"The picture is not just going to be black, because it's also maybe a chance to reinvent a new type of relation in the world," said Monique Barbut, CEO of the Global Environment Facility, a leading environmental funding agency.

She said, for example, that climate concerns have led Paris commuters to bicycle more, a change that not only saves greenhouse emissions from automobiles but also brings them in closer touch with the city.

Florida Gov. Charlie Crist also was optimistic. "It's almost stunning to me how much this issue is being talked about, how much is being done in this area," he said. "That gives me tremendous encouragement that this is all going to work out."

Bjorn Lomborg, the Danish author of "The Skeptical Environmentalist," said he thought there had been too much hand-wringing already.

"In 10 years time, there is a real risk that we will have over-worried so much about climate that by then we will be sick and tired of over-worrying and perhaps end up under-worrying," he said.

SEA ICE MELTS, STORMS BREW

Even with all the optimism, most of the experts agreed that global warming problems will get more serious over the decade.

Krupp said Arctic sea ice, which melted to the lowest level ever recorded late last month, according to US scientists, will liquefy even more over the next 10 years. Greenhouse emissions already in the atmosphere could make it worse.

"It's going to be hotter for sure. I'm not buying another coat," Barbut told the summit.

Poor countries that can least afford to relocate their citizens, such as Indonesia and Bangladesh, could be hurt the most in 10 years by flooding and stronger storms, Krupp added.

Droughts and heat waves could sear other regions. "I think life will be a lot more difficult in Africa if these scenarios hold," said Achim Steiner, head of the UN Environment Program.

Fortunately, alarm over rising temperatures has already begun to spur technological innovations.

Krupp said the energy system, the top source of greenhouse gas emissions, could be changed on the sort of quick timeline that the cell phone and the BlackBerry have evolved in the last 10 years.

The trick is to harness market forces to spark innovations in low-carbon technology like energy efficiency, solar and wind power, clean coal and nuclear power, the experts said.

Europe's market on heat-trapping emissions, though criticized for giving away too much to industry, has helped lead to investments in renewable technologies and could be a model for other regions, Krupp said.

The US Congress is mulling bills on reducing emissions, and candidates in next year's US presidential election say they want to regulate the gases to create such a market.

In China, focus on alternative energy has sharpened as government ministers worry that melting Tibetan glaciers could hurt agriculture irrigation, hitting food production and jobs.