Two environmental groups filed suit Thursday to force the Environmental Protection Agency to disclose its correspondence with the Heartland Institute, a conservative think tank that has led a years-long campaign to discredit climate science.

The complaint by the Southern Environmental Law Center and the Environmental Defense Fund (EDF) suggests that contact between the EPA and Heartland has been far more extensive than previously known. An EPA Freedom of Information Act official told EDF last year that an agency search had yielded "between 200 to 600 records" of such correspondence, according to the lawsuit filed in federal court in Virginia.

"EPA's efforts to promote climate change deniers and undermine peer-reviewed science behind closed doors is not only a failure of its mission, it is illegal," said Kym Hunter, an attorney for the Southern Environmental Law Center. "The public has a clear and protected right to know what the EPA is doing and with whom they are communicating, including those pushing a climate-denier agenda."

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The EPA did not immediately respond to a request for comment on the case.

At Issue: Pruitt's 'Red Team, Blue Team' Plan

The environmental groups filed their Freedom of Information Act requests for communications between EPA and the Heartland Institute last year. Under FOIA law, the agency is required to "promptly" provide information that is subject to public disclosure, and is to make a determination within 20 working days of receiving a request. The groups said that after initially acknowledging the requests, EPA has stopped communicating with the Southern Environmental Law Center and has only offered vague responses to EDF.

At issue in the FOIA dispute is EPA Administrator Scott Pruitt's repeated push for what he refers to as a "red team, blue team" review of climate science in which rival "teams" would debate the scientific consensus on climate change. The idea is opposed by most climate scientists as seeking to create the appearance of a debate where there is none in mainstream science. But Heartland Institute spokesperson Jim Lakely was quoted last July as saying that the EPA had reached out to the think tank for help in identifying team members, and that Heartland was "happy to oblige."

News reports say that White House Chief of Staff John Kelly opposed Pruitt's plan as politically risky and that his deputy, Rick Dearborn, told the EPA administrator in December that the idea was "dead" and not to be discussed further. But Pruitt has insisted as recently as this week that the idea remains under consideration.

Heartland, Pruitt Promote Each Other

Heartland hosts an annual conference of scientists skeptical of humanity's role in global warming and publishes reports seeking to rebut the work of the Intergovernmental Panel on Climate Change. Tax records show that the Illinois-based think tank, founded in 1984, has over the years received money from fossil fuel interests like Exxon and groups organized by the oil magnate Koch brothers. Heartland has told InsideClimate News that it "supported and promoted scientists skeptical of man-caused global warming on principle."

In recent years, a major Heartland funder has been billionaire hedge fund manager Robert Mercer, who also was the largest outside donor to President Donald Trump's campaign. The Mercer Family Foundation has donated more than $5 million to Heartland, according to its tax returns, and Mercer and his daughter, Rebekah, who runs the foundation, made a rare public appearance as attendees of Heartland's annual climate change conference last year.

While the EPA has been keeping the agency's contacts with Heartland under wraps, the mutual admiration between Pruitt and Heartland is evident.

Just last Friday, the EPA sent out a press release to tout an op-ed in which Heartland President Tim Huelskamp argued that "Pruitt is leading the EPA toward greatness" by rejecting mainstream climate science. "Trump and Pruitt share an understanding that climate change is not a significant threat to the prosperity and health of Americans," he wrote.

Heartland did not immediately respond to a request for comment on the FOIA suit.

Ben Levitan, an attorney for EDF, said: "Americans have a right to know who is influencing Pruitt's decisions and who is shaping the agenda at the agency in charge of protecting our health and safety."