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.

The first report, released in February, concluded with "near certainty" that human activity was primarily responsible for rising concentrations of greenhouse gases in the atmosphere. Global temperatures have risen about 1.5 degrees since the beginning of the Industrial Revolution in the 18th century; greenhouse-gas emissions have increased 70 percent since 1970 and could rise an additional 90 percent by 2030 if nothing is done. The second report, released in April, detailed the effects of global warming: flooding, droughts, shifting agricultural production and mass species extinctions.

Agreement on the fact of global warming has not produced action on what to do about it. Many developed countries, the United States in particular, reject mandatory actions that risk slowing, if not stopping, their economies. They also complain that current plans, such as the Kyoto Protocol, do not impose equal burdens on developing countries that are producing prodigious amounts of greenhouse gases. For example, if China continues on its current trajectory, its yearly emissions will overtake those of the U.S. this year and double them in less than a decade.