Volume one of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report describes the latest collective understanding of the drivers of climate change and climate processes. It builds upon past IPCC assessments and incorporates new findings from the past six years of research. This summary for policymakers is drawn from substantive sections of the full report, and highlights key aspects of relevance to policymakers and non-scientists. It does not provide specific recommendations for action, as these will be covered in forthcoming volumes.
The report concludes that:
- global atmospheric concentrations of greenhouse gases have increased markedly as a result of human activities. Increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture
- that global warming is occurring is now an absolute certainty
- the understanding of warming and cooling influences on climate as a result of human activities has improved since the Third Assessment Report (TAR) in 2001. There is now very high confidence that human activities are contributing to climate change
- long-term changes in climate have been observed at large scales (for example, at the level of regions and ocean basins). There is now higher confidence in projected patterns of warming at these levels. However, some aspects of climate have not been observed to change, such as trends in the extent of Antarctic sea ice
- human influences are now shown to extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns
- the sensitivity of the climate system to increased warming is now able to be assessed for the first time
- for the next two decades a warming of about 0.2 degrees Centigrade per decade is projected. Warming and sea level rise will still continue for centuries even if greenhouse gas concentrations are stabilised