Animals are living color. Wasps buzz with painted warnings. Birds shimmer their iridescent desires. Fish hide from predators with body colors that dapple like light across a rippling pond. And all this color on all these creatures happened because other creatures could see it.

The natural world is so showy, it’s no wonder scientists have been fascinated with animal color for centuries. Even today, the questions how animals see, create, and use color are among the most compelling in biology.

Until the last few years, they were also at least partially unanswerable—because color researchers are only human, which means they can’t see the rich, vivid colors that other animals do. But now new technologies, like portable hyperspectral scanners and cameras small enough to fit on a bird’s head, are helping biologists see the unseen. And as described in a new Science paper, it's a whole new world.

Visions of Life

The basics: Photons strike a surface—a rock, a plant, another animal—and that surface absorbs some photons, reflects others, refracts still others, all according to the molecular arrangement of pigments and structures. Some of those photons find their way into an animal’s eye, where specialized cells transmit the signals of those photons to the animal’s brain, which decodes them as colors and shapes.

It's the brain that determines whether the colorful thing is a distinct and interesting form, different from the photons from the trees, sand, sky, lake, and so on it received at the same time. If it’s successful, it has to decide whether this colorful thing is food, a potential mate, or maybe a predator. “The biology of color is all about these complex cascades of events,” says Richard Prum, an ornithologist at Yale University and co-author of the paper.

In the beginning, there was light and there was dark. That is, basic greyscale vision most likely evolved first, because animals that could anticipate the dawn or skitter away from a shadow are animals that live to breed. And the first eye-like structures—flat patches of photosensitive cells—probably didn't resolve much more than that. It wasn't enough. “The problem with using just light and dark is that the information is quite noisy, and one problem that comes up is determining where one object stops and another one starts. ” says Innes Cuthill, a behavioral ecologist at the University of Bristol and coauthor of the new review.

Color adds context. And context on a scene is an evolutionary advantage. So, just like with smart phones, better resolution and brighter colors became competitive enterprises. For the resolution bit, the patch light-sensing cells evolved over millions of years into a proper eye—first by recessing into a cup, then a cavity, and eventually a fluid-filled spheroid capped with a lens. For color, look deeper at those light-sensing cells. Wedged into their surfaces are proteins called opsins. Every time they get hit with a photon—a quantum piece of light itself—they transduce that signal into an electrical zap to the rudimentary animal's rudimentary brain. The original light/dark opsin mutated into spin-offs that could detect specific ranges of wavelengths. Color vision was so important that it evolved independently multiple times in the animal kingdom—in mollusks, arthropods, and vertebrates.

In fact, primitive fish had four different opsins, to sense four spectra—red, green, blue, and ultraviolet light. That four-fold ability is called tetrachromacy, and the dinosaurs probably had it. Since they're the ancestors of today’s birds, many of them are tetrachromats, too.

But modern mammals don't see things that way. That's probably because early mammals were small, nocturnal things that spent their first 100 million years running around in the dark, trying to keep from being eaten by tetrachromatic dinosaurs. “During that period the complicated visual system they inherited from their ancestors degraded,” says Prum. “We have a clumsy, retrofitted version of color vision. Fishes, and birds, and many lizards see a much richer world than we do."

In fact, most monkeys and apes are dichromats, and see the world as greyish and slightly red-hued. Scientists believe that early primates regained three-color vision because spotting fresh fruit and immature leaves led to a more nutritious diet. But no matter how much you enjoy springtime of fall colors, the wildly varicolored world we humans live in now isn't putting on a show for us. It's mostly for bugs and birds. “Flowering plants of course have evolved to signal pollinators,” says Prum. “The fact that we find them beautiful is incidental, and the fact that we can see them at all is because of an overlap in the spectrums insects and birds can see and the ones we can see.”

Covered in Color

And as animals gained the ability to sense color, evolution kickstarted an arms race in displays—hues and patterns that aided in survival became signifiers of ace baby-making skills. Almost every expression of color in the natural world came about to signal, or obscure, a creature to something else.

For instance, "aposematism" is color used as a warning—the butterfly’s bright colors say “don’t eat me, you'll get sick.” "Crypsis" is color used as camouflage. Color serves social purposes, too. Like, in mating. Did you know that female lions prefer brunets? Or that paper wasps can recognize each others’ faces? “Some wasps even have little black spots that act like karate belts, telling other wasps not to try and fight them,” says Elizabeth Tibbetts, an entomologist at the University of Michigan.

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But animals display colors using two very different methods. The first is with pigments, colored substances created by cells called chromatophores (in reptiles, fish, and cephalopods), and melanocytes (in mammals and birds). They absorb most wavelengths of light and reflect just a few, limiting both their range and brilliance. For instance, most animals cannot naturally produce red; they synthesize it from plant chemicals called carotenoids.

