US president Barack Obama has laid out a broad new plan to fight climate change, using executive powers to get around "flat Earth" science deniers who have blocked action in Congress.

Mr Obama called for new restrictions on existing and new power plants to curb carbon emissions, pledged to push new generation clean energy sources and to lead a fresh global effort to stem global warming.

Officials said the plan would allow the United States to meet a goal of cutting greenhouse gas emissions by 17 per cent below 2005 levels by 2020, a pledge Mr Obama made at the inconclusive Copenhagen summit in 2009.

The president argued that Americans across the country were already paying the "price of inaction" against climate change, describing 2012 as the warmest year in human history, which parched farmlands in the US heartland.

"As a president, as a father, and as an American, I am here to say we need to act," he said, in a speech delivered in the sweltering early afternoon heat outside Georgetown University, with an eye on his political legacy.

Mr Obama said he had no patience for climate change deniers, including many in Congress, who dispute the science holding that carbon dioxide emissions contribute to a dangerously warming planet.

"We don't have time for a meeting of the Flat Earth Society," he said.

"Sticking your head in the sand might make you feel safer, but it is not going to protect you from the coming storm."

Keystone pipeline put on notice

Mr Obama also touched on the Keystone XL pipeline, which is designed to carry oil from the tar sands of Canada to the US Gulf Coast and has become a cause celebre for environmentalists.

He warned the project, currently under state department review to determine whether it is in the US national interest, should not be approved if it contributes to global warming.

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"Our national interest will be served only if this project does not significantly exacerbate the problem of carbon pollution," Mr Obama said.

The president is widely expected to approve the long-delayed project when it reaches his desk. The state department has already concluded in a draft report that it would not significantly harm the environment.

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Environmentalists, however, insist the pipeline would lead to the expansion of tar sands extraction in Alberta - a process they say creates the "dirtiest" oil on Earth.

The president's plan is based on a three-pronged approach: cutting carbon pollution in the US, mitigating the impact of climate change, and seeking international action to address it.

No support for coal-fired power plants abroad

Mr Obama committed to withdrawing support for coal-fired power plants abroad and offered to discuss new initiatives with big emitters like India and China.

He directed the Environmental Protection Agency (EPA) to write rules to impose new standards for carbon emissions on new and existing power plants.

The plan calls for $US8 billion in loan guarantees to support investments in innovative technologies and aims for a 20 per cent increase in energy efficiency in commercial, industrial and residential buildings.

Some opponents of his approach have warned the plan could result in older coal-fired plants being taken offline and may thereby raise electricity prices for consumers, which could disproportionately hurt the poor.

Officials counter that the plan will reduce the amount of electricity used thereby reducing fuel bills.

The specifics of much of his plan were unclear, and many of Mr Obama's new rules could face court challenges that would delay their implementation.

The president will be using the executive powers of his office since Congress - where there is widespread skepticism of climate change science and fear about the economic impact of mitigation efforts - has refused to act.

Mr Obama also set a goal of reducing carbon pollution by three billion metric tons by 2030 - a figure equivalent to more than half of the annual carbon pollution from the US energy sector.

Republicans have accused Mr Obama of waging a "war on coal" that would slap onerous regulations and unreasonable environmental targets on power stations.

AFP