A. Introduction
This Summary sets out the key policy-relevant findings of the Fourth Assessment of Working Group II of the Intergovernmental Panel on Climate Change (IPCC).
The Assessment is of current scientific understanding of the impacts of climate change on natural, managed and human systems, the capacity of these systems to adapt and their vulnerability. It builds upon past IPCC assessments and incorporates new knowledge gained since the Third Assessment.
Statements in this Summary are based on chapters in the Assessment and principal sources are given at the end of each paragraph.