical thresholds are reached. A very important example for such a threshold is the transition from frozen water to liquid water at around 0°C that can lead to rapid acceleration of ice-melt or permafrost thaw (e.g., Abram et al., 2013; Trusel et al., 2018). Such thresholds often act as tipping points, as they are associated with rapid and abrupt changes even when the underlying forcing changes gradually (Figure 1.1a, 1.1c). Tipping elements include, for example, the collapse of the ocean’s large-scale overturning circulation in the Atlantic (Section 6.7), or the collapse of the West Antarctic Ice Sheet though a process called marine ice sheet instability (Cross-Chapter Box 8 in Chapter 3; Lenton et al., 2008). Potential ocean and cryosphere tipping elements form part of the scientific case for efforts to limit climate warming to well below 2oC (IPCC, 2018). 

Anthropogenically forced change occurs against a backdrop of substantial natural variability (Figure 1.1b). The anthropogenic signal is already detectable in global surface air temperature and several other climate variables, including ocean temperature and salinity (IPCC, 2014), but short observational records and large year-to-year variability mean that formal detection is not yet the case for many expected ocean and cryosphere changes (Jones et al., 2016). ‘Time of Emergence’ refers to the time when anthropogenic change signals emerge from the background noise of natural variability in a pre-defined reference period Hawkins and Sutton, 2012; (Figure 1.1b; Section 5.2, Box 5.1). For some variables, (e.g., for those associated with ocean acidification), the current signals emerge from this natural variability within a few decades, whereas for others, such as primary production and expected Antarctic-wide sea ice decline, the signal may not emerge for many more decades even under high emission scenarios (Collins et al., 2013; Keller et al., 2014; Rodgers et al., 2015; Frölicher et al., 2016; Jones et al., 2016). 

‘Detection and Attribution’ assesses evidence for past changes in the ocean and cryosphere, relative to normal/reference-interval conditions (detection), and the extent to which these changes have been caused by anthropogenic climate change or by other factors (attribution) (Bindoff et al., 2013; Cramer et al., 2014; Knutson et al., 2017; Figure 1.1d). Reliable detection and attribution is fundamental to our understanding of the scientific basis of climate change (Hegerl et al., 2010). For example, the main attribution conclusion of the IPCC 4th Assessment Report (AR4), in other words, that ‘most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations’, has had a strong impact on climate policy (Petersen, 2011). In AR5 this attribution statement was elevated to ‘extremely likely’ (Bindoff et al., 2013). Statistical approaches for attribution often involve using contrasting forcing scenarios in climate model experiments to detect the forcing that best explains an observed change (Figure 1.1d). In addition to passing the statistical test, a successful attribution also requires a firm process understanding. Confident attribution remains challenging though, especially when there are multiple or confounding factors that influence the state of a system (Hegerl et al., 2010). Particular challenges to detection and attribution in the ocean and cryosphere include the often short observational records (Section 1.8.1.1, Figure 1.3), which are particularly confounding given the long adjustment time scales to anthropogenic forcing of many properties of interest.

Extreme climate events (e.g., marine heatwaves or storm surges) push a system to near or beyond the ends of its normally observed range ( Seneviratne et al., 2012; Figure 1.1b; Chapter 6;). Extremes can be very costly in terms of loss of life, ecosystem destruction, and economic damage. In a system affected by climate change, the recurrence and intensity of these extreme events can change much faster and have greater impacts than changes of the average system state (Easterling et al., 2000; Parmesan et al., 2000; Hughes et al., 2018). Of particular concern are ‘compound events’, when the joint probability of two or more properties of a system is extreme at the same time or closely connected in time and space (Cross-Chapter Box 5 in Chapter 1; Sections 4.3.4, 6.8). Such a compound event is given, for example, when marine heatwaves co-occur with very low nutrient levels in the ocean potentially resulting in extreme impacts (Bond et al., 2015). The interconnectedness of the ocean and cryosphere (Section 1.2.2) can also lead to cascading effects where changes in one element trigger secondary changes in completely different but connected elements of the systems, including its socioeconomic aspects. (Figure 1.1e). An example is the large change in ocean productivity triggered by the changes in circulation and iron inputs induced by the large outflow of melt waters from Greenland (Kanna et al., 2018). New methodologies for attributing extreme events and the risks they bring to climate change have emerged since AR5 (Trenberth et al., 2015; Stott et al., 2016; Kirchmeier-Young et al., 2017; Otto, 2017), especially also for the attribution of individual events through an assessment of the fraction of attributable risk (Figure 1.1f).

1.4

Changes in the Ocean and Cryosphere

Earth’s climate, ocean and cryosphere vary across a wide range of time scales. This includes the seasonal growth and melting of sea ice, interannual variation of ocean temperature caused by the El Niño-Southern Oscillation and ice age cycles across tens to hundreds of thousands of years.

Climate variability can arise from internally generated (i.e., unforced) fluctuations in the climate system. Variability can also occur in response to external forcings, including volcanic eruptions, changes in the Earth’s orbit around the Sun, oscillations in solar activity and changing atmospheric greenhouse gas concentrations.

Since the onset of the industrial revolution, human activities have had a strong impact on the climate system, including the ocean and cryosphere. Human activities have altered the external forcings acting on Earth’s climate (Myhre et al., 2013) by changes in land use (albedo), and changes in atmospheric aerosols (e.g., soot) from the burning of biomass and fossil fuels. Most significantly, human activities have led to an accumulation of greenhouse gases (including CO2) in the atmosphere as a result of the burning of fossil fuels, cement production, agriculture and land use change. In 2016, the global average atmospheric CO2 concentration crossed 400 parts per million, a level Earth’s atmosphere did not experience for at least the past 800,000 years and possibly much longer (Lüthi et al., 2008; Fischer et al., 2018). These anthropogenic forcings have not only warmed the ocean and begun to melt the cryosphere, but have also led to widespread biogeochemical changes driven by the oceanic uptake of anthropogenic CO2 from the atmosphere (IPCC, 2013).

It is now nearly three decades since the first assessment report of the IPCC, and over that time evidence and confidence in observed and projected ocean and cryosphere changes have grown (very high confidence; Table SM1.1). Confidence in climate warming and its anthropogenic causes has increased across assessment cycles; robust detection was not yet possible in 1990, but has been characterised as unequivocal since AR4 in 2007. Projections of near-term warming rates in early reports have been realised over the subsequent decades, while projections have tended to err on the side of caution for sea level rise and ocean heat uptake that have developed faster than predicted (Brysse et al., 2013; Section 4.2, 5.2). Areas of concern in early reports which were expected but not observable are now emerging. The expected acceleration of sea level rise is now observed with high confidence (Section 4.2). There is emerging evidence in sustained observations and from long-term palaeoclimate reconstructions for the expected slow-down of AMOC (medium confidence), although this remains to be properly attributed (Section 6.7). Significant sea level rise contributions from Antarctic ice sheet mass loss (very high confidence), which earlier reports did not expect to manifest this century, are already being observed (Section 3.3.1). Other newly emergent characteristics of ocean and cryosphere change (e.g., marine heat waves; Section 6.4) are assessed for the first time in SROCC. 

AR5 (IPCC, 2013; IPCC, 2014) provides ample evidence of profound and pervasive changes in the ocean and cryosphere (Sections 1.4.1, 1.4.2), and along with the recent SR15 report (IPCC, 2018), is the point of departure for the updated assessments made in SROCC.

1.4.1

Observed and Projected Changes in the Ocean

Increasing greenhouse gases in the atmosphere cause heat uptake in the Earth system (Section 1.2) and as reported since 1970, there is high confidence that the majority (more than 90%) of the extra thermal energy in the Earth’s system is stored in the global ocean (IPCC, 2013). Mean ocean surface temperature has increased since the 1970s at a rate of 0.11 (0.090.13)°C per decade (high confidence), and forms part of a long-term warming of the surface ocean since the mid-19th century. The upper ocean (0700 m, virtually certain) and intermediate ocean (700 to 2,000 m, likely) have warmed since the 1970s. Ocean heat uptake has continued unabated since AR5 (Sections 3.2.1.2.1, 5.2), increasing the risk of marine heat waves and other extreme events (Section 6.4). During the 21st century, ocean warming is projected to continue even if anthropogenic greenhouse gas emissions cease (Sections 1.3, 5.2). The global water cycle has been altered, resulting in substantial regional changes in sea surface salinity (high confidence; Rhein et al., 2013), which is expected to continue in the future (Sections 5.2.2, 6.3, 6.5). 

The rate of sea level rise since the mid-19th century has been larger than the mean rate of the previous two millennia (high confidence). Over the period 1901 to 2010, global mean sea level rose by 0.19 (0.170.21) m (high confidence) (Church et al., 2013; Table SM1.1). Sea level rise continues due to freshwater added to the ocean by melting of glaciers and ice sheets, and as a result of ocean expansion due to continuous ocean warming, with a projected acceleration and century to millennial-scale commitments for ongoing rise (Section 4.2.3). In SROCC, recent developments of ice sheet modelling are assessed (Sections 1.8, 4.3, Cross-Chapter Box 8 in Chapter 3) and the projected sea level rise at the end of 21st century is higher than reported in AR5 but with a larger uncertainty range (Sections 4.2.3.2, 4.2.3.3).

By 2011, the ocean had taken up about 30 ± 7% of the anthropogenic CO2 that had been released to the atmosphere since the industrial revolution (Ciais et al., 2013; Section 5.2). In response, ocean pH decreased by 0.1 since the beginning of the industrial era (high confidence), corresponding to an increase in acidity of 26% (Table SM1.1) and leading to both positive and negative biological and ecological impacts (high confidence) (Gattuso et al., 2014). Evidence is increasing that the ocean’s oxygen content is declining (Oschlies et al., 2018). AR5 did not come to a final conclusion with regard to potential long-term changes in ocean productivity due to short observational records and divergent scientific evidence (Boyd et al., 2014; Section 5.2.2). Ocean acidification and deoxygenation are projected to continue over the next century with high confidence (Sections 3.2.2.3, 5.2.2).

