Conservative donor Rebekah Mercer attended the 12th International Conference on Climate Change, hosted by The Heartland Institute in Washington this week. (Oliver Contreras for The Washington Post)

The atmosphere was buoyant at a conference held by the conservative Heartland Institute last week at a downtown Washington hotel, where speakers denounced climate science as rigged and jubilantly touted deep cuts President Trump is seeking to make to the Environmental Protection Agency.

Front and center during the two-day gathering were New York hedge fund executive Robert Mercer and his daughter Rebekah Mercer, Republican mega-donors who with their former political adviser Stephen K. Bannon helped finance an alternative media ecosystem that amplified Trump’s populist themes during last year’s campaign.

The Mercers’ attendance at the two-day Heartland conference offered a telling sign of the low-profile family’s priorities: With Trump in office, the influential financiers appear intent on putting muscle behind the fight to roll back environmental regulations, a central focus of the new administration.

On Thursday, the father and daughter joined Heartland Institute President Joseph Bast at his table for the keynote luncheon speech, held in a ballroom of the Grand Hyatt Hotel. They listened intently as Patrick J. Michaels, director of the Cato Institute’s Center for the Study of Science, argued that the Obama administration erred in finding that greenhouse gas emissions endanger public health.

The Mercers’ presence indicates that the wealthy family is continuing to support the work of the Heartland Institute — a group that embraces views that have long been considered outlier positions by the scientific community, but that are ascendant in Trump’s Washington.

Hedge fund executive Robert Mercer speaks on the phone during a climate change conference hosted by The Heartland Institute in Washington this week. (Oliver Contreras for The Washington Post)

“Many of the people who are now prominent in the Trump administration attended our conferences, even spoke at our conferences, read our publications,” Bast said in an interview. “I think we’re seeing the fruit of a decade of hard work on this issue.”

Half a dozen Trump transition officials and administration advisers attended the gathering, including Myron Ebell, director of energy and global warming policy at the Competitive Enterprise Institute, who headed Trump’s EPA transition team.

Ebell, who has regularly challenged various aspects of the scientific consensus that humans are driving the warming of the planet, received Heartland’s “Speaks Truth to Power Award.”

During a session Friday titled “Resetting Climate Policy” that the Mercers attended, Ebell thanked “the people in this room and people like you around the country.”

“It’s the people who have worked persistently against global warming alarmism that made this election result possible,” he added.

But exactly where the Mercers stand on climate change — and the scope of their environmental agenda — remains a mystery.

When approached by a Washington Post reporter at the event, Rebekah Mercer declined to be interviewed.

The Heartland Institute has been one of the biggest beneficiaries of the Mercer family’s foundation, which gave the group more than $5 million between 2008 and 2015, according to tax filings. But the size of the Mercers’ contributions dropped sharply in recent years, from $885,000 in 2014 to $100,000 in 2015.

Heartland officials declined to comment on the Mercers’ support, saying they do not discuss their donors.

During the same two-year period, the Mercer foundation contributed $500,000 to Berkeley Earth, a nonprofit research organization whose founder, Richard Muller, is a physicist and onetime climate change skeptic who declared in 2012 that his research shows that humans are indeed driving global warming.

Berkeley Earth set out in 2010 to reanalyze the highly influential surface temperature data kept by scientific institutions such as NASA and the National Oceanic and Atmospheric Administration — data that document considerable global warming and have come under fire from climate change doubters. The ultimate Berkeley Earth analysis, however, largely vindicated the original temperature records, reporting that concerns raised by doubters “did not unduly bias the record.”

In an interview Friday, Muller said that Robert Mercer contacted him after Muller gave a speech about big data and climate science at Renaissance Technologies, Mercer’s hedge fund.

“He has been very supportive of our work and never once did he indicate to us that he had a hope for outcomes in what we did,” Muller said. He added that Berkeley Earth continues to receive funding from Mercer, whom he described as “very open.”

