Douglas Kenrick, rangy and grizzled, squints through the shimmering heat of a late-summer afternoon in the Sonora desert. “You live here long enough,” he says, crossing to the south side of an empty street for the five-minute walk across the campus of Arizona State University, “and you become like a desert animal, searching out shade.” Having grown up on Long Island, and coming from the frequently snowbound campus of Montana State University, he relished the heat when he moved to Phoenix in 1980, but by the end of his first full summer, it had become oppressive. “I came from New York with the attitude that it can’t ever be too hot for me,” says Kenrick, “but I was wrong.” It seems likely that most people who move to Phoenix, where the temperature reached 118 degrees one day last June, make the same discovery, but as an evolutionary psychologist, Kenrick wanted to do more than complain about the climate. So he did an experiment.

His method had the elegance of all great science: He recruited a volunteer to stop her car at a green light and he counted the seconds until the driver behind honked the horn. He did this once a week from April to August, on days when the high temperature ranged from 84 degrees to 108, and he found that the thermometer accurately predicted how soon, and how many times, thwarted drivers would protest before the light changed. “When the weather was comfortably cool, the typical driver just politely tapped on the horn for a second,” Kenrick wrote. “When it got up near 100, though, they started blaring their horns, yelling out the window, and making hand signals they probably did not learn in driver’s education.”

The link between heat and anger—people are “fired up” or “steamed up,” or they “keep their cool”—is so deeply embedded in folk wisdom that it has gone mostly unquestioned. But it is increasingly a subject for psychologists and other social scientists concerned about the implications of a world in which 108 degrees may no longer be exceptional. Under one scenario studied by the Centers for Disease Control and Prevention, by the end of the century, today’s North Carolina summers would become the norm for New Hampshire, while Louisiana’s climate would migrate up to Illinois. In Phoenix itself, “temperatures could regularly hit the 130s...by the second half of this century,” University of Arizona climatologist Jonathan Overpeck has predicted.

The various environmental effects of greenhouse gases are potentially devastating, as we have often heard. The latest Intergovernmental Panel on Climate Change report, made public in March, underscored the danger of widespread hunger, even starvation, resulting from crop failures. Other health threats have been enumerated by Robert Repetto, a United Nations Foundation economist, who says climate change will intensify smog, leading to “increased outbreaks of asthma and allergies,” and “exacerbate vector-borne diseases such as hantavirus, West Nile virus, Lyme disease and dengue fever.” Repetto also worries about the “extreme weather events” that some researchers say climate change will engender. “Biological systems and engineering systems are all designed for a range of climatic conditions,” he says. “Within those limits, we’re OK, ...but outside those limits, the damage increases rapidly and becomes catastrophic, and we’re going outside those limits.” Heat waves themselves pose a health risk, especially for young children and the elderly—and world-class athletes. Temperatures at the Australian Open in January reached 104 degrees for four consecutive days, a condition that one tennis player called “inhumane” after competitors collapsed on the court.

The weather is always changing, to be sure, and any given event might have happened independent of global warming, but some trends are clear. Melting glaciers and disappearing sea ice, combined with the thermal expansion of the oceans, will almost certainly lead to increased coastal flooding of low-lying areas around the world, including parts of the United States. Like the iconic polar bear stranded on a shrinking ice floe, we are all facing an uncertain and perilous ecological future.

There may be hordes of climate refugees, fleeing homes on islands and coasts made uninhabitable by climate change—anywhere from 25 million to 1 billion people by 2050, according to the International Organization for Migration. Even people who don’t have to move will experience a bewildering sense of dislocation as the environment changes around them—as Northern winters start to be measured in weeks rather than months. Glenn Albrecht, an Australian philosopher, coined the term “solastalgia” for this emotion, a kind of homesickness you can experience without leaving home.

“We will see the emergence of novel climates, environments we’ve not seen before in human times, and the extinction of others, around the Arctic and in high Alpine regions,” says Laurence C. Smith, a professor of geography at UCLA and author of The World in 2050. Smith says cities, industry and agriculture may benefit in places such as Canada and Scandinavia, though at some cost in psychological and cultural disruption. “Very bitterly cold winters will be less common in some places,” he says, “but instead of a nice blanket of white snow, they will have slush.” And people who move north for the weather, or for jobs that may open up as the Arctic melts, will discover that climate change doesn’t make the winter nights any shorter.

But climate is about more than ecology: It’s also a force in human behavior, a fact often overlooked in global-warming scenarios. And new research suggests that a hotter world may, for one thing, be more dangerous, and not just because of road rage. Craig A. Anderson, of Iowa State University, pioneered research on climate and aggression, and derived the formula that each additional degree of warming increases the rate of violent crime (homicides and assaults) by 4.19 cases per 100,000 people. Solomon Hsiang, a public policy specialist at UC Berkeley, has found that climate change historically leads to social disruption, up to and including war. Property crime, personal violence, domestic violence, police violence—everything you want less of, climate change seems to bring more of, either directly by making individuals more violence-prone, or indirectly by promoting conflict related to diminishing resources or deteriorating economic conditions.

For reasons Hsiang is still studying, hotter temperatures depress economic activity. In a study of 28 Caribbean economies, he found that “short-term increases in surface temperature are associated with large reductions in economic output. I was stunned by how large the effect was. I don’t want to be alarmist, but I think the evidence is extremely concerning, and it hasn’t been seriously considered by policy makers.”

Violence, disease, social chaos—these are irresistible themes for science fiction, at least since the classic “Twilight Zone” episode “The Midnight Sun” in 1961, in which a cosmic accident sends the Earth out of its orbit and spiraling toward the Sun. Since then, of course, we’ve come to realize that humanity has supplied the mechanism for calamity all by itself, through greenhouse gas emissions. Global warming does pose some special challenges for fiction, as the editor Gordon Van Gelder points out: “It’s hard to write a story where the characters are grappling with climate change. You can’t just pull out a laser gun and shoot at it.” Still, Van Gelder managed to recruit 16 contributors for his 2011 collection of stories, Welcome to the Greenhouse. Families driven out of their homes struggle to reach the Arctic, where temperatures are bearable; monster tornadoes level whole towns; the military battles six-inch-long honeybees. And, in a story in Van Gelder’s magazine Fantasy & Science Fiction, tribunals in the future pass judgment on “tippers,” the wastrels whose giant carbon footprints led the world over the edge to disaster.

Science fiction is one way to get a feel for what daily life might be like in a hotter world. Another way is to go to Phoenix during a late-September heat wave when temperatures hover around 105, where the first thing you learn about the future is that it will apparently be lived indoors.

***

It is, as they say, a dry heat. On the East Coast, summer heat envelops you, like a hot, wet blanket, but step outside in Phoenix and it swats you, like a rolled-up newspaper. “When I worked in Atlanta it was hot and humid, but there was never a day I couldn’t go outside and hit a tennis ball,” says Royal Norman, a meteorologist for station KTVK. “But there are days here where I’m never outside except to get in and out of my car.” An advertisement for air conditioners in Phoenix uses the slogan, “Some of the best moments in life happen indoors,” which could well be true, unless your passion is, say, golf or gardening. Newcomers have to learn the hard way what happens to a soda can left inside a car parked in the sun, or to dogs whose owners take them out on sidewalks without protective booties.