The other way animals make color is with nanoscale structures. Insects, and, to a lesser degree, birds, are the masters of color-based structure. And compared to pigment, structure is fabulous. Structural coloration scatters light into vibrant, shimmering colors, like the shimmering iridescent bib on a Broad-tailed hummingbird, or the metallic carapace of a Golden scarab beetle. And scientists aren't quite sure why iridescence evolved. Probably to signal mates, but still: Why?

Decoding the rainbow of life

The question of iridescence is similar to most questions scientists have about animal coloration. They understand what the colors do in broad strokes, but there's till a lot of nuance to tease out. This is mostly because, until recently, they were limited to seeing the natural world through human eyes. “If you ask the question, what’s this color for, you should approach it the way animals see those colors,” says Tim Caro, a wildlife biologist at UC Davis and the organizing force behind the new paper. (Speaking of mysteries, Caro recently figured out why zebras have stripes.)

Take the peacock. “The male’s tail is beautiful, and it evolved to impress the female. But the female may be impressed in a different way than you or I,” Caro says. Humans tend to gaze at the shimmering eyes at the tip of each tail feather; peahens typically look at the base of the feathers, where they attach to the peacock’s rump. Why does the peahen find the base of the feathers sexy? No one knows. But until scientists strapped to the birds' heads tiny cameras spun off from the mobile phone industry, they couldn't even track the peahens' gaze.

Another new tech: Advanced nanomaterials give scientists the ability to recreate the structures animals use to bend light into iridescent displays. By recreating those structures, scientists can figure out how genetically expensive they are to make.

Likewise, new magnification techniques have allowed scientists to look into an animal’s eye structure. You might have read about how mantis shrimp have not three or four but a whopping 12 different color receptors, and how they see the world in psychedelic hyperspectral saturation. This isn’t quite true. Those color channels aren’t linked together—not like they are in other animals. The shrimp probably aren’t seeing 12 different, overlapping color spectra. “We are thinking maybe those color receptors are being turned on or off by some other, non-color, signal,” says Caro.

But perhaps the most important modern innovation in biological color research is getting all the different people from different disciplines together. “There are a lot of different sorts of people working on color,” says Caro. “Some behavioral biologists, some neurophysiologists, some anthropologists, some structural biologists, and so on.”

And these scientists are scattered all over the globe. He says the reason he brought everyone to Berlin is so they could finally synthesize all these sub-disciplines together, and move into a broader understanding of color in the world. The most important technology in understanding animal color vision isn't a camera or a nanotech surface. It's an airplane. Or the internet.

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Nick Goldschmidt has been lucky so far. A wildfire has burned more than 8,000 acres just north of his vineyards in Geyserville, California, but so far his vines are OK. So is his house in Healdsburg, roughly midway between Geyserville and a 36,000-acre fire that destroyed more than 2,800 homes in Santa Rosa.

But now, amid the charred, empty spaces that scar northern California’s winegrowing region, under skies yellowed by smoke, Goldschmidt has a race to win. Wildfires can ruin the flavor of wine grapes, a problem called smoke taint. “I’ve worked with smoke before,” Goldschmidt says. “It is not an easy thing to fix. But in my experience, it’s more about contact time. So the key thing is, if you have vineyards near the fire, you’ve got to get the grapes off.”

Depending on wind, smoke from the Atlas Fire could potentially reach Goldschmidt’s Napa vineyard, where about 15 percent of the fruit remains to be harvested. He now plans to harvest the rest by the weekend.

That’s typical of Napa, where 80 to 85 percent of the 2017 harvest is done. In nearby Sonoma, 90 percent of the grapes are in. But that still means that a few grapes could get exposed to smoke, and fire and heat could damage the vines. In a region key to California’s $34 billion wine industry—and that figure doesn’t even include the enormous tourist business—that’s a big deal. Fires have killed 31 people so far, destroyed thousands of homes, and consumed the efforts of more than 8,000 firefighters. And the winemakers of the area are trying to make sure the damage to their livelihoods doesn’t get worse.

Winemaking regions around the world, especially in Australia, have been dealing with the consequences of more active fire seasons near vineyards since at least the turn of the century—but the problems haven’t really hit California yet. The state’s frequent fires haven’t intersected with its vineyards. Until now.

