U.S. President Donald Trump climate adviser William Happer once compared the “demonization of carbon dioxide” to how Jews were treated under Adolf Hitler in Nazi Germany.

An American physicist who has specialized in the study of atomic physics, optics and spectroscopy, he is a physics professor emeritus at Princeton University.

Happer, who sits on the National Security Council as Trump’s deputy assistant for emerging technologies, said in 2014, “The demonization of carbon dioxide is just like the demonization of the poor Jews under Hitler. Carbon dioxide is actually a benefit to the world, and so were the Jews.”

The remark resurfaced in a New York Times article on Monday about the Trump administration’s approach to the issue of climate change.