The League of Conservation Voters will launch a $1.5 million campaign Tuesday targeting five House Republicans who question the connection between human activity and climate change, in an effort to test whether the issue can sway voters.

Prominent conservative Republicans have challenged the scientific consensus that greenhouse gas emissions from fossil fuels and other sources are transforming the Earth’s climate. But it has not emerged as a central issue in a national political campaign, and President Obama, who pushed unsuccessfully for national limits on greenhouse gas emissions at the start of his term, has played down the issue over the past two years.

The League of Conservation Voters, which has endorsed both Democrats and Republicans in the past, aims to unseat Reps. Ann Marie Buerkle (N.Y.), Dan Benishek (Mich.) and three other yet-to-be-named House Republicans — they’ve dubbed the group “the Flat Earth Five” — by attacking their global warming stance and ties to the fossil fuel industry.

“There’s still a debate about how to address these issues, but Americans expect their politicians to be informed and to accept basic science,” said Navin Nayak, the group’s senior vice president for campaigns. “Independents are with us. All of these members are in places where they have to win a majority of independent voters to win reelection.”

According to a Washington Post-Stanford University poll conducted in June, 77 percent of Americans say rising global temperatures are at least partly caused by the things people do, compared with 22 percent who say warming stems only from natural causes. Among independents, who often decide key races, 79 percent say humans play a role. But the issue consistently ranks toward the bottom of voters’ priorities in national polls.

The League of Conservation Voters will launch a $1.5 million campaign Tuesday targeting five House Republicans who question the connection between human activity and climate change. (League of Conservation Voters)

Both Buerkle, who faces a rematch against Democratic former congressman Dan Maffei, whom she defeated two years ago; and Benishek, who is running against hay farmer and former UPS driver Gary McDowell, have questioned humans’ impact on the climate. Maffei and McDowell, by contrast, say greenhouse gas emissions are helping drive climate change.

During a televised campaign debate in 2010, Buerkle said that “a lot of the global warming myth has been exposed.” While she later explained that she was specifically referring to pirated e-mails from climate scientists, which came to light in an incident known as Climate-gate, she added that “the jury’s still out” on whether fossil fuel burning contributes to global warming.

Buerkle’s campaign manager, David Ray, declined to comment on the question of climate change science but said that the congresswoman “has always supported clean air and clean water. She’s taken the time to meet with and listen to the concerns of constituents who are concerned about the environment. What she doesn’t support is Dan Maffei and Nancy Pelosi’s cap-and-trade energy tax that would raise electricity rates by 40 percent without doing anything to help the environment.”

Benishek dismissed the idea of climate change in a 2010 interview with the conservative candidate-tracking organization iCaucus. “I think it’s all baloney. It’s all baloney. I think it’s just some scheme,” he said. “I just don’t believe it, I just don’t believe it. You know, I’m a scientist, I’m a surgeon, I’ve done scientific research papers, there’s a lot of skepticism.”

Benishek spokesman Raffi Williams wrote in an e-mail, “It is troubling that Gary McDowell and his Washington allies would rather attack Dr. Benishek than explain to Northern Michigan families why he supports Nancy Pelosi’s failed policies such as the national energy tax that would destroy millions of jobs and raise gas prices.”

Stuart Rothenberg, editor of the Rothenberg Political Report, said he has identified these two races as “toss-ups,” with Buerkle’s leaning Democratic and Benishek’s leaning Republican. The League of Conservation Voters’ spending “could have an effect on the race,” he said, though he questioned whether it could “make this the kind of issue voters vote on, where everywhere else people will vote on jobs and the economy.”