Smoke is complicated stuff. Everyone in the Bay Area has gotten a taste in the past few days—that medicinal, ashy, burnt flavor comes from, among other ingredients, molecules called polycyclic aromatic hydrocarbons, nitrogen and sulfur oxides, other organic compounds, and even tiny particles carried aloft by heat and air currents. If you’ve ever sat near a campfire or cooked on a grill, you know it’s not necessarily an unpleasant aroma, as cognitively dissonant as that may feel when you realize it comes from blazes that have destroyed the lives of thousands.

But what’s delicious in bacon or lox generally isn’t—depending on how much you have—in wine. The actual flavor compounds are molecules called volatile phenols. “Volatile” means they evaporate, and in chemistry “phenols” are benzene rings (a hexagon of carbon atoms with hydrogen atoms sticking off like a snowflake) connected to a hydrogen-and-an-oxygen. You might know them better as the aroma of peat in some whiskies or of antiseptic or Band-Aids. Their volatility means that in your mouth, they turn into a vapor that gets sucked up retronasally, through the back of the throat to the sensitive layer of nerve endings behind your nose that translates chemicals into odors.

Smoke taint in grapes has two specific markers: guaiacol and 4-methylguaiacol. They taste like, well, smoke. Expose grapes on the vine to them, and the wine will taste smoky. Obvious, right? Except no. “The mechanism is a little bit unclear,” says Kerry Wilkinson, an oenologist who studies smoke taint at the University of Adelaide. Leaves have pores called stomata involved in respiration, “but when grapevines are exposed to smoke, the stomata close almost immediately and photosynthesis stops,” she says. “The guaiacol conjugates are getting to not only the skins but the pulp of the fruit. I think it’s just permeation, but I don’t think anyone’s done the research.”

Making things even more complicated, grapevines have their own way of dealing with a barbecue. “Those compounds, once they’re taken up, the grapevine will stick one or more sugar molecules on them,” Wilkinson says. “We think that’s to make them less toxic to the plant.” This process—it’s called glycosylation, and the sugars are called glycosides—turns the volatile phenols non-volatile. Which means you can’t taste them in the grape juice.

But ferment that juice into wine, and acids in it will break those sugars off. Poof: Smoke gets in your wines.

I don’t mean to be flip here; smoke taint from the Canberra bushfires of 2003 cost Australian vineyards more than $4 million; fires in 2004 cost another $7 million. Once grapes are tainted, the wine isn’t easy to fix. Those ashy flavors are too strong; you can’t just try to blend in other, untainted wine to cover it up. Efforts to filter it with activated charcoal and reverse osmosis can filter out flavors you might want in the wine, too. Heck, guaiacol and 4-methylguaiacol are markers for oak-barrel aging, too. Nobody ever describes an over-oaked Chardonnay as “smoke-tainted,” but—well, maybe they should, actually. And some grape varietals—shiraz, particularly—already have naturally high guaiacol levels.

All of which might be fine. Most of the grapes were picked before the fires came. In general, “if the fruit’s already been harvested this year, it should be OK,” Wilkinson says. A couple dozen wineries suffered damage so far, from minor to total. But Northern California has almost 250,000 acres of wine grape vines—more than 100,000 of them in Napa and Sonoma Counties as of 2016.

It looks like the grapes those vines produce will be OK next year. “There’s no carryover effect from one season to the other,” Wilkinson says. “We haven't seen any evidence to suggest that any of those smoke compounds are bound up from one season to another in the grapevine.” They get into the grapes, which come off, and the leaves, which fall off or get pruned. (And a little more luck: The grapes left to harvest in Napa are mostly Cabernet Sauvignon, which turns out to be more resistant to smoke taint than some other varietals.)

But vines themselves are sensitive to heat. “They can be scorched, and if it’s severe, that can permanently damage or kill grapevines,” Wilkinson says. “If there’s just a little bit of scorching, vines can recover, but the yield can be decreased in the season immediately after.”

It turns out it’s pretty hard to burn down a California vineyard. In part that’s because most of them are irrigated, so they’re wet and thus resistant to fire. Even when the cover crop growing between the vines gets burned in a fast-moving wildfire, “it’s pretty damn hard” to get a California vineyard to catch, Goldschmidt says.

When he was working in Chile, though, he saw a wind-driven wildfire very much like the ones affecting California destroy a vineyard. “That was devastating,” Goldschmidt says. “A lot of those vineyards are dry-farmed, so they burned much more easily.”

Heat damage is a lot like frost damage, something California vintners know a lot about. Proper pruning and treatment can save an injured vine. The trick is knowing if they’re injured, and how badly. Sometimes vintners will have to cut through the trunks of the vines to assess whether the phloem, the living and respiring part of the wood, is still healthy. But that’s a destructive test—sometimes destroying the vine in an attempt to save it.

