The US Government has declared greenhouse gases threaten human health.
The move allows the US Environmental Protection Agency to order cuts in emissions without the approval of Congress.
EPA administrator Lisa Jackson said the agency was ``authorised and obligated to make reasonable efforts’’ to cut greenhouse gases.
The news came as global climate talks got under way in Copenhagen aimed at forging a deal on major emissions cuts.
Australia told the summit it’s time for ``bold action’’ on climate change.
``We want a success at Copenhagen, in fact we want a resounding success,’’ Australia’s climate change ambassador Louise Hand told the conference’s opening session.
``We’re committed to bold action, we’re committed to a strong outcome.’‘
Australia was speaking on behalf of the Umbrella Group, an informal group of developed countries not from the European Union.
Australians will also be among sceptics in Copenhagen.
Family First Senator Steve Fielding will attend next week the same time as US President Barack Obama as a representative of the US-based Committee For a Constructive Tomorrow (CFACT), which seeks to cast doubt on climate change.
Australian scientists will also speak at a CFACT conference starting tonight.
A new poll of 24,000 people worldwide found most believed climate change was a very serious problem.