The effort would also have to be global and all but immediate, because unless meaningful policy change happens in the next decade it will be too late to reverse damage already done to the climate, policy experts and conservationists said.

"If we don't call for a moratorium, we don't make it," Ed Mazria, director of Architecture 2030, told mayors attending the third annual Sundance Summit.

Co-sponsored by Salt Lake City Mayor Rocky Anderson, actor and activist Robert Redford, the U.S. Environmental Protection Agency and business and environmental organizations, the summit aims to teach local leaders how to curb global warming.

The summit follows a May report by the Intergovernmental Panel on Climate Change that said industrialization since 1750 had so warmed Earth's climate that oceans could rise by 20 feet by 2100, leaving more than 1 million dead and costing hundreds of billions of dollars. Some of the changes are already irrevocable, the IPCC said. But if left unchecked, warming due to global industrialization could continue for more than a millennium.

That means people can change all the light bulbs and plant all the trees they want, but conventional power plants that burn pulverized coal will wipe out any efforts to curb carbon dioxide emissions, Mazria said. With 151 conventional coal-fired power plants now in development in the United States, coal is the one fossil fuel that has the power to ruin us, he said.

Mayors now find themselves in a position of unusual power, because they can pressure governors to cut greenhouse gas emissions through statewide efficiencies and new approaches to transportation and building, said Philip Clapp, president of the National Environmental Trust and a former legislative director for U.S. Sen. Tim Wirth, D-Colo.

Clapp said that despite complaints of little to no leadership at the federal level on global warming, Congress and the Bush administration see a need to move fast. In the next three years, Clapp said, new policies will emerge that will govern the nation's efforts for the next decade.

The goal must be to stabilize and then reduce greenhouse gas emissions by 80 percent with 1990 as the baseline. This must be accomplished by 2050, Clapp said. But if there are no tangible results by 2020, the effort is doomed.

There is a danger that the president, Congress and industry will focus their efforts on weak legislation, using up precious time even as the rest of the world looks to the United States for crucial leadership, Clapp said.

"We're not going to have a second chance to do this," Clapp said. "This is really our one shot."

Mazria told the mayors that because 76 percent of all energy that comes from coal in the United States is used in buildings, they can through planning ordinances, zoning changes and executive orders subvert the need for coal.

Mayor Robert Cluck of Arlington, Texas, a self-described conservative Republican, said his fight against TXU Energy's plans to build 18 new polluting coal-fired power plants led him to call on other Texas cities to help him fight the utility giant.

The plants would have spewed 150 million tons of CO2 per year, which Cluck, a physician, knew posed a public health threat. After what he called a "vicious fight," TXU entered buy-out negotiations with investors who agreed to build just three plants and limit emissions to 20 million per year.

Of the 24 U.S. mayors and one Canadian mayor who attended the summit, five were from capital cities and most were from smaller municipalities - a sign of growing awareness of global warming, said Mayor Glen Gilmore of Hamilton, N.J.

"People are noticing the seasons are changing in a way not seen before," he said. "This isn't just about preaching to the choir. It's about looking for real actions by learning from each other."

The conference continues through today.