1.4.2

Observed and Projected Changes in the Cryosphere

Changes in the cryosphere documented in AR5 included the widespread retreat of glaciers (high confidence), mass loss from the Greenland and Antarctic ice sheets (high confidence) and declining extents of Arctic sea ice (very high confidence) and Northern Hemisphere spring snow cover (very high confidence; IPCC, 2013; Vaughan et al., 2013).

A particularly rapid change in Earth’s cryosphere has been the decrease in Arctic sea ice extent in all seasons (Section 3.2.1.1). AR5 assessed that there was medium confidence that a nearly ice-free summer Arctic Ocean is likely to occur before mid-century under a high emissions future (IPCC, 2013), and SR15 assessed that ice-free summers are projected to occur at least once per century at 1.5oC of warming, and at least once per decade at 2oC of warming above pre-industrial levels (IPCC, 2018). Sea ice thickness is decreasing further in the Northern Hemisphere and older ice that has survived multiple summers is rapidly disappearing; most sea ice in the Arctic is now ‘first year’ ice that grows in the autumn and winter but melts during the spring and summer (AMAP, 2017).

AR5 assessed that the annual mean loss from the Greenland ice sheet very likely substantially increased from 34 (-674) Gt yr–1 (billion tonnes yr-1) over the period 19922001, to 215 (157274) Gt yr–1 over the period 20022011 (IPCC, 2013). The average rate of ice loss from the Antarctic ice sheet also likely increased from 30 (-3797) Gt yr–1 over the period 1992–2001, to 147 (72221) Gt yr–1 over the period 20022011 (IPCC, 2013). The average rate of ice loss from glaciers around the world (excluding glaciers on the periphery of the ice sheets), was very likely 226 (91361) Gt yr-1 over the period 19712009, and 275 (140410) Gt yr-1 over the period 19932009 (IPCC, 2013). The Greenland and Antarctic ice sheets are continuing to lose mass at an accelerating rate (Section 3.3) and glaciers are continuing to lose mass worldwide (Section 2.2.3, Cross-Chapter Box 6 in Chapter 2). Confidence in the quantification of glacier and ice sheet mass loss has increased across successive IPCC reports (Table SM1.1) due to the development of remote sensing observational methods (Section 1.8.1). 

Changes in seasonal snow are best documented for the Northern Hemisphere. AR5 reported that the extent of snow cover has decreased since the mid-20th century (very high confidence). Negative trends in both snow depth and duration are also detected with station observations (medium confidence), although results depend on elevation and observational period (Section 2.2.2). AR5 assessed that permafrost temperatures have increased in most regions since the early 1980s (high confidence), and the rate of increase has varied regionally (IPCC, 2013). Methane and carbon dioxide release from soil organic carbon is projected to continue in high mountain and polar regions (Box 2.2), and SROCC has used multiple lines of evidence to reduce uncertainty in permafrost change assessments (Cross-Chapter Box 5 in Chapter 1, Section 3.4.3.1.1). 

 

Table CB1.1. Projected change in global mean surface air temperature and key ocean variables for the near term (20312050) and end-of-century (20812100) relative to the recent past (19862005) reference period from CMIP5. See Table SM1.2 for the list of CMIP5 models and ensemble member used for calculating these projections. Small differences in the projections given here compared with AR5 (e.g., Table 12.2 in Collins et al., 2013) reflect differences in the number of models available now compared to at the time of the AR5 assessment (Table SM1.2). 

Near term: 20312050 End-of-century: 20812100
Scenario Mean 595% range Mean 595% range
Global Mean Surface Air temperature (°C) a RCP2.6 0.9 0.51.4 1.0 0.31.7
RCP4.5 1.1 0.71.5 1.8 1.02.6
RCP6.0 1.0 0.51.4 2.3 1.43.2
RCP8.5 1.4 0.91.8 3.7 2.64.8
Global Mean Sea Surface Temperature (°C)

(Section 5.2.5)

RCP2.6 0.64 0.330.96 0.73 0.201.27
RCP8.5 0.95 0.601.29 2.58 1.643.51
Surface pH (units) b

(Section 5.2.2.3)

RCP2.6 -0.072 -0.072 to -0.072 -0.065 -0.065 to -0.066
RCP8.5 -0.108 -0.106 to -0.110 -0.315 -0.313 to -0.317
Dissolved Oxygen (100600 m) (% change)

(Section 5.2.2.4)b

RCP2.6 -0.9 -0.3 to -1.5 -0.6 0.0 to –1.2
RCP8.5 -1.4 -1.0 to -1.8 -3.9 -2.9 to -5.0

 

1.5

Risk and Impacts Related to Ocean and Cryosphere Change

SROCC assesses the risks (i.e., potential for adverse consequences) and impacts (i.e., manifested risk) resulting from climate-related changes in the ocean and cryosphere. Knowledge on risk is essential for conceiving and implementing adequate responses. Cross-Chapter Box 2 in Chapter 1 introduces key concepts of risk, adaptation, resilience and transformation, and explains why and how they matter for this report. 

In SROCC, the term ‘natural system’ describes the biological and physical components of the environment, independent of human involvement but potentially affected by human activities. ‘Natural systems’ may refer to portions of the total system without necessarily considering all its components (e.g., an ocean upwelling system). Throughout the assessment usage of ‘natural system’ does not imply a system unaltered by human activities. 

‘Human systems’ include physiological, health, socio-cultural, belief, technological, economic, food, political, and legal systems, among others. Humans have depended upon the Earth’s ocean (WOA, 2016; IPBES, 2018b) and cryosphere (AMAP, 2011; Hovelsrud et al., 2011; Watt-Cloutier, 2018) for many millennia (Redman, 1999). Contemporary human populations still depend directly on elements of the ocean and cryosphere, and the ecosystem services they provide, but at a much larger scale and with greater environmental impact than in pre-industrial times (Inniss and Simcock, 2017). 

An ecosystem is a functional unit consisting of living organisms, their non-living environment, and the interactions within and between them. Ecosystems can be nested within other ecosystems and their scale can range from very small to the entire biosphere. Today, most ecosystems either contain humans as key organisms, or are influenced by the effects of human activities in their environment. In SROCC, a social-ecological system describes the combined system and all of its sub-components and refers specifically to the interaction of natural and human systems.

The ocean and cryosphere are unique systems that have intrinsic value, including the ecosystems and biodiversity they support. Frameworks of Ecosystem Services and Nature’s Contributions to People are both used within SROCC to assess the impacts of changes in the ocean and cryosphere on humans directly, and through changes to the ecosystems that support human life and civilisations (Sections 2.3, 3.4.3.2, 4.3.3.5, 5.4, 6.4, 6.5, 6.8). The Millennium Ecosystem Assessment (MEA, 2005) established a conceptual Ecosystem Services framework between biodiversity, human well-being, and drivers of change. This framework highlights that natural systems provide vital life-support services to humans and the planet, including direct material services (e.g., food, timber), non-material services (e.g., cultural continuity, health), and many services that regulate environmental status (e.g., soil formation, water purification). This framework supports decision-making by quantifying benefits for valuation and trade-off analyses. The Ecosystem Services framework has been challenged as monetising the relationships of people with nature, and undervaluing small-scale livelihoods, cultural values and other considerations that contribute little to global commerce (Díaz et al., 2018). More recent frameworks, such as Nature’s Contributions to People (Díaz et al., 2018), used in the Intergovernmental Platform on Biodiversity and Ecosystem Services assessments (IPBES), aim to better encompass the non-commercial ways that nature contributes to human quality of life. 

1.5.1

Hazards and Opportunities for Natural Systems, Ecosystems, and Human Systems

Hazards faced by marine and coastal organisms, and the ecosystem services they provide are generally dependent on future greenhouse gas emission pathways, with moderate likelihood under a low-emission future, but high to very high likelihood under higher emission scenarios (very high confidence) (Mora et al., 2013; Gattuso et al., 2015). Hazards to marine ecosystems assessed in AR5 (IPCC, 2014) included degradation of coral reefs (high confidence), ocean deoxygenation (medium confidence) and ocean acidification (high confidence). Shifts in the ranges of plankton and fish were identified with high confidence regionally, but with uncertain trends globally. SROCC provides more evidence for global shifts in the distribution of marine organisms, and in how the phenology of animals is responding to ocean change (Sections 3.2.3, 5.2). The signature of climate change is now detected in almost all marine ecosystems. Similar trends of changing habitat due to climate change are reported for the cryosphere (Sections 2.2, 3.4.3.2). The risk of irreversible loss of many marine and coastal ecosystems increases with global warming, especially at 2°C or more (high confidence; IPCC, 2018). Risk also increases for habitat displacements, both poleward (Section 3.2.4) and to greater ocean depths (Section 5.2.4), or habitat reductions, such as that caused by glacier retreat (Section 2.2.3). 

