technical-summary — Global Warming of 1.5 ºC

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Summary for Policymakers

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IIntroduction
AUnderstanding Global Warming of 1.5°C*
BProjected Climate Change, Potential Impacts and Associated Risks
CEmission Pathways and System Transitions Consistent with 1.5°C Global Warming
DStrengthening the Global Response in the Context of Sustainable Development and Efforts to Eradicate Poverty
+Core Concepts Central to this Special Report
+Acknowledgements
+Citation
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Framing and Context

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1.1Assessing the Knowledge Base for a 1.5°C Warmer World
1.2Understanding 1.5°C: Reference Levels, Probability, Transience, Overshoot, and Stabilization
1.3Impacts at 1.5°C and Beyond
- 1.3.1Definitions
- 1.3.2Drivers of Impacts
- 1.3.3Uncertainty and Non-Linearity of Impacts
1.4Strengthening the Global Response
1.5Assessment Frameworks and Emerging Methodologies that Integrate Climate Change Mitigation and Adaptation with Sustainable Development
- 1.5.1Knowledge Sources and Evidence Used in the Report
- 1.5.2Assessment Frameworks and Methodologies
1.6Confidence, Uncertainty and Risk
1.7Storyline of the Report
FAQsFrequently Asked Questions
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Mitigation pathways compatible with 1.5°C in the context of sustainable development

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2.1Introduction to Mitigation Pathways and the Sustainable Development Context
2.2Geophysical Relationships and Constraints
- 2.2.1Geophysical Characteristics of Mitigation Pathways
  - 2.2.1.1Geophysical uncertainties: non-CO₂ forcing agents
  - 2.2.1.2Geophysical uncertainties: climate and Earth system feedbacks
- 2.2.2The Remaining 1.5°C Carbon Budget
  - 2.2.2.1Carbon budget estimates
  - 2.2.2.2CO₂ and non-CO₂ contributions to the remaining carbon budget
2.3Overview of 1.5°C Mitigation Pathways
2.4Disentangling the Whole-System Transformation
- 2.4.1Energy System Transformation
- 2.4.2Energy Supply
- 2.4.3Energy End-Use Sectors
  - 2.4.3.1Industry
  - 2.4.3.2Buildings
  - 2.4.3.3Transport
- 2.4.4Land-Use Transitions and Changes in the Agricultural Sector
2.5Challenges, Opportunities and Co-Impacts of Transformative Mitigation Pathways
- 2.5.1Policy Frameworks and Enabling Conditions
- 2.5.2Economic and Investment Implications of 1.5°C Pathways
  - 2.5.2.1Price of carbon emissions
  - 2.5.2.2Investments
- 2.5.3Sustainable Development Features of 1.5°C Pathways
2.6Knowledge Gaps
- 2.6.1Geophysical Understanding
- 2.6.2Integrated Assessment Approaches
- 2.6.3Carbon Dioxide Removal (CDR)
FAQsFrequently Asked Questions
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Impacts of 1.5ºC global warming on natural and human systems

