President Obama said the effects of climate change are “terrifying” and that his effort to fight global warming will be the most consequential piece of his legacy.

The statement came in a wide-ranging interview he gave The New York Times last week in Hawaii, which the newspaper published Thursday.

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“What makes climate change difficult is that it is not an instantaneous catastrophic event,” Obama told the Times. “It’s a slow-moving issue that, on a day-to-day basis, people don’t experience and don’t see.”

In the interview, Obama explored his history on fighting climate change, including divisive fights with Republicans early on and the failure to pass his cap-and-trade legislation.

But shortly after he was inaugurated into his second term in 2013, he made it clear to presidential historians in a meeting that he found climate change to be an existential problem.

“If we don’t do anything on the climate issue, all bets are off,” Douglas Brinkley, one of the historians, recalled Obama saying at the meeting.

He later took unilateral actions like rolling out the Clean Power Plan and signing on to the Paris climate agreement.

Obama also lamented the fact that Americans don’t find climate change to be a high priority, despite the fact that scientists generally do.

“My top science adviser, John Holdren, periodically will issue some chart or report or graph in the morning meetings,” he said, “and they’re terrifying.”

He scolded Republicans for repeatedly working against him on climate and denying that it is happening or caused by humans.

“There is the notion that there’s something I might have done that would prevent Republicans to deny climate change,” Obama said. “I guess, hypothetically, maybe there was some trick up my sleeve that would have cast a spell on the Republican caucus and changed their minds.”

He acknowledged that if Republican presidential nominee Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE is elected president this year, much of Obama’s climate legacy could be reversed.

“I think it’s fair to say that if Donald Trump is elected, for example, you have a pretty big shift now with how the [Environmental Protection Agency] operates,” he said.