The Heat Will Kill You First: Life and Death on a Scorched Planet

by Jeff Goodell

The salmon’s journey is one of the great wonders of nature. But it is also a fragile one. Warm runoff in the rivers—shallow water can heat up quickly as it flows down out of the mountains—made it difficult for the struggling salmon to breathe (the warmer the water, the faster oxygen molecules vibrate with kinetic energy, allowing them to flee their molecular bonds and escape into the air. “It leaves fish feeling like they are breathing with a plastic bag over their heads,” one wildlife biologist told me). Their iridescent silvery skin broke out in red lesions. Cottony puffs of fungus grew on their backs.

As with most heat waves today, the people who died first were elderly folks who lived alone, or who were too poor to afford air-conditioning, or who had a medical problem that left them vulnerable. In this sense, a heat wave is a predatory event, one that culls out the most vulnerable people. But that will change. As heat waves become more intense and more common, they will become more democratic.

The difficulty of understanding the consequences of heat is amplified by conventional notions of what it means to be hot. In pop culture, hot is sexy. Hot is cool. Hot is new. Websites publish “hot lists” of the latest books, movies, TV shows, and actors.

As the temperature rises, it will drive a great migration—of humans, of animals, of plants, of jobs, of wealth, of diseases. They will all seek out cooler ecological niches where they can thrive. Some will fare better than others. Robins can migrate more easily than elephants. Poison ivy can move more quickly than an oak tree. Farmers who grow wheat have more options than farmers who grow peaches. And some creatures have nowhere to go. Polar bears in the Arctic can’t migrate farther north. Frogs in Costa Rica aren’t going to hop up to Canada.

study in The Lancet, a prestigious medical journal, estimated that 489,000 people worldwide died from extreme heat in 2019. That’s far more than all other natural disasters combined, including hurricanes and wildfires. It is also more than the number of deaths from guns or illegal drugs. And those are only the deaths that are directly attributable to heat.

The toll is enormous: globally, between 260,000 and 600,000 people die each year inhaling smoke from wildfires. Smoke pollution doesn’t only kill people near fires either. Wildfires in western Canada have been directly linked to spikes in hospitalizations three thousand miles away on the East Coast of the US.

Earth’s history is full of wild temperature swings, driven by volcanic eruptions, meteor strikes, and geologic mayhem. There have been palm trees in the Arctic and two thousand feet of ice over New York City. But for the last three million years or so, while humans evolved, the climate has been relatively stable. Stable enough, anyway, that our ancestors could migrate, adapt, and thrive.

One recent study found that a heat wave like the one that cooked the Pacific Northwest is 150 times more likely today than it was before we began loading the atmosphere with CO2 at the beginning of the industrial age. The ocean, which hundreds of millions of people depend on for their food supply and which has a big influence on weather, was the hottest ever recorded in 2023. Even Antarctica, the coldest place on Earth, is not immune. In March of 2022, a heat wave invaded the ice-bound continent, pushing temperatures seventy degrees—seventy degrees!—above normal.

Life on Earth is like a finely calibrated machine, one that has been built by evolution to work very well within its design parameters. Heat breaks that machine in a fundamental way, disrupting how cells function, how proteins unfold, how molecules move.

If there is one idea in this book that might save your life, it is this: The human body, like all living things, is a heat machine. Just being alive generates heat. But if your body gets too hot too fast—it doesn’t matter if that heat comes from the outside on a hot day or the inside from a raging fever—you are in big trouble.

If it is hot outside, we push blood toward our skin so it can be cooled by sweat. That’s why dry heat is often less dangerous than wet heat—the more humid the air is, the more difficult it is for our sweat to evaporate and dissipate heat.

Anytime you flex a muscle, it generates heat. In fact, when you move a muscle, only about 20 percent of the energy you expend actually goes to muscle contraction; the other 80 percent is released as heat.

There is a lot of confusion about the relationship between water and heat exhaustion and heatstroke. Water is necessary to keep sweat flowing. If you get dehydrated, you can’t sweat. And if you can’t sweat, you can’t cool off. But drinking water does not in itself cool off inner-core body temperatures. Put another way, dehydration can exacerbate heat exhaustion and heatstroke, but you can still die of heatstroke and be well hydrated.

Sam Cheuvront, a heat and hydration expert who spent more than twenty years at the US Army Research Institute of Environmental Medicine in Massachusetts, put it to me this way: “Both heat exhaustion and heatstroke can occur in the absence of dehydration. We can speculate that proper hydration can, however, delay heat exhaustion because dehydration exacerbates heat exhaustion. But proper hydration cannot prevent heatstroke.”

Birds, which are flying dinosaurs, are also warm-blooded. (“Birds are not like flying dinosaurs,” a scientist once corrected me. “They are flying dinosaurs.”)

