President Barack Obama described climate change as one of the key challenges of our time today as he announced the first ever 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."
"Most of the time, the issues we deal with are ones that are temporally bound and we can anticipate things getting better if we plug away at it, even incrementally," he said in the East Room of the White House.
"But 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. And we may not be able to adapt sufficiently."
As a step to try to adapt, Obama announced power plant owners must cut carbon dioxide emissions by 32 per cent from 2005 levels by 2030.
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 months-long environmental drive that will shape his legacy.
Later this August, Obama will visit the Arctic state of Alaska to highlight the impact of climate change.
"Our fellow Americans have already seen their communities devastated by melting ice and rising oceans," Obama said.
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).
