(CNN) — National parks are important. They're home to irreplaceable ecosystems, cultural sites and extraordinary wildlife.
The study revealed that temperatures across the country's 417 protected areas have increased by 1.8 degrees Fahrenheit, double the amount compared to the rest of the country. While both temperatures and aridity went up, precipitation rates have drastically gone down.
Why this is happening
Patrick Gonzalez, a climate change scientist at the University of California Berkeley and one of the study's authors, says the reason why the national parks are adversely affected is usually because of their locations. A lot of national parks are in the Arctic, at high elevations or in dry weather ares in the southwestern United States.
The high temperatures, according to the study, often occur because a large portion of national parks are at high elevations, "where warming occurs more quickly due to a thinner atmosphere."
More than half of the country's parks -- 63% -- are in Alaska and have seen the worst temperature increase.
"The permafrost is melting," Gonzalez told CNN. "The ground there is frozen because of the cold climate through most of the year, so once you heat it up, the ground melts." When the snow melts, Gonzalez said, the land's color turns darker, with the snow gone.
"And we all know that darker colors absorb more sunlight and get hotter."
That puts not only glaciers at risk, but polar bears as well, who depend on the sea ice.
The study found precipitation was also down by 12% across the country's national parks, while it had only decreased by 3% in the US as a whole.
What this means for parks
Between 1948 and 2000, Muir Glacier in the Glacier Bay National Park in Alaska has shed over 2,099 feet; forests in the Noatak National Preserve and Yosemite National Park have thinned and shifted.
Vast areas of forests are dying in Yellowstone National Park from droughts and bark beetles, which have thrived due to climate change are attacking the trees.
And in areas like Yosemite National Park and preserves in Alaska, trees are growing in meadows and tundra.
It could get much worse, scientists say.
Yellowstone National Park -- the world's first national park -- could see up to 10 times more areas burned by wildfires by 2100, while Joshua Tree National Park could see its famous Joshua trees die out.
Temperatures in the country's national parks could increase six times faster in the 21st century than they did in the 20th century. Alaska's national parks alone could see up to a 16 degrees Fahrenheit temperature increase.
What can be done about it
There's a way back, Gonzalez said. The temperature increases can be attributed to human-caused climate change.
"Carbon dioxide has risen to its highest level in 800,000 years, well beyond the natural range of variation," Gonzalez said. Plus, the carbon that scientists have found in the atmosphere has a unique chemical signature, different from the carbon that comes from volcanoes or plants.
"We have quantified the carbon pollution to cars, power plants and deforestation. We have found that human activities pump nine billion tons of carbon into the atmosphere every year but growing forests and ocean waters only absorb five billions tons a year."
Reducing greenhouse gas emissions, according to the study, could reduce projected temperature increases by at least a half and possibly up to two-thirds.
Go car-free, he suggests.
"Walk, bike, take public transit," Gonzales said. "Cutting carbon pollution from human sources can save parks from the most extreme heat."