National and international science academies and scientific societies have assessed current scientific opinion on climate change. These assessments are generally consistent with the conclusions of the Intergovernmental Panel on Climate Change, the IPCC Fourth Assessment Report summarized:
Warming of the climate system is unequivocal, as evidenced by increases in global average air and ocean temperatures, the widespread melting of snow and ice, and rising global average sea level.[5]
Most of the global warming since the mid-20th century is very likely due to human activities.[6]
Benefits and costs of climate change for [human] society will vary widely by location and scale.[7] Some of the effects in temperate and polar regions will be positive and others elsewhere will be negative.[7] Overall, net effects are more likely to be strongly negative with larger or more rapid warming.[7]
The range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time.[8]
The resilience of many ecosystems is likely to be exceeded this century by an unprecedented combination of climate change, associated disturbances (e.g. flooding, drought, wildfire, insects, ocean acidification) and other global change drivers (e.g. land-use change, pollution, fragmentation of natural systems, over-exploitation of resources).[9]
No scientific body of national or international standing maintains a formal opinion dissenting from any of these main points; the last was the American Association of Petroleum Geologists,[10] which in 2007[11] updated its 1999 statement rejecting the likelihood of human influence on recent climate with its current non-committal position.[12] Some other organizations, primarily those focusing on geology, also hold non-committal positions.