Changes in the ocean and cryosphere bring hazards that affect the health, wellbeing, safety and security of populations in coastal, mountain and polar environments (Section 2.3.5, 3.4.3, 4.3.2). Some impacts are direct, such as sea level rise or coastal erosion that can displace coastal residents (4.3.2.3, 4.4.2.6, Box 4.1). Other effects are indirect; for example, rising ocean temperatures have led to increases in maximum wind speed and rainfall rates in tropical cyclones (Section 6.3), creating hazards with severe consequences for natural and human systems (Sections 4.3, 6.2, 6.3, 6.8). The multiple category 4 and 5 Atlantic hurricanes in 2017 caused the loss of over 3300 lives and more than 350 billion USD in economic damages (Cross-Chapter Box 9; Andrade et al., 2018; Murakami et al., 2018; NOAA, 2018). In mountain regions, glacial lake outburst floods have caused severe impacts on lives, livelihoods and infrastructure that often extend beyond the directly affected areas (Section 2.3.2 and 6.2.2). Some hazards related to ocean and cryosphere change involve abrupt and irreversible changes (Section 1.3), which generate sometimes unpredictable risks, and multiple hazards can coincide to greatly elevate the total risk (Section 6.8.2). For example, combinations of thawing permafrost, sea level rise, loss of sea ice, ocean surface waves and extreme weather events (Thomson and Rogers, 2014; Ford et al., 2017) have damaged Arctic infrastructure (e.g., buildings, roads) (AMAP, 2015; AMAP, 2017), impacted reindeer husbandry livelihoods for Sami and other Arctic Indigenous peoples and impeded access to hunting grounds, other communities and travel routes fundamental to the livelihoods, food security and wellbeing of Inuit and other Northern cultures (Section 3.4.3). In some Arctic regions, tipping points may have already been reached such that adaptive practices can no longer work (Section 3.5).

Climate change impacts on the ocean and cryosphere can also present opportunities, in at least the near- and medium-term. For example, in Nepal warming of high mountain environments and accelerated melting of snow and ice have extended the growing season and crop yields in some regions (Section 2.3; Gaire et al., 2015; Merrey et al., 2018), while tourism and shipping has increased in the Arctic with loss of sea ice (Section 3.2.4). Moreover, rising ocean temperatures redistribute the global fish population, allowing new fishing opportunities while reducing some established fisheries (Bell et al., 2011; Fenichel et al., 2016; Section 5.4). To gain from new opportunities, while also avoiding or mitigating new or increasing hazards, it is necessary to be aware of trade-offs between risks and benefits to understand who is and is not benefiting. For example, opportunities can involve trade-offs with mitigation and/or SDGs (Section 3.5.2), and the balance of economic costs and benefits may differ substantially between the near-term and long-term future (Section 5.4.2.2). 

1.5.2

Exposure of Natural Systems, Ecosystems, and Human Systems

Exposure to hazards in cryosphere systems occur in the immediate vicinity of cryosphere components, and at regional to global scales where cryosphere changes link to other natural systems. For example, decreasing Arctic sea ice increases exposure for organisms that depend upon habitats provided by sea ice, but also has far-reaching impacts through the resulting direct albedo feedback and amplification of Arctic climate warming (e.g., Pistone et al., 2014) that then locally increases surface melting of the Greenland ice sheet (Liu et al., 2016; Stroeve et al., 2017). Additionally, ice loss from ice sheets contribute to the global-scale exposure of sea level rise, and more local-scale modifications and losses of coastal habitats and ecosystems (Sections 3.2.3 and 4.3.3.5). Interactions within and between natural systems also influence the spatial reach of risks associated with cryosphere change. Permafrost degradation, for example, interacts with ecosystems and climate on various spatial and temporal scales, and feedbacks from these interactions range from local impacts on topography, hydrology and biology, to global-scale impacts via biogeochemical cycling (e.g., methane release) on climate (Sections 2.2, 2.3, 3.4; Kokelj et al., 2015; Grosse et al., 2016).

Exposure to climate change risk exists for virtually all coastal organisms, habitats and ecosystems (Section 5.2), through processes such as inundation and salinisation (Section 4.3), ocean acidification and deoxygenation (Sections 3.2.3, 5.2.3), increasing marine heatwaves (Section 6.4.1.2), and increases in harmful algal blooms and invasive species (Glibert et al., 2014; Gobler et al., 2017; Townhill et al., 2017; Box 5.3). Aggregate impacts of multiple drivers are dramatically altering ecosystem structure and function in the coastal and open ocean (Boyd et al., 2015; Deutsch et al., 2015; Przeslawski et al., 2015), such as coral reefs under increasing pressure from both rising ocean temperature and acidification (Section 5.3.4). Increasing exposure to climate change hazards in open ocean natural systems includes ocean acidification (O’Neill et al., 2017; Section 5.2.3), changes in ocean ventilation, deoxygenation (Shepherd et al., 2017; Breitburg et al., 2018; Section 5.2.2.4), increased cyclone and flood risk (Section 6.3.3) and an increase in extreme El Niño and La Niña events (Section. 6.5.1). Heat content is rapidly increasing within the ocean (Section 5.2.2) and marine heat waves are becoming more frequent across the world ocean (Section 6.4.1).

People who live close to the ocean and/or cryosphere, or depend directly on their resources for livelihoods, are particularly exposed to climate change impacts and hazards (very high confidence) (Barange et al., 2014; Romero-Lankao et al., 2014; AMAP, 2015). These exposures can result in infrastructure damage and failure (Sections 2.3.1.3, 3.4.3, 3.5., 4.3.2), loss of habitability (Sections 2.3.7, 3.4.3, 3.5, 4.3.3), changes in air quality (Section 6.5.2), proliferation of disease vectors (Sections 3.4.3.2.2, 5.4.2.1.1), increased morbidity and mortality due to injury, infectious disease, heat stress, and mental health and wellness challenges (Section 3.4.3.3), compromised food and water security (Sections 2.3.1, 3.4.3.3, 4.3.3.6, 5.4.2.1, 6.8.4), degradation of ecosystem services (Sections 2.3.1.2, 2.3.3.4, 4.3.3, 5.4.1, 6.4.2.3), economic and non-economic impacts due to reduced production and social network system disruption (Section 2.3.7), conflict (Sections 2.3.1.14, 3.5) and widespread human migration (Sections 2.3.7, 4.4.3.5; Oppenheimer et al., 2014; van Ruijven et al., 2014; AMAP, 2015; Cunsolo and Ellis, 2018). 

This report documents how people residing in coastal and cryosphere regions are already exposed to climate change hazards, and which of these hazards are projected to increase in the future. For example, mountain communities have been exposed to increased rockfall, rock avalanches and landslides due to permafrost degradation and glacier shrinkage, and to changes in snow avalanche type and seasonal timing (Section 2.3.1). Cryosphere changes that can impact water availability in mountain regions and for downstream populations (Sections 2.3.1, 2.3.4, 2.3.5) have implications for drinking water, irrigation, livestock grazing, hydropower production and tourism (Section 2.3). Some declining mountain glaciers hold sacred and symbolic meanings for local communities who will experience spiritual losses (Section 2.3.4, 2.3.5, and 2.3.6). Exposures to extreme warming, and continued sea ice and permafrost loss in the Arctic, challenge Indigenous communities with close interdependent relationships of economy, lifestyles, cultural identity, self-sufficiency, Indigenous knowledge, health and wellbeing with the Arctic cryosphere (Section 3.4.3, 3.5). 

The population living in low elevation coastal zones (land less than 10 m above sea level) is projected to increase to more than one billion by 2050 (Section 4.3.2.2). These people and communities are particularly exposed to future sea level rise, rising ocean temperature (including marine heat waves; Section 6.4), enhanced coastal erosion, increasing wind, wave height, storm intensity and ocean acidification (Section 4.3.4). These exposures bring associated risks for livelihoods linked to fisheries, tourism and trade, as well as loss of life, damaged assets, and disruption of basic services including safe water supplies, sanitation, energy and transportation networks (Chapters 4, 5, and 6; Cross-Chapter Box 9). 

1.5.3

Vulnerabilities in Natural Systems, Ecosystems, and Human Systems

Direct and indirect risks to natural systems are influenced by vulnerability to climate change as well as deterioration of ecosystem services. For example, about half of species assessed on the northeast United States continental shelf exhibited high to very high climate vulnerability due to temperature preferences and changes in habitat space (Hare et al., 2016), with corresponding northward range shifts for many species (Kleisner et al., 2017) and increased vulnerability for organisms or ecosystems unable to migrate or evolve at the rate required to adapt to ocean and cryosphere changes (Miller et al., 2018). Non-climatic pressures also magnify the vulnerability of ocean and cryosphere ecosystems to climate-related changes, such as overfishing, coastal development, and pollution, including plastic pollution (Halpern et al., 2008; Halpern et al., 2015; IPBES, 2018a; IPBES, 2018b; IPBES, 2018c; IPBES, 2018d). Conventional (fossil fuel-based) plastics produced in 2015 accounted for 3.8% of global CO2 emissions and could reach up to 15% by 2050 (Zheng and Suh, 2019). 

The vulnerability of mountain, Arctic and coastal communities is affected by social, political, historical, cultural, economic, institutional, environmental, geographical and/or demographic factors such as gender, age, race, class, caste, Indigeneity and disability (Thomas et al., 2019; Sections 2.3.6 and 3.5; Cross-Chapter Box 9). Disparities and inequities in such factors may result in social exclusion, inequalities and non-climatic challenges to health and wellbeing, economic development and basic human rights (Adger et al., 2014; Olsson et al., 2014; Smith et al., 2014). Those less advantaged often also have reduced access to and control over the social, financial, technological and environmental resources that are required for adaptation and transformation (Oppenheimer et al., 2014; AMAP, 2015), thus limiting options for coping and adapting to change (Hijioka et al., 2014). However, even populations with greater wealth and privilege can be vulnerable to some climate change risks (Cardona et al., 2012; Smith et al., 2014), especially if sources of wealth and wellbeing depend upon established infrastructure that is poorly suited to ocean or cryosphere change. 

Institutions and governance can shape vulnerability and adaptive capacity, and it can be challenging for weak governance structures to respond effectively to extreme or persistent climate change hazards (Sections 6.4 and 6.9; Cross-Chapter Box 3 in Chapter 1; Berrang-Ford et al., 2014; Hijioka et al., 2014). Furthermore, populations can be negatively impacted by inappropriate climate change mitigation and/or adaptation policies, particularly ones that further marginalise their knowledge, culture, values and livelihoods (Field et al., 2014; Cross-Chapter Box 4 in Chapter 1). 

