Moments for scientists don't get much more dramatic than the scene in Paris on February 2, 2007, as lead authors of the 2007 report from the Intergovernmental Panel on Climate Change (I.P.C.C.) described evidence pointing to an increasingly human-heated planet. This report, the fourth assessment of the causes and consequences of climate change in the nearly 20-year history of the panel, was the first to conclude with greater than 90 percent confidence that humans had become the main force driving warming and that centuries of rising temperatures and seas could be blunted only if emissions of heat-trapping gases were substantially reduced.

At the news conference following presentations, reporters pressed for the human element. One journalist asked Susan Solomon, one of the two supervising authors and an award-winning atmospheric scientist for the United States government, “to sum up what kind of urgency this sort of report should convey to policy makers.” She gave the furthest thing from a convenient sound bite: