Groups pushing for legislation to fight climate change are turning to Republicans and conservatives for their support during an election year.

Their strategy is quite simple. Without Republican support and leadership, there can be no climate policy.

“We have bet the ranch for years that the only lasting solution is bipartisan, and that therefore you had to have Republican leadership,” said Mark Reynolds, executive director of the nonpartisan Citizens’ Climate Lobby.

[Also read: Trump's NASA chief explains his recent shift on climate change]

His group is a 100,000-member grassroots organization whose sole focus is to support a free-market climate policy that the GOP and conservatives can rally around.

The problem is, “as soon as a Democrat introduces a bill, it becomes a partisan issue,” Reynolds said. “We’ve never seen any reason to put our weight behind a Democrat-only bill, because it’s not going to go anywhere.”

Instead, the group has been promoting a carbon fee-and-dividend, which some call a carbon tax. The difference is that the climate lobby’s conservative plan is revenue neutral. That means carbon dioxide emitters pay a fee that is collected by the government, but the money — the dividend — goes to the consumer instead of staying in the Treasury.

More than 1,000 of Reynolds' volunteer members were on Capitol Hill last week to lobby Congress. What they want is straightforward: Support or introduce legislation to enact the carbon fee. But that might be a high hurdle for lawmakers in an election year.

“We really hoped that there would be a bill in play already this year,” Reynolds said.

“We had been given quite a bit of encouragement from Republican offices that they thought that there would be a bill introduced by now,” he said. “But it’s June in a campaign year, it’s hard to think that something gets introduced at this point.”

A better opportunity will come after the November elections, or next year, he added. “I don’t think that is as easy to predict as most people do, at this point,” he said.

Some of the top Republicans who have entertained the idea of a carbon tax in the past have been silent in recent months, including Sens. Lindsey Graham of South Carolina and John McCain of Arizona.

National security issues such as North Korea are getting in the way, according to Graham's office.

Graham endorsed placing “a price on carbon” last year while speaking at a climate conference at Yale University. But he hasn't said much about the topic recently.

“We are up to our eyeballs in North Korea,” an aide said. “I haven’t had discussions with him about anything on this in a long time.”

McCain has been recovering at home in Arizona from treatment for brain cancer, and his communications have been limited to mostly national security issues.

One of the plans being circulated is the “Carbon Dividends Plan” suggested by James A. Baker and George Schultz, former Treasury secretaries under former President Ronald Reagan and Richard Nixon, respectively, according to congressional staff. Schultz is a member of the Citizens’ Climate Lobby’s advisory board.

The Baker-Schultz plan, which is similar to the climate lobby’s fee-and-dividend idea, is being floated by the Climate Leadership Council, a coalition formed last year that includes a diverse array of founding members, from Exxon Mobil and Shell, to the Nature Conservancy and the late Nobel Prize-winning physicist Stephen Hawking.

The group believes “that America needs a consensus climate solution that bridges partisan divides, strengthens our economy and protects our shared environment."

Although Democratic Sen. Sheldon Whitehouse of Rhode Island has introduced a bill to place a price on carbon, it’s seen as dead on arrival without GOP support, said Dan Richter, vice president for government affairs at Citizens’ Climate Lobby.

“This doesn’t matter unless it becomes law,” he said, explaining that there is “no way” it can get enough votes without GOP support. “We need to get Republicans.”

Although the Whitehouse bill is seen as helpful, it’s not the bill of choice for the lobby.

The number of Republicans who want to address climate change is growing both on Capitol Hill and at the grassroots level.

Craig Preston, a member of the Citizens’ Climate Lobby’s “conservative caucus,” said there has been a “five-fold increase” in caucus members. Just two years ago, the caucus stood at 80 members. Now it has 500 members.

Part of the appeal to conservatives is the group’s plan, which is focused on combining an economic solution with good risk assessment. If the risk is sizable that climate change is occurring, “it shouldn’t be ignored” and steps must be taken to address it, Preston said.

Increasing numbers of Republican students are also pushing the party to adopt a market-based system for fighting climate change. Most climate scientists blame carbon dioxide and other greenhouse gases for causing the Earth's temperature to rise.

Alexander Posner, president of the Students for Carbon Dividends, was on Capitol Hill last week talking to lawmakers about supporting a carbon price, but with a twist. His group sees an opportunity to make a “grand bargain” with Democrats on passing a revenue-neutral carbon tax in exchange for no new climate change regulations.

Posner said his group's version of the carbon price is different than the Citizens’ Climate Lobby's plan, but they are working together. He said his group supports the Baker-Schultz plan.

Lawmakers should get used to seeing Posner and his group of university students on Capitol Hill. The Students for Carbon Dividends filed a few weeks back to become a registered 501(c)3 nonprofit group. That means it can work to educate policymakers, but cannot lobby.

Posner said he will see how it goes in acquiring a nonprofit license from the IRS before applying for 501(c)4 status to lobby.

On Capitol Hill, the House Climate Solutions Caucus has grown by leaps and bounds in the last year after being established in early 2017.

The caucus is evenly split between Republicans and Democrats with 78 members as of May. The bipartisan caucus is headed by founders Florida Reps. Carlos Curbelo, a Republican, and Ted Deutch, a Democrat.

“We believe that growing the caucus and simply getting Republicans and Democrats talking to each other is important,” Reynolds said. “And while we’ve been accused by some groups on the Left of helping to greenwash some candidates, we think that anytime a Republican speaks up on climate change that’s a good thing. And its huge progress from where it was before.”

Grover Norquist, the head of the conservative Americans for Tax Reform, has accused a number of free-market groups, such as the R Street Institute, RepublicEn, Niskanen Center, and others, of being Democrats in disguise in floating the idea of a carbon tax to Republicans. Carbon tax critics are supporting a House resolution introduced this year by Steve Scalise, R-La., the party's majority whip, that opposes a carbon tax or fee.

"There is a resurgence of ... efforts to push solutions that Republicans purportedly would like, but you don’t see that broad support in Congress," said Robert Dillon, a consultant and former spokesman for Sen. Lisa Murkowski, R-Alaska. "They do feel like they have momentum, though."

The issue is shaping up a little differently in the Senate. A group of 13 prominent Republican senators began reaching out to President Trump this month, urging him to support an amendment to the Montreal Protocol treaty established by President Reagan to save the ozone layer.

The amendment would phase out chemical coolants used in air conditioning and other cooling devices, because they have been found to exacerbate global warming. The U.S. agreed to the global deal in Kigali, Rwanda, ahead of the 2016 presidential elections.

The letter they sent to Trump was released as the Citizens' Climate Lobby was beginning its day of lobbying on Capitol Hill.

It was “very helpful” to see the 13 senators getting behind what is essentially a climate change agreement, Richter said.

The senators want Trump to send the Kigali agreement to the Senate, so it can be ratified.

“By sending this amendment to the Senate, you will help secure America’s place as the global leader in several manufacturing industries, and in turn give American workers an advantage against their competitors in the international marketplace,” the letter read.