President Barack Obama renewed his campaign to curb carbon emissions Saturday, saying the debate over climate change is over.

Obama, who made the battle against climate change a core promise of his 2008 election campaign, has been stymied at the federal level by opposition from lawmakers.

Congress "is full of folks who stubbornly and automatically reject the scientific evidence," Obama told a crowd of more than 30,641 people, including thousands of graduates at the University of California, Irvine.

"They'll tell you climate change is a hoax, or a fad. One says the world might actually be cooling."

Two weeks ago, Obama unveiled a contentious plan to cut carbon emissions from US power plants by 30 percent from 2005 levels by 2030.

The plan would let US states choose their own approaches as long as each enforces restrictions on carbon emissions.

The president used his speech to the university graduates to present a $1-billion competition for funds to help communities hit by natural disasters linked to climate change.

"Climate change is no longer a distant threat," the president emphasized.

"In some parts of the country, weather-related disasters like droughts, fires, storms and floods are going to get harsher and costlier."

He stressed that climate change remains "one of the most significant long-term challenges" to the United States and the world.

- Debate 'over' -

"The climate change deniers suggest there's still a debate over the science. There's not," Obama said.

"I've got to admit, though, it's pretty rare that you'll encounter someone who says the problem you're trying to solve doesn't even exist."

When president John F. Kennedy set the United States on a course for the moon, Obama added, "I don't remember anyone saying the moon wasn't real, or that it was made of cheese."

Of the $1 billion funding Obama announced Saturday, about $820 million will be available to any state that experienced a "Presidentially-declared major disaster" between 2011 and 2013.

States affected by Hurricane Sandy -- which killed more than 200 people, affected 650,000 houses and caused months-long power cuts -- will be eligible to compete for the rest, about $180 million, the White House said in a statement.

The money "will support innovative resilience projects at the local level while encouraging communities to adopt policy changes and activities that plan for the impacts of extreme weather and climate change and rebuild affected areas to be better prepared for the future," it said.

In May, the White House called for urgent action to combat climate change with the release of a four-year study on the impact of global warming across the United States and key sectors of the American economy.

Leading scientists warned of the risks of rising sea levels, droughts, fires and pest outbreaks if the world does not tackle the repercussions of greenhouse gas emissions.

But Obama also sounded a positive note, touting advances that "have created jobs, grown our economy, and helped cut our carbon pollution to levels not seen in about 20 years."

Since 2006, he said, no other country has reduced its carbon pollution as much as the United States.