The Intergovernmental Panel on Climate Change (IPCC), the world's most authoritative assessment of the causes and impacts of global warming, last week released the third in its series of studies, this time focusing on ways to avoid the catastrophic effects of climate change. While even detractors now admit that global warming must be dealt with, the battles over actions to take are as pitched as ever. They must stop: Global warming is a fact, and the longer states delay implementation of a global plan to cut greenhouse-gas emissions, the more difficult and costly will be the adjustment.