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Chapter 1
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Summary for Policymakers
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I
Introduction
A
Understanding Global Warming of 1.5°C*
B
Projected Climate Change, Potential Impacts and Associated Risks
C
Emission Pathways and System Transitions Consistent with 1.5°C Global Warming
D
Strengthening the Global Response in the Context of Sustainable Development and Efforts to Eradicate Poverty
+
Core Concepts Central to this Special Report
+
Acknowledgements
+
Citation
SD
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Framing and Context
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Executive Summary
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1.1
Assessing the Knowledge Base for a 1.5°C Warmer World
1.1.1
Equity and a 1.5°C Warmer World
1.1.2
Eradication of Poverty
1.1.3
Sustainable Development and a 1.5°C Warmer World
1.2
Understanding 1.5°C: Reference Levels, Probability, Transience, Overshoot, and Stabilization
1.2.1
Working Definitions of 1.5°C and 2°C Warming Relative to Pre-Industrial Levels
1.2.1.1
Definition of global average temperature
1.2.1.2
Choice of reference period
1.2.1.3
Total versus human-induced warming and warming rates
1.2.2
Global versus Regional and Seasonal Warming
1.2.3
Definition of 1.5°C Pathways: Probability, Transience, Stabilization and Overshoot
1.2.3.1
Pathways remaining below 1.5°C
1.2.3.2
Pathways temporarily exceeding 1.5°C
1.2.3.3
Impacts at 1.5°C warming associated with different pathways: transience versus stabilisation
1.2.4
Geophysical Warming Commitment
1.3
Impacts at 1.5°C and Beyond
1.3.1
Definitions
1.3.2
Drivers of Impacts
1.3.3
Uncertainty and Non-Linearity of Impacts
1.4
Strengthening the Global Response
1.4.1
Classifying Response Options
1.4.2
Governance, Implementation and Policies
1.4.3
Transformation, Transformation Pathways, and Transition: Evaluating Trade-Offs and Synergies Between Mitigation, Adaptation and Sustainable Development Goals
1.5
Assessment Frameworks and Emerging Methodologies that Integrate Climate Change Mitigation and Adaptation with Sustainable Development
1.5.1
Knowledge Sources and Evidence Used in the Report
1.5.2
Assessment Frameworks and Methodologies
1.6
Confidence, Uncertainty and Risk
1.7
Storyline of the Report
FAQs
Frequently Asked Questions
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Mitigation pathways compatible with 1.5°C in the context of sustainable development
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2.1
Introduction to Mitigation Pathways and the Sustainable Development Context
2.1.1
Mitigation Pathways Consistent with 1.5°C
2.1.2
The Use of Scenarios
2.1.3
New Scenario Information since AR5
2.1.4
Utility of Integrated Assessment Models (IAMs) in the Context of this Report
2.2
Geophysical Relationships and Constraints
2.2.1
Geophysical Characteristics of Mitigation Pathways
2.2.1.1
Geophysical uncertainties: non-CO
2
forcing agents
2.2.1.2
Geophysical uncertainties: climate and Earth system feedbacks
2.2.2
The Remaining 1.5°C Carbon Budget
2.2.2.1
Carbon budget estimates
2.2.2.2
CO
2
and non-CO
2
contributions to the remaining carbon budget
2.3
Overview of 1.5°C Mitigation Pathways
2.3.1
Range of Assumptions Underlying 1.5°C Pathways
2.3.1.1
Socio-economic drivers and the demand for energy and land in 1.5°C pathways
2.3.1.2
Mitigation options in 1.5°C pathways
2.3.1.3
Policy assumptions in 1.5°C pathways
2.3.2
Key Characteristics of 1.5°C Pathways
2.3.2.1
Variation in system transformations underlying 1.5°C pathways
2.3.2.2
Pathways keeping warming below 1.5°C or temporarily overshooting it
2.3.3
Emissions Evolution in 1.5°C Pathways
2.3.3.1
Emissions of long-lived climate forcers
2.3.3.2
Emissions of short-lived climate forcers and fluorinated gases
2.3.4
CDR in 1.5°C Pathways
2.3.4.1
CDR technologies and deployment levels in 1.5°C pathways
2.3.4.2
Sustainability implications of CDR deployment in 1.5°C pathways
2.3.5
Implications of Near-Term Action in 1.5°C Pathways
2.4
Disentangling the Whole-System Transformation
2.4.1
Energy System Transformation
2.4.2
Energy Supply
2.4.2.1
2.4.2.2
2.4.2.3
2.4.3
Energy End-Use Sectors
2.4.3.1
Industry
2.4.3.2
Buildings
2.4.3.3
Transport
2.4.4
Land-Use Transitions and Changes in the Agricultural Sector
2.5
Challenges, Opportunities and Co-Impacts of Transformative Mitigation Pathways
2.6
Knowledge Gaps
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Impacts of 1.5ºC global warming on natural and human systems
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Chapter 3 Citation
3.1 About the Chapter
3.2
3.2.1
How are Changes in Climate and Weather at 1.5°C versus Higher Levels of Warming Assessed?
