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."