Insects bask in the sunlight to superheat their bodies and cook invading organisms; humans do the same by running a fever.

Camels evolved in North America roughly forty million years ago, and their best-known features—their long eyelashes, their wide feet, their humps—may have come in response to North American winters. They crossed the land bridge at the Bering Strait about fourteen thousand years ago, ending up on the Arabian Peninsula, among other places. They have been domesticated for thousands of years, nearly as long as horses.

The liquid the glands secrete is 99.5 percent water—its only function is to wet your skin.

To make our sweat glands even more effective, however, Lucy’s offspring made another evolutionary adjustment: they lost their body hair. For the evaporative sweat to really work, hair (or fur, which is just another name for hair on nonhuman animals) gets in the way, matting down when wet and interfering with the efficient transfer of heat away from your body. The only place we still have significant hair is on our heads, and that’s because our brains are so sensitive to heat, and in this situation, hair works as a sunshade to help keep our brains cool. (It also adds cushioning in a fall.) The loss of hair on our bodies and the development of eccrine sweat glands were important evolutionary events, perhaps as important as the use of tools or fire.

A lion or a hyena can move very fast for short distances, but it can’t pant while it runs. In the heat, it has to stop, rest, pant, and recover its thermal equilibrium. Humans figured out a way to keep cool in motion. We don’t have to stop and pant. We sweat as we go. In the story of human evolution, this was a very big deal. By managing heat, humans were able to go farther from water holes, begin long-distance travel, and expand their hunting range.

With their superior heat management systems, they could literally run down an animal until it has heatstroke. This practice continues today. In the Kalahari Desert in southern Africa, modern hunter-gatherers are able to kill a kudu, a kind of antelope that is far faster than humans over short distances, by chasing it for hours in the middle of the hot day, until it literally collapses of heat exhaustion.

Air conditioners exhaust hot air, exacerbating the problem of urban heat buildup. Downtown Phoenix can be as much as twenty degrees hotter than the surrounding area. New York City averages two to five degrees warmer than its leafy suburbs during the day—and sometimes twenty degrees warmer at night. This phenomenon, known to city planners and heat researchers as the urban heat island effect, is so pervasive that climate skeptics once claimed that climate change is merely an illusion created by thousands of once-rural meteorological stations becoming surrounded by urban development (the argument, like most arguments pushed by climate skeptics, has been thoroughly debunked).

“What will the Hurricane Katrina of extreme heat look like?” he wondered aloud as we sat in a café near the ASU campus a few years ago. Hurricane Katrina, which hit New Orleans in 2005, resulting in nearly two thousand deaths and more than $100 billion in economic damage, demonstrated just how unprepared a city can be for extreme climate events.

Climate change compounds risks for cities: heat, floods, failing infrastructure, displaced people. After the floods in 2015, which submerged large parts of Chennai, the Tamil Nadu Urban Habitat Development Board in Chennai began moving people out of huts and shacks in low-lying areas of the city and forcibly moving them to “safer” housing.

After raising four kids in Ohio, Pullman had moved to Arizona in 1988 to escape the cold Ohio winters. She worked in a hospital, then retired in 2011 and lived on a fixed income of less than $1,000 a month. During the summer of 2018, she was late to pay her electric bill and owed $176.84. On September fifth, Pullman paid $125, leaving $51.84 unpaid. Two days later, when the temperature hit 107 degrees, her electric company, Arizona Public Service (APS), cut off her power. A week later, Pullman’s daughter became worried when she hadn’t heard from her mother and alerted locals. A Maricopa County sheriff entered the house and found Pullman dead in her bed. Cause of death: heat exposure. A few months later, Phoenix New Times published an account of Pullman’s death, including the fact that APS had turned off Pullman’s power over an unpaid bill of $51. In 2018, APS cut off power to customers more than 110,000 times, according to the company’s own data. Of those, more than 39,000 cutoffs happened during the particularly scorching months of May through September.

When Hurricane Harvey hit Houston, it dumped trillions of gallons of water onto a concrete-and-asphalt city that was not designed for climate catastrophe. Hurricanes are heat engines, powered by warm, moist air rising over warm oceans (that’s why there are no hurricanes in the Arctic). The hotter our world gets, the more intense hurricanes become. During Harvey, hundreds of thousands of homes were inundated, and tens of thousands of people fled to hotels and shelters on higher ground. Others slept in their cars on overpasses.

Orange, I later learned, is an old industrial seaport town on the border with Louisiana, pop. 18,000. Orange has been hit repeatedly by recent hurricanes: In 2005, Rita ravaged the city. Three years later, Ike breeched the city’s levee and flooded the streets with as much as fifteen feet of water. Three people died. “We were just dealing with water all the time, constant flooding,” McGowan said from under the hood. “The whole place is going under.” “Harvey was it for us,” Elliott added. “Too much water, we can’t deal with this anymore. We are going to San Diego.”

