Nations around the world are hoping the United States is set to come in from the cold and take a leading role in the fight against climate change as President-elect Barack Obama prepares to take office.

"It's a very exciting time. It's a moment we have been waiting for, many of us, for some period of time; we intend to pick up the baton and really run with it," Democratic Senator John Kerry told reporters, as he prepared to head to international climate change talks in Poland.

Obama has been "very, very clear that after eight years of obstruction and delay and denial, the US is going to rejoin the world community in tackling this global challenge," he added.

Although no member of Obama's transition team will be at the UN talks, Kerry is heading to Poznan, Poland, as an observer for the December 1-12 conference.

He said the US message will be "that America is back, we are back in a position of participation, of respecting views and having real discussions and trying to find the best framework for all of us."

The United States, which is the world's biggest emitter of greenhouse gases, walked away from the Koyto protocol under the administration of President George W. Bush.

That snub left other nations struggling to define a coherent policy for tackling carbon emissions with the United States left out of the framework.

Last week Obama vowed he would "engage vigorously" in global climate change talks. In a surprise video message to an international conference in California, he said there would be new leadership on the issue as soon as he takes office on January 20.

The president-elect also addressed a message directly to delegates at the Poland talks, saying he had asked observers to report back to him.

"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."

Experts believe that while the incoming administration will be serious in tackling climate change, getting to the root of the causes could take time in a country addicted to relatively cheap fuel supplies.

"For the first time in many years you will have an administration prepared to negotiate a commitment on the part of the US. Without that there are no prospects for an agreement," Elliott Diringer, vice president for international strategy at the Pew Center for Global climate change, told AFP.

"Will the world will be disappointed, that depends on expectations and I think expectations in some places are too high," Diringer said.

"But I think the president elected sent a very clear signal of what to expect in his statement last week when he said returning US emissions to 1990 levels by 2020. That is what he will try to deliver.

"It won't be easy but it can be done."

The US Senate will take up two sweeping global warming bills in January, in the latest sign that Obama's election could quickly reverse years of US foot-dragging on climate change.

Barbara Boxer, chairwoman of the Senate Environment and Public Works committee, said one bill would combat harmful gas emissions by providing 15 billion dollars a year to spur clean energy innovation and the development of advanced biofuels.

The other piece of legislation will direct the US Environmental Protection Agency to set up a cap-and-trade system to stem greenhouse gas emissions.

Obama has said he is in favor of a "cap-and-trade" system, which was vigorously opposed by Bush, under which gas emissions for industries and vehicles would be capped or could be "sold" among participants.

But Diringer said it would be difficult to win approval for such a system, especially at a time of economic crisis, as it is likely to encounter stiff opposition from Republican lawmakers.

The aim would be to get a US system in place before talks in Copenhagen in December 2009, when a proposed UN deal, the most ambitious environmental pact ever attempted, is set to be agreed.

The deal would take effect from the end of 2012, when the current provisions of the UN Framework Convention on Climate Change, known as the Kyoto Protocol, expire.

But Diringer warned that if Obama is stymied in Congress "it will be difficult for the US to actually negotiate a specific target in Copenhagen so we will not foresee a full and final agreement at the Copenhagen conference.

"If the US is not ready to negotiate a commitment other countries won't be either," he warned.

"It's more practical to aim for an intermediary agreement. Maybe an agreement on the architecture of the post 2012 framework, not the specific commitment each country will have, but an overall architecture."