Among Republican presidential nominee Donald Trump's many debate gaffes Monday night, one of the most blatant was his claim that he never said climate change was a hoax.

At the Hofstra University debate, Democratic nominee Hillary Clinton challenged Trump's stance on the environment stating, "Donald thinks that climate change is a hoax perpetrated by the Chinese. I think it's real." Trump quickly interrupted her with "I did not, I do not say that."

Not only was this a lie—one social media users quickly fact-checked—but Trump has also said that, if elected, he would implement a decidedly anti-climate platform that includes weakening the U.S. Environmental Protection Agency (EPA); abolishing President Barack Obama's Clean Power Plan, without which the U.S. has little chance of meeting its Paris climate pledge; promoting increased fossil fuel exploration; and employing oil and gas executives, including high-profile climate skeptic Myron Ebell, to lead his cabinet.

The outcry from Trump's many denials prompted his campaign manager, Kellyanne Conway, to tell CNN's Alisyn Camerota that the GOP nominee does, in fact, believe in climate change—he just doesn't believe it's caused by humans.

"He believes that global warming is naturally occurring," Conway said. "There are shifts naturally occurring."

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That, too, is scientifically false. In fact, 97 percent of scientists agree that climate change is real and man-made.

In fact, Trump's climate stance appears to be too unrealistic for even his running mate to get behind. Vice presidential nominee and Indiana Governor Mike Pence, who is well known for his staunchly right-wing policies, said Tuesday there is "no question" that human activity affects the environment.

In a separate appearance on CNN, Pence said, "Let's follow the science...There's no question that the activities that take place in this country and in countries around the world have some impact on the environment and some impact on climate."