A senior adviser to Donald Trump once compared the "demonisation" of carbon dioxide to the treatment of Jews in the Holocaust.
William Happer leads the Trump administration's efforts to overturn air pollution restrictions and other factors that contribute to global warming.
The Princeton-educated physicist sits as a deputy assistant for emerging technologies on the National Security Council.
Absolutely insane: “The demonization of carbon dioxide is just like the demonization of the poor Jews under Hitler,” said William Happer.
Happer is a member of Trump's National Security Council, advising on climate change and emerging technologies. pic.twitter.com/CBHjcyDjmt
— Justice Democrats (@justicedems) May 28, 2019
Mr Happer made the comments about carbon dioxide, a gas widely recognised by scientists as causing global warming, to the US news channel CNBC in 2014.
He said: "The demonisation of carbon dioxide is just like the demonisation of the poor Jews under Hitler.
"Carbon dioxide is actually a benefit to the world and so were the Jews."
His remarks have resurfaced after the New York Times reported that Mr Happer is proposing a new "climate review panel" within the Trump administration.
More from US
The panel would reportedly follow other White House efforts to overturn measures designed to tackle global warming.
Mr Happer's proposal is backed by Mr Trump's national security adviser John Bolton.
He is also said to have the support of Robert Mercer, a billionaire who funds efforts to disprove climate science.