Schwarzenegger put the final stamp on California's leading global warming action by signing into law the state's landmark bill calling for a 25% reduction in greenhouse gases by 2020.

"We simply must do everything we can in our power to slow down global warming before it is too late, Schwarzengger said, adding the bill will "change the course of history."

The goal of the bill is to reduce the state's emissions of carbon dioxide and other greenhouse gases by an estimated 25 per cent by 2020.