Vulnerability is not static in place and time, nor homogeneously experienced. The vulnerabilities of individuals, groups, and populations to climate change is dynamic and diverse, and reflects changing societal and environmental conditions (Thomas et al., 2019). SROCC examines vulnerability following the conceptual definition presented in Cross-Chapter Box 2 in Chapter 1, and vulnerability in human systems is treated in relative rather than absolute terms.

1.6

Addressing the Causes and Consequences of Climate Change for the Ocean and Cryosphere

Effective and ambitious mitigation of climate change would be required to meet the temperature goal of the Paris Agreement (UNFCCC, 2015; IPCC, 2018). Similarly, effective and ambitious adaptation to climate change impacts on the ocean and cryosphere is necessary to enable CRDPs that minimise residual risk, and loss and damage (very high confidence; Cross-Chapter Box 2 in Chapter 1; IPCC, 2018). Mitigation refers to human actions to limit climate change by reducing the emissions and enhancing the sinks of greenhouse gases. Adaptation refers to processes of adjustment by natural or human systems to actual or expected climate and its effects, intended to moderate harm or exploit beneficial opportunities. The presidency of the 23rd Conference Of the Parties of United Nations Framework Convention on Climate Change (UNFCCC) introduced the oceans pathway into the climate solution space, acknowledging both the importance of the ocean in the climate system and that ocean commitments for adaptation and mitigation are available through Nationally Determined Contributions under the UNFCCC (Gallo et al., 2017).

1.6.2

Adaptation in Natural Systems, Ecosystems, and Human Systems

In AR5, a range of changes in ocean and cryosphere natural systems were linked with medium to high confidence to pressures associated with climate change (Cramer et al., 2014). Climate change impacts on natural ecosystems are variable in space and time. The multiplicity of pressures these natural systems experience impedes attribution of population or ecosystem responses to a specific ocean and/or cryosphere change. Moreover, the interconnectivity of populations within ecosystems means that a single ‘adaptive response’ of a population, or the aggregate response of an ecosystem (the adaptive responses of the interconnected populations), is influenced not just by direct pressures of climate change, but occurs in concert with the adaptive responses of other species in the ecosystem, further complicating efforts to disentangle specific patterns of adaptation.

Notwithstanding the network of pressures and adaptations, much effort has gone into resolving the mechanisms, interactions and feedbacks of natural systems associated with the ocean and cryosphere. Chapters 4, 5 and 6, as well as Cross-Chapter Box 9, assess new knowledge on the adaptive responses of wetlands, coral reefs, other coastal habitats, and the populations of marine organisms encountering ocean-based risks, including. Likewise, Chapters 2 and 3 describe emerging knowledge on how ecosystems in high-mountain and polar areas are adapting to cryosphere decline. 

AR5 and SR15 have highlighted the importance of evolutionary adaptation as a component of how populations adapt to climate change pressures (e.g., Pörtner et al., 2014; Hoegh-Guldberg et al., 2018). Acclimatisation (variation in morphology, physiology or behaviour) can result from changes in gene expression but does not involve change in the underlying DNA sequence. Responses related to acclimatisation can occur both within single generations and over several generations. In contrast, evolution requires changes in the genetic composition of a population over multiple generations; for example, by differential survival or fecundity of different genotypes (Sunday et al., 2014). Adaptive evolution is the subset of evolution attributable to natural selection, and natural selection may lead to populations becoming more fit (Sunday et al., 2014) or extend the range of environments where populations persist (van Oppen et al., 2015). The efficacy of natural selection is affected by population size (Charlesworth, 2009), standing genetic variation, the ability of a population to generate novel genetic variation, migration rates and the frequency of genetic recombination (Rice, 2002). Many studies have shown evolution of traits within and across life stages of populations (Pespeni et al., 2013; Hinners et al., 2017), but there are fewer studies on how evolutionary change can impact ecosystem or community function, and whether trait evolution is stable (Schaum and Collins, 2014). Although acclimatisation and evolutionary adaptation are separate processes, they influence each other, and both adaptive and maladaptive variation of traits can facilitate evolution (Schaum and Collins, 2014; Ghalambor et al., 2015). Natural evolutionary adaptation may be challenged by the speed and magnitude of current ocean and cryosphere changes, but emerging studies investigate how human actions may assist evolutionary adaptation and thereby possibly enhance the resilience of natural systems to climate change pressures (e.g., Box 5.4 in Section 5.5.2). Through acclimatisation and evolutionary adaptation to the pressures from climate change (and all other persistent pressures), populations, species and ecosystems present a constantly changing context for the adaptation of human systems to climate change. 

There are several human adaptation options for climate change impacts on the ocean and cryosphere. Adaptive responses include nature- and ecosystem-based approaches (Renaud et al., 2016; Serpetti et al., 2017). Additionally, more social-based approaches for human adaptation range from community-based and infrastructure-based approaches to managed retreat, along with other forms of internal migration (Black et al., 2011; Hino et al., 2017). Building on AR5 (Wong et al., 2014), Chapter 4 describes four main modes of adaptation to mean and extreme sea level rise: protect, advance, accommodate, and retreat. This report demonstrates that all modes of adaptation include mixes of institutional, individual, socio-cultural, engineering, behavioural and/or ecosystem-based measures (e.g., Section 4.4.2). 

The effectiveness and performance of different adaptation options across spatial and social scales is influenced by their social acceptance, political feasibility, cost-efficiency, co-benefits and trade-offs (Jones et al., 2012; Adger et al., 2013; Eriksen et al., 2015). Scientific evaluation of past successes and future options, including understanding barriers, limits, risks and opportunities, are complex and inadequately researched (Magnan and Ribera, 2016). In the end, adaptation priorities will depend on multiple parameters including the extent and rate of climate change, the risk attitudes and social preferences of individuals and institutions (and the returns they may gain) (Adger et al., 2009; Brügger et al., 2015; Evans et al., 2016; Neef et al., 2018) and access to finances, technology, capacity and other resources (Berrang-Ford et al., 2014; Eisenack et al., 2014).

Since AR5, transformational adaptation (i.e., the need for fundamental changes in private and public institutions and flexible decision-making processes to face climate change consequences) has been increasingly studied (Cross-Chapter Box 2 in Chapter 1). The recent literature documents how societies, institutions, and/or individuals increasingly assume a readiness to engage in transformative change, via their acceptance and promotion of fundamental alterations in natural or human systems (Klinsky et al., 2016). People living in and near coastal, mountain and polar environments often pioneer these types of transformations, since they are at the forefront of ocean and cryosphere change (e.g., Solecki et al., 2017). Community led and indigenous led adaptation research continues to burgeon (Ayers and Forsyth, 2009; David-Chavez and Gavin, 2018), especially in many mountain (Section 2.3.2.3), Arctic (Section 3.5), and coastal (Section 4.4.4.4, 4.4.5.4, Cross-Chapter Box 9) areas, and demonstrate potential for enabling transformational adaptation (Dodman and Mitlin, 2013; Chung Tiam Fook, 2017). Similarly, the concepts of scenario planning and ‘adaptation pathway’ design have expanded since AR5, especially in the context of development planning for coastal and delta regions (Section 4.4, Cross-Chapter Box 9; Wise et al., 2014; Maier et al., 2016; Bloemen et al., 2018; Flynn et al., 2018; Frame et al., 2018; Lawrence et al., 2018).

1.6.1

Mitigation and Adaptation Options in the Ocean and Cryosphere

Mitigation and adaptation pathways to avoid dangerous anthropogenic interference with the climate system (United Nations, 1992) are considered in SR15 (IPCC, 2018). SROCC assesses several ocean and cryosphere-specific measures for mitigation and adaptation including options for to address the causes of climate change, support biological and ecological adaptation, and enhance societal adaptation (Figure 1.2). Other measures have been proposed, including solar radiation management and several other forms of carbon dioxide removal, but these are not addressed in SROCC as they are covered in other products of the IPCC Sixth Assessment Cycle (SR15 and AR6 Working Group III) and are outside the scope of SROCC. SROCC does assess indirect mitigation measures that involve the ocean and the cryosphere (Figure 1.2) by supporting biological and ecological adaptation, such as through reducing nutrient and organic carbon pollution (which moderates ocean acidification in eutrophied areas) and conservation (which preserves biodiversity and habitats) in coastal regions (Billé et al., 2013).

A literature-based expert assessment shows that ocean-related mitigation measures have trade-offs, with the greatest benefits derived by combining global and local measures (high confidence; Gattuso et al., 2018). Local measures, such as pollution reduction and conservation, provide significant co-benefits and few adverse side effects (high confidence; Sections 5.5.1, 5.5.2). They can be relatively rapidly implemented, but are generally less effective in addressing the global problem (high confidence; Sections 5.5.1, 5.5.2). Likewise, local efforts to decrease air pollution near mountain glaciers and other cryosphere components, for example reducing black carbon emissions, can bring regional-scale benefits for health and in reducing snow and ice-melt (Shindell et al., 2012; Box 2.2).

Well-chosen human interventions can enhance the adaptive capacity of natural systems to climate change. Such interventions through manipulating an ecosystem’s structural or functional properties (e.g., restoration of mangroves) may minimise climate change pressures, enhance natural resilience and/or re-direct ecosystem responses to reduce cascading risks on societies. In human systems, adaptation can involve both infrastructure (e.g., enhanced sea defences) and community-based action (e.g., changes in policies and practices). Adaptation options to ongoing climate change are most effective when considered together with mitigation strategies because there are limits to effective adaptation, mitigation actions can make adaptation more difficult, and some adaptation measures may increase greenhouse gas emissions.

