And now President-elect Donald Trump seems to be changing his tune on climate change.
In 2012, Trump tweeted: "The concept of global warming was created by and for the Chinese in order to make US manufacturing non-competitive."
But today, speaking to journalists from the New York Times, the President-elect indicated he had rethought the matter - at least somewhat.
Asked if he thought human activity was linked to climate change, Trump responded: "I think there is some connectivity. Some, something. It depends on how much."
The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive.— Donald J. Trump (@realDonaldTrump) November 6, 2012
When asked if the President-elect would withdraw from climate change accords, Trump said: "I'm looking at it very closely. I have an open mind to it."
"I think there is some connectivity" between humans and climate change, Trump says.— Maggie Haberman (@maggieNYT) November 22, 2016
"Clean air is vitally important," Trump says about climate change. Says he is keeping "an open mind."— Maggie Haberman (@maggieNYT) November 22, 2016
It comes after speculation that the incoming President is set to slash Nasa's budget for monitoring climate change, and would instead want the agency to focus on bigger goals.
Bob Walker, who advised Trump on space policy, said that Nasa had been reduced to "a logistics agency concentrating on space station resupply and politically correct environmental monitoring".
He told the Telegraph: "We would start by having a stretch goal of exploring the entire solar system by the end of the century."