WASHINGTON » The Senate was headed into another all-nighter Monday evening as 26 Democrats who call themselves the "climate caucus" planned to speak nonstop about climate change from about 6:30 p.m. until 9 a.m. Tuesday.

The talkathon is the latest effort by the group, which is working with a parallel House caucus, to elevate the issue of global warming. The members know that serious climate change legislation stands no chance of passage in this divided Congress, where many lawmakers in the Republican-majority House deny the science of human-caused global warming.

Climate caucus members say their objective is to raise the urgency of global warming and build toward a time when the political landscape may have shifted enough that a bill could pass. They argue that there are signs that the political winds may already be changing.

"It’s aimed towards the day when something more concrete can be legislated," said Sen. Edward J. Markey, D-Mass., a veteran of climate and clean-energy policy battles.

Markey, who made climate change the centerpiece of his campaign when he ran in a special election for the Senate last year, was part of a group of House Democrats who started pushing in the 1990s for a bill to increase vehicle fuel economy standards. The auto industry lobbied fiercely and effectively against the bill for years, but Markey kept going in floor speeches, meetings and behind-the-scenes efforts. Opinion eventually began to change as public support grew and Republicans who had once opposed tougher standards changed their minds. The landmark law was passed in 2007 and signed by President George W. Bush.

"What we’re trying to do here is accomplish the same thing," Markey said.

A rising class of younger senators has also begun embracing climate change as an issue, among them Martin Heinrich of New Mexico and Brian Schatz of Hawaii, both Democrats.

In addition to Monday’s overnight session, members of the group give regular speeches on the floor of the House and the Senate about the urgency of fighting climate change. They hold weekly meetings with environmentalists, lobbyists and some corporate leaders who support their policies. Sen. Sheldon Whitehouse, D-R.I., a leading member of the caucus, is planning a trip to Iowa centered on events related to climate change, in the hope of elevating the issue before the 2016 presidential caucuses.

The members of the Senate climate caucus say they do not expect a bill to pass this year, but their efforts, combined with changes in opinion in Washington and in the country overall, could lay the groundwork for passage of a major climate bill in the next three to five years.

Among the biggest recent changes is the injection of hundreds of millions of dollars to support candidates who make climate change a priority. California hedge fund billionaire Tom Steyer has pledged to spend up to $100 million in this year’s midterm elections to help elect candidates who support strengthened climate policy. His infusion has helped lead to the rise of what advocates call "climate candidates" — mainstream politicians who make climate change a central issue of their platform.

Last year, Steyer spent $11 million in the Virginia governor’s race targeting Kenneth T. Cuccinelli II, a Republican who questioned the science of climate change and lost to Terry McAuliffe, the Democrat. Steyer and other environmental groups spent heavily in Markey’s campaign as well. Now those groups are planning to invest in an Iowa Senate race in which Rep. Bruce Braley, the Democratic candidate, is running on a platform of tackling climate change.

Other Democrats are also talking more about the issue. President Barack Obama, who during his 2012 re-election campaign was warned by his political advisers to avoid speaking about global warming, has since given a series of speeches on the topic and plans to issue a set of climate change regulations through the Environmental Protection Agency. Sen. Harry Reid, D-Nev., the majority leader, who was to take part in the Senate climate session, has also begun speaking more forcefully on the issue. "Climate change is the worst problem facing the world today," Reid told reporters last week.

Still, no legislation will pass without Republican support, or enough support from moderate Democrats in states where fossil fuels are a vital part of the economy. None of the four most vulnerable Democratic incumbent senators in the midterm elections — Mark Begich of Alaska, Kay Hagan of North Carolina, Mary L. Landrieu of Louisiana and Mark Pryor of Arkansas — were to take part in Monday night’s event. Begich, Landrieu and Pryor are from states where oil or gas production is a major part of the economy.

Michael McKenna, a Republican energy lobbyist with close ties to House Republican leaders, said that while Markey’s strategy may have worked on the fuel economy legislation, it would be difficult to translate that strategy to the broader and more politically contentious issue of climate change. "Ed Markey is a really smart guy, and he’s right, policy happens when the ground’s been prepared and the moment is correct," McKenna said. "But I think he’s barking up a completely different tree."

Climate change legislation — which would most likely place a price on carbon pollution — could raise gasoline and electricity costs, which would be deeply unpopular with voters. Advocacy groups with links to the fossil fuel industry and libertarian billionaires Charles and David Koch, who aggressively oppose strengthening climate policy, are expected to continue to spend heavily to block any such policies and fight the candidates who support them.

Coral Davenport, New York Times

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