The natural balance will be restored only when carbon dioxide and other greenhouse gasses dip to 25 percent or 30 percent of current levels, said Kevin Trenberth, who leads the climate analysis section of the National Center for Atmospheric Research in Boulder, Colo.

Trenberth joined Wednesday with Salt Lake City Mayor Rocky Anderson at the University of Utah College of Law to discuss the science and politics of climate change. Both noted such pollution controls were on the docket Wednesday at the U.S. Supreme Court, where the Utah Attorney General's Office has sided with the Bush administration against using the Clean Air Act to control carbon dioxide.

Anderson criticized the federal government and many state governments, including Utah, for a lack of leadership on the issue. He focused instead on the actions being taken by citizens, local government and business to reduce the greenhouse gasses behind climate change.

"The good news," Anderson said, "is we have the means to make a tremendous difference - at least in the short term."

Trenberth highlighted trends in climate science that have become familiar in the public debate about climate change.

Utah, he noted, can expect shorter winter seasons. And related precipitation changes means the Earth's surface has a tougher time cooling itself, so that there is a greater likelihood of more frequent and deeper droughts that will force the issue of how to address water management, especially in the West.

"This is going to be a major challenge in the future," Trenberth said.

Trenberth reminded his audience - an assembly of law students, meteorologists and political activists - that lower soil moisture is likely to mean more heat waves, like the one in 2003 that left 30,000 dead in Europe, and more wildfires, like the massive Hayman wildfires in 2002 that burned more than 100 Colorado homes.

fahys@sltrib.com