"The truth is, the United States cannot meet this (climate) challenge alone. Solving this problem will require all of us working together," Obama said in a surprise video message to the Bi-Partisan Governors Global Climate Summit in Los Angeles Tuesday morning.

Besides governors from 22 key US states, top government officials from several countries including India, China, Brazil, Britain, Canada, Indonesia and Australia are participating in the meeting.

In a four-minute video message Obama said: "My presidency will mark a new chapter in America's leadership on climate change that will strengthen our security and create millions of new jobs in the process."

Observing that Washington has too often failed to show the kind of leadership needed to tackle such an important issue, Obama said his administration would start with a federal cap and trade system.

"We will establish strong annual targets that set us on a course to reduce emissions to their 1990 levels by 2020 and reduce them an additional 80 percent by 2050," Obama said, according to the transcripts of the message made available by the Obama Transition Office.

Announcing that his administration would invest $15bn each year to catalyze private sector efforts to build a clean energy future, Obama said: "We will invest in solar power, wind power, and next generation biofuels. We will tap nuclear power, while making sure it's safe. And we will develop clean coal technologies."

Terming it as one of the most pressing issues confronting the world, Obama used the occasion to send his message to the international community: "Let me also say a special word to the delegates from around the world who will gather at Poland next month: your work is vital to the planet.

"Once I take office, you can be sure that the United States will once again engage vigorously in these negotiations, and help lead the world toward a new era of global cooperation on climate change," Obama said.

The president-elect said he had asked members of the US Congress, who would be attending the conference as observers, to report to him on what they learn there.

"Now is the time to confront this challenge once and for all. Delay is no longer an option. Denial is no longer an acceptable response. The stakes are too high. The consequences, too serious," he said.

Given the complexity of the issue and differences among nations, Obama conceded that stopping climate change will not be easy and it will not happen overnight.

"But 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," he asserted.