In the past decade, scientists who study the movement of animals have found that of the four thousand species that they’d tracked, between 40 and 70 percent had altered their distribution. On average, terrestrial creatures are moving nearly twenty kilometers every decade. Marine creatures, who are largely free of barriers to seeking cooler waters, are moving four times faster than land-based animals. Some animals are making spectacular leaps. Scientists estimate that Atlantic cod are moving north at a rate of a hundred miles per decade. In the Andes, frogs and fungi species have climbed four hundred meters upward over the past seventy years. Even the most seemingly immobile wild creatures are on the move. In Japan, several species of coral polyps, which form the branching thickets of coral reefs, were found by scientists to be traveling about two miles north every year. Plants are on the move too. In the eastern US, trees are shifting north and westward at an average rate of about two miles per decade.

In many places in the world today, heat is rising faster than our ability to adapt to it. Some people may try to stick around and fight it out with Mother Nature, but most will not. “People will do what they have done for thousands of years,” said Vivek Shandas of Portland State University. “They will migrate to better climates.”

Globally, the climate crisis has put people on the run. Increasingly unpredictable rainfall in Southeast Asia has made farming more difficult and has helped push more than eight million people to move toward the Middle East, Europe, and North America. In the African Sahel, millions of rural people are streaming toward the coasts and the cities amid drought and widespread crop failures. The UN estimates that four out of five African countries don’t have sustainably managed water resources and that seven hundred million people will be on the move by 2030. In 2022, catastrophic floods in Pakistan—caused in part by the heat-driven melt of glaciers in the Himalayas, and in part by the fact that hotter air holds more water—displaced 33 million people, which is about 15 percent of the entire Pakistani population.

Also, places with higher climate risks tend to be cheaper to live in and have more space and access to nature (for the moment, anyway). According to the Redfin analysis, storms (including winter storms) are the only climate risk people are moving away from, with counties with the smallest share of risk growing faster than the counties with the largest share of risk. So when you look at migration in the US, it’s fair to say that people are moving away from storms and toward heat. According to Redfin’s analysis, the most attractive hot place in America is Williamson County, Texas, which is part of the Austin metro area. Williamson County, where every home faces high heat risk, saw its population grow 16 percent due to positive net migration from 2016 through 2020. That’s the highest growth rate of the fifty counties the company analyzed. It was followed by Pinal County, Arizona (just south of Phoenix), which had a positive net migration rate of 15 percent. Rounding out the top five were three Florida counties: Pasco County, Osceola County, and Manatee County.

For twenty years, I lived in upstate New York, which is one of the best places to live in America if you take climate change seriously. It’s not too hot in the summer, there is plenty of farmland and water, it’s far from the rising seas, it has a politically engaged local population, easy access to the Adirondacks, a strong arts culture, and decent transportation, including one of the great train rides in America down the Hudson to New York City.

A few days earlier, the body of Gurupreet Kaur, a six-year-old girl from India who was crossing the border with her mother and other family members, was discovered within a few hundred yards from where we were hiking.

She was surprised to see how many people had their windows open—which, Otto knew, might seem logical but is exactly the wrong thing to do when you don’t have air-conditioning (in the city, especially if there are no cooling winds, it’s better to close the windows and draw the curtains early in the day to keep out both the sun and the heat).

In Hinduism, heat is a path to enlightenment. The Aztecs painted their gods in red ochre, symbolizing what one scholar described as “their privileged relationship with heat.” For many Native Americans, sweat lodges are linked with spiritual rituals, such as the Sun Dance of the Lakota Sioux, in which participants sought to reconnect with nature and the supernatural.

Or to put it another way, temperature is the average speed of a collection of molecules. Something is cold when the average speed of its molecules is low and it is hot when the average speed is high. Still, heat does flow—but it doesn’t flow like a river. Grab hold of the door handle of your car on a hot summer day and it feels like heat is moving into your hand. But that’s not what is happening. When you grab the door handle, its faster-moving molecules bump into the slower-moving molecules in your hand, which causes the speed of the molecules in your hand to increase and those in the handle to slow down. Your brain senses the increased speed of the molecules in your hand as warmth; the temperature of your hand has increased. But there is no actual current of heat flowing into your hand. The molecules in the door handle stay in the door handle, and the molecules in your hand stay in your hand. The molecules in the door handle are just agitated, and they spread that agitation into your hand. “Heat moves less like a river through a canyon and more like laughter through a crowd,” writes physicist Brian Greene.

