We already knew that people who deny climate change are wrong. But now, environmentalist nonprofit Greenpeace says that some academics who come out against climate change may be paid off to do it—and some are willing to cover the money up.

During a sting operation, undercover investigators at the controversial, 44-year-old nonprofit Greenpeace posed as employees of coal and oil companies, and quietly approached academics at Princeton and Penn State universities, offering to pay them to author papers, "promoting the benefits of CO2 and the use of coal in developing countries," according to Greenpeace.

The faux fossil fuel industry reps then mentioned to the academics that they would like their contribution to be left undisclosed. It is standard procedure to list the names of any major funders on scientific and academic papers, and publications like Nature have called for even better and more thorough disclosure. Yet, the academics acquiesced to the request to cloak the donations.

One of the academics, Dr. Frank Clemente, justified his decision by pointing out that such disclosure is not legally required, nor is it always clear in instances like court statements, which also may be "sponsored" by industry groups. Clemente is an emeritus professor of sociology at Penn State who specializes in research on the socioeconomic aspects of energy policy. Until 2013, he ran a Twitter account devoted solely to spreading "energy facts," like "Coal is the proven path to elevating the human condition." (Fun game: Count how many times he says "path" on his Twitter feed. This is not a safe drinking game.)

According to Greenpeace, Clemente appeared to disclose that he had been bought off before, stating that, "In none of [Clemente's previous climate articles and testimony] is the sponsor identified. All my work is published as an independent scholar."

Similarly, physics professor William Happer of Princeton, a well-known climate change denier, agreed to write a paper praising fossil fuels for the benefit of an unnamed Middle Eastern oil and gas company. He also hinted that he could help weaken the peer review process to get support for the paper, though he admitted this would also lessen its odds of being published in a reputable journal.

Perhaps to Happer's credit, he asked that he not be paid directly, but that the money offered be donated instead to a nonprofit called the CO2 Coalition. It does exactly what you would guess. (Another game: Count the number of leaves on their site, gently reminding you that CO2 feeds plants so it must be good.)

Happer and Clemente both defend their actions, which do not violate any laws. However, they face strong criticism from their opposition. Happer, for his part, just testified on Dec. 8 at a hearing of the Senate subcommittee on Space, Science and Competitiveness, whose chairman is Sen. Ted Cruz. According to The Nation, 80 percent of the witnesses who presented at the hearing were climate change deniers. Yet according to NASA, only about 3 percent of scientific experts doubt that climate change is happening and is largely caused by human activity.

Princeton University has declined to comment for this story.