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.

Yosemite National Park

Climate change has already touched one of the Sierra Nevada’s most valuable sites. Yosemite National Park has been forced to close several times in recent years because of extreme heat, deadly wildfires or dangerous air quality from fire smoke.

The average temperature in Yosemite may increase by up to 10 degrees Fahrenheit by the end of the century, which is several degrees higher than global temperatures are predicted to surge.

A deer grazes in Cook's Meadow at Yosemite.

And it’s not a future threat. Park rangers and scientists have already observed the shrinking snowpack, dried-up waterfalls, increasing fire activity and more tree die-offs like those Dickman observed.

“People come to Yosemite because we have some of the biggest trees on Earth,” Dickman said. “But the whole experience in Yosemite is starting to be altered … We’re just kind of seeing that tree line lift up in a weird way.”

As average temperature increases, it increases the elevation of where trees can grow. Dickman said forecast models show this part of the Sierra Nevada could look more like the mountains around Los Angeles, where trees can grow at a higher elevation because of the warmer temperatures.

Over 5 million visitors head to Yosemite annually to take in the sights, including the California Tunnel Tree--the only remaining tunnel tree in the park.
Yosemite's biggest restoration in history
01:36 - Source: CNN

Studies have also showed the range of small mammals in Yosemite has shifted upslope over the last century as the area warmed.

Dickman told CNN even 10 years ago he was concerned about different threats, pointing to how the park dealt more with flooding from powerful storms coming off the Pacific Ocean and less with dangerous wildfires.

“For our preparedness now, it’s really going to be around fire, and to get fire back on the ground in a good way to ward off some of the effects of these climate- and fuels-driven fires,” he said.

Glacier National Park

Scientists at Glacier National Park are bracing for its namesakes to disappear entirely.

“If you wanted to see a glacier, go to Glacier National Park in Montana,” Beissinger said “But you better get there soon, because the glaciers are going to be gone from Glacier National Park, probably sometime in the next decade or two. They’ve been disappearing.”

The Jackson Glacier Overlook, along the east side of Going-to-the-Sun Road is one of the easiest spots in the park to see a glacier.

In the past 50 years, some of the Montana park’s 26 glaciers have lost as much as 80% of their area. Loss of glacier ice is a huge threat for aquatic ecosystems within the park that rely on cold freshwater. It also threatens the surrounding area with increased flooding.

Much like the flooding at Yellowstone in June, the climate crisis is expected to trigger more flooding at Glacier. As Yellowstone closed down to visitors during its flooding disaster, officials at Glacier warned visitors their park was also experiencing dangerous water levels.

Melting glaciers are also a significant source of sea level rise. Caitlyn Florentine, a research physical scientist at the US Geological Survey who studies US glaciers, noted the glaciers at Glacier National Park are already quite small. But when taken together with other glaciers globally under a warming climate, they are enough to cause significant sea level rise around the planet.

“The meltwater from these glaciers affects the streams that are very high in the alpine environment,” Florentine told CNN, pointing to a study which found “the presence or absence of glacier meltwater will be felt by water in the rivers that feed agricultural communities to the east of the park.”

Given the rate at which climate change is accelerating, researchers say the timing of the loss depends highly on how much fossil fuel we burn in the future.

Sequoia National Park

Just south of the Yosemite Valley in California, the West’s megadrought is weakening and destroying the nation’s largest, oldest trees in Sequoia National Park.

Six fires over the course of six years burned more than 85% of the giant sequoia grove acreage across the larger Sierra Nevada, compared to around 25% over the previous 100 years, the National Park Service reported. Three of those fires crossed into Sequoia and Kings Canyon National Parks, forcing officials to close the parks to the public and take dramatic steps to protect the trees.

01 sequoia trees climate
Climate change could wipe out iconic California landmarks
03:04 - Source: CNN

In September 2021, park biologists wrapped the base of General Sherman – the planet’s largest living tree – in protective foil as the flames of the KNP Complex fire approached. General Sherman is estimated to be anywhere from 2,200 to 2,700 years old, and has grown to 275 feet.

The tree’s diameter is more than 36 feet at its base, which is about as wide as six average cars.

Park scientists have already seen “major effects” of climate change, said Christy Brigham, chief of resource management and science at Sequoia and Kings Canyon National Parks, mainly in the form of hotter, drier droughts and how they fuel extreme wildfires.

