Former Vice President Al Gore says the climate crisis is intensifying “way faster” than people realize and compared the climate emergency to historic events like 9/11.

“The burden to act on the shoulders of the generation of the people alive today is a challenge to our moral imagination,” Gore said Wednesday as he delivered closing remarks at a panel session at the World Economic Forum in Davos, Switzerland.

“This is Thermopylae. This is Agincourt. This is Dunkirk. This is the Battle of the Bulge. This is 9/11,” Gore added about the climate crisis. “We have to rise to this occasion.”

The comments from the former vice president come following the hottest year on record for the world’s oceans, the second-hottest year for global average temperatures and unprecedented wildfires in the U.S., Amazon and Australia.

Gore also praised teen climate activist Greta Thunberg, who made a passionate plea to world leaders to make climate change a top priority.

In a tweet, Gore said he was “struck by her potent and sobering call to action. Nobody speaks truth to power as she does: ‘Our house is still on fire. Your inaction is fueling the flames by the hour.’”

Gore won the 2007 Nobel Peace Prize for his environmental activism.