Washington (AFP) - US President Barack Obama will unveil what he called the "biggest, most important step we've ever taken" to combat climate change Monday, slapping tough emission targets on power plants.

Obama will tell plant owners they must cut carbon dioxide emissions by 32 percent from 2005 levels by 2030, in the first ever mandatory targets.

The president was to deliver his eagerly anticipated remarks at the White House at 2:15 pm (1815 GMT), firing the starting gun on a months-long environmental drive that will shape his legacy.

Later this August, Obama is expected to visit the Arctic state of Alaska to highlight the impact of climate change.

In September, when he will host Pope Francis at the White House, they are expected to make an impassioned collective call for action.

And in December, representatives from around the world will gather in Paris to hash out rules designed to limit global temperature increases to two degrees Celsius (3.6 degrees Fahrenheit).

"Climate change is not a problem for another generation. Not anymore," Obama said in a video message foreshadowing the formal announcement.

Anticipating stern opposition from the Republican-controlled Congress, Obama warned that climate change is a threat to the economy, health and security of America.

Power plants account for some 40 percent of US emissions of carbon dioxide, the most common greenhouse gas that contributes to climate change.

"Existing power plants can still dump unlimited amounts of harmful carbon pollution into the air weekly," he said.

"For the sake of our kids, for the health and safety of all Americans, that's about to change."

Obama argued the plans will lead to lower energy bills and create jobs in the renewable energy sector.

- Hot-button issue -





But the plans have be met with fury by the Republican Party, which described the measures as "overreach" and "heavy-handed".

Republican National Committee Chairman Reince Priebus warned the measures would have "devastating consequences for our economy."

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Coal producers, who provide almost 40 percent of US electricity, are also set to lose out.

The American Coalition for Clean Coal Electricity, an industry lobby group, previewed likely legal action, saying Obama's administration was "pursuing an illegal plan that will drive up electricity costs and put people out of work."

In its initial proposal a year ago, the Obama administration had set the carbon emissions cut from the power sector at 30 percent.

Climate change is a hot-button issue in American politics and cuts are politically sensitive because coal, among the dirtiest energy sources, remains a major US industry.

It also has some influential supporters, including Senate Majority Leader Mitch McConnell, a senator from coal-rich Kentucky.

Some Republican opponents dispute the existence of global warming and others cast doubt on whether humans are to blame for the phenomenon.

"Climate change will not be solved by grabbing power from states or slowly hollowing out our economy," said candidate Jeb Bush.

"The real challenge is how do we grow and prosper in order to foster more game-changing innovations and give us the resources we need to solve problems like this one."

But Gina McCarthy, head of the Environmental Protection Agency, insisted the rules were "reasonable" and "achievable".

"They can cut carbon pollution in whatever way makes the most sense to them," McCarthy said.

"No plant has to meet them alone or all at once, they have to meet them as part of the grid and over time."

Hillary Clinton, the Democrat hoping to take over from Obama after the 2016 election, welcomed the announcement as a "significant step forward in meeting the urgent threat of climate change.

"And it drives investments in clean energy and energy efficiency, reduces asthma attacks and premature deaths, and promotes a healthier environment and a stronger economy."