President Obama sharply criticized Republican intransigence on climate change last night, rebuking those who disbelieve in man-made carbon effects in an effort to cast a clear choice between him and his opponent, Mitt Romney.

His comments mark some of the strongest assertions on climate in the presidential race, coming as the campaigns sprint into the straightaway before November's election. They also may give comfort to his uneasy allies, environmental groups, which were eager to see him respond to a joke Romney made about rising tides last week.

"And yes, my plan will continue to reduce the carbon pollution that's heating our planet, because climate change is not a hoax," Obama told a roaring crowd at the Democratic National Convention. "More droughts and floods and wildfires are not a joke. They're a threat to our children's future, and in this election, you can do something about it."

The president's blunt confrontation with Romney is what many climate advocates have been pining for since the former Massachusetts governor dismissed Obama's goals to address sea level rise as an unattainable promise and one that ignores pressing needs among American families.

"Protecting our families' future is not a joke," Larry Schweiger, president of the National Wildlife Federation, said in an interview before Obama's speech. "And I think President Obama needs to respond to that comment. My children and my grandchildren are going to suffer the consequences, and that's a family value matter for me."

He added that Romney's joke amounts to "throwing down the gauntlet with climate change."

"I think President Obama needs to address this family values matter," Schweiger said, "this notion that we have obligations not just to the current voters, but to the generations yet unborn, to the generations that are too young to vote, and so I think the climate issue needs to be framed in a family values issue."

Others thought it would be best if Obama avoided a direct response to Romney's joke, saying it could tarnish the presidency by engaging in a back-and-forth volley of one-upmanship. Instead, these advocates said Obama should have provided a no-nonsense assessment of rising temperatures and their impacts.

But after two years of rising partisanship over the scientific basis for climbing temperatures, and months of near-silence from the White House on climate change, Obama's direct response last night promises to energize his green legions two months before the election.

"President Obama should go at that full force, head-on," said Heather Taylor, director of the Natural Resources Defense Council Action Fund, regarding Romney's jibe before the president's remarks.

"Why run away from this fight?" she added, arguing that Democrats have been too hesitant to talk about climate change since the collapse of cap-and-trade legislation in 2010. "I think it's become this folklore that people don't care about this issue."

May Boeve, executive director of 350 Action Fund, said in a statement: "Hopefully, those who think climate change is a joke were watching tonight and will learn to stop denying the obvious -- the world is warming, we are causing it, and we have a responsibility to do something about it."

Touts record on energy efficiency and renewables

Yet apart from Obama playing the disciplinarian, his speech did not offer any new ideas about how to reduce greenhouse gas emissions here and abroad. His acceptance of the Democratic nomination comes after his administration has made real, but not comprehensive, advances on energy efficiency and renewable power.

"We're offering a better path, a future where we keep investing in wind and solar and clean coal," Obama said. "Where farmers and scientists harness new biofuels to power our cars and trucks. Where construction workers build homes and factories that waste less energy."

With economic issues at the forefront of voters' concern, some of the president's allies believe he is missing an opportunity to bring climate change policies into that discussion. Schweiger said rising temperatures are connected to a host of pocketbook issues from food prices and farm productivity to catastrophe losses and energy prices.

Thus, he believes the president's message on renewable energy and the economy is incomplete without talking about ways to price carbon dioxide.

"This could all be done through private money with the right carbon policies," Schweiger said. "This is not a government program, as has been suggested. This is about internalizing the cost -- the true cost -- of carbon pollution. So I think we could do a very rapid deployment and that would create literally millions of jobs in this country. To me, that's the storyline. That's how this all has to be bundled. You can't talk about clean energy jobs unless you talk about the real problem, which is climate change."

But that is a complicated pitch for a president grappling with high unemployment and an opponent who would likely describe a carbon price as an added burden on families.

A simpler one would strongly defend the administration's investments in clean energy, including the failed gamble in Solyndra that cost taxpayers $535 million, said Joe Trippi, a Democratic adviser to former presidential candidates. He believes Obama has not responded strongly enough to those attacks.

"It's better to make the case to the country ... why he's taken the path that he wants taken to the future, versus just sitting there and get whacked [on Solyndra] and take all the negatives that the Republicans are going to throw at him and never explain the positive," Trippi said in an interview this week. "I don't think that's a good strategy."

Republicans sharpened their barbs on that failed investment yesterday, which marked the one-year anniversary of Solyndra's bankruptcy.

But those attacks can also expose Romney to attacks that he opposes clean energy. And Obama is not the only Democrat to make use of Republican skepticism about climate change following Romney's remarks last week at his own convention in Tampa, Fla.

"Despite what you heard in Tampa, an exceptional country does care about the rise of the oceans and the future of the planet," Massachusetts Sen. John Kerry said at the convention last night. "That is a responsibility from the Scriptures -- and that, too, is a responsibility of the leader of the free world."