Hurricane Michael, the third most intense storm on record to make landfall in the U.S., has caused widespread destruction, turning places like Mexico Beach, Florida, into a hellscape of broken homes and overturned cars. It will be a while before we learn the full extent of the damage — and the human suffering and death — caused by the storm’s 155 mph winds and the 14-foot storm surge that swamped the coastline.

Bad as the hurricane was, imagine the damage and destruction if that storm surge had been 15 feet or so higher. And if instead of receding, that wall of water never went away. That is what we could be facing in the not-so-distant future if we don’t dramatically cut fossil-fuel pollution.

If that sounds alarmist, watch this short video. In it, you’ll see a scientist named Richard Alley in a Skype discussion with students at Bard College, as well as with Eban Goodstein, director of the Graduate Programs in Sustainability at Bard. It would be just another nerdy Skype chat except Alley is talking frankly about something that few scientists have the courage to say in public: As bad as you think climate change might be in the coming decades, reality could be far worse. Within the lifetime of the students he’s talking with, Alley says, there’s some risk — small but not as small as you might hope — that the seas could rise as much as 15-to-20 feet.