So grape-growers look for other ways to assess their vines. “We look at things like, are the irrigation lines melted? Is there indication of scorching of the trunk and canopy? How much fire damage was there to anything growing in between the vines?” Wilkinson says.

That’s an assessment that’ll probably have to wait until the fires are under control. Maybe Goldschmidt’s luck will hold out. “This is my 29th vintage in Sonoma. It’s the first time the Alexander Valley was earlier in maturity than the Napa Valley. Usually it’s 10 days later,” he says. “If it had been the other way I would have really been hammered.”

Ordinarily I might end the story with that, but in this case it’s not as lucky as it sounds. Napa and Sonoma did indeed have a weird year. It rained hard after years of drought, and then over the summer it got really hot. Vintners irrigated when they might not have, which lowered the sugar levels in the grapes as they took up the water…and then it got hot again. “It’s been really hard to make a harvest decision based on sugar,” Goldschmidt says. “It’s been more about flavor and tannin.”

Based on those organoleptic assessments—the fanciest possible way of saying “how it tastes”—most of Napa and Sonoma brought in their fruit in July and August instead of, well, now.

To whom should the vintners send a thank-you? “Over the last five years or so we’ve had this period of very high temperatures that coincided with low precipitation, punctuated by very wet conditions,” says Noah Diffenbaugh, a climate researcher at Stanford. It’s exactly what Diffenbaugh’s group warned would happen in a prescient 2006 paper in the Proceedings of the National Academy of Sciences titled “Extreme heat reduces and shifts United States premium wine production in the 21st century.”

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Their point? At first, heat and rare-but-extreme rain is going to change how winegrowing regions work. Eventually more northerly regions will be better for grapes—hello, Oregon’s Willamette Valley—and existing grape-growing regions will change the varieties they grow.

It’s in the nature of global warming that extreme climate events will become less rare. “We’ve done a lot of work trying to understand how global warming impacts temperature extremes,” Diffenbaugh says. “The extremes are really where we feel the climate.”

The vagaries of climate change let the 2017 vintage mostly dodge the economic devastation that smoke taint would have caused. It’s a faintly silver lining to the clouds of ash and smoke now parked over thousands of acres of death and destruction. But that silver lining won’t last. These won’t be the last fires; next time, maybe the harvest won’t happen first. The most frightening truth about the extreme climate event that is the northern California fires is that such events won’t always be extreme. They’ll be normal.

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Inside a red-bricked building on the north side of Washington DC, internist Shantanu Nundy rushes from one examining room to the next, trying to see all 30 patients on his schedule. Most days, five of them will need to follow up with some kind of specialist. And odds are they never will. Year-long waits, hundred-mile drives, and huge out of pocket costs mean 90 percent of America’s most needy citizens can’t follow through on a specialist referral from their primary care doc.

But Nundy’s patients are different. They have access to something most people don’t: a digital braintrust of more than 6,000 doctors, with expert insights neatly collected, curated, and delivered back to Nundy through an artificial intelligence platform. The online system, known as the Human Diagnosis Project, allows primary care doctors to plug into a collective medical superintelligence, helping them order tests or prescribe medications they’d otherwise have to outsource. Which means most of the time, Nundy’s patients wait days, not months, to get answers and get on with their lives.

In the not-too-distant future, that could be the standard of care for all 30 million people currently uninsured or on Medicaid. On Thursday, Human Dx announced a partnership with seven of the country’s top medical institutions to scale up the project, aiming to recruit 100,000 specialists—and their expert assessments—in the next five years. Their goal: close the specialty care gap for 3 million Americans by 2022.

In January, a single mom in her 30s came to see Nundy about pain and joint stiffness in her hands. It had gotten so bad that she had to stop working as a housekeeper, and she was growing desperate. When Nundy pulled up her chart, he realized she had seen another doctor at his clinic a few months prior who referred her to a specialist. But once the patient realized she’d have to pay a few hundred dollars out of pocket for the visit, she didn’t go. Instead, she tried get on a wait list at the public hospital, where she couldn’t navigate the paperwork—English wasn’t her first language.

Now, back where she started, Nundy examined the patient’s hands, which were angrily inflamed. He thought it was probably rheumatoid arthritis, but because the standard treatment can be pretty toxic, he was hesitant to prescribe drugs on his own. So he opened up the Human Dx portal and created a new case description: “35F with pain and joint stiffness in L/R hands x 6 months, suspected AR.” Then he uploaded a picture of her hands and sent out the query.

Within a few hours a few rheumatologists had weighed in, and by the next day they’d confirmed his diagnosis. They’d even suggested a few follow-up tests just to be sure and advice about a course of treatment. “I wouldn’t have had the expertise or confidence to be able to do that on my own,” he says.

