The Working Group I contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) provides a comprehensive assessment of the physical science basis of climate change. It builds upon the Working Group I contribution to the IPCC's Fourth Assessment Report in 2007 and incorporates subsequent new findings from the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, as well as from research published in the extensive scientific and technical literature. The assessment considers new evidence of past, present and projected future climate change based on many independent scientific analyses from observations of the climate system, paleoclimate archives, theoretical studies of climate processes and simulations using climate models.

Scope of the Report

During the process of scoping and approving the outline of its Fifth Assessment Report, the IPCC focussed on those aspects of the current understanding of the science of climate change that were judged to be most relevant to policymakers.

In this report, Working Group I has extended coverage of future climate change compared to earlier reports by assessing near-term projections and predictability as well as long-term projections and irreversibility in two separate chapters. Following the decisions made by the Panel during the scoping and outline approval, a set of new scenarios, the Representative Concentration Pathways, are used across all three Working Groups for projections of climate change over the 21st century.