Last year was one for the record books. In 2006, the United States experienced the warmest surface temperature since 1895. It was also the eleventh year since 1995 to rank among the warmest worldwide ever recorded. The decade prior saw many other extreme weather events. In 2003, a brutal summer heat wave in Europe killed at least 22,000 people. In 1998, Hurricane Mitch stalled over Central America and released six feet of rain, causing massive mudslides and claiming 11,000 lives. After that storm, Honduras reported thousands of cases of cholera, malaria, and dengue fever.

Although climate change can't be blamed for any one particular weather disaster, it is responsible for longer-term trends that intensify weather around the world, spawning more heat waves, droughts, intense downpours, and floods. There are also fewer extreme cold events-bitterly cold days and nights-over most land areas. Even frost has become less frequent. Yet there is more intense precipitation, both rain and snow. So there is a greater likelihood of winter snowstorms but not more cold snaps.

There is a greater than 90% likelihood that such weather events will continue to become more frequent, and it is equally likely that global sea level rise will accelerate and that snow cover will recede during this century. Moreover, there is a 66–90% likelihood that future tropical cyclones (hurricanes and typhoons) will become more intense, with greater peak wind speeds and heavier rains, and that the land area affected by drought will increase. Many semi-arid subtropical regions, already plagued by drought, could have as much as a 20% drop in rainfall by 2100. In other regions, it is already raining less often but harder, causing more extensive floods.

Those are some conclusions of the most recent assessment of the UN Intergovernmental Panel on Climate Change (IPCC), which on 2 February 2007 issued an 18-page summary of The Physical Science Basis, the first volume of the assessment. Hundreds of scientists write and review IPCC major assessments, which are released every six to seven years and represent a consensus of scientific opinion around the world. Working Group II is finalizing the assessment's second volume, Impacts, Adaptation, and Vulnerability, the summary of which is due for release 6 April 2007. The summary of the Working Group III volume, Mitigation of Climate Change, will be released in May 2007. The volumes themselves should be issued later in the year 

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