Nundy joined Human Dx in 2015, after founder Jayanth Komarneni recruited him to pilot the platform’s core technologies. But the goal was always to go big. Komarneni likens the network to Wikipedia and Linux, but instead of contributors donating encyclopedia entries or code, they donate medical expertise. When a primary care doc gets a perplexing patient, they describe their background, medical history, and presenting symptoms—maybe adding an image of an X-ray, a photo of a rash, or an audio recording of lung sounds. Human Dx’s natural language processing algorithms will mine each case entry for keywords to funnel it to specialists who can create a list of likely diagnoses and recommend treatment.

Now, getting back 10 or 20 different doctors’ takes on a single patient is about as useful as having 20 friends respond individually via email to a potluck invitation. So Human Dx’s machine learning algorithms comb through all the responses to check them against all the project’s previously stored case reports. The network uses them to validate each specialist's finding, weight each one according to confidence level, and combine it with others into a single suggested diagnosis. And with every solved case, Human Dx gets a little bit smarter. “With other online tools if you help one patient you help one patient,” Komarneni says. “What’s different here is that the insights gained for one patient can help so many others. Instead of using AI to replace jobs or make things cheaper we’re using it to provide capacity where none exists.”

Komarneni estimates that those electronic consults can handle 35 to 40 percent of specialist visits, leaving more time for people who really need to get into the office. That’s based on other models implemented around the country at places such as San Francisco General Hospital, UCLA Health System, and Brigham and Women’s Hospital. SFGH’s eReferral system cut the average waiting time for an initial consult from 112 days to 49 within its first year.

That system, which is now the default for every SFGH specialty, relies on dedicated reviewers who get paid to respond to cases in a timely way. But Human Dx doesn’t have those financial incentives—its service is free. Today, though, by partnering with the American Board of Medical Specialities, Human Dx can now offer continuing education and improvement credits to satisfy at least some of the 200 hours doctors are required to complete every four years. And the American Medical Association, the nation’s largest physician group, has committed to getting its members to volunteer, as well as supporting program integrity by verifying physicians on the platform.

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It’s a big deal to have the AMA on board. Physicians have historically been wary of attempts to supplant or complement their jobs with AI-enabled tools. But it’s important to not mistake the organization’s participation in the alliance for a formal pro-artificial intelligence stance. The AMA doesn’t yet have an official AI policy, and it doesn’t endorse any specific companies, products, or technologies, including Human Dx’s proprietary algorithms. The medical AI field is still young, with plenty of potential for unintended consequences.

Like discrepancies in quality of care. Alice Chen, the chief medical officer for the San Francisco Health Network and co-director of SFGH’s Center for Innovation in Access and Quality, worries that something like Human Dx might create a two-tiered medical system, where some people get to actually see specialists and some people just get a computerized composite of specialist opinions. “This is the edge of medicine right now,” Chen says. “You just have to find the sweet spot where you can leverage expertise and experience beyond traditional channels and at the same time ensure quality care.”

Researchers at Johns Hopkins, Harvard, and UCSF have been assessing the platform for accuracy and recently submitted results for peer review. The next big hurdle is money. The project is currently one of eight organizations in contention for a $100 million John D. and Catherine T. MacArthur Foundation grant. If Human Dx wins, they’ll spend the money to roll out nationwide. The alliance isn’t contingent on the $100 million award, but it would certainly be a nice way to kickstart the process—especially with specialty visits accounting for more than half of all trips to the doctor’s office.

So it’s possible that the next time you go in for something that stumps your regular physician, instead of seeing a specialist across town, you’ll see five or 10 from around the country. All it takes is a few minutes over lunch or in an elevator to put on a Sherlock Holmes hat, hop into the cloud, and sleuth through your case.

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A young, fit US soldier is marching in a Middle Eastern desert, under a blazing summer sun. He’s wearing insulated clothing and lugging more than 100 pounds of gear, and thus sweating profusely as his body attempts to regulate the heat. But it’s 108 degrees out and humid, too much for him bear. The brain is one of the first organs affected by heat, so his judgment becomes impaired; he does not recognize the severity of his situation. Just as his organs begin to fail, he passes out. His internal temperature is in excess of 106 degrees when he dies.

An elderly woman with cardiovascular disease is sitting alone in her Chicago apartment on the second day of a massive heatwave. She has an air conditioner, but she’s on a fixed income and can’t afford to turn it on again—or maybe it broke and she can’t afford to fix it. Either way, she attempts to sleep through the heat again, and her core temperature rises. To cool off, her body’s response is to work the heart harder, pumping more blood to her skin. But the strain on her heart is too much; it triggers cardiac arrest, and she dies.

