The launch of the first part of the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) is a milestone in climate science. The Working Group I (WGI) Report assesses insights from over 14,000 peer-reviewed publications and synthesizes them into a high-level summary of the understanding of "the current state of the climate, including how it is changing and the role of human influence, the state of knowledge about possible climate futures, climate information relevant to regions and sectors, and limiting human-induced climate change" (IPCC, 2021).
The report benefits from improved knowledge gained from an expanded climate observations network, new climate model simulations, new analyses, and methods combining multiple lines of evidence to provide an improved understanding of human influences on a wider range of climate variables, including weather and climate extremes. Global surface temperature was around 1.1°C higher in 2011– 2020 compared to pre-industrial, with larger increases observed over land than over the ocean. Most of this observed global warming is due to greenhouse gas emissions and is affecting every region of our planet as well as the entire climate system. Unless there are immediate, rapid, and large-scale reductions in greenhouse gas emissions, the report concludes that limiting warming to 1.5°C or even 2°C above the pre-industrial baseline will be beyond reach. A drastic reduction in emissions is needed immediately to stabilize Earth’s climate and limit the disruption to our ecosystems and economies that will otherwise result from changes in the Earth’s climate, including the intensity, frequency, and duration of extreme weather and climate events – some of which are already being experienced.
WCRP congratulates and acknowledges the tremendous efforts of the IPCC WGI team, led by Valérie Masson-Delmotte and Panmao Zhai and including over 230 authors, coordinating lead authors and review editors, many from the WCRP community. For over four decades, WCRP has coordinated climate science around the world and, especially, established and led the Coupled Model Intercomparison Project (CMIP) and the Coordinated Regional Climate Downscaling Experiment (CORDEX), which together provide the multi-model database of coupled climate and Earth system model simulations that are central to IPCC assessments. WCRP remains committed to playing this role in the decades ahead. We welcome the advances in science and technology that underpin this report and its conclusions and that will continue to help us to provide the science needed for future IPCC Assessment Reports. Certainly, this includes the development of new climate observations, new and improved simulations of the Earth’s climate system, improved process understanding, as well as advances in the science of attribution.
The pathway that emissions, and thus temperature, will take in the next few decades is unknown. The details of that pathway are of critical importance to the challenges that we will face. Society requires decision-relevant, evidence-based, climate information to support adaptation planning and mitigation strategies, realized in the context of the United Nations Sustainable Development Goals (SDGs). WCRP is committed to ensuring that decision-makers have access to the very best climate science available in every region of the globe and will continue to provide the science that forms the basis of future IPCC climate assessments.
Detlef Stammer and Helen Cleugh
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. In Press.