In interviews Albrecht conducted over the past few years, scores of Australians described their deep, wrenching sense of loss as they watch the landscape around them change. Familiar plants don't grow any more. Gardens won't take. Birds are gone. "They no longer feel like they know the place they've lived for decades," he says.

Albrecht believes that this is a new type of sadness. People are feeling displaced. They're suffering symptoms eerily similar to those of indigenous populations that are forcibly removed from their traditional homelands. But nobody is being relocated; they haven't moved anywhere. It's just that the familiar markers of their area, the physical and sensory signals that define home, are vanishing. Their environment is moving away from them, and they miss it terribly.

Albrecht has given this syndrome an evocative name: solastalgia. It's a mashup of the roots solacium (comfort) and algia (pain), which together aptly conjure the word nostalgia. In essence, it's pining for a lost environment. "Solastalgia," as he wrote in a scientific paper describing his theory, "is a form of homesickness one gets when one is still at home.'"

It's also a fascinating new way to think about the impact of global warming. Everyone's worrying about resource management and the spooky, unpredictable changes in the ecosystem. We fret over which areas will get flooded as sea levels rise. We estimate the odds of wars over clean water, and we tally up the species -- polar bears, whales, wading birds -- that'll go extinct.

But we should also be concerned about the huge toll climate change will inflict on our mental health. In the modern, industrialized West, many of us have forgotten how deeply we rely on the stability of nature for our psychic well-being. In a world of cheap airfares, laptops, and the Internet, we proudly regard mobility as a sign of how advanced we are. Hey, we're nomadic hipster capitalists! We love change. Only losers get attached to their hometowns.

This is a neat mythos, but in truth it's a pretty natural human urge to identify with a place and build one's sense of self around its comforts and permanence. I live in Manhattan, where the globe-hopping denizens tend to go berserk if their favorite coffee shop closes down. How will they react in 20 or 30 years if the native trees can't handle the 5-degree spike in average temperature? Or if weird new bugs infest the city in summer, fall shrinks to a single month, and snow becomes a distant memory? "We like to think that we're cool, 21st-century people, but the basic sense of a connection to the land is still big," Albrecht says. "We haven't evolved that much."

What's more, Albrecht has noticed that the more quickly environmental change occurs, the more intense the solastalgia. The mental-health effects can be powerful. In the Australian outback, industrial activity -- notably open-pit coal mining -- has turned verdant areas into moonscapes seemingly overnight, and the suicide rate in the region has skyrocketed. Or witness New Orleans, where a Harvard survey found that survivors of Hurricane Katrina reported suffering a "serious mental illness" at roughly double the rate of the city's residents three years earlier. Fully 6 percent have thought about suicide. Trauma and personal loss obviously play a role in this, but the decimation of the city's physical environment surely does as well.

Ironically, we may simply be rediscovering a syndrome that we thought was dead and buried. Back in the 1940s, the military considered homesickness to be a serious and potentially fatal illness, because drafted soldiers who got shipped overseas would often become savagely depressed. These days, Americans are rarely dislocated against their will, and the army is all-volunteer. Few of us have the experience of being unmoored in the world.

But that may be changing rapidly. In a world that's quickly heating up and drying up, you can't go home again -- even if you never leave.