Hydrogen, for example, is not a greenhouse gas, but CO2 is. What’s the difference? CO2, like other greenhouse gases, has a molecular structure that makes it more sensitive to the heat that the Earth absorbs from the sun and reflects back into the atmosphere, creating thermal radiation. CO2 molecules react to this radiation, causing them to vibrate and bend and jitterbug. As more greenhouse gases accumulate in the atmosphere, the jitterbugging in the sky above us accelerates. That’s why, as we burn fossil fuels and release CO2 molecules into the atmosphere, our world is heating up. The sky is literally vibrating faster.

One prominent scientist, Roger Revelle, speculated that in the twenty-first century the greenhouse effect might in fact exert “a violent effect on the earth’s climate.” In 1957, Revelle told a Congressional committee that the greenhouse effect might someday turn Southern California and Texas into “real deserts.”

Then in 1984, a landmark paper on heat waves by scientists Linda Mearns and Stephen Schneider was one of the first to explore the possibility of extreme heat events and their connection to things we care about. It wasn’t just that the world was getting warmer, they pointed out. “Even small changes in [average] temperatures sometimes result in large changes in event probabilities,” they wrote. As an example, they showed that a five-day heat wave of at least 95 degrees in Iowa—which could be devastating to corn crops—was three times more likely with an average global warming of 3 degrees.

In 2010, a major heat wave cooked Russia with temperatures as high as 104 degrees. More than 55,000 people died.

Nobody expected a 70-degree jump in temperature during a heat wave in Antarctica in 2022. And yet it happened. Nobody expected 121 degrees in British Columbia. And yet it happened. Nobody expected 104 degrees in London. And yet it happened.

Atmospheric dynamics is a fancy way of talking about how the air above us moves around the planet, creating our weather. One way to think about atmospheric circulation is as a giant heat transport system, one that is constantly circulating warm air from the tropics up to the poles, and bringing the cooler air from the poles down to the tropics. The main engine of this heat transport system is called the jet stream, which blows west to east in the upper atmosphere.

Heat waves are created most often by changes in the jet stream.

It wasn’t just Texas. In 2022, extreme heat hurt crop harvests all over the world. The corn harvest in France was the lowest in three decades. Throughout the European Union, soybean and sunflower yields were projected to be 10 percent lower due to extreme heat. In India, the wheat crop was significantly below projections, leading the government to put a ban on wheat exports, alarming grain traders and food security analysts.

Without enough food, there is only hunger, chaos, and violence. Malevolent rulers and dictators throughout history have known this and exploited it for their own ends. Russian president Vladimir Putin not only understands the political power of food, he also weaponizes it. With the Russian invasion of Ukraine in 2022, he deliberately disrupted the country’s wheat supply, triggering a global food crisis. Until the invasion, Ukraine was one of the top wheat exporters in the world. By blockading Ukrainian ports, blowing up rail lines, stealing grain, and killing farmers, Putin effectively took about 20 million tons of wheat off the market. Global wheat production is about 850 million tons, so that was hardly enough to cause a worldwide famine. But it was enough to cause the price of wheat to jump more than 60 percent. In the US, where the average American spends less than 10 percent of their income on food, rising food prices put the squeeze on many working families and became a hot political issue in the 2022 midterm elections. But for people in the developing world, many of whom spend 40 percent or more of their income on food, a big jump in the price of wheat was the difference between eating and going hungry. In 2022, high food prices sparked riots in Sri Lanka and pushed an additional twenty-three million people toward starvation in sub-Saharan Africa. “By attacking Ukraine, the breadbasket of the world, Putin is attacking the world’s poor, spiking global hunger when peo...

And Putin was not the only one who was exploiting this situation. Commodity traders make money off wild price swings, shippers make money off people desperate for grain, fertilizer manufacturers make money off farmers desperate to maximize their yields, and protofascist politicians are happy to exploit rising food prices as evidence of the failure of democracy.

For every degree Celsius of increase in global mean temperature, yields are expected to decrease by 7 percent for corn, 6 percent for wheat, and 3 percent for rice. It is true that farmers have had to deal with wild weather for as long as humans have been putting seeds in the ground. But this is different. This is not about freaky hailstorms and random cold snaps. As Donald Ort, a professor of plant biology at the University of Illinois Urbana-Champaign, explained to me, “The largest single global change that threatens food security is high temperature.”

When it gets hot, plants do more or less what humans do—they sweat (in plants, it’s called transpiration). Instead of sweat glands, plants have tiny openings in the underside of their leaves that release water vapor, similar to skin pores. Most plants transpire their weight in water every day (if humans sweated that much, we’d have to drink twenty gallons of water a day).

Rice grown in high-CO2 conditions has lower amounts of protein, iron, zinc, and B vitamins.

I started to explain how some scientists hypothesize that the freeze that hit Texas in 2021—which I froze through myself—was one of the consequences of a warming Arctic. I said, “The Arctic is warming four times as fast as the rest of the planet, and as a result, it is pushing the jet stream farther south, allowing the cold arctic air to move down to Texas.”