A study from Drexel University shows that much of the money funding the effort to deny climate change is coming from conservative foundations funded with “dark money,” meaning it comes from concealed donors, Scientific American reported.

The study, the first to examine the “organizational underpinnings and funding behind the climate denial movement,” found that money coming from these foundations whose funding cannot be traced has “risen dramatically over the past five years.”

And while the amount of “dark money” continues to grow, the traceable cash sources, like donations from Koch Industries, have all but dried up.

Author of the study Robert Brulle, an environmental sociologist at Drexel, said in a statement:

“The climate change countermovement has had a real political and ecological impact on the failure of the world to act on global warming. Like a play on Broadway, the countermovement has stars in the spotlight — often prominent contrarian scientists or conservative politicians — but behind the stars is an organizational structure of directors, script writers and producers. If you want to understand what’s driving this movement, you have to look at what’s going on behind the scenes.”

During his analysis of 118 “influential climate denial organizations” in the country and their funding sources, he found that the biggest and most-consistent donors were conservative foundations that tout “ultra-free-market-ideas,” like the Searle Freedom Trust, the John Williams Pope Foundation, the Howard Charitable Foundation, etc.

But the surprising findings involved the aforementioned Koch Industries and the ExxonMobil foundation.

Brulle found that from 2003 to 2007, Exxon and Koch-affiliated foundations were “heavily involved” in funding the efforts against climate change progress. But the Koch’s efforts have decreased sharply and Exxon hasn’t made a “publically traceable contribution since 2008.”

To Brulle, the source of these donations is much more important than just dollars and cents.

“Without a free flow of accurate information, democratic politics and government accountability become impossible,” he said. “Money amplifies certain voices above others and, in effect, gives them a megaphone in the public square.”

“At the very least, American voters deserve to know who is behind these efforts.”