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3.1About the Chapter
3.2How are Risks at 1.5°C and Higher Levels of Global Warming Assessed in this Chapter?
- 3.2.1How are Changes in Climate and Weather at 1.5°C versus Higher Levels of Warming Assessed?
- 3.2.2How are Potential Impacts on Ecosystems Assessed at 1.5°C versus Higher Levels of Warming?
3.3Global and Regional Climate Changes and Associated Hazards
3.4Observed Impacts and Projected Risks in Natural and Human Systems
- 3.4.1Introduction
- 3.4.2Freshwater Resources (Quantity and Quality)
  - 3.4.2.1Water availability
  - 3.4.2.2Extreme hydrological events (floods and droughts)
  - 3.4.2.3Groundwater
  - 3.4.2.4Water quality
  - 3.4.2.5Soil erosion and sediment load
- 3.4.3Terrestrial and Wetland Ecosystems
  - 3.4.3.1Biome shifts
  - 3.4.3.2Changes in phenology
  - 3.4.3.3Changes in species range, abundance and extinction
  - 3.4.3.4Changes in ecosystem function, biomass and carbon stocks
  - 3.4.3.5Regional and ecosystem-specific risks
  - 3.4.3.6Summary of implications for ecosystem services
- 3.4.4Ocean Ecosystems
  - 3.4.4.1Observed impacts
  - 3.4.4.2Warming and stratification of the surface ocean
  - 3.4.4.3Storms and coastal runoff
  - 3.4.4.4Ocean circulation
  - 3.4.4.5Ocean acidification
  - 3.4.4.6Deoxygenation
  - 3.4.4.7Loss of sea ice
  - 3.4.4.8Sea level rise
  - 3.4.4.9Projected risks and adaptation options for oceans under global warming of 1.5°C or 2°C above pre-industrial levels
  - 3.4.4.10Framework organisms (tropical corals, mangroves and seagrass)
  - 3.4.4.11Ocean foodwebs (pteropods, bivalves, krill and fin fish)
  - 3.4.4.12Key ecosystem services (e.g., carbon uptake, coastal protection, and tropical coral reef recreation)
- 3.4.5Coastal and Low-Lying Areas, and Sea Level Rise
  - 3.4.5.1Global / sub-global scale
  - 3.4.5.2Cities
  - 3.4.5.3Small islands
  - 3.4.5.4Deltas and estuaries
  - 3.4.5.5Wetlands
  - 3.4.5.6Other coastal settings
  - 3.4.5.7Adapting to coastal change
- 3.4.6Food, Nutrition Security and Food Production Systems (Including Fisheries and Aquaculture)
  - 3.4.6.1Crop production
  - 3.4.6.2Livestock production
  - 3.4.6.3Fisheries and aquaculture production
- 3.4.7Human Health
  - 3.4.7.1Projected risk at 1.5°C and 2°C of global warming
- 3.4.8Urban Areas
- 3.4.9Key Economic Sectors and Services
  - 3.4.9.1Tourism
  - 3.4.9.2Energy systems
  - 3.4.9.3Transportation
- 3.4.10Livelihoods and Poverty, and the Changing Structure of Communities
  - 3.4.10.1Livelihoods and poverty
  - 3.4.10.2The changing structure of communities: migration, displacement and conflict
- 3.4.11Interacting and Cascading Risks
- 3.4.12Summary of Projected Risks at 1.5°C and 2°C of Global Warming
- 3.4.13Synthesis of Key Elements of Risk
3.5Avoided Impacts and Reduced Risks at 1.5°C Compared with 2°C of Global Warming
- 3.5.1Introduction
- 3.5.2 Aggregated Avoided Impacts and Reduced Risks at 1.5°C versus 2°C of Global Warming
  - 3.5.2.1RFC 1 – Unique and threatened systems
  - 3.5.2.2RFC 2 – Extreme weather events
  - 3.5.2.3RFC 3 – Distribution of impacts
  - 3.5.2.4RFC 4 – Global aggregate impacts
  - 3.5.2.5RFC 5 – Large-scale singular events
- 3.5.3 Regional Economic Benefit Analysis for the 1.5°C versus 2°C Global Goals
- 3.5.4 Reducing Hotspots of Change for 1.5°C and 2°C of Global Warming
  - 3.5.4.1Arctic sea ice
  - 3.5.4.2Arctic land regions
  - 3.5.4.3Alpine regions
  - 3.5.4.4Southeast Asia
  - 3.5.4.5Southern Europe and the Mediterranean
  - 3.5.4.6West Africa and the Sahel
  - 3.5.4.7Southern Africa
  - 3.5.4.8Tropics
  - 3.5.4.9Small islands
  - 3.5.4.10Fynbos and shrub biomes
- 3.5.5 Avoiding Regional Tipping Points by Achieving More Ambitious Global Temperature Goals
  - 3.5.5.1Arctic sea ice
  - 3.5.5.2Tundra
  - 3.5.5.3Permafrost
  - 3.5.5.4Asian monsoon
  - 3.5.5.5West African monsoon and the Sahel
  - 3.5.5.6Rainforests
  - 3.5.5.7Boreal forests
  - 3.5.5.8Heatwaves, unprecedented heat and human health
  - 3.5.5.9Agricultural systems: key staple crops
  - 3.5.5.10Agricultural systems: livestock in the tropics and subtropics
3.6Implications of Different 1.5°C and 2°C Pathways
- 3.6.1Gradual versus Overshoot in 1.5°C Scenarios
- 3.6.2Non-CO2 Implications and Projected Risks of Mitigation Pathways
- 3.6.3Implications Beyond the End of the Century
  - 3.6.3.1Sea ice
  - 3.6.3.2Sea level
  - 3.6.3.3Permafrost
3.7Knowledge Gaps
- 3.7.1 Gaps in Methods and Tools
- 3.7.2 Gaps in Understanding
  - 3.7.2.1Earth systems and 1.5°C of global warming
  - 3.7.2.2Physical and chemical characteristics of a 1.5°C warmer world
  - 3.7.2.3Terrestrial and freshwater systems
  - 3.7.2.4Ocean Systems
  - 3.7.2.5Human systems
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Strengthening and implementing the global response