Adaptation and mitigation decisions are connected with economic concerns. In SROCC, two main economic approaches are used. The first comprises the Total Economic Value method and the valuation of ecosystem services. SROCC considers the paradigm of sustainable development, and the linkages between climate impacts on ecosystem services (Section 5.4.1) and the consequences on SDGs including food security or poverty eradication (Section 5.4.2). The second economic approach used are formal decision analysis methods, which help to identify options (also called alternatives) that perform best or well with regards to given objectives. These methods include cost-benefit analysis, multi-criteria analysis and robust decision-making and are specifically relevant for appraising long-term investment decisions in the context of coastal adaptation (Section 4.4.4.6).

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1.7

Governance and Institutions

SROCC conceptualises governance as deciding, managing, implementing and monitoring policies in the context of ocean and cryosphere change. Institutions are defined as formal and informal social rules that shape human behaviour (Roggero et al., 2017). Governance guides how different actors negotiate, mediate their interests and share their rights and responsibilities (Forino et al., 2015; See SROCC Annex I: Glossary and Cross-Chapter Box 3 in Chapter 1 for definition). Governance and institutions interface with climate and social-ecological change process across local, regional and global scales (Fischer et al., 2015; Pahl-Wostl, 2019). 

SROCC explores how the interlinked social-ecological systems affect challenge current governance systems in the context of ocean and cryosphere change. These challenges include three aspects. First, the scale of changes to ocean and cryosphere properties driven by global warming, and in the ecosystems they support and services they provide, are poorly matched to existing scales of governance (Sections 2.2.2.1; 2.3.1.3; 3.2.1; 3.5.3). Second, the nature of changes in ecosystem services resulting from changes in ocean and cryosphere properties, including services provided to humans living far from the mountains and coasts, are poorly matched to existing institutions and processes (Section 4.4.4). Third, many possible governance responses to these challenges could be of limited or diminished effectiveness unless they are coordinated on scales beyond that of currently available governance options (Section 6.9.2; Box 5.5) 

Hydrological processes in the high mountain cryosphere connect through upstream and downstream areas of river basins (Molden et al., 2016; Chen et al., 2018), including floodplains and deltaic regions (Kilroy, 2015; Cross-Chapter Box 3 in Chapter 1). These cross boundary linkages challenge local-scale governance and institutions that determine how the river-based ecosystem services that sustain food, water and energy are used and distributed (Rasul, 2014; Warner, 2016; Lele et al., 2018; Pahl-Wostl et al., 2018). Small Island States face rising seas that threaten habitability of their homeland and the possibility of losing their nation-state, cultural identity and voices in international governance (Gerrard and Wannier, 2013; Philip, 2018; Section 1.4, Cross-Chapter Box 9), highlighting the need for transboundary components to governance.

These governance challenges cannot be met without working across multiple organisations and institutions, bringing varying capacities, frameworks and spatial extents (Cross-Chapter Box 3 in Chapter 1). Progress in governance for ocean and cryosphere change will require filling gaps in legal frameworks (Amsler, 2016), aligning spatial mismatches (Eriksen et al., 2015; Young, 2016; Cosens et al., 2018), improving the ability for nations to cooperate effectively (Downie and Williams, 2018; Hall and Persson, 2018) and integrating across divided policy domains, most notably of climate change adaptation and disaster risk reduction (e.g., where slow sea level change also alters the implications for civil defense planning and the management of extreme events; Mysiak et al., 2018). 

Harmonising local, regional and global governance structures would provide an overarching policy framework for action and allocation of necessary resources for adaptation. Coordinating the top-down and bottom-up governance processes (Bisaro and Hinkel, 2016; Sabel and Victor, 2017; Homsy et al., 2019) to increase effectiveness of responses, mobilise and equitably distribute adequate resources and access private and public sector capabilities requires a polycentric approach to governance (Ostrom, 2010; Jordan et al., 2015). Polycentric governance connotes a complex form of governance with multiple centres of decision making working with some degree of autonomy (Carlisle and Gruby, 2017; Baldwin et al., 2018; Mewhirter et al., 2018; Hamilton and Lubell, 2019).

1.8

Knowledge Systems for Understanding and Responding to Change

Assessments of how climate change interacts with the planet and people are largely based on scientific knowledge from observations, theories, modelling and synthesis to understand physical and ecological systems (Section 1.8.1), societies (e.g., Cross-Chapter Box 2 in Chapter 1, Section 1.5) and institutions (e.g., Cross-Chapter Box 3 in Chapter 1). However, humans integrate information from multiple sources to observe and interact with their environment, respond to changes, and solve problems. Accordingly, SROCC also recognises the importance of Indigenous knowledge and local knowledge in understanding and responding to changes in the ocean and cryosphere (Sections 1.8.2, 1.8.3; Cross-Chapter Box 4 in Chapter 1).

 

1.8.1

Scientific Knowledge

1.8.1.2

Reanalysis Products

Advances have been made over the past decade in developing more reliable and more highly resolved ocean and atmosphere reanalysis products. Reanalysis products combine observational data with numerical models through data assimilation to produce physically consistent, and spatially complete ocean and climate products (Balmaseda et al., 2015; Lellouche et al., 2018; Storto et al., 2018; Zuo et al., 2018). Ocean reanalyses are widely used to understand changes in physical properties (Section 3.2.1, 5.2), extremes (Sections 6.3 to 6.6), circulation (Section 6.6, 6.7) and to provide climate diagnostics (Wunsch et al., 2009; Balmaseda et al., 2013; Hu and Sprintall, 2016; Carton et al., 2018). Reanalysis products are used in SROCC for assessing climate change process that cause changes in the ocean and cryosphere (e.g., Sections 2.2.1, 3.2.1, 3.3.1, 3.4.1, 5.2.2, 6.3.1, 6.6.1, 6.7.1). Improvements in reanalysis products provide more realistic forcing for regional models, which are used for assessing regional ocean and cryosphere changes that cannot be resolved in global-scale models (e.g., Section 2.2.1; Mazloff et al., 2010; Fenty et al., 2017). The weather forecasts, and seasonal to decadal predictions building on reanalysis products have important applications in the early warning systems that reduce risk and aid human adaptation to extreme events (Sections 6.3.4, 6.4.3, 6.5.3, 6.7.3, 6.8.5).

1.8.1.3

Model Simulation Data

Models are numerical approximations of the Earth system that allow hypotheses about the mechanisms of ocean and cryosphere change to be tested, support attribution of observed changes to specific forcings (Section 1.3), and are the best available information for assessing future change (Figure 1.3). General Circulation Models (GCMs) typically simulate the atmosphere, ocean, sea ice, and land surface, and sometimes also incorporate terrestrial and marine ecosystems. Earth System Models (ESM) are climate models that explicitly include the carbon cycle and may include additional components (e.g., atmospheric chemistry, ice sheets, dynamic vegetation, nitrogen cycle, but also urban or crop models). The systematic set of global-scale model experiments (Taylor et al., 2012) used in SROCC were produced by CMIP5 (Cross-Chapter Box 1 in Chapter 1), including both GCMs and ESMs. 

Models may differ in their spatial resolution, and in the extent to which processes are explicitly represented or approximated (parameterised). Model output can be biased due to uncertainties in their physical equations or parameterisations, specification of initial conditions, knowledge of external forcing factors, and unaccounted processes and feedbacks (Hawkins and Sutton, 2009; Deser et al., 2012; Gupta et al., 2013; Lin et al., 2016). Since AR5 there have been advances in modelling the dynamical processes of the Greenland and Antarctica ice sheets, leading to better representation of the range of potential future sea level rise scenarios (Sections 4.2.3). Downscaling, including the use of regional models, makes it possible to improve the spatial resolution of model output in order to better resolve past and future climate change in specific areas, such as high mountains and coastal seas (e.g., Sections 2.2.2, 3.2.3, 3.5.4, 4.2.2, 6.3.1). For biological processes, such as nutrient levels and organic matter production, model uncertainty at regional scales is the main issue limiting confidence in future projections (Sections 5.3, 5.7). While model projections of range shifts for fishes agree with theory and observations, at a regional scale there are known deficiencies in the ways models represent the impacts of ocean variables such as temperature and productivity (Sections 5.2.3, 5.7).

1.8.1.4

Palaeoclimate Data

Palaeoclimate data provide a way to establish the nature of ocean and cryosphere changes prior to direct measurements (Figure 1.3), including natural variability and early anthropogenic climate change (Masson-Delmotte et al., 2013; Abram et al., 2016). Palaeoclimate records utilise the accumulation of physical, chemical or biological properties within natural archives that are related to climate at the time the archive formed. Commonly used palaeoclimate evidence for ocean and cryosphere change comes from marine and lake sediments, ice layers and bubbles, tree growth rings, past shorelines and shallow reef deposits. In many mountain areas, centuries to millennia of palaeoclimate information is now being lost through widespread melting of glacier ice (Cross-Chapter Box 6 in Chapter 2). Palaeoclimate data are spatially limited (Figure 1.3), but often represent regional to global-scale climate patterns, either individually or as syntheses of networks of data (PAGES2K Consortium, 2017)

Palaeoclimate data provide evidence for multi-metre global sea level rises and shifts in climate zones and ocean ecosystems during past warm climate states where temperatures were similar to those expected later this century (Hansen et al., 2016; Fischer et al., 2018; Section 4.2.2). Palaeoclimate reconstructions give context to recent ocean and cryosphere changes that are unusual in the context of variability over past centuries to millennia, including acceleration in Greenland and Antarctic Peninsula ice-melt (Section 3.3.1), declining Arctic sea ice (Section 3.2.1), and emerging evidence for a slowdown of AMOC (Section 6.7.1). Assessments of climate model performance across a wider-range of climate states than is possible using direct observations alone also draws on palaeoclimate data (Flato et al., 2013), and since AR5 important progress has been made to calibrate modelled ice sheet processes and future sea level rise based on palaeoclimate evidence (Cross-Chapter Box 8 in Chapter 3).

