A coalition of 16 of the world’s biggest cities, five banks, one former president and companies and groups that modernize aging buildings pledged today to invest billions of dollars to cut urban energy use and releases of greenhouse gases linked to global warming.

The loans and interest would be paid back with savings accrued through reduced energy costs, organizers of the initiative said at a news conference in Manhattan. Typically, such upgrades can cut energy use and costs from 20 percent to 50 percent, they said.

Making more efficient use of energy is considered by many scientists to be the best starting point for addressing global warming, particularly because there is a potential immediate financial payoff along with the long-term environmental benefit.

At the news conference, Mayor Michael R. Bloomberg said that investing in retrofitting existing buildings was vital because they will make up 85 percent of the buildings that will stand in New York City in 2030.

He said banks and corporations appeared to be grasping the importance of considering long-term environmental risks when making investments. “Major business and financial institutions increasingly understand that shrinking the world’s carbon footprint is a pro-growth strategy, indeed the only pro-growth strategy for the long term,” Mr. Bloomberg said.

Energy use in buildings accounts for about a third of global releases of heat-trapping greenhouse gases. In densely populated older cities, like New York City and London, buildings are the dominant source of greenhouse gases.

The first targets under the initiative, organizers said, would be municipal buildings in the participating cities, which are: Bangkok; Berlin; Chicago; Houston; Johannesburg; Karachi, Pakistan; London; Melbourne, Australia; Mexico City; Mumbai, India; New York; Rome; São Paulo, Brazil; Seoul, South Korea; Tokyo and Toronto.

The project is aimed at propelling energy-saving investments that otherwise tend not to happen even when long-term financial benefits are clear — because cities or property owners lack access to capital, organizers said.

Also today, the National Academy of Sciences and the scientific academies of 12 other countries issued a joint statement calling on world leaders to address global warming by boosting energy efficiency, promoting a shift to less-polluting energy sources, and intensifying research into new energy technologies that produce no emissions.

“Increasing energy efficiency is a first crucial step toward solving the climate-energy problem,” the statement said. It emphasized the importance of developing financial mechanisms for encouraging such investments and on sharing technology and information that could spur such changes.

The plan was announced at the end of a three-day meeting of mayors, business leaders and environmental experts organized by former President Bill Clinton’s foundation and other partners as part of a two-year-old initiative aimed at advancing local actions that could blunt global warming.

“Climate change is a global problem that requires local action,” Mr. Clinton said. “The businesses, banks and cities partnering with my foundation are addressing the issue of global warming because it’s the right thing to do, but also because it’s good for their bottom line. They’re going to save money, make money, create jobs and have a tremendous collective impact on climate change all at once.”

Mr. Clinton’s remarks on climate change have been a talking point this spring for his wife, Senator Hillary Rodham Clinton of New York, as she pursues the Democratic nomination for president. Because Mrs. Clinton has yet to give a major speech on climate change, her campaign views Mr. Clinton’s highly visible work on the matter as a political plus.

Advisers to Mrs. Clinton, meanwhile, are keen to avoid ceding the political issue of global warming and climate change to another Democratic candidate — or, especially, to former Vice President Al Gore, who has turned climate change into a civic and political cause worldwide.

As president, Mr. Clinton drew some criticism for not seeking Senate ratification of the Kyoto Protocol, the climate treaty that requires industrialized countries to cut emissions. The Bush administration has rejected the treaty.

Today, Mr. Clinton said the strength of the new initiative was that it would quickly produce concrete change on the ground, demonstrating that a transition away from fossil fuels need not be a burden on economies of rich or developing countries.

“We all know that this is a global problem that requires a successor to Kyoto and national legislation, but we also know that as you reduce greenhouse gas emissions you must do it place by place, specifically company by company, building by building,” he said. “The mayors are in a remarkable position to do this.”

Several experts not involved with the Clinton Foundation’s new project said it appeared to be a valuable initial step in limiting the human impact on climate.

One challenge, said Thomas J. Wilbanks, an expert on energy and climate at the Oak Ridge National Laboratory, is that the accelerating building boom in fast-growing developing countries means that investing in making new buildings energy efficient will be far more important in the long run than tightening up old ones.

“Potentials for energy-saving retrofits are significant in industrialized countries, but the real challenge in rapidly growing developing countries is increasing the efficiency of new building construction,” Dr. Wilbanks said.

Dr. Wilbanks, who was also an author of one of the recent United Nations climate reports, said that “the greatest value of this initiative is that it jump-starts an inevitable global process of making buildings more energy-efficient.”

The first step under the Clinton foundation’s retrofitting project will be energy audits of older municipal buildings, identifying systems or structures that could be replaced, organizers said.

The financial instruments for paying for the upgrades are being designed by the Clinton Climate Initiative, set up by the foundation and Hannon Armstrong, a company specializing in arranging such investments, along with the participating banks: Citigroup, UBS, Deutsche Bank, ABN Amro and JPMorgan Chase & Company.

The upgrades would be done by four international energy-services companies that are already seeing a booming business in these types of conversions. They would guarantee a certain level of energy and monetary savings for particular projects under the plan.

The influx of capital from the new project could potentially double global business in such energy upgrades, which is several billion dollars a year now, bankers and business representatives said.

“I’ve been involved in a couple billion dollars worth of projects in the last several years,” said Bob Dixon, senior vice president of Siemens Building Technologies, one of the energy-services companies. “They’ve all paid for themselves in energy savings.”