This Summary for Policymakers (SPM) presents key findings of the Working Group I (WGI) contribution to the IPCC’s Sixth Assessment Report (AR6) on the physical science basis of climate change. The report builds upon the 2013 Working Group I contribution to the IPCC’s Fifth Assessment Report (AR5) and the 2018–2019 IPCC Special Reports of the AR6 cycle and incorporates subsequent new evidence from climate science. This SPM provides 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. Based on scientific understanding, key findings can be formulated as statements of fact or associated with an assessed level of confidence indicated using the IPCC calibrated language.