Calling climate change an urgent challenge, U.S. president-elect Barack Obama promised Tuesday that Washington would take a leading role in combating it in the United States and throughout the world.

"My presidency will mark a new chapter in America's leadership on climate change," Obama said in a video message to governors and others attending a Los Angeles summit on the issue.

In the roughly four-minute message, Obama reiterated his support for a cap-and-trade system approach to cutting greenhouse gases. He would establish annual targets to reduce emissions to their 1990 levels by 2020 and reduce them another 80 per cent by 2050.

Obama also promoted anew his proposal to invest $15 billion US each year to support private sector efforts toward clean energy.

President George W. Bush has been criticized for failing to do enough to combat climate change and Obama has promised quick action to address the issue.

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At a news conference Tuesday, a coalition called the U.S. Climate Action Partnership — made up of 32 leading corporations, including electric utilities and oil companies, and environmental groups — urged Obama to press Congress to approve legislation next year for a mandatory cap-and-trade system to limit the release of carbon dioxide from burning fossil fuels and other greenhouse gases.

Opponents of such action argue controls on carbon dioxide emissions will increase energy costs.

Under a cap-and-trade program, the government would establish a ceiling on the amount of carbon dioxide that can be released into the air from burning fossil fuels. A utility or industrial plant would have to purchase emission allowances for every tonne of pollution released. Anyone who exceeds the cap must either make pollution reductions or buy additional allowances, while those who cut emissions below the cap would be able to sell allowances.

Several environmental groups praised Obama's focus on global warming, including Environmental Defence president Fred Krupp. He said Obama is "clearly rejecting the timid, business-as-usual approach" to dealing with climate and energy problems.

In his remarks to the summit, Obama criticized Washington for failing to lead on the issue in the past.

"I promise you this: When I am president, any governor who's willing to promote clean energy will have a partner in the White House. Any company that's willing to invest in clean energy will have an ally in Washington. And any nation that's willing to join the cause of combating climate change will have an ally in the United States of America."

Scientists, environmentalists and government and industry officials were attending the two-day Governors' Global Climate Summit in Los Angeles, held ahead of a United Nations gathering in Poland next month.