Families are no doubt looking for a cheaper vacation this year. Millions will head for our national parks. Load the car with the kids and a tent, and you’re set for a vacation adventure that doesn’t cost a couple months’ salary.

Add the chance to see a spectacular landscape, a rare animal or plant in the wild, or just a special evening around the campfire and it’s clear why a road trip to a park is an American tradition apt to play out even more than usual nowadays.

This year’s visitors to our national parks will be seeing something different.

 • Amid the beauty in Yellowstone, they may notice forests of dead trees, needles blanched dull red.

 • In Glacier, the glaciers might seem small – melting so fast they’ll be gone in 15 years.

 • At Mount Rainier, it’s not only shrinking glaciers you’ll see, but also trails and roads washed out from unusually intense storms that are hitting more often.

 • In Everglades, the landmark Flamingo Lodge is gone, razed by hurricanes Katrina and Wilma in 2005.

 • Astute observers will notice subtler things – like little piles of dried grasses and leaves, cached by cousins of rabbits called pikas, beneath rocks in Yosemite’s high country. Now some mountaintops have gotten so hot the pikas are gone, leaving behind nothing but those mini-haystacks, harvested but never used, nature’s version of a ghost town.

All these things – and many more like them, from southern Africa to the high Arctic – are telling us that our world’s parks and preserves are suffering the onset of heatstroke. Average global temperature is climbing above the normal range these ecosystems evolved to withstand.

Those forests in Yellowstone are dying because winters are no longer cold enough to kill the invading pine beetles. Glaciers are melting and mountaintop species are declining because of longer, hotter summers. It’s too expensive to rebuild Flamingo because insurance companies worry that warming oceans will fuel more frequent severe hurricanes.

For humans, heatstroke is a condition with warning signs that at first seem mild – fatigue, headache. Caught early, it is simple to treat: Find shade or a cool mountain stream. Ignored, it is fatal.

So, too, with the rest of nature. Heatstroke’s early warning signs are the dead trees, missing species, unusual storms, more frequent fires.

Unchecked, in just a generation or two it leads to extinction of species and destruction of whole ecosystems that the world has spent considerable time and money trying to protect.

Treating nature’s heatstroke involves slowing global warming – well within humanity’s grasp if we have the will – by minimizing greenhouse gas emissions at the personal, corporate and global levels.

It also involves creating and protecting migration corridors so that species can move to more hospitable areas as a changing climate spoils their current home.

Our parks are the last vestiges of so-called “natural” ecosystems, holding a large portion of the world’s biodiversity. The global problem is that as climate changes within them, their species have no place to run to. Losing our parks’ biodiversity would cost hundreds of millions of dollars per year, but even more staggering would be the loss of all those family vacations.

My kids put it best. Last year our jobs took us to South America, so we were looking for vacations there. We bounced options off our two daughters, but they barely even paused to say: “Let’s go to the rainforest. It may not be there when we grow up.”

They may be right. Climate models predict that tropical rainforests – in fact the very one we went to – are in danger of disappearing. But by taking individual and global responsibility, we still have the chance to prove my daughters wrong.

Anthony D. Barnosky, the author of “Heat-stroke,” is a professor of integrative biology at the University of California at Berkeley.