It's Getting Hotter in Here ... And It's Your Fault

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. Then the wording--but not the science--of the 21-page "Summary for Policy Makers" got worked over by 300 delegates from 113 governments this week in Paris. The bottom line is that "there's an irrefutable consensus that [global warming] is real," says geoscientist Michael Oppenheimer of Princeton University in New Jersey. And "there's an irrefutable consensus that it will get worse" if greenhouse emissions are not reined in.

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.