US President Barack Obama challenged America and the world to step up efforts to fight global warming today.

He made the comments at the formal unveiling of his administration's controversial plan to cut carbon emissions from US power plants.

President Obama said climate change was the greatest threat facing the world.

He said the regulation requiring the power sector to cut its emissions by 32% from 2005 levels by 2030 would reduce Americans' energy bills and improve the health of vulnerable populations nationwide.

The plan, which also mandates a shift to renewable energy from coal-fired electricity, is meant to put the United States in a strong position at international talks in Paris later this year on reaching a deal to curb global warming.

President Obama is enacting the plan by executive order, by passing Congress, which rejected legislative attempts to reduce pollution from carbon dioxide, a common greenhouse gas blamed by scientists for heating the earth.

The regulations face certain legal challenges from states and industries, and their long-term fate depends on their ability to withstand such challenges.

The Clean Power Plan is intended to be a key part of the president’s legacy on global warming, which he pledged to fight as a candidate for the White House in 2008.

"We're the first generation to feel the impact of climate change. We're the last generation that can do something about it," President Obama told an audience at the White House.

"We only get one home. We only get one planet. There's no plan B," he said.