Democrats held the Senate floor to talk climate change into the morning hours Tuesday, though they're not holding their breath on comprehensive legislation clearing Congress soon.

Instead, organizer Brian Schatz, D-Hawaii, described the event as an "opening salvo," as the more than two dozen senators who participated in the all-night affair are hoping to lay the groundwork for a sweeping measure.

"Despite overwhelming scientific evidence and overwhelming public opinion, climate change deniers still exist. Sorry to say, in this Congress. In the House and in the Senate," Senate Majority Leader Harry Reid, D-Nev., said to open the event at around 6:30 p.m. Monday, which is expected to close at 9 a.m. "It's time to stop acting like those who ignore this crisis -- for example, the oil baron Koch brothers and their allies in Congress -- have a valid point of view. They don't."

Still, Democrats have work to do within their own caucus. Democrats up for re-election in key red-leaning states this year -- including Mary Landrieu of Louisiana, Kay Hagan of North Carolina, Mark Pryor of Arkansas and Mark Begich of Alaska -- were notably absent for the event.

The more sleep-deprived of Democrats insisted their entire caucus is on board with the overwhelming scientific consensus that climate change is caused by humans, largely from burning fossil fuels. The differences arise in approaches to tamping down greenhouse gas emissions, they said.

For now, that divergence is significant enough to thwart substantial climate legislation for the near future — even Reid's participation in the overnight endeavor can't obscure that.

"I think we've got a little bit more work to do to open up some political space on this. I think if it went immediately to a vote, it probably wouldn't be successful," Sen. Sheldon Whitehouse, D-R.I., said during a Monday media call. "[We] can put ourselves in a position where we can get a serious climate bill passed."

That will take some time.

Although Republicans present an obstacle to legislation -- no GOP members participated in the Senate climate marathon -- some Senate Democrats also oppose such action. To understand that, one only has to look at the fight Begich is waging to fend off accusations from outside groups that he has supported a tax on carbon emissions. (He hasn't.)

Whitehouse said his goal was to raise the profile of climate change so that people like Pryor can point out to his constituents that Bentonville, Ark.-based Walmart invests in clean energy. He said that would enable similar candidates to support climate-friendly policies without being called extreme.

"The more that we bring that out, that allows Mark Pryor more room in his state," Whitehouse said.

Whether climate change can overcome other issues in states in the midst of an energy boom that has turned the United States into a sudden energy powerbroker remains to be seen.

Many of the Senate's vulnerable Democrats hail from energy-producing states or host industries that use large amounts of fossil fuels, leading them to tout newfound domestic oil and gas as an economic and jobs winner. At the same time, they have broken with the Obama administration to criticize environmental regulations that they have labeled too aggressive.

On top of that, abundant supplies of cheap natural gas have increasingly driven electric utilities to burn that fuel instead of coal, helping push U.S. carbon emissions last year to their lowest levels since 1994. In some respects, that's made climate change a more difficult subject for "climate hawks" to navigate.

While Democrats are trying to shift discussion from Capitol Hill, outsiders are spending money to elevate climate change at the polls.

Billionaire Tom Steyer, a former hedge fund manager, has pledged to spend $50 million of his own money through his NextGen Climate Action PAC to support climate-friendly candidates in the 2014 midterm elections. The League of Conservation Voters Action Fund, the environmental group's campaign arm, also figures to be a player after spending nearly $14 million in 2012. Both Steyer and the League of Conservation Voters Action Fund backed Democratic Gov. Terry McAuliffe in the Virginia gubernatorial race last fall to the tune of $11 million and roughly $2 million, respectively.

Sen. Martin Heinrich, D-N.M., said that although some in Congress have blocked climate action, the rest of the country is responding. He pointed to companies that have baked climate scenarios into their business forecasts.

"This is real and we have to address it," he said. "I think the markets are already starting to adjust to the fact that this is a reality based on science and that we can't ignore [it]."

In the immediate term, the senators admitted smaller steps are more realistic than something like the cap-and-trade bill that passed the House but fizzled in the Senate in 2010. Sen. Ben Cardin, D-Md., told the Washington Examiner that climate-friendly policies can be found in President Obama's proposed budget and an energy-efficiency bill co-sponsored by Sens. Jeanne Shaheen, D-N.H., and Rob Portman, R-Ohio, that has broad bipartisan support.

"The Democratic caucus is fairly united on this," Cardin said of climate change. "I know there's different views among Democrats on this. But we're still fairly united."