The Mercers appeared deeply immersed in the arguments showcased at the Heartland conference. They attended half a dozen panels over two days, including one billed as a discussion of how climate science shows that “nature, not human activity, is the chief driver of changes to the earth’s climate.” Before Thursday’s keynote speech, Rebekah Mercer, wearing her signature diamond-studded glasses, chatted animatedly with Bast, while her famously taciturn father sat next to her, quietly eating his salad.

The Heartland Institute has been challenging various aspects of the scientific consensus on human causation of global warming for years through gatherings such as last week’s International Conference on Climate Change . The group also helps organize the Nongovernmental International Panel on Climate Change, which offers a contrary view to the leading authority on climate change, the United Nations Intergovernmental Panel on Climate Change.

In 2012, Heartland paid for a Chicago billboard that read, “I still believe in Global Warming. Do you?” alongside a picture of Ted Kaczynski, the Unabomber, triggering major backlash and criticism.

Bast, the group’s president, said at the time that the billboard was intended “to be an experiment,” noting that it got people’s attention.

Kenneth Kimmell, president of the Union of Concerned Scientists, said Heartland “has a long history of promoting ‘alternative facts’ about climate change as well as crank climate denialist theories that are far out of the mainstream scientific consensus.”

Kimmell said the fact that key Trump administration officials are embracing some of their theories is alarming.

“It is distressing to see us going backwards on basic climate science,” he said.

In a statement, Bast called the union “one of the environmental advocacy groups most responsible for politicizing climate science. I’m not at all surprised that they disapprove of an open objective debate over the causes and consequences of climate change.”

Several organizations that have received funding from the Mercer foundation helped sponsor the Heartland conference, including the Media Research Center, the Heritage Foundation and the Center for the Defense of Free Enterprise, a small group based in Bellevue, Wash., whose vice president once vowed to “destroy environmentalists by taking their money and their members.”

The gathering drew about 300 people to the Grand Hyatt, whose corridors buzzed with chatter about carbon levels and “fake” climate science. A man marketing the film “Climate Hustle” bore a sign that read, “Hello, My Name is Al Gore.”

The overarching theme of the two-day gathering: that fossil fuels and elevated levels of carbon dioxide actually benefit human health, the environment and regional stability.

In a session titled “Fossil Fuels and World Peace,” speakers said that fossil fuels and climate change could help boost food production. Craig Idso, chairman of the Center for the Study of Carbon Dioxide and Global Change, said that without fossil fuels, the world risks “chaos and mass starvation.”

Climate research, however, suggests many possible risks to crops, such as wheat and corn, as a result of warming and associated consequences such as drought in some regions.

Idso did not deny climate change, but embraced it. “It will be next to impossible to meet the challenge of feeding Earth’s population without a rise in the Earth’s temperature,” he said. “CO2 is not a pollutant. It is the very elixir of life.”

Throughout the conference, speakers repeatedly accused climate change scientists of manipulating their studies to produce results supporting their theories.

Rep. Lamar Smith (R-Tex.), chairman of the House science committee, who issued a subpoena to National Oceanic and Atmospheric Administration scientists over a study finding that there had been no slowdown or pause in global warming, told the group that it’s time for “good science, rather than politically correct science.”

Steven Milloy, publisher of, said the government has “perverted science.”

“There is no science going on in NOAA or NASA or EPA,” said Milloy, who served on the Trump EPA transition team, to chuckles and applause. “There is no such thing as climate science.”

Ebell warned attendees that getting their agenda through will not be easy, swiping at Secretary of State Rex Tillerson as “part of the swamp” that likes to attend international climate meetings. And he noted that Trump’s daughter Ivanka Trump and her husband, Jared Kushner, reportedly support the United States remaining in the Paris climate accord.

He urged those in the room to press for several top priorities: making a 31 percent budget cut to the EPA, overturning the agency’s finding that carbon dioxide endangers public health and withdrawing from the Paris climate accord, an issue on which the administration has not yet adopted an official policy.

“You add all these up,” he said, “and it changes the entire direction of the country.”

Brady Dennis and Steven Mufson contributed to this report.