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1.8.1.1

Ocean and Cryosphere Observations 

Long-term sustained observations are critical for detecting and understanding the processes of ocean and cryosphere change (Rhein et al., 2013; Vaughan et al., 2013). Scientific knowledge of the ocean and cryosphere has increased through time and geographical space (Figure 1.3). In situ ocean subsurface temperature and salinity observations have increased in spatial and temporal coverage since the middle of the 19th century (Abraham et al., 2013), and near global coverage (60°S–60°N) of the upper 2,000 m has been achieved since 2007 due to the international Argo network (Riser et al., 2016; Figure 1.3). Improved data quality and data analysis techniques have reduced uncertainties in global ocean heat uptake estimates (Sections 1.4.1, 5.2.2). In addition to providing deep ocean measurements, repeated hydrographic physical and biogeochemical observations since AR5 have led to improved estimates of ocean carbon uptake and ocean deoxygenation (Sections 1.4.1, 5.2.2.3, 5.2.2.4). Targeted observational programmes have improved scientific knowledge for specific regions and physical processes of particular concern in a warming climate, including the Greenland and West Antarctic ice sheets (Section 3.3), and the AMOC (Section 6.7). Ocean and cryosphere mass changes and sea level studies have benefited from sustained or newly implemented satellite-based remote sensing technologies, complemented by in situ data such as tide gauges measurements (Sections 3.3, 4.2; Dowell et al., 2013; Raup et al., 2015; PSMSL, 2016). Glacier length measurements in some locations go back many centuries (Figure 1.3), but it is the systematic high resolution satellite monitoring of a large number of the world’s glaciers since the late 1970s that has improved global assessments of glacier mass loss (Sections 2.2.3, 3.3.2). 

Limitations in knowledge of ocean and cryosphere change remain, creating knowledge gaps for the SROCC assessment. Ocean and cryosphere datasets are frequently short, and do not always span the key IPCC assessment time intervals (Cross-Chapter Box 1 in Chapter 1), so for many parameters the full magnitude of changes since the pre-industrial period is not observed (Figure 1.3). The brevity of ocean and cryosphere measurements also means that some expected changes cannot yet be detected with confidence in direct observations (e.g., Antarctic sea ice loss in Section 3.2.1, AMOC weakening in Section 6.7.1), or other observed changes cannot yet be robustly attributed to anthropogenic factors (e.g., ice sheet mass loss in Section 3.3.1). Observations for many key ocean variables (Bojinski et al., 2014), such as ocean currents, surface heat fluxes, oxygen, inorganic carbon, subsurface salinity, phytoplankton biomass and diversity, etc., do not yet have global coverage or have not reached the required density or accuracy for detection of change. Some ocean and cryosphere areas remain difficult to observe systematically, for example, the ocean under sea ice, subsurface permafrost, high mountain areas, marginal seas, coastal areas (Section 4.2.2.3) and ocean boundary currents (Hu and Sprintall, 2016), basin interconnections (Section 6.6) and the Southern Ocean (Sections 3.2, 5.2.2). Measurements that reflect ecosystem change are often location or species specific, and assessments of long-term ocean ecosystem changes are currently only feasible for a limited subset of variables, for example coral reef health (e.g., coral reef health) (Section 5.3; Miloslavich et al., 2018). The deep ocean below 2,000 m is still rarely observed (Talley et al., 2016), limiting (for example) the accurate estimate of deep ocean heat uptake and, consequently the full magnitude of Earth’s energy imbalance (e.g., von Schuckmann et al., 2016; Johnson et al., 2018; Sections 1.2, 1.4, 5.2.2).

1.8.2

Indigenous Knowledge and Local Knowledge

Humans create, use, and adapt knowledge systems to interact with their environment (Agrawal, 1995; Escobar, 2001; Sillitoe, 2007), and to observe and respond to change (Huntington, 2000; Gearheard et al., 2013; Maldonado et al., 2016; Yeh, 2016). Indigenous knowledge (IK) refers to the understandings, skills, and philosophies developed by societies with long histories of interaction with their natural surroundings. It is passed on from generation to generation, flexible, and adaptive in changing conditions, and increasingly challenged in the context of contemporary climate change. Local knowledge (LK) is what non-Indigenous communities, both rural and urban, use on a daily and lifelong basis. It is multi-generational, embedded in community practices and cultures and adaptive to changing conditions (FAO, 2018). Each chapter of SROCC cites examples of IK and LK related to ocean and cryosphere change.

IK and LK stand on their own, and also enrich and complement each other and scientific knowledge. For example, Australian Aboriginal groups’ Indigenous oral history provides empirical corroboration of the sea level rise 7,000 years ago (Nunn and Reid, 2016), and their seasonal calendars direct hunting, fishing, planting, conservation and detection of unusual changes today (Green et al., 2010). LK works in tandem with scientific knowledge, for example, as coastal Australian communities consider the impacts and trade-offs of sea level rise (O’Neill and Graham, 2016).

Both IK and LK are increasingly used in climate change research and policy efforts to engage affected communities to facilitate site-specific understandings of, and responses to, the local effects of climate change (Hiwasaki et al., 2014; Hou et al., 2017; Mekonnen et al., 2017). IK and LK enrich CRDPs particularly by engaging multiple stakeholders and the diversity of socioeconomic, cultural and linguistic contexts of populations affected by changes in the ocean and cryosphere (Cross-Chapter Box 4 in Chapter 1). 

Global environmental assessments increasingly recognise the importance of IK and LK (Thaman et al., 2013; Beck et al., 2014; Díaz et al., 2015). References to IK in IPCC assessment reports increased 60% from AR4 to AR5, and highlighted the exposures and vulnerabilities of Indigenous populations to climate change risks related to socioeconomic status, resource-based dependence and geographic location (Ford et al., 2016a). All four IPBES assessments in 2018 (IPBES, 2018a; IPBES, 2018b; IPBES, 2018c; IPBES, 2018d) engaged IK and LK (Díaz et al., 2015; Roué and Molnar, 2017; Díaz et al., 2018). Peer-reviewed research on IK and LK is burgeoning (Savo et al., 2016), providing information that can guide responses and inform policy (Huntington, 2011; Nakashima et al., 2012; Lavrillier and Gabyshev, 2018). However, most global assessments still fail to incorporate ‘the plurality and heterogeneity of worldviews’ (Obermeister, 2017), resulting ‘in a partial understanding of core issues that limits the potential for locally and culturally appropriate adaptation responses’ (Ford et al., 2016b).

IK and LK provide case specific information that may not be easily extrapolated to the scales of disturbance that humans exert on natural systems (Wohling, 2009). Some forms of IK and LK are also not amenable to being captured in peer-reviewed articles or published reports, and efforts to translate IK and LK into qualitative or quantitative data may mute the multidimensional, dynamic and nuanced features that give IK and LK meaning (DeWalt, 1994; Roncoli et al., 2009; Goldman and Lovell, 2017). Nonetheless, efforts to collaborate with IK and LK knowledge holders (Baptiste et al., 2017; Karki et al., 2017; Lavrillier and Gabyshev, 2017; Roué et al., 2017; David-Chavez and Gavin, 2018) and to systematically assess published IK and LK literature in parallel with scientific knowledge result in increasingly effective usage of the multiple knowledge systems to better characterise and address ocean and cryosphere change (Huntington et al., 2017; Nalau et al., 2018; Ford et al., 2019).

1.8.3

The Role of Knowledge in People’s Responses to Climate, Ocean and Cryosphere Change

To hold global average temperature to well below 2°C above pre-industrial levels, substantial changes in the day-to-day activities of individuals, families, communities, the private sector, and governance bodies will be required (Ostrom, 2010; Creutzig et al., 2018). Enabling these changes at a meaningful societal scale requires sensitivity to communities and their use of multiple knowledge systems to best motivate effective responses to the risks and opportunities posed by climate change (medium confidence) (1.8.2, Cross-Chapter Box 4 in Chapter 1). Meaningful engagement of people and communities with climate change information depends on that information cohering with their perception of how the world works (Crate and Fedorov, 2013). The values and identities people hold affect how acceptable they find the behavioural changes, technological solutions and governance that climate change action requires (Moser, 2016). 

Education and climate literacy contribute to climate change action and adaptation (high confidence). Although public understanding of humanity’s role in both causing and abating climate change has increased in the last decade (Milfont et al., 2017), levels of climate concern vary greatly globally (Lee et al., 2015). Educational attainment has the strongest effect on raising climate change awareness (Lee et al., 2015), and research documents the value of evidence-based climate change education, particularly during formal schooling (Motta, 2018). People further understand climate change as a serious threat when they experience it in their lives and have knowledge of its human causes (Lee et al., 2015; Shi et al., 2016). Education and tailored climate communication strategies that are respectful of people’s values and identity can aid acceptance and implementation of the local to global-scale approaches and policies required for effective climate change mitigation and adaptation (Shi et al., 2016; Anisimov and Orttung, 2018; Sections 3.5.4, 4.4), while also supporting CRDPs (see also Cross-Chapter Box 2 in Chapter 1, and FAQ1.2). 