3.2.2
How are Potential Impacts on Ecosystems Assessed at 1.5°C versus Higher Levels of Warming?
3.3
3.3.1
3.3.2
3.3.2.1
Observed and attributed changes in regional temperature means and extremes
3.3.2.2
Projected changes in regional temperature means and extremes at 1.5°C versus 2°C of global warming
3.3.3
3.3.3.1
Observed and attributed changes in regional precipitation
3.3.3.2
Projected changes in regional precipitation at 1.5°C versus 2°C of global warming
3.3.4
3.3.4.1
Observed and attributed changes
3.3.4.2
Projected changes in drought and dryness at 1.5°C versus 2°C
3.3.5
3.3.5.1
Observed and attributed changes in runoff and river flooding
3.3.5.2
Projected changes in runoff and river flooding at 1.5°C versus 2°C of global warming
3.3.6
3.3.7
3.3.8
3.3.9
3.3.10
3.3.11
3.4
3.4.1
3.4.2
3.4.2.1
Water availability
3.4.2.2
Extreme hydrological events (floods and droughts)
3.4.2.3
Groundwater
3.4.2.4
Water quality
3.4.2.5
Soil erosion and sediment load
3.4.3
3.4.3.1
Biome shifts
3.4.3.2
Changes in phenology
3.4.3.3
Changes in species range, abundance and extinction
3.4.3.4
Changes in ecosystem function, biomass and carbon stocks
3.4.3.5
Regional and ecosystem-specific risks
3.4.3.6
Summary of implications for ecosystem services
3.4.4
3.4.5
3.4.6
3.4.6.1
Crop production
3.4.6.2
Livestock production
3.4.6.3
Fisheries and aquaculture production
3.4.7
3.4.7.1
Projected risk at 1.5°C and 2°C of global warming
3.4.8
3.4.9
3.4.9.1
Tourism
3.4.9.2
Energy systems
3.4.9.3
Transportation
3.4.10
3.4.10.1
Livelihoods and poverty
3.4.10.2
The changing structure of communities: migration, displacement and conflict
3.4.11
3.4.12
3.4.13
3.5
3.5.1
Introduction
3.5.2
Aggregated Avoided Impacts and Reduced Risks at 1.5°C versus 2°C of Global Warming
3.5.2.1
RFC 1 – Unique and threatened systems
3.5.2.2
RFC 2 – Extreme weather events
3.5.2.3
RFC 3 – Distribution of impacts
3.5.2.4
RFC 4 – Global aggregate impacts
3.5.2.5
RFC 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
3.5.4.1
Arctic sea ice
3.5.4.2
Arctic land regions
3.5.4.3
Alpine regions
3.5.4.4
Southeast Asia
3.5.4.5
Southern Europe and the Mediterranean
3.5.4.6
West Africa and the Sahel
3.5.4.7
Southern Africa
3.5.4.8
Tropics
3.5.4.9
Small islands
3.5.4.10
Fynbos and shrub biomes
3.5.5
Avoiding Regional Tipping Points by Achieving More Ambitious Global Temperature Goals
3.5.5.1
Arctic sea ice
3.5.5.2
Tundra
3.5.5.3
Permafrost
3.5.5.4
Asian monsoon
3.5.5.5
West African monsoon and the Sahel
3.5.5.6
Rainforests
3.5.5.7
Boreal forests
3.5.5.8
Heatwaves, unprecedented heat and human health
3.5.5.9
Agricultural systems: key staple crops
3.5.5.10
Agricultural systems: livestock in the tropics and subtropics
3.6
3.7
3.7.1
Gaps in Methods and Tools
3.7.2
Gaps in Understanding
3.7.2.1
3.7.2.2
3.7.2.3
3.7.2.4
3.7.2.5
Frequently Asked Questions chapter 3
Supplementary Material
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Strengthening and implementing the global response
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Sustainable Development, Poverty Eradication and Reducing Inequalities
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Glossary
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