Nasa scientist: 'We're toast' without drastic action on global warming

Exactly 20 years after warning America about global warming, a top NASA scientist said the situation has gotten so bad that the world's only hope is drastic action.

James Hansen told Congress on Monday that the world has long passed the "dangerous level" for greenhouse gases in the atmosphere and needs to get back to 1988 levels.

He said Earth's atmosphere can stay this loaded with man-made carbon dioxide for only a couple more decades without changes such as mass extinction, ecosystem collapse and dramatic sea level rises.