A tourist takes in Liberty Cap and Nevada Falls at Yosemite National Park in California.
CNN  — 

When Garrett Dickman drove through Yosemite National Park early this week, he passed through a diverse band of large trees – conifer, red fir, lodgepole pine – and noticed a grim pattern: many of the trees were either dead or dying.

“It was really striking to see that every single tree seems to be getting hit by either climatic changes; it could be dying from drought, or it could be insect attack or fungus, but they’re certainly weakened,” Dickman, a forest ecologist with the National Park Service, told CNN. “There’s a big shift happening right now, and it’s right in front of our eyes.”

The consequences of the climate crisis – more wildfires, devastating drought, sea level rise, flooding, ecological disease – are plaguing the country’s national parks. Most recently, unprecedented flash flooding overwhelmed Yellowstone National Park and some of its surrounding areas.

Scientists and officials say it signals a dramatic change unfolding at the nation’s most prized parks. And unless the planet slashes fossil fuel emissions, scientists believe the climate crisis could drastically alter the landscapes, cultural sites and ecosystems in the parks, potentially making them inaccessible for humans and uninhabitable for other species.

Employee housing fell into Yellowstone River during flooding on June 13, 2022.
Yellowstone's North Entrance Road was washed out by the flooding.

What happened at Yellowstone is also a classic example of the climate crisis converging with failed emergency disaster response, said Marcy Rockman, a former climate change adaptation coordinator for the Park Service.

“When I heard they were evacuating every visitor from Yellowstone, I was like, ‘Oh my god, evacuating every visitor was not a part of our climate change scenarios,’ ” Rockman told CNN. “Seeing what my former colleagues at Yellowstone are having to deal with now, it’s like … I’m worried for them.”

That the parks’ climate change response “now involves ‘how do you evacuate everyone from a park’ is just a gut-punch that I don’t think we had fully taken in when we started the climate program,” she said.

As more climate change-fueled events occur, CNN talked to Park Service officials and scientists to see how the climate crisis may alter the ecosystems and landscapes of some of the country’s most beloved national treasures.