There are many possible warmer worlds in the future. This infographic illustrates three storylines of these possible warmer worlds based on different mitigation options as outlined in Special Report on Global Warming of 1.5°C Cross-Chapter Box 8, Table 2 from Chapter 3, which draws knowledge across chapters such as Chapter 2’s mitigation scenarios, Chapter 3’s assessments of changes in regional climate and accounting for different characteristics of internal climate variability in the next decade, and other elements from Chapters 4 and 5 of the report.

All three storylines illustrate how differing actions to mitigate and adapt to climate change, as well as how the Earth’s internal climate variability, can result in very different future warmer worlds. The three different storylines show: a path among a best-case scenario where there is a collective, early move to mitigation; an intermediate, mid-case scenario where delayed action occurs only after a warm decade in the 2020s; and a worst case scenario where there is uncoordinated action that occurs only late in 21st century. In the intermediate and worst-case storylines, internal climate variability plays a role in determining climate action (realisation vs overlooking of urgency).

For more information on specific terms, a glossary is provided at the end of the infographic.

IPCC Special Report 1.5

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(definitions are adapted from the SR15, SROCC and SRCCL Glossaries)

Mitigation scenarios and pathways

Mitigation refers to human intervention to reduce emissions or enhance the
sinks of greenhouse gases. A mitigation scenario is a plausible description of
the future that describes how the (studied) system responds to the
implementation of mitigation policies and measures. A mitigation pathway is a
temporal evolution of a set of mitigation scenario features, such as
greenhouse gas emissions and socio-economic development.

Climate variability

Climate variability refers to deviations of climate variables from a given
mean state (including the occurrence of extremes, etc.) at all spatial and
temporal scales beyond that of individual weather events. Variability may be
intrinsic, due to fluctuations of processes internal to the climate system
(internal variability), or extrinsic, due to variations in natural or
anthropogenic external forcing (forced variability).

Human activities are estimated to have caused approximately 1.0°C of
global warming above pre-industrial levels. Estimated anthropogenic global
warming is currently increasing at 0.2°C (likely between 0.1°C and 0.3°C) per
decade due to past and ongoing emissions. Superimposed internal climate
variability can modulate decadal temperature variations and other climate
characteristics at the global and regional scales.

These three storylines explore contrasted characteristics of internal
variability in the next decade (2020s). The orange world’s very warm
conditions in the 2020s is the result of a scenario that follows higher
transient warming in that decade as a result of internal climate variability,
in addition to human-induced trends. In contrast, the red world portrays a
scenario in which the mean warming in the 2020s is slightly lower than that
expected from human-induced trends due to natural climate variability. In both
scenarios, internal variability is back to normal after 2030.

Negative emissions

Removal of greenhouse gases from the atmosphere by deliberate human
activities, i.e., in addition to the removal that would occur via natural
carbon cycle processes.

Ecosystem services

Ecological processes or functions having monetary or non-monetary value to
individuals or society at large. These are frequently classified as (1)
supporting services such as productivity or biodiversity maintenance, (2)
provisioning services such as food or fibre, (3) regulating services such as
climate regulation or carbon sequestration, and (4) cultural services such as
tourism or spiritual and aesthetic appreciation.

Carbon sink

Any process, activity or mechanism which removes a greenhouse gas, an aerosol
or a precursor of a greenhouse gas from the atmosphere.

Overshoot pathways

Pathways that exceed the stabilization level (concentration, forcing, or
temperature) before the end of a time horizon of interest (e.g., before 2100)
and then decline towards that level by that time. Once the target level is
exceeded, removal by sinks of greenhouse gases is required.