Such scenarios could surely happen today, if they haven’t already. But as the world warms due to climate change, they’ll become all too common in just a few decades—and that’s according to modest projections.

This is not meant to scare you quite like this month’s cover story in New York magazine, “The Uninhabitable Earth.” That story was both a sensation and quite literally sensational, attracting more than two million readers with its depiction of “where the planet is heading absent aggressive action.” In this future world, humans in many places won’t be able to adapt to rising temperatures. “In the jungles of Costa Rica, where humidity routinely tops 90 percent, simply moving around outside when it’s over 105 degrees Fahrenheit would be lethal. And the effect would be fast: Within a few hours, a human body would be cooked to death from both inside and out,” David Wallace-Wells writes. “[H]eat stress in New York City would exceed that of present-day Bahrain, one of the planet’s hottest spots, and the temperature in Bahrain ‘would induce hyperthermia in even sleeping humans.’”

These scenarios are supported by the science. “For heat waves, our options are now between bad or terrible,” Camilo Mora, a geography professor at University of Hawaii at Manoa, told CNN last month. Mora was the lead author of a recent study, published in the journal Nature, showing that deadly heat days are expected to increase across the world. Around 30 percent of the world’s population today is exposed to so-called “lethal heat” conditions for at least 20 days a year. If we don’t reduce fossil-fuel emissions, the percentage will skyrocket to 74 percent by the year 2100. Put another way, by the end of the century nearly three-quarters of the Earth’s population will face a high risk of dying from heat exposure for more than three weeks every year.

This is the worst-case scenario. Even the study’s best-case scenario—a drastic reduction in greenhouse gases across the world—shows that 48 percent of humanity will be exposed regularly to deadly heat by the year 2100. That’s because even small increases in temperature can have a devastating impact. A study published in Science Advances in June, for instance, found that an increase of less than one degree Fahrenheit in India between 1960 and 2009 increased the probability of mass heat-related deaths by nearly 150 percent.

And make no mistake: Temperatures are rising, in multiple ways. “We’ve got a new normal,” said Howard Frumkin, a professor at the School of Public Health at the University of Washington. “I think all of the studies of trends to date show that we’re having more extreme heat, and we’ve having higher average temperatures. Superimposed on that, we’re seeing more short-term periods of extreme heat. Those are two different trends, and they’re both moving in the wrong direction.” Based on those trends, the US Global Change Research Program predicts “an increase of thousands to tens of thousands of premature heat-related deaths in the summer … each year as a result of climate change by the end of the century.” And that’s along with the deaths we’ve already seen: In 2015, Scientific American noted that nine out of the ten deadliest heat waves ever have occurred since 2000; together, they’ve killed 128,885 people.

In other words, to understand how global warming wreaks havoc on the human body, we don’t need to be transported to some imagined dystopia. Extreme heat isn’t a doomsday scenario but an existing, deadly phenomenon—and it’s getting worse by the day. The question is whether we’ll act and adapt, thereby saving countless lives.

There are two ways a human body can fail from heat. One is a direct heat stroke. “Your ability to cool yourself down through sweating isn’t infinite,” said Georges Benjamin, executive director of the American Public Health Association. “At some point, your body begins to heat up just like any other object. You go through a variety of problems. You become dehydrated. Your skin dries out. Your various organs begin to shut down. Your kidneys, your liver, your brain. As gross as this may sound, you in effect, cook.” (So maybe Wallace-Wells wasn’t being hyperbolic after all.)

Heat death can also be happen due to a pre-existing condition, the fatal effects of which were triggered by high temperature. “Heat stress provokes huge amounts of cardiovascular strain,” said Matthew Cramer of the Institute of Exercise and Environmental Medicine. “For these people, it’s not necessarily that they’ve cooked, but the strain on their cardiovascular system has led to death.” This is much more common than death by heat stroke, but is harder to quantify since death certificates cite the explicit cause of death—“cardiac arrest,” for instance, rather than “heat-related cardiac arrest.”

In both scenarios, the body’s natural ability to cool itself off through sweating has either reached its capacity or has been compromised through illness, injury, or medication. There are many people who have reduced capacity for sweating, such as those who have suffered severe burns over large parts of their bodies. Cramer, who studies heat impacts on burned people, says 50,000 people suffer severe burn injuries per year in America, and the World Health Organization considers burns “a global public health problem,” with the majority of severe burn cases occurring in low- and middle-income countries.

