A combination picture shows the coal-fired Castle Gate Power Plant operating November 27, 2012 (top) and the same plant sitting idle outside Helpher, Utah August 3, 2015. The plant was closed in the Spring of 2015 in anticipation of new EPA regulations. [Photo/Agencies]

WASHINGTON - US President Barack Obama challenged America and the world to step up efforts to fight global warming on Monday at the formal unveiling of his administration's controversial, ramped-up plan to cut carbon emissions from US power plants.

Declaring climate change the greatest threat facing the world, Obama said the regulation requiring the power sector to cut its emissions by 32 percent 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.

The United States has pledged to slash its greenhouse gas emissions across the economy by 26 to 28 percent below 2005 levels by 2025. Cuts from the high-emitting power sector will be critical to the effort, and the White House hopes this plan will prove Washington's commitment to that goal as it prods other countries to follow suit.

Obama is enacting the plan by executive order, bypassing 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.

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

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