In sweeping proposals released after four years of frustrated efforts, Mr Obama ordered new curbs on carbon emissions from power plants and called for America to ready its defences against an already-changing climate.
The president also surprised environmentalists by signalling he would reject a controversial oil pipeline if it was found to “significantly exacerbate” the problem of carbon pollution.
“I refuse to condemn your generation and future generations to a planet that is beyond fixing,” Mr Obama told students at Georgetown University. “As a president, as a father and as an American I’m here to say we need to act.”
Mr Obama first promised a new push on climate change during his inagural address on a freezing morning in January, warning that failing to cut emissions “would betray our children”.
Today, as Washington sweltered in the summer heat, Mr Obama finally laid out the details of his plan, which can be carried out by executive order and therefore do not need Congressional approval.
He announced he was imposing the first-ever limits on carbon emissions from power plants, the single largest source of pollution in the US.
Coupled with new efficiency standards for vehicles, appliances and buildings the limits are intended to help reduce carbon emissions by three billion metric tonnes over 17 years.
The plan commits to cutting hydrofluorocarbons, the “super greenhouse gases” emitted by refrigerators and air conditioning units, part of a commitment reached last month with China.
The government will also issue permits for wind and solar energy projects on government land intended to eventually power more than six million homes.
On the coasts barriers would be strengthened to fight against Hurricane Sandy-like storms while in the heartland farmers will be given more support in the face of drought and wildfires.
Mr Obama also made an unexpected reference to the Keystone XL pipeline, which would carry oil from the tar sands of Canada down to Texas and is the target of intense campaign by green groups.
The president said he would only approve the project if it could be shown not to significantly increase carbons emissions.
“The net effects of the pipeline’s impact on our climate will be absolutely critical to determining if this project is allowed to go forward,” he said.
The overall plan is intended to help meet Mr Obama’s pledges to the UN climate change summit in Copenhagen, where he promised that by 2020 the US would cut emissions by 17 per cent from their 2005 levels.
Mr Obama’s proposals were largely applauded by environmental groups.
“President Obama is really resetting the climate agenda and it’s a wonderful thing to see that he’s reclaiming this issue,” said Andrew Steer, president of the World Resources Institute.
But even before the speech was delivered, Republicans seized on comments by an outside advisor to the White House who urged the declaration of a “war on coal”.
Daniel Schrag, a Harvard academic who advises on climate change, had told the New York Times that while the White House was hesitant to use such language, a “war on coal is exactly what’s needed”.
Mitch McConnell, the Republican senate leader, said Mr Obama’s effort to curb coal industry emissions represented “a war on jobs”.
“It’s tantamount to kicking the ladder out from beneath the feet of many Americans struggling in today’s economy,” said Mr McConnell, who represents coal-rich Kentucky.
Yesterday’s speech was the latest step in what has been a long and frustrating journey for Mr Obama as he tried to fulfill his 2008 campaign pledges to fight climate change.
Soon after taking office in 2009, the new president backed a bill that would have set a national limit on the amount of carbon the US could emit.
The legislation, nicknamed “cap and trade”, was vigorously opposed by Republicans as well as conservative Democrats, and was defeated in the Senate in 2010.