Human psychology complicates engagement with climate change, due to complex social factors, including values (Corner et al., 2014), identity (Unsworth and Fielding, 2014), ideology (Smith and Mayer, 2019) and the framing of climate messaging. Additionally, psychology effects adaptation actions, motivated by perceptions that others are already adapting, avoidance of an unpleasant state of mind, feelings of self-efficacy and belief in the efficacy of the adaptation action (van Valkengoed and Steg, 2019). Better understandings of the psychological implications across diverse communities and social and political contexts will facilitate a just transition of both emissions reduction and adaptation (Schlosberg et al., 2017). Impacts of climate change on natural and human environments (e.g., extreme weather) or human-caused modifications to the environment (e.g., adaptation) will raise further psychological challenges. This includes psychological impacts to the emotional wellbeing of people adversely affected by climate change (Ogunbode et al., 2018), resulting in solastalgia (Albrecht et al., 2007), a distress akin to homesickness while in their home environment (McNamara and Westoby, 2011).

1.9

Approaches Taken in this Special Report

1.9.1

Methodologies Relevant to this Report

SROCC assesses literature on ocean and cryosphere change and associated impacts and responses, focusing on advances in knowledge since AR5. The literature used is primarily published, peer-reviewed scientific, social science and humanities research. In some cases, grey literature sources (for example, published reports from governments, industry, research institutes and non-government organisations) are used where there are important gaps in available peer-reviewed literature. It is recognised that published knowledge from many parts of the world most vulnerable to ocean and cryosphere change is still limited (Czerniewicz et al., 2017). 

Where possible, SROCC draws upon established methodologies and/or frameworks. Cross-Chapter Boxes in Chapter 1 address methodologies used for projections of future change (Cross-Chapter Box 1 in Chapter 1), for assessing and reducing risk (Cross-Chapter Box 2 in Chapter 1), for governance options relevant to a problem or region (Cross-Chapter Box 3 in Chapter 1), and for using IK and LK (Cross-Chapter Box 4 in Chapter 1). It is recognised in the assessment process that multiple and non-static factors determine human vulnerabilities to climate change impacts, and that ecosystems provide essential services that have both commercial and non-commercial value (Section 1.5). Economic methods are also important in SROCC, for estimating the economic value of natural systems, and for aiding decision-making around mitigation and adaptation strategies (Section 1.6).

1.9.2

Communication of Confidence in Assessment Findings

SROCC uses calibrated language for the communication of confidence in the assessment process (Mastrandrea et al., 2010; Mach et al., 2017). Calibrated language is designed to consistently evaluate and communicate uncertainties that arise from incomplete knowledge due to a lack of information, or from disagreement about what is known or even knowable. The IPCC calibrated language uses qualitative expressions of confidence based on the robustness of evidence for a finding, and (where possible) uses quantitative expressions to describe the likelihood of a finding (Figure 1.4).

Qualitative expressions (confidence scale) describe the validity of a finding based on the type, amount, quality and consistency of evidence, and the degree of agreement between different lines of evidence (Figure 1.4, step 2). Evidence includes all knowledge sources, including IK and LK where available. Very high and high confidence findings are those that are supported by multiple lines of robust evidence with high agreement. Low or very low confidence describe findings for which there is limited evidence and/or low agreement among different lines of evidence, and are only presented in SROCC if they address a major topic of concern. 

Quantitative expressions (likelihood scale) are used when sufficient data and confidence exists for findings to be assigned a quantitative or probabilistic estimate (Figure 1.4, step 3). In the scientific literature, a finding is often said to be significant if it has a likelihood exceeding 95% confidence. Using calibrated IPCC language, this level of statistical confidence would be termed extremely likely. Lower levels of likelihood than those derived numerically can be assigned by expert judgement to take into account structural or measurement uncertainties within the products or data used to determine the probabilistic estimates (e.g., Table CB1.1). Likelihood statements may be used to describe how climate changes relate to the ends of distribution functions, such as in detection and attribution studies that assess the likelihood that an observed climate change or event is different to a reference climate state (Section 1.3). In other situations, likelihood statements refer to the central region across a distribution of possibilities. Examples are the estimates of future changes based on large ensembles of climate model simulations, where the central 66% of estimates across the ensemble (i.e., the 17–83% range) would be termed a likely range (Figure 1.4, step 3). 

It is increasingly recognised that effective risk management requires assessments not just of ‘what is most likely’ but also of ‘how bad things could get’ (Mach et al., 2017; Weaver et al., 2017; Xu and Ramanathan, 2017; Spratt and Dunlop, 2018; Sutton, 2018). In response to the need to reframe policy relevant assessments according to risk (Section 1.5; Mach et al., 2016; Weaver et al., 2017; Sutton, 2018), an effort is made in SROCC to report on potential changes for which there is low scientific confidence or a low likelihood of occurrence, but that would have large impacts if realised (Mach et al., 2017). In some cases where evidence is limited or emerging, phenomena may instead be discussed according to physically plausible scenarios of impact (e.g., Table 6.1). 

In some cases, deep uncertainty (Cross-Chapter Box 5 in Chapter 1) may exist in current scientific assessments of the processes, rate, timing, magnitude, and consequences of future ocean and cryosphere changes. This includes physically plausible high-impact changes, such as high-end sea level rise scenarios that would be costly if realised without effective adaptation planning and even then may exceed limits to adaptation. Means such as expert judgement, scenario building, and invoking multiple lines of evidence enable comprehensive risk assessments even in cases of uncertain future ocean and cryosphere changes.

1.10

Integrated Storyline of this Special Report

The chapters that follow in this special report are framed around geographies or climatic processes where the ocean and/or cryosphere are particularly important for ecosystems and people. The chapter order follows the movement of water from Earth’s shrinking mountain and polar cryosphere into our rising and warming ocean. 

Chapter 2 assesses High Mountain areas outside of the polar regions, where glaciers, snow and/or permafrost are common. Chapter 3 moves to the Polar Regions of the northern and southern high latitudes, which are characterised by vast stores of frozen water in ice sheets, glaciers, ice shelves, sea ice and permafrost, and by the interaction of these cryosphere elements and the polar oceans. Chapter 4 examines Sea Level Rise and the hazards this brings to Low-Lying Regions, Coasts and Communities. Chapter 5 focuses on the Changing Ocean, with a particular focus on how climate change impacts on the ocean are altering Marine Ecosystems and affecting Dependent Communities. Chapter 6 is dedicated to assessing Extremes and Abrupt Events, and reflects the potential for rapid and possibly irreversible changes in Earth’s ocean and cryosphere, and the challenges this brings to Managing Risk. The multitude ways in which Low-Lying Islands and Coasts are exposed and vulnerable to the impacts of ocean and cryosphere change, along with resilience and adaptation strategies, opportunities and governance options specific to these settings, is highlighted in integrative Cross-Chapter Box 9. 

This report does not attempt to assess all aspects of the ocean and cryosphere in a changing climate. Examples of research themes that will be covered elsewhere in the IPCC Sixth Assessment Cycle and not SROCC include: assessments of ocean and cryosphere changes in the CMIP6 experiments (AR6), cryosphere changes outside of polar and high mountain regions (e.g., snow cover in temperate and low altitude settings; AR6), and a thorough assessment of mitigation options for reducing climate change impacts (SR15, AR6 WGIII). 

Each chapter of SROCC presents an integrated storyline on the ocean and/or cryosphere in a changing climate. The chapter assessments each present evidence of the pervasive changes that are already underway in the ocean and cryosphere (Figure 1.5). The impacts that physical changes in the ocean and cryosphere have had on ecosystems and people are assessed, along with lessons learned from adaptation measures that have already been employed to avoid adverse impacts. The assessments of future change in the ocean and cryosphere demonstrate the growing and accelerating changes projected for the future and identify the reduced impacts and risks that choices for a low greenhouse gas emission future would have compared with a high emission future (Figure 1.5). Potential adaptation strategies to reduce future risks to ecosystems and people are assessed, including identifying where limits to adaptation may be exceeded. The local- to global-scale responses for charting CRDPs are also assessed.

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FAQ 1.1: How do changes in the ocean and cryosphere affect our life on planet Earth? 

 

The ocean and cryosphere regulate the climate and weather on Earth, provide food and water, support economies, trade and transportation, shape cultures and influence our well-being. Many of the recent changes in Earth’s ocean and cryosphere are the result of human activities and have consequences on everyone’s life. Deep cuts in greenhouse gas emissions will reduce negative impacts on billions of people and help them adapt to changes in their environment. Improving education and combining scientific knowledge with Indigenous knowledge and local knowledge helps communities to further address the challenges ahead.

The ocean and cryosphere—a collective name for the frozen parts of the Earth—are essential to the climate and life giving processes on our planet. 

Changes in the ocean and cryosphere occur naturally, but the speed, magnitude, and pervasiveness of the global changes happening right now have not been observed for millennia or longer. Evidence shows that the majority of ocean and cryosphere changes observed in the past few decades are the result of human influences on Earth’s climate. 

Every one of us benefits from the role of the ocean and cryosphere in regulating climate and weather. The ocean has absorbed about a third of the carbon dioxide humans have emitted from the burning of fossil fuels since the Industrial Revolution, and the majority (more than 90%) of the extra heat within the Earth system. In this way, the ocean has slowed the warming humans and ecosystems have experienced on land. The reflective surface of snow and ice reduce the amount of the sun’s energy that is absorbed on Earth. This effect diminishes as snow and ice melts, contributing to amplified temperature rise across the Arctic. The ocean and cryosphere also sustain life giving water resources, by rain and snow that come from the ocean, and by melt water from snow and glaciers in mountain and polar regions.

Nearly two billion people live near the coast, and around 800 million on land less than 10 m above sea level. The ocean directly supports the food, economies, cultures and well-being of coastal populations (see FAQ 1.2). The livelihoods of many more are tied closely to the ocean through food, trade, and transportation. Fish and shellfish contribute about 17% of the non-grain protein in human diets and shipping transports at least 80% of international imports and exports. But the ocean also brings hazards to coastal populations and infrastructure, and particularly to low-lying coasts. These populations are increasingly exposed to tropical cyclones, marine heat waves, sea level rise, coastal flooding and saltwater incursion into groundwater resources.