Bodies that are battling illness or on medication may also struggle with heat regulation. Diuretics tend to dehydrate people; anticholinergics and antipsychotics reduce sweating and inhibit heat dissipation. An analysis of the 2003 heat wave in France that killed 15,000 people suggested that many of these deaths could have been avoided had people been made aware of the side effects of their drugs. As for illnesses, “Anything that impairs the respiratory or circulatory system will increase risk,” said Mike McGheehin, who spent 33 years as an environmental epidemiologist at the Centers for Disease Control and Prevention. “Obesity, diabetes, COPD, heart disease, and renal disease.” Kidney disease, mental illness, and multiple sclerosis. The list goes on and on.

This summer has presented many opportunities for bodies to break down from heat. Temperature records, some more than a century old, have been broken across California, Nevada, Utah, Idaho and Arizona. (Speaking of Arizona, it’s been so hot there that planes can’t fly.) And it’s not just America. Last month, Iran nearly set the world record for highest temperature ever recorded. The May heatwave that hit India and Pakistan set new world records as well, including what the New York Times called “potentially the hottest temperature ever recorded in Asia”: 129.2 degrees Fahrenheit. Worldwide, 2017 is widely expected to be the second-hottest year, after 2016, since we began keeping global average temperature records in 1880.

These trends have public health professionals concerned about how people are going to deal with the heat when it comes their way. “Clearly this is one of the most important problems we’re going to see from a public health perspective,” Benjamin said. “This is not a tomorrow problem. It’s a significant public health problem that we need to address today.”

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It’s a public health problem especially in cities, says Brian Stone, a professor at Georgia Tech’s City and Regional Planning Program. “Our fundamental work shows that larger cities are warming at twice the rate of the planet,” he said, describing a phenomenon known as urban heat islands, where built-up areas tend to be hotter than surrounding rural areas, mainly because plants have been replaced by heat-absorbing concrete. Global warming is making that phenomenon worse. “We’re really worried about the rate of how quickly we’re starting to see cities heat up,” Stone said.

According to Stone’s analysis, the most rapidly warming city is Louisville, Kentucky, followed by Phoenix, Arizona, and Atlanta, Georgia. But he’s less concerned about cities like Phoenix, which already have infrastructure to deal with brutally high temperatures, than he is about Chicago, Buffalo, and other cities in the northern United States that have really never had to deal with extreme heat. That is precisely why the Chicago heat wave of 1995 that killed 759 people was so deadly. According to the Chicago Tribune, the city was “caught off guard,” and had “a power grid that couldn’t meet demand and a lack of awareness on the perils of brutal heat.”

In other words, Stone and others say, excessive death rates are not always due to just extreme temperatures, but unusual temperatures. People are more likely to die when they are confronted with temperatures they don’t expect and thus aren’t prepared for. That’s why officials in cities not experiencing heat-related extremes need to improve emergency response systems, now. “Those people have got to start thinking in term of, ‘two years ago we had four hot days, the year after we had eight hot days,’” Benjamin said. “Public health systems should be put in place to respond to prolonged heat waves. Emergency cooling centers where people can go should be built. Identify where the people who are most socially isolated live.” Absent preventative action, heat-related deaths in New York City could quintuple by the year 2080, according to recent research.

Some cities have already started to prepare. Stone recently completed a heat adaptation study for Louisville that includes not only emergency management planning but also ways the city can prevent itself from getting so hot (by improving energy efficiency and installing green roofs, for instance). But as for now, he said, it’s rare to see a city actually adopt policies supportive of heat management. “We do see flooding adaptation plans—New York City has one, and New Orleans has one—but heat adaptation planning is a very new idea, in the US and really around the world,” he said. “It takes a lot to convince a mayor that a city can actually cool itself down. It’s not intuitive.”

The good news is that humans adapt to heat, both physiologically (through acclimatization) and socially (with air conditioning, for instance). That will continue, according to the US Global Change Research Program, which states with very high confidence that adaptation efforts in humans “will reduce the projected increase in deaths from heat.”

But there’s a limit to this. “There’s no way to adapt to heat that’s more than a certain amount,” Frumkin said. “And socially, there’s always going to be people we miss, who don’t have access to air conditioning.” McGeehin noted those people will likely be poor, elderly, and minority populations. “It’s a quintessential public health problem in that it impacts the most disenfranchised of our society. Young, healthy, middle-class people will largely be left alone,” he said.

Air conditioners also have limits, especially in cities where blackouts can occur. “It is inevitable,” Stone said, that large cities will see blackouts during future heat waves. “The number of blackouts we see year over year is increasing dramatically,” he said. “Whether that’s caused by the heatwave or just happens during the heatwave doesn’t really matter…. The likelihood of an extensive blackout during a heatwave is high, and getting higher as we add more devices and stressors to the grid.”

