Image caption The coal industry says carbon capture technology is currently too expensive

US President Barack Obama has unveiled a proposal to limit carbon emissions on new power plants built in the US.

It would be the first federal attempt to impose limits on the pollution blamed for global warming.

"Climate change - caused by carbon pollution - is one of the most significant public health threats of our time," said Environmental Protection Agency head Gina McCarthy.

But the proposal is opposed by the coal industry and congressional Republicans.

According to the plan outlined by Ms McCarthy, new gas-fired power plants would be limited to 1,000lb (450kg) of carbon dioxide emissions per megawatt hour. New coal-powered plans would be limited to 1,100lb.

Currently, the average coal plant emits about 1,800lb of carbon dioxide per hour.

The proposal would eventually affect existing power plants, which account for around a third of all US greenhouse gas emissions.

To meet the standard, coal plants would need to install new carbon capture technology, which the industry has said is currently too expensive.

'Limitless dumping'

Mr Obama has previously said he wants to end what he has called "the limitless dumping of carbon pollution" from US power plants.

In his second inaugural address in January, he promised a renewed focus on climate change - a signature of his first election campaign that was essentially ignored during his first term as president in favour of healthcare reform.

"We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations," said Mr Obama in his January speech.

He said that while "some may still deny the overwhelming judgment of science... none can avoid the devastating impact of raging fires, and crippling drought, and more powerful storms".

Although the plan unveiled on Friday has been in the works since April 2012, it faces steep opposition from both industry groups and congressional Republicans, who say efforts to force plants to install expensive carbon cleaning technology could hurt job creation.

Currently, coal-powered plants account for around 40% of US electricity consumption, a share which has been shrinking recently.

The plan will be subject to a 60-day comment period, and officials hope to implement it by the fall of 2014.