Summary/Abstract
This Working Group I contribution to the IPCC’s Sixth Assessment Report is the most up-to-date physical understanding of the climate system and climate change, bringing together the latest advances in climate science. The report draws on improvements in observationally based estimates and information from paleoclimate archives to provide a comprehensive view of each component of the climate system and its changes to date. The report’s core conclusions are, among others, that increases in well-mixed greenhouse gas concentrations are unequivocally caused by human activities, that human-induced climate change is already affecting weather and and climate extremes in every region across the globe, and that limiting human-induced global warming to a specific level requires limiting cumulative CO2 emissions, reaching at least net zero CO2 emissions, and strong reductions in other greenhouse gas emissions.