Obama: Climate is most pressing challenge

US President Barack Obama framed climate change as the toughest and most pressing challenge of our time on Monday, as he unveiled limits on US power plant emissions.

"No challenge poses a greater threat to our future and future generations than a change in climate," Obama said, warning: "There is such a thing as being too late."

"This is one of those rare issues, because of its magnitude, because of its scope, that if we don't get it right we may not be able to reverse," he said at the White House. "We may not be able to adapt sufficiently."

In an attempt to at least try to slow the process, Obama announced that power plant owners must cut carbon dioxide emissions by 32 percent from 2005 levels by 2030.

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

Obama described the move as "the single most important step America has ever taken in the fight against global climate change".

The announcement fires the starting gun on a monthslong environmental drive that will shape his legacy.

Later this month, Obama will become the first president to visit the Alaskan Arctic.

"Our fellow Americans have already seen their communities devastated by melting ice and rising oceans," Obama said.

In September, when Obama hosts Pope Francis at the White House, the two are expected to make an impassioned 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 2 degrees.

But Obama's invocations got short shrift from the Republican-controlled Congress, which described the measures as "overreach" and "heavy-handed".

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