Vice President Joe Biden tells a group of firefighters visiting the White House that the dramatic increase of forest fires in the United States was likely a result of climate change – even though he couldn’t prove it.

“The truth of the matter is, we don’t know for certain whether this increase, this up-tempo you guys are going through the last 15 years is because of climate change. I can’t prove any one fire is a consequence of climate change,” he said.

He added that they didn’t have to be a climatologist or a nuclear engineer to understand that the climate had changed, declaring that it was likely causing more forest fires.

“The consequence of this change, and I believe a lot of it has to do with climate change, the bottom line is your job is getting a hell of a lot more dangerous and the operation tempo is increasing and there is no likely change in that in the foreseeable future,” he said.

Biden’s remarks are the latest in a series of dramatic speeches on climate change as President Obama prepares to visit Paris for an international climate change summit. Biden, who recently announced that he would not run for president in 2016 denounced Republicans for continuing to deny climate change.

“We can all argue a whole hell of a lot about whether there is climate change. I don’t think there is much of an argument. The only people I know who deny climate change are the same people who deny gravity,” he said.

Afterwards, he joked that he was likely in a room full of Republican firefighters.

“I know a lot of you guys in here are Republicans, which worries the hell out of me,” he added.