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

Obama said "no challenge poses a greater threat to our future and future generations than a change in climate".

He warned: "there is such a thing as being too late."

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

Electric power plants account for some 40 per cent of US emissions of carbon dioxide, the most common greenhouse gas that contributes to climate change.