Democrats on Friday warned of the "existential threat" posed by climate change, hammering President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE's inaction on the topic while vowing to move aggressively next year on legislation designed to tackle the global issue.

"The reality of the crisis has to be met with the actuality of action that we take," Speaker Nancy Pelosi Nancy PelosiPelosi: Trump Supreme Court pick 'threatens' Affordable Care Act Sunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election Will Democrats attempt to pack the Supreme Court again? MORE (D-Calif.) told reporters in the Capitol, calling it "the existential threat to this generation."

Pelosi was joined by a group of Democrats who also participated this week in a climate summit in Madrid, where world leaders, scientists, businesses and environmental activists gathered for talks aimed at boosting the 2015 Paris climate accord, the Obama-era pact forged to reduce global greenhouse gas emissions.

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Trump has promised to pull the United States out of that landmark agreement, claiming it would threaten America's economy. Pelosi and other congressional Democrats attended the Madrid summit in large part to reassure the other participants in the accord that Trump's position is no indication the United States is abandoning the effort.

"The world was hungry for that," said Sen. Sheldon Whitehouse Sheldon WhitehouseSupreme Court fight pushes Senate toward brink The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Feinstein 'surprised and taken aback' by suggestion she's not up for Supreme Court fight MORE (D-R.I.), who was also on the trip.

Rep. Raúl Grijalva (D-Ariz.), chairman of the House Natural Resources Committee, delivered a similar message.

"It's not only an issue of survival for species and for human beings, it is an issue that deals with the economics and the future generations of this country. And this visit reaffirms ... the fact that we have a role — a principled role — in the fight against climate change," Grijalva said.

He added that "the fact that this administration has chosen not to" is not "the will or the desire of the American people."

Upon retaking the Speaker's gavel this year, Pelosi created a special panel — the House Select Committee on the Climate Crisis — to examine the threat posed by a warming planet and draft a report outlining remedies.

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That report will be released next spring, said Rep. Kathy Castor Katherine (Kathy) Anne CastorOVERNIGHT ENERGY: House passes sweeping clean energy bill | Pebble Mine CEO resigns over secretly recorded comments about government officials | Corporations roll out climate goals amid growing pressure to deliver OVERNIGHT ENERGY: Democrats push resolution to battle climate change, sluggish economy and racial injustice | Senators reach compromise on greenhouse gas amendment stalling energy bill | Trump courts Florida voters with offshore drilling moratorium Trump courts Florida voters with moratorium on offshore drilling MORE (D-Fla.), who chairs the panel, and Democrats will move afterwards to transfer those recommendations into targeted legislation.

"We're running out of time," Castor said, lamenting the "leadership vacuum" in the White House.

That legislation is almost certainly dead on arrival in the Republican-controlled Senate, where Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellHawley warns Schumer to steer clear of Catholic-based criticisms of Barrett Senate GOP set to vote on Trump's Supreme Court pick before election Harris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' MORE (R-Ky.) has long defended the coal and other fossil fuel industries from the imposition of tougher environmental standards.

Still, Democrats are hoping the issue will resonate with the public heading into the 2020 elections, particularly among younger voters who tend to be more active in the climate debate.

"Public sentiment is everything," Pelosi said.

Rep. Sean Casten Sean CastenThe Hill's Campaign Report: Buzz builds around Warren for VP Gun control group rolls out House endorsements Human Rights Campaign rolls out congressional endorsements on Equality Act anniversary MORE (D), an Illinois freshman, rejected the Republicans' argument that tougher, federal climate change standards pose a threat to business. In fact, he said, inaction is the larger hazard.

"The American business community understands that when you spend money to shift from fossil-fuel intensive assets that cost money to renewable and efficiency assets that don't cost money to operate, that's not a cost, that's an investment," Casten said. "There is no scientific reason not to act. There is no economic reason not to act. But we desperately need U.S. leadership at the table."

Since taking office, Trump has taken a series of steps to rollback Obama-era environmental regulations, including Environmental Protection Agency rules governing methane and power plant emissions. Those changes have been hailed by Republicans and many businesses interests, who have opposed such standards as expensive and overly burdensome. Democrats and environmentalists have countered with warnings that the roll-backs pose a long-term detriment to both human health and the economy.

Trump has not always been opposed to efforts to tackle climate change. On Dec. 6, 2009 — exactly a decade ago — a group of business leaders had taken out a full-page ad in The New York Times urging then-President Obama and Congress to take aggressive steps to reduce global emissions ahead of a climate summit in Copenhagen.

"Please don't postpone the earth," the ad reads. "If we fail to act now, it is scientifically irrefutable that there will be catastrophic and irreversible consequences for humanity and our planet."

Among the signatories were Donald J. Trump; his two oldest sons, Donald Jr. and Eric; and his daughter Ivanka.

Speaking at a NATO summit in London this week, the president alluded to his past statements as evidence that he views climate change as "very important."

“I’ve done many environmental impact statements over my life,” Trump said. “I believe very strongly in very, very crystal clear, clean water and clean air. That's a big part of climate change."

Pointing to the Times ad, Pelosi and the Democrats said they're hoping the old Trump returns.

"Who knows," said Whitehouse. "Maybe we can have the 2009 Donald show up again."