During his first 100 days, US President Barack Obama has kept his word to reverse the environmental policies of his predecessor. But the success of his battle over global warming ultimately depends on Congress.

"The President has laid out ambitious goals for climate policy," said Michael Levi, climate change expert at the Council on Foreign Relations.

In addition to measures promoting environmentally-friendly industries contained in Mr Obama's economic stimulus package, the US Environmental Protection Agency earlier this month declared carbon dioxide and other greenhouse gases a health risk, a landmark U-turn that could impact climate change regulation.

Greenhouse gases, primarily CO2, are emitted by cars, aircraft and coal-burning power plants and are widely blamed for global warming.

The EPA appears to be paving the way for regulating about seven billion tons of carbon dioxide spewed into the atmosphere annually by about 1.5 million polluters, which may now fall under the jurisdiction of the 1970 Clean Air Act.

However, the White House said it would prefer to avoid CO2 regulation, arguing the adoption of a law introducing a ceiling for greenhouse gas emissions as well as a so-called "cap and trade" system would create strong economic incentives to develop new clean energy sources and create millions of new jobs.

Mr Obama has urged Congress to create such a market and has included in his first budget proposals a call to reduce greenhouse gas emissions by 14 per cent by 2020, compared to their 2005 level.

Responding to the President's appeal, the House of Representatives unveiled in late March draft energy legislation calling for a 20 per cent reduction of greenhouse gas emissions by 2020.

Congressional hearings last week revealed strong opposition to the "cap and trade" principle from the Republican minority, which strongly represents industry and business circles, particularly coal and oil companies.

Citing an "independent" study by the Massachusetts Institute of Technology, influential Republican congressman Mike Pence insisted an emissions market would cost the average American family 3,128 dollars a year and eventually result in the loss of millions of jobs.

However, centrist Democrats are also said to be concerned by the proposals to create a CO2 reduction mechanism without including such countries as China and India.

Without the support of centrists from both parties the emissions Bill had little chance of being adopted, Mr Levi warned.

But he said he believed the President "can be successful if he is patient and pragmatic ... And he showed that he can be both."