In high mountains and the Arctic, around 700 million people live in close contact with the cryosphere. These people, including many Indigenous Peoples, depend on snow, glaciers and sea ice for their livelihoods, food and water security, travel and transport, and cultures (see FAQ 1.2). They are also exposed to hazards as the cryosphere changes, including flood outbursts, landslides and coastal erosion. Changes in the polar and high mountain regions also have far-reaching consequences for people in other parts of the world (see FAQ 3.1).

Warming of the climate system leads to sea level rise. Melt from glaciers and ice sheets is adding to the amount of water in the ocean, and the heat being absorbed by the ocean is causing it to expand and take up more space. Today’s sea level is already about 20 cm higher than in 1900. Sea level will continue to rise for centuries to millennia because the ocean system reacts slowly. Even if global warming were to be halted, it would take centuries or more to halt ice sheet melt and ocean warming.

Enhanced warming in the Arctic and in high mountains is causing rapid surface melt of glaciers and the Greenland ice sheet. Thawing of permafrost is destabilising soils, human infrastructure, and Arctic coasts, and has the potential to release vast quantities of methane and carbon dioxide into the atmosphere that will further exacerbate climate change. Widespread loss of sea ice in the Arctic is opening up new routes for shipping, but at the same time is reducing habitats for key species and affecting the livelihoods of Indigenous cultures. In Antarctica, glacier and ice sheet loss is occurring particularly quickly in places where ice is in direct contact with warm ocean water, further contributing to sea level rise. 

Ocean ecosystems are threatened globally by three major climate change-induced stressors: warming, loss of oxygen and acidification. Marine heat waves are occurring everywhere across the surface ocean, and are becoming more frequent and more intense as the ocean warms. These are causing disease and mass-mortality that put, for example, coral reefs and fish populations at risk. Marine heat waves last much longer than the heat waves experienced on land, and are particularly harmful for organisms that cannot move away from areas of warm water. 

Warming of the ocean reduces not only the amount of oxygen it can hold, but also tend to stratify it. As a result, less oxygen is transported to depth, where it is needed to support ocean life. Dissolved carbon dioxide that has been taken up by the ocean reacts with water molecules to increase the acidity of seawater. This makes the water more corrosive for marine organisms that build their shells and structures out of mineral carbonates, such as corals, shellfish and plankton. These climate-change stressors occur alongside other human-driven impacts, such as overfishing, excessive nutrient loads (eutrophication), and plastic pollution. If human impacts on the ocean continue unabated, declines in ocean health and services are projected to cost the global economy 428 billion USD yr-1 by 2050, and 1.979 trillion USD yr-1 by 2100. 

The speed and intensity of the future risks and impacts from ocean and cryosphere change depend critically on future greenhouse gas emissions. The more these emissions can be curbed, the more the changes in the ocean and cryosphere can be slowed and limited, reducing future risks and impacts. But humankind is also exposed to the effects of changes triggered by past emissions, including sea level rise that will continue for centuries to come. Improving education and using scientific knowledge alongside local knowledge and Indigenous knowledge can support the development of context-specific options that help communities to adapt to inevitable changes and respond to challenges ahead.

FAQ 1.2: How will changes in the ocean and cryosphere affect meeting the SDGs? 

Ocean and cryosphere change affect our ability to meet the United Nations Sustainable Development Goals (SDGs). Progress on the SDGs support climate action that will reduce future ocean and cryosphere change, and as well as the adaptation responses to unavoidable changes. There are also trade-offs between SDGs and measures that help communities to adjust to their changing environment, but limiting greenhouse gas emissions opens more options for effective adaptation and sustainable development.

The SDGs were adopted by the United Nations in 2015 to support action for people, planet and prosperity (FAQ 1.2, Figure 1). The 17 goals and their 169 targets strive to end poverty and hunger, protect the planet and reduce gender, social and economic inequities by 2030.

SDG 13 (Climate Action) explicitly recognises that changing climatic conditions are a global concern. Climate change is already causing pervasive changes in Earth’s ocean and cryosphere (FAQ 1.1). These changes are impacting food, water and health securities, with consequences for achieving SDG 2 (Zero Hunger), SDG 3 (Good Health and Well-Being), SDG 6 (Clean Water and Sanitation), and SDG 1 (No Poverty). Climate change impacts on Earth’s ocean and cryosphere also affect the environmental goals for SDG 14 (Life below Water) and SDG 15 (Life on Land), with additional implications for many of the other SDGs.

SDG 6 (Clean Water and Sanitation) will be affected by ocean and cryosphere changes. Melting mountain glaciers bring an initial increase in water, but as glaciers continue to shrink so too will the essential water they provide to millions of mountain dwellers, downstream communities, and cities. These populations also depend on water flow from the high mountains for drinking, sanitation, and irrigation, and for SDG 7 (Affordable and Clean Energy). Water security is also threatened by changes in the magnitude and seasonality of rainfall, driven by rising ocean temperatures, which increases the risk of severe storms and flooding in some regions, or the risk of more severe or more frequent droughts in other regions. Among other effects, ongoing sea level rise is allowing salt water to intrude further inland, contaminating drinking water and irrigation sources for some coastal populations. Actions to address these threats will likely require new infrastructure to manage rain, melt water, and river flow, in order to make water supplies more reliable. These actions would also benefit SDG 3 (Good Health and Well-Being) by reducing the risk of flooding and negative health outcomes posed by extreme rainfall and outbursts of glacial melt.

Climate change impacts on the ocean and cryosphere also have many implications for progress on food security that is addressed in SDG 2 (Zero Hunger). Changes in rainfall patterns caused by ocean warming will increase aridity in some areas and bring more (or more intense) rainfall to others. In mountain regions, these changes bring varying challenges for maintaining reliable crops and livestock production. Some adaptation opportunities might be found in developing strains of crops and livestock better adapted to the future climate conditions, but this response option is also challenged by the rapid rate of climate change. In the Arctic, very rapidly warming temperatures, diminishing sea ice, reduced snow cover and degradation of permafrost are restricting the habitats and migration patterns of important food sources (SDG 2 Zero Hunger), including reindeer and several marine mammals (SDG 15 Life on Land; SDG 14 Life below Water), resulting in reduced hunting opportunities for staple foods that many northern Indigenous communities depend upon.

Rising temperatures, and changes in ocean nutrients, acidity and salinity are altering SDG 14 (Life Below Water). The productivity and distributions of some fish species are changing in ways that alter availability of fish to long-established fisheries, whereas the range of fish populations may move to become available in some new coastal and open ocean areas. 

Ocean changes are of concern for small island developing states and coastal cities and communities. Beyond possible reductions in marine food supply and related risks for SDG 2 (Zero Hunger), their lives, livelihoods and well-being are also threatened in ways that are linked to several SDGs, including SDG 3 (Good Health and Wellbeing), SDG 8 (Decent Work and Economic Growth), SDG 9 (Industry, Innovation, and Infrastructure), and SDG 11 (Sustainable Cities and Communities). For example, sea level rise and warming oceans can cause inundation of coastal homes and infrastructure, more powerful tropical storms, declines in established economies such as tourism and losses of cultural heritage and identity. Improved community and coastal infrastructure can help to adapt to these changes, and more effective and faster disaster responses from health sectors and other emergency services can assist the populations who experience these impacts. In some situations, the most appropriate responses may involve relocation of critical services and, in some cases, communities; and for some populations, migration away from their homeland may become the only viable response.

Without transformative adaptation and mitigation, climate change could undermine progress towards achieving the 2030 SDGs, and make it more difficult to implement CRDPs in the longer term. Reducing global warming (mitigation) provides the best possibility to limit the speed and extent of ocean and cryosphere change and give more options for effective adaptation and sustainable development. Progress on SDG 4 (Quality Education), SDG 5 (Gender Equality) and SDG 10 (Reduced Inequalities) can moderate the vulnerabilities that shape people’s risk to ocean and cryosphere change, while SDG 12 (Responsible Consumption and Production), SDG 16 (Peace, Justice and Institutions) and SDG 17 (Partnerships for the Goals) will help to facilitate the scales of adaptation and mitigation responses required to achieve sustainable development. Investment in social and physical infrastructure that supports adaptation to inevitable ocean and cryosphere changes will enable people to participate in initiatives to achieve the SDGs. Current and past IPCC efforts have focused on identifying CRDPs. Such adaptation and mitigation strategies, supported by adequate investments, and understanding the potential for SDG initiatives to increase the exposure or vulnerability of the activities to climate change hazards, could also constitute pathways for progress on the SDGs.

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Footnotes

  1.  In this report, the following summary terms are used to describe the available evidence: limited, medium, or robust; and for the degree of agreement: low, medium or high. A level of confidence is expressed using five qualifiers: very low, low, medium, high and very high, and typeset in italics, for example, medium confidence. For a given evidence and agreement statement, different confidence levels can be assigned, but increasing levels of evidence and degrees of agreement are correlated with increasing confidence (see Section 1.9.2 and Figure 1.4 for more details).
  2. In this report, the following terms have been used to indicate the assessed likelihood of an outcome or a result: Virtually certain 99–100% probability, Very likely 90–100%, Likely 66–100%, About as likely as not 33–66%, Unlikely 0–33%, Very unlikely 0–10%, and Exceptionally unlikely 0–1%. Additional terms (Extremely likely: 95–100%, More likely than not >50–100%, and Extremely unlikely 0–5%) may also be used when appropriate. Assessed likelihood is typeset in italics, for example, very likely (see Section 1.9.2 and Figure 1.4 for more details). This Report also uses the term ‘likely range’ to indicate that the assessed likelihood of an outcome lies within the 17–83% probability range.
  3. Confidence/likelihood statements in Sections 1.4.1 and 1.4.2 derived from AR5 and SR15, unless otherwise specified

High Mountain Areas