"We are trading lives for oil," he told an audience at the 2006 Sundance Summit.
Hart said mayors can make the case in Washington that climate change, energy security and national security are inseparable issues that ought to be the nation's top priorities.
The Sundance meeting has been for the past two years a place where mayors can share tools for tackling climate change at home.
This year's two-day summit looked a lot like last years', with 29 mayors from Alaska to Florida assembled at actor Robert Redford's ski and meeting resort in American Fork Canyon. And, while a smaller number attended this year - 46 participated in 2005 - their ambitions appeared a bit bigger, with an eye on how to get national leaders to take meaningful action.
Hart urged the mayors to use their clout with members of Congress to elevate climate change on the national agenda. He said reducing the nation's dependence on Mideast oil would help save the lives of soldiers, improve energy security, national security and reduce greenhouse gases that have created a climate crisis.
"You have great might," he told the mayors.
Salt Lake City Mayor Rocky Anderson, a co-founder of the summit, is working with Hart and others on a bipartisan "Climate Action Plan" for 2008 presidential candidates.
It would be a blueprint the next president can apply during the first 100 days in office for cutting the pollution - much of it produced by the engines that heat our homes, power our industries and fuel our cars and trucks - blamed for global warming. The blueprint also offers ideas for saving energy.
"The successes in municipalities are going to help lead to a sensible national policy," said Anderson.
Yet the Salt Lake City mayor added local action alone will not be enough to turn the tide on climate change. "In the end, we need huge changes in federal policy."
Gainsville, Fla., Mayor Pegeen Hanrahan agreed. She said cities can do a lot by applying the kinds of ideas discussed at the summit, such as planting trees, energy-efficient lighting and heating, and smart traffic management.
"Ultimately," she concluded, "the state and national policies need to change."
Mayors announced a new Web site on Monday, coolmayors.org, that offers information and local strategies for communicating about climate change.