While the debate rages over Angus King’s involvement in the wind industry, the independent candidate for the U.S. Senate picked up an endorsement from one of the country’s largest environmental organizations.

The Sierra Club announced Monday that it was backing King’s candidacy. The group said King’s promotion of land conservation, clean energy and efforts to curb the effects of global warming were the impetus for the endorsement.

"Angus King will be a champion for the values and policies that the Sierra Club works for every day," said Becky Bartovics, Sierra Club Maine’s Executive Committee Chair in a news release.  "He knows that investing in a clean-energy future will create new jobs in Maine and across the U.S., and protect our planet for generations to come."

The Sierra Club identified King’s support for federal efforts to limit the effects of global warming, higher fuel efficiency standards for cars, drawing down subsidies for oil companies and his past support for subsidies for wind and solar energy.

The latter position has been made a source of contention by Republican groups, who claim King used his political connections to obtain a government-backed loan for the Record Hill wind project in Roxbury. King has defended the project and said that he personally received "zero" federal dollars.

The Sierra Club also championed King’s opposition to drilling in the Arctic National Wildlife Refuge, as well as Maine policy initiatives he supported as governor when he enacted the Land for Maine’s Future program and helped bring Amtrak passenger rail service to Maine.

“Conservation and renewables are a big part of this country’s future if we want to wean ourselves from foreign oil, and I believe that conservation and renewable energy technologies can not only take us to a cleaner energy future, but can create good jobs at home as well," King said in the release. 

The endorsement isn’t surprising given King’s previous support for environmental initiatives and his position in the latest polls. Democratic candidate Cynthia Dill supports many of the initiatives backed by the Sierra Club, but was a distant third as of the last poll. Republican candidate Charlie Summers, meanwhile, recently said during a debate that he doesn’t believe humans are the primary cause for climate change. 

Dill, in a written statement, said the King endorsement was "inexplicable" given his support for hydro-fracking to tap natural gas reserves and his reluctance to outright oppose a pipeline that would bring tar sands oil from Canada to the U.S.

"On the 50th anniversary of Rachel Carson’s ‘Silent Spring,’ a coveted environmental group has endorsed the unenrolled candidate, who thinks hydro-fracking is probably safe and who won’t make a firm decision on the destructive Keystone XL tar sands pipeline," Dill said. "He (King) also won’t support the feasibility study of a ‘gift’ of a national park land in northern Maine at a time when preserved common space can support a green economy and jobs."

News reports indicate that the Sierra Club has begun to re-evaluate its early support for natural gas development after scientists linked the fracking method of drilling to polluted water and increased methane emissions. The group has not formally opposed natural gas development, but a recent Bloomberg story reported that Sierra earlier this year turned down a $30 million gift from the nation’s second largest natural gas supplier, Chesapeake Energy Corp. Sierra Club disclosed in 2010 that it received a $21 million gift from Chesapeake subsidiaries, but has since halted accepting similar corporate donations.

Dill said that despite the Sierra Club’s "error" and "the gender bias that so many national special interests have regarding this race," that she promised to remain true to her values. 

"In the final analysis, I don’t need environmental endorsements to verify that I am an environmentalist," Dill said. 

Meanwhile, the Summers campaign, citing King’s support for "blasting Maine’s mountaintops" for wind energy, said the independent’s environmental record was "anything but clean."

The campaign noted that King spurned a federal mandate to participate in a vehicle emissions program. The program, part of the 1991 Clear Air Act adopted by Congress, charged car owners $24 to perform emissions tests. 

Republican Gov. John McKernan halted the program in 1994. King maintained the suspension when he was elected and later joined the rest of New England’s governors to oppose the initiative.

That same year a citizen initiative was launched to repeal the initiative, which motorists said was too costly and inaccurate. The Legislature instead repealed the law. 

In 1998, facing the loss of an estimated $100 million in federal highway funds for spurning the emissions law, King and the Legislature enacted a scaled-back version that mandated auto testing only in Cumberland County.