A report of working group I of the Intergovernmental Panel on Climate Change: summary for policymakers

Changes in the atmospheric abundance of greenhouse gases and aerosols, in solar radiation and in land surface properties alter the energy balance of the climate system.
The Working Group I contribution to the IPCC Fourth Assessment Report describes progress in understanding of the human and natural drivers of climate change, observed climate change, climate processes and attribution, and estimates of projected future climate change.
It builds upon past IPCC assessments and incorporates new findings from the past six years of research.