Californian governor Arnold Schwarzenegger has launched a new plan to reduce the US state's greenhouse gas emissions.

The policy, revealed at the opening of the UN World Environmental Day conference, involves setting targets to reduce emissions to 2000 levels by 2010, 1990 levels by 2020, and 80 per cent below 1990 levels by 2050.

"Today, California will be a leader in the fight against global warming," promised Mr Schwarzenegger.

"I say the debate is over. We know the science, we see the threat and we know the time for action is now."

Environmental groups have welcomed the news, believing that California's commitment to reducing climate change could influence the Bush administration to take a more aggressive stance towards lowering emissions.

Jason Mark, California director of the Union for Concerned Scientists, told the San Francisco Chronicle he felt the governor's voice "adds immeasurably" to the low-emissions drive.

The next step is for the state's lawmakers to introduce legislation to meet the targets.

California has been one of the leading states in the US in the development of the hydrogen economy, and has also introduced a slew of stringent emissions legislation in recent years.