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Climate Change 2021: The Physical Science Basis

The Working Group I contribution to the Sixth Assessment Report addresses the most up-to-date physical understanding of the climate system and climate change, bringing together the latest advances in climate science.

Summary for Policymakers

The Summary for Policymakers provides a high-level summary of the current state of the climate, how it is changing, the role of human influence, and possible climate futures.

Technical Summary

The Technical Summary provides a synthesis of the key findings of the Report and serves as a bridge between the Summary for Policymakers and the chapters of the full report.

Full Report

The 13 chapters of the Working Group I report provide a comprehensive assessment of the current evidence on the physical science of climate change.

Frequently Asked Questions

The Frequently Asked Questions explain important aspects of the report for a broad audience. They are related to the specific Chapters where they appear, but can be relevant to multiple Chapters.

Fact Sheets

These outreach products provide an entry point for information relevant to regions and sectors. They are fully traceable to the underlying report and Interactive Atlas.

Interactive Atlas

The novel AR6 WGI Interactive Atlas allows for a flexible spatial and temporal analysis of both data-driven climate change information and assessment findings.

Chapters

Chapter 1

Framing, Context and Methods

Chapter 1 introduces the WGI contribution to AR6, its framing and context, and the methods used in the report.

Chapter 2

Changing State of the Climate System

Chapter 2 provides evidence for large-scale past changes in selected components of the climate system.

Chapter 3

Human Influence on the Climate System

Chapter 3 assesses human influence on the climate system and evaluates climate models on large scales.

Chapter 4

Future Global Climate: Scenario-based Projections and Near-term Information

Chapter 4 assesses simulations of future global climate change over the near term, mid- to long term, and out to year 2300.

Chapter 5

Global Carbon and other Biogeochemical Cycles and Feedbacks

Chapter 5 identifies biogeochemical feedbacks with potentially significant climatic effects.

Chapter 6

Short-lived Climate Forcers

Chapter 6 discusses the evolution of reactive compounds and their effects on climate and global air quality.

Chapter 7

The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity

Chapter 7 assesses the major physical processes affecting the evolution of Earth’s energy budget and the associated changes in temperature and the climate system.

Chapter 8

Water Cycle Changes

Chapter 8 explores the changing water cycle and its sensitivity to multiple drivers.

Chapter 9

Ocean, Cryosphere and Sea Level Change

Chapter 9 assesses the physical processes underlying global and regional changes in the ocean, cryosphere and sea level.

Chapter 10

Linking Global to Regional Climate Change

Chapter 10 assesses the foundations of how regional climate information is distilled from multiple, sometimes contrasting, lines of evidence.

Chapter 11

Weather and Climate Extreme Events in a Changing Climate

Chapter 11 assesses observed changes in weather and climate extremes, their attribution to human influence, and future projections at global warming levels of +1.5°C, +2°C and +4°C.

Chapter 12

Climate Change Information for Regional Impact and for Risk Assessment

Chapter 12 assesses the climate information relevant to regional impact and risk assessment.

Atlas

The Atlas provides a region-by-region assessment of climate change and includes an innovative online tool, the Interactive Atlas.

Front Matter, Annexes, and Index

Front Matter

Includes Foreword, Preface, Dedication, and Table of Contents

Annex I

Observational Products

Annex II

Models

Annex III

Radiative Forcing

Annex IV

Modes of Variability

Annex V

Monsoons

Annex VI

Climatic Impact-Drivers and Extreme Indices

Annex VII

Glossary

Annex VIII

Acronyms

Annex IX

List of Contributors

Annex X

Expert Reviewers

Index