Energy Secretary Steven Chu is stepping down. A possible replacement is already drawing criticism. (Chip Somodevilla/Getty Images)

He’s not even an official nominee yet, but Ernest Moniz, who is said to be the White House’s top candidate for energy secretary, is already prompting grousing among the enviro set.

Moniz, a scientist and professor at Massachusetts Institute of Technology, is the most-mentioned pick to replace Steven Chu, who plans to return to Stanford. As was the case with Chu, Moniz’s academic background — and his lack of political baggage — is thought to be a plus.

But before Moniz has gotten the President’s nod, environmental groups are already crying foul, expressing concern about his support for natural gas and nuclear power as energy sources.

Moniz has endorsed the use of natural gas, and a study he authored asserted that the risks of the controversial practice of fracking were manageable, which is anathema to greenie groups.

Environmentalists also are questioning Moniz’s stint as a director of the MIT Energy Initiative, an industry-funded organization.

“We urge him to leave dangerous nuclear energy and toxic fracking behind while focusing on safe, clean energy sources like wind and solar,” Sierra Club legislative director Melinda Pierce told Greenwire. In the same article, Public Citizen called the pick “disappointing.”

More piling on: An official with the Center for Biological Diversity told the Hill newspaper that Moniz “could very well be a political hack for the natural gas industry.”

Guess it’s never too soon to sharpen those knives.