Summary for Policymakers
Drafting Authors
Richard P. Allan (United Kingdom)
Paola A. Arias (Colombia)
Sophie Berger (France/Belgium)
Josep G. Canadell (Australia)
Christophe Cassou (France)
Deliang Chen (Sweden)
Annalisa Cherchi (Italy)
Sarah L. Connors (France/United Kingdom)
Erika Coppola (Italy)
Faye Abigail Cruz (Philippines)
Aïda Diongue-Niang (Senegal)
Francisco J. Doblas-Reyes (Spain)
Hervé Douville (France)
Fatima Driouech (Morocco)
Tamsin L. Edwards (United Kingdom)
François Engelbrecht (South Africa)
Veronika Eyring (Germany)
Erich Fischer (Switzerland)
Gregory M. Flato (Canada)
Piers Forster (United Kingdom)
Baylor Fox-Kemper (United States of America)
Jan S. Fuglestvedt (Norway)
John C. Fyfe (Canada)
Nathan P. Gillett (Canada)
Melissa I. Gomis (France/Switzerland)
Sergey K. Gulev (Russian Federation)
José Manuel Gutiérrez (Spain)
Rafiq Hamdi (Belgium)
Jordan Harold (United Kingdom)
Mathias Hauser (Switzerland)
Ed Hawkins (United Kingdom)
Helene T. Hewitt (United Kingdom)
Tom Gabriel Johansen (Norway)
Christopher Jones (United Kingdom)
Richard G. Jones (United Kingdom)
Darrell S. Kaufman (United States of America)
Zbigniew Klimont (Austria/Poland)
Robert E. Kopp (United States of America)
Charles Koven (United States of America)
Gerhard Krinner (France/Germany)
June-Yi Lee (Republic of Korea)
Irene Lorenzoni (United Kingdom/Italy)
Jochem Marotzke (Germany)
Valérie Masson-Delmotte (France)
Thomas K. Maycock (United States of America)
Malte Meinshausen (Australia/Germany)
Pedro M.S. Monteiro (South Africa)
Angela Morelli (Norway/Italy)
Vaishali Naik (United States of America)
Dirk Notz (Germany)
Friederike Otto (United Kingdom/Germany)
Matthew D. Palmer (United Kingdom)
Izidine Pinto (South Africa/Mozambique)
Anna Pirani (Italy)
Gian-Kasper Plattner (Switzerland)
Krishnan Raghavan (India)
Roshanka Ranasinghe (The Netherlands/Sri Lanka/Australia)
Joeri Rogelj (United Kingdom/Belgium)
Maisa Rojas (Chile)
Alex C. Ruane (United States of America)
Jean-Baptiste Sallée (France)
Bjørn H. Samset (Norway)
Sonia I. Seneviratne (Switzerland)
Jana Sillmann (Norway/Germany)
Anna A. Sörensson (Argentina)
Tannecia S. Stephenson (Jamaica)
Trude Storelvmo (Norway)
Sophie Szopa (France)
Peter W. Thorne (Ireland/United Kingdom)
Blair Trewin (Australia)
Robert Vautard (France)
Carolina Vera (Argentina)
Noureddine Yassaa (Algeria)
Sönke Zaehle (Germany)
Panmao Zhai (China)
Xuebin Zhang (Canada)
Kirsten Zickfeld (Canada/Germany)
Citation Information
This Summary for Policymakers should be cited as:
IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 3−32, doi:10.1017/9781009157896.001.
Introduction
Decision IPCC/XLVI-2.
Special Reports:
Global Warming of 1.5°C
Climate Change and Land
Ocean and Cryosphere in a Changing Climate
Assessment covers scientific literature up to 31 January 2021.
Each finding evaluates underlying evidence and agreement with five confidence levels: very low, low, medium, high, and very high.
Terms used to indicate likelihood:
Virtually certain (99-100%)
Very likely (90-100%)
Likely (66-100%)
About as likely as not (33-66%)
Unlikely (0-33%)
Very unlikely (0-10%)
Exceptionally unlikely (0-1%).
Differences in terms typeset in italics (e.g., very likely).
By convention, ranges are included in square brackets, e.g., [x to y].
The Current State of the Climate
A. The Current State of the Climate
Concise overview of changes and indicators of climate impact:
Human Influence: Human activity unequivocally warmed the atmosphere, oceans, and land, leading to widespread changes in the atmosphere, ocean, cryosphere, and biosphere.
Greenhouse Gas Concentrations:
Pre-1750 CO2 levels increased by 410 ppm (2019).
Methane increased by 1866 ppb.
Nitrous oxide reached 332 ppb.
Global absorption of CO2 emissions by land and ocean remains stable at ~56% globally.
A.1 Temperature and Weather Patterns
A.1.1 Global Temperature Changes
Global surface temperature increased by 0.99°C (2001–2020 vs. 1850-1900).
Higher warming over land (1.59°C) compared to oceans (0.88°C).
Estimated increase since last assessment (AR5) attributed to warming post 2003-2012 (0.19°C).
A.1.2 Extreme Weather Events
Human influence significantly affects the frequency of weather and climate extremes.
E.g., heatwaves and unprecedented temperature trends.
A.1.3 Glacial Systems and Sea Ice
Global glacial and sea ice levels declined significantly since 1990s, especially in the Arctic region, which saw a 40% decrease in minimum summer sea ice (1979-2019).
A.1.4 Ocean Acidification
Strong evidence that human-caused emissions have increased CO2-induced ocean acidification.
A.1.5 Sea Level Rise
Global average sea levels increased by 0.20 m (1901-2018) at an increasing rate from 1.3 mm/yr to 3.7 mm/yr between 2006-2018.
A.1.6 Biodiversity Changes
Significant shifts in climate zones and ecosystems due to increased temperatures and human influence.
A.2 Carbon Dioxide Emissions
Atmospheric CO2 levels were higher than any time in at least 2 million years by 2019.
A.3 Climate-Driven Extremes
Numerous weather extremes, including heatwaves and droughts, have become more frequent and intense.
A.4 Projections
Future climate projection scenarios indicating significant changes based on carbon emission trajectories.
Limiting Future Climate Change
D.1 Carbon Budgets
Cumulative CO2 emissions impact future temperature increases, and each 1000 GtCO2 correlates roughly to a 0.45°C increase in temperature.
D.2 Global Climate Response
Emission reductions will take years to show detectable changes in temperature trends. This is affected by natural variability.