Washington - President Barack Obama has signalled a sharp departure from climate change politics-as-usual in the United States, but this is only the beginning.

The Obama administration on Monday took some initial steps towards reversing the policies of former president George W Bush, drawing widespread praise from US environmental groups who had felt sidelined for much of the last eight years under Bush.

Obama named Todd Stern as the country's first-ever climate change envoy to lead international negotiations. He also signed executive orders allowing US states like California to enact tougher vehicle emissions rules - the first step towards reversing a Bush administration block on such state action.

"We will make it clear to the world that America is ready to lead," Obama said. In a not-so-subtle rebuke of the Bush administration, he also vowed his policies would be dictated by the "sound science" behind climate change, rather than "rigid ideology."

But Obama's actions mark only the first steps in a long and complicated process, both in the United States and abroad, which environmental groups say will require an ongoing commitment from the new administration in order to make a serious dent in US and global climate policy.

Obama's first moves have been "bolder" than even many environmentalists expected, Reid Detchon, head of the Energy Future Coalition, said in an interview.

But "this is going to require a sustained effort, and more importantly political leadership" from the president himself, Detchon said.

Stern will become the country's chief negotiator in international climate talks that have already entered the final phase. Governments have resolved to agree on a comprehensive climate treaty that would impose tough new restrictions on greenhouse-gas emissions by the end of this year.

Stern led the US delegation to the Kyoto Protocol talks in 1997, which resulted in the world's first climate treaty. That experience will allow Obama's administration to get up and running immediately, shaving as much as four to six months off the transition process had Obama chosen a less veteran negotiator, said Detchon.

But while former president Bill Clinton signed the Kyoto Protocol, widespread opposition among lawmakers meant it was never ratified by the US Senate. The talks on a successor to Kyoto also remain in the balance.

US opposition to the Kyoto treaty rested on its failure to include emerging countries in its emissions targets. Developing countries have said that advanced economies, which industrialized earlier, bear greater responsibility for the Earth's warming to this point and should pay a heavier prices.

Many of the current sticking points on replacing Kyoto, which expires in 2012, revolve around the same issue.

Obama has not backed away from calling on developing countries, such as China and India, to share more of the burden in reducing emissions.

But he hopes to set an example for those countries by enacting sweeping new restrictions on polluting industries at home in the United States.

Obama pledged during the presidential campaign to push for a cap- and-trade plan through Congress that would effectively put a price on industries' carbon emissions blamed for global warming.

Supporters express hope that such legislation could be approved by December, when government delegates from around the world meet in Copenhagen to thrash out a global climate deal.

But that could be a tough sell with the US facing a serious recession and US carmakers - who will bear the brunt of tougher fuel efficiency standards - threatened with bankruptcy.

Obama has framed the debate over climate change and renewable energy as one that goes to the heart of the country's economic model: Investments and incentives for green energy will create millions of new green jobs, he says. But many lawmakers remain skeptical.

"The president is going to have to use some of his political capital to raise the awareness of the American people" and Congress, Detchon said. (dpa)