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4.1Accelerating the Global Response to Climate Change
4.2Pathways Compatible with 1.5°C: Starting Points for Strengthening Implementation
- 4.2.1 Implications for Implementation of 1.5°C-Consistent Pathways
  - 4.2.1.1Challenges and Opportunities for Mitigation Along the Reviewed Pathways
  - 4.2.1.2 Implications for Adaptation Along the Reviewed Pathways
- 4.2.2System Transitions and Rates of Change
  - 4.2.2.1Mitigation: historical rates of change and state of decoupling
  - 4.2.2.2Transformational adaptation
  - 4.2.2.3Disruptive innovation
4.3Systemic Changes for 1.5°C-Consistent Pathways
- 4.3.1Energy System Transitions
  - 4.3.1.1 Renewable electricity: solar and wind
  - 4.3.1.2Bioenergy and biofuels
  - 4.3.1.3Nuclear energy
  - 4.3.1.4Energy storage
  - 4.3.1.5Options for adapting electricity systems to 1.5°C
  - 4.3.1.6Carbon dioxide capture and storage in the power sector
- 4.3.2 Land and Ecosystem Transitions
  - 4.3.2.1 Agriculture and food
  - 4.3.2.2Forests and other ecosystems
  - 4.3.2.3Coastal systems
- 4.3.3 Urban and Infrastructure System Transitions
  - 4.3.3.1Urban energy systems
  - 4.3.3.2Urban infrastructure, buildings and appliances
  - 4.3.3.3Urban transport and urban planning
  - 4.3.3.4Electrification of cities and transport
  - 4.3.3.5Shipping, freight and aviation
  - 4.3.3.6Climate-resilient land use
  - 4.3.3.8Sustainable urban water and environmental services
  - 4.3.3.7Green urban infrastructure and ecosystem services
- 4.3.4Industrial Systems Transitions
  - 4.3.4.1Energy efficiency
  - 4.3.4.2Substitution and circularity
  - 4.3.4.3Bio-based feedstocks
  - 4.3.4.4Electrification and hydrogen
  - 4.3.4.5CO2 capture, utilization and storage in industry
- 4.3.5 Overarching Adaptation Options Supporting Adaptation Transitions
  - 4.3.5.1Disaster risk management (DRM)
  - 4.3.5.2Risk sharing and spreading
  - 4.3.5.3Education and learning
  - 4.3.5.4Population health and health system adaptation options
  - 4.3.5.5Indigenous knowledge
  - 4.3.5.6Human migration
  - 4.3.5.7Climate services
- 4.3.6Short-Lived Climate Forcers
- 4.3.7 Carbon Dioxide Removal (CDR)
  - 4.3.7.1Bioenergy with carbon capture and storage (BECCS)
  - 4.3.7.2 Afforestation and reforestation (AR)
  - 4.3.7.3 Soil carbon sequestration and biochar
  - 4.3.7.4Enhanced weathering (EW) and ocean alkalinization
  - 4.3.7.5Direct air carbon dioxide capture and storage (DACCS)
  - 4.3.7.6Ocean fertilization
- 4.3.8Solar Radiation Modification (SRM)
  - 4.3.8.1Governance and institutional feasibility
  - 4.3.8.2Economic and technological feasibility
  - 4.3.8.3Social acceptability and ethics
4.4Implementing Far-Reaching and Rapid Change
4.5Integration and Enabling Transformation
4.6Knowledge Gaps and Key Uncertainties
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Sustainable Development, Poverty Eradication and Reducing Inequalities

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5.1Scope and Delineations
5.2Poverty, Equality and Equity Implications of a 1.5°C Warmer World
5.3Climate Adaptation and Sustainable Development
5.4Mitigation and Sustainable Development
- 5.4.1Synergies and Trade-Offs between Mitigation Options and Sustainable Development
- 5.4.2Sustainable Development Implications of 1.5°C and 2°C Mitigation Pathways
  - 5.4.2.1Air pollution and health
  - 5.4.2.2Food security and hunger
  - 5.4.2.3Lack of energy access/energy poverty
  - 5.4.2.4Water security
5.5Sustainable Development Pathways to 1.5°C
5.6Conditions for Achieving Sustainable Development, Eradicating Poverty and Reducing Inequalities in 1.5°C Warmer Worlds
- 5.6.1Finance and Technology Aligned with Local Needs
- 5.6.2Integration of Institutions
- 5.6.3Inclusive Processes
- 5.6.4Attention to Issues of Power and Inequality
- 5.6.5 Reconsidering Values
5.7Synthesis and Research Gaps
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Glossary

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