It’s a “cruel irony,” Frumkin said, that as the world gets hotter, we need more air conditioning, and thus consume more electricity. And if that electricity comes from fossil fuel sources, it will create more global warming, which in turn will increase the demand for air conditioning. The answer, he said, is to “decarbonize the electric grid.” But that’s easier said than done, especially when the Trump administration is devoted to increasing the use of fossil fuels to support the country’s electrical grid.

As with many other efforts to fight climate change, though, cities don’t need Washington’s help to take action on heat adaptation. “Cities can manage their own heat islands on their own, and that’s where we most need to be focused,” Stone said. But that will require convincing elected leaders that extreme heat is big a threat as, say, rising seas—and one that can’t be addressed with something as obvious as a sea wall. That’s the challenge, says McGeehin: “Heat as a major natural disaster is mostly overlooked in this country.” It’s a quiet killer, and perhaps more lethal because of it.

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As I understand it, the whole point of cooking a turkey is to take it at some temperature and then increase it to a higher temperature. Sure, maybe there's something about family togetherness in there, but really, Thanksgiving is all about thermal transfer. The USDA recommends a minimum internal temperature of 165°F (74°C). I guess this is the minimum temperature to kill all the bad stuff in there—or maybe it is the lowest temperature that it can be and still taste great.

Either way, if you want to increase the temperature of the turkey you need to add energy. Perhaps this energy comes from fire, or an oven or even from hot oil—but it needs energy. But be careful. There is a difference between energy and temperature. Let me give you an example.

Suppose you put some leftover pizza in the oven to heat it up. Since you don't want to make a mess, you just rip off a sheet of aluminum foil and put the pizza on that and then into the oven. The oven is set to 350 degrees Fahrenheit so that after 10 minutes, both the pizza and the foil are probably close to that temperature. Now for the demonstration. You can easily grab the aluminum foil without burning yourself, but you can't do the same to the pizza. Even though these two objects have the same temperature, they have different amounts of thermal energy.

The thermal energy in an object depends on the object's mass, the object's material and the object's temperature. The change in thermal energy for an object then depends on the change in temperature.

In this expression, m is the mass of the object and the variable c is the specific heat capacity. The specific heat capacity is a quantity that tells you how much energy it takes to one gram of the object by 1 degree Celsius. The specific heat capacity of water is 4.18 Joules per gram per degree Celsius. For copper, the specific heat capacity is 0.385 J/g/°C (yes, water has a very high specific heat capacity).

But what about turkey? What is the energy needed to heat up 1 gram of turkey by 1°C? That is the question I want to answer. Oh sure, I could probably just do a quick search online for this answer, but that's no fun. Instead I want to calculate this myself.

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Here is the basic experimental setup. I am going to take a turkey breast (because I am too impatient to use the whole turkey) and put it in a known amount of hot water. I will then record the change in temperature of the water and the change in temperature of the turkey. Of course, this will have to be in an insulated container such that all of the energy that leaves the water will go into the turkey.

With the change in temperature of the water, I can calculate (based on the known specific heat capacity of water) the energy lost. Assuming all this energy goes into the turkey, I will then know the increase in energy of the turkey. With the mass and change in turkey temperature, I will have the specific heat capacity of a turkey.

Just to be clear, I can set the changes in energy to be opposite from each other and then solve for the specific heat capacity of the turkey. Like this.

OK, it's experiment time. I am going to start with 2,000 mL (2 kilograms) of hot water and add it to a foam box with my turkey breast. I will monitor both the temperature of the water and the turkey. Oh, the turkey has a mass of 1.1 kilograms. Here's what this looks like (without the box lid).

I collected data for quite a while and I assumed that the water and the turkey would reach an equilibrium temperature—but I was wrong. Apparently it takes quite a significant amount of time for this turkey to heat up. Still, the data should be good enough for a calculation.

Hopefully it's clear that the red curve is the hot water and the blue is for the turkey. From this plot, the water had a change in temperature of -21.7°C and the turkey had +27°C. Putting these values along with the mass of the water and turkey, I get a turkey specific heat capacity of 6.018 J/g/°C. That's a little bit higher than what I was expecting—but at least it is in the ballpark of the value for water. But overall, I'm pretty happy.

But what can you do with the specific heat capacity for a turkey? What if you want to do a type of sous-vide cooking in which the turkey is placed in a vacuum-sealed bag and then added water at a particular temperature? Normally, the temperature of the water is kept at some constant temperature. But what if you want to start with hot water and cold turkey and then end up with perfect temperature turkey? In order to do this, you could calculate the starting mass and temperature of water that would give you the best ending turkey temperature. I will let you do this as a homework assignment.

Of course there is another way to cook a turkey. You could drop it from some great height such that it heats up when it lands. Oh, wait—I already did this calculation.

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