“We had a historic superintendent’s building burned down in a recent wildfire,” Brigham told CNN. “So those kinds of impacts are already happening in lots of national parks, and will continue to happen.”

NPS personnel fold up fire resistant aluminum and fiberglass blankets as they unwrap General Sherman.
Assistant Fire Manager Leif Mathiesen, of the Sequoia & Kings Canyon Nation Park Fire Service, looks for an opening in the burned-out sequoias in Redwood Mountain Grove.

Brigham added the climate crisis is “already changing our day-to-day operational business of managing our national parks.”

Besides maintaining public amenities and ensuring endangered species are safe, she said park employees – who have also been personally impacted by wildfires – are working even harder to clear up trails and engage in new emergency response systems to prepare for events such as fire risks.

“People who work in these places like me and all the other staff really care deeply about keeping these places the spectacular environments that they are for the enjoyment of visitors, and we are seeing changes,” Brigham said. “I came to Sequoia National Park from a different Park in 2015, and we were already seeing lots of dead trees from hotter drought, and that’s only been made worse by the wildfires.”

National parks, like Sequoia National Park, “is a place where we share values, as Americans, in terms of our heritage,” she added. “It’s a place where we can connect and see the impacts and maybe make some choices to reduce those impacts in the future.”

Grand Canyon National Park

The impact of warmer temperatures, severe lack of rainfall and stunted streamflow on the Colorado River is alarming at Grand Canyon National Park, said Mark Nebel, the park’s geosciences program manager.

The climate crisis is critically altering the Arizona park’s ecosystems, habitats for species, as well as its hydrology, Nebel told CNN.

“We’re seeing snow melting about a month earlier than it did a century ago, and there’s evaporation as well, and that really affects the levels of water in the [Grand Canyon’s groundwater] aquifer,” Nebel said. “We’re concerned about how it will affect the springs, which are our drinking water source, as well as the vast majority of the biodiversity around the springs.”

Vasey’s Paradise Spring is one which has gone from consistently reliable to bone dry.

What Vasey's Paradise Spring looks like in a normal springtime flow.
Vasey's Paradise Spring in 2022. Park officials say they dont totally understand why the spring is cut off, but they suspect it was caused by the lower groundwater table.  There are other normally reliable springs in the park that are also showing erratic behavior.

The West’s megadrought has devastated the Colorado River, which is a vital resource for the national park. Increased flooding, rock slides, wildfires, and heavy storms also pose severe challenges to Grand Canyon’s cultural sites, infrastructure, surrounding communities, fisheries and other wildlife.

Because of a hotter and drier climate, as well as aging infrastructure, Nebel said the park is changing the source of their water supply from groundwater, which has long relied on one of Grand Canyon’s springs, to surface water supply elsewhere.

The plummeting level of Lake Powell upstream on the Colorado River – the nation’s second-largest reservoir – is affecting species in the river downstream and at the park according to Nebel.

“With the water level lowering at Lake Powell, these warm-water invasive fish that are normally near the surface are coming through the dam and getting into the Grand Canyon National Park and threatening native fisheries,” he said. “Our fisheries folks have been working really hard to remove like invasive trout from streams, where these native fish reproduce.”

Nebel acknowledge for most visitors who are only there for a few days, the impacts of climate change in the park are largely imperceptible. It’s different for the park researchers and staff who live with them day in and day out.

“For most of us who work at Grand Canyon, we see these crises, we see the danger, we see the damage,” Nebel said, and “we see that it’s gonna get worse.”

Joshua Tree National Park

For Steve Beissinger, ecology professor at the University of California in Berkeley, national parks like Joshua Tree in Southern California are vital for scientific research. But over the years he has seen how climate change has threatened the park’s biodiversity by pushing many species – including small mammals and birds – toward the brink of extinction.

“When we go back and resurvey places [in Joshua Tree] that the early scientists at UC Berkeley visited a century ago, we find about half as many birds, and that’s because it’s warmed and dried so much,” Beissinger told CNN. “What we’re seeing is a whole kind of change in a community; a collapse in the case of birds. For park managers, there’s limits of what they can actually do to reverse this because of the climate change effects.”

The extreme heat, dire lack of rain and drought conditions at Joshua Tree have