On Wednesday, President-elect Donald Trump met with environmentalist and actor Leonardo DiCaprio. Trump has remained skeptical about climate change and even tweeted previously that the issue is a hoax, despite the agreement of at least 97 percent of actively publishing climate scientists that it is real and likely exacerbated by humans.

Trump's meeting with DiCapripo— coupled with reports that he met with former Vice President Al Gore last week — is sending mixed messages about his stance on climate change and the environment.

Though the aforementioned meetings may give some hope that Trump is open to learning about climate change, a recent appointment signals otherwise. Hours before meeting with DiCaprio, the president-elect nominated climate change skeptic and fossil fuel ally Scott Pruitt to lead the Environmental Protection Agency.

The appointment by Trump follows a pattern of “disastrous changes,” according to Dr. Roger Barry, a professor and researcher of environmental science at The University of Colorado Boulder.

“If [Pruitt] undoes the regulations that Obama set in place to try to limit greenhouse gas emissions, then that’s just going to accelerate the warming trend,” Barry said in an interview with ATTN:.

The effects of the "warming trend" are not new, Barry noted, pointing to a pair of heat waves going back just over a decade responsible for the deaths of tens of thousands in Western Europe and Russia, respectively. Scientists have found that climate change increased the severity of a heat wave in 2003, which is consistent with the theory that climate change can make extreme weather more extreme.

Barry said that these heat waves were “probably unprecedented,” but that some of the damage already done by climate change was likely to speed the warming of the planet.

He pointed to the following example: “Permafrost is thawing globally and releasing methane … about 25 times more potent a greenhouse gas than carbon dioxide [into the atmosphere]." This process — melting ice, releasing dangerous gasses, that will lead to more melted ice — is just one vicious cycle in the climate crisis.

The nomination of Pruitt is the clearest sign yet that Trump could undo the environmental legacy of President Obama. However, it is perhaps not the most devastating appointment that he could make.

While many politicos have focused on the possibility that Mitt Romney could become Secretary of State, ExxonMobil CEO Rex Tillerson could also receive the nomination.

This would be “disastrous” and "potentially more damaging," Barry said, because it would signal that Trump might allow ExxonMobil to drill below the Arctic with the help of Russian oil companies. The only reason that the fossil fuel giant hasn't already made such a move is due to sanctions placed on Russia by President Obama — which Trump could reverse. The sanctions blocked the ExxonMobile from working with its Russian counterpart.