From Science:
The Intergovernmental Panel on Climate Change (IPCC) made no bones about where it stands on global warming in its fourth report, released early today in Paris. “Warming of the climate system is unequivocal,” its report stated, adding that most of the warming is “very likely” due to human activity. If people keep spewing greenhouse gases into the atmosphere, they will “very likely” change climate in this century much more than they did in the 20th century, the report concludes.
The IPCC hasn’t rushed to judgment on climate change. It took 600 authors from 40 countries 6 years to produce hundreds of pages, which in turn were scanned by 600 reviewers. The IPCC’s heightened confidence flows from several developments of the past few years. More observations of climate–from satellites to tree rings–have been analyzed. More computer models have grown more realistic and been run multiple times. And the natural world has continued to behave as if it is warming under a strengthening greenhouse. So IPCC upgraded its 2001 statement that “most of the observed warming … is likely to have been due to” rising greenhouse gases to the warming being “very likely” human-caused.
More here.