Where were you when New York City’s climate was reclassified from humid continental to humid subtropical? I was in a borrowed apartment on 101st Street, overlooking the west side of Central Park. The apartment belonged to a widower, a man who kept a gun in a filing cabinet that he warned us not to open. His hallways were lined to the ceiling with boxes overflowing with photos and paper scraps, a memorial of sorts to his deceased wife, and to the grief he would not let go of. There was no table in this apartment, so we stacked some of these boxes by the window overlooking the park, a view worth more money than I’d ever care to have. Living in that apartment felt like one of those rare summer days in this century—not too hot, almost indecently pleasant, but already unraveling at the edges. The type of day where sublimity is found in a makeshift table of a single plank of wood laid upon a lifetime’s worth of loss.

I was sitting at that makeshift table when I saw the July 2020 New York Times’ headline, tucked into the Climate section, a headline worthy of the opening lines to a romance novel: “Sultry Nights and Magnolia Trees: New York City Is Now Subtropical.” As I sent the article to friends, I realized its insinuations of pleasant, exotic things like palm trees and mild winters did not aid my insistence to anyone who would listen that this mattered. That August was ranked the third hottest on record globally—a title that was superseded just last month. Despite the heat, or perhaps amplified by it, demonstrations for racial justice were shaking the streets of nearly every major city across the U.S. A close friend of mine, who was encamped outside New York’s City Hall, called me after sleepless nights of being terrorized by the police, insisting that the revolution was nigh. I believed her. The city's energy that summer felt unstoppable, ready to build a new world from the detritus we’d leave behind. And amidst the cacophony of protests, joyous and furious alike, a different barrier was crossed. Though that threshold break barely registered as news, our city on the North Atlantic is now, climatologically speaking, a part of the tropics.

The Earth’s climate resists Cartesian logic, yet humans persist in their classifications. The Köppen system, the most renowned climate classification system, was created by Wladimir Köppen in 1884, a botanist so hubristic that he believed all life forms could be named and classified. He used the same logic to fit all the earth’s continents and regions into five discrete climate zones.

The ongoing usage of Köppen’s zones, and their ever-shifting boundaries, offer a dire signal that geological changes are occurring on human timescales. But there are other, bitter ironies attached to the continued use of a system that dates from an era when European empires were carving up the planet. There were other consequences to devising systems of classification, like Köppen’s, to render colonized landscapes and peoples, many of them in the tropics, legible to northern ears and tongues. In Köppen’s system, there are five major climate types: A (tropical), B (arid), C (temperate), D (continental), and E (polar). All of them use temperature as their primary criterion, except for B. While the system has evolved since its early twentieth-century origins, it still bears the logic of its age, reducing the world’s complexity to five letters and swathing the Earth in colored bands on commonly reproduced maps. On the day the climate zone shifted, it was clear that we had to find new colors for subtropical New York City on these maps.

The word tropic derives from the Greek tropikós, meaning “a turn” and once referred to the point at which the sun reaches its apogee at the solstice. To call a place tropical is to place it at the imagined center of the Earth, where heat resides, within the celestial realm where the sun hangs high. The tropics are now expanding at a rate of 30 miles per decade—a prophecy that recalls past epochs in Earth’s history. 50 million years ago, palm trees, those eternal symbols of tropical delight, grew in the Arctic. If the Köppen categories were in competition with each other to consume more of the Earth, it is Type A, tropical, that stands poised to devour the rest.

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When the whole world is tropical, what words will we use to describe and define ourselves?

We bemoan the fact that every summer is now one of the hottest summers ever. But the notion of “records” as benchmarks to be broken no longer holds weight. What is the point of a record when the certainty of its being broken is undeniable and in close sight? Will future records revolve around how cool a summer is? Where will the line be drawn between the era of accounting for the hottest summers and that of accounting for the coolest ones? After decades of denialism around the perils of fossil fuel use, which saw companies like ExxonMobil spend millions on marketing campaigns to frame those perils as “potential long-term risks,” not even certain to occur, it’s not hard to understand why many are tempted to see the planet’s crisis as a mere shift. A crisis, by definition, should abide by binary logic—either there is one or there is not. It’s harder to see a crisis as a creep or ever-worsening condition. This binary between crisis and non-crisis demonstrates one of the many ways in which our classification systems fail in the face of climate breakdown. We cover our eyes from both consequence and source. As Amitav Ghosh has reminded us, the climate crisis isn’t singular or new; it’s inseparable from the history of colonialism, whose primary actors, in the ruthless pursuit for riches, relied on classification systems to render the world and its beings knowable and expendable. Our systems of classification, as we know them, are often not far removed from our systems of exploitation.

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What anchors a memory of heat? I remember that on June 24, this past summer, temperatures breached 100 degrees. Descending to the train platform uptown felt like entering into the innards of a large, inhospitable animal, its density a flesh that my body had to press through. It was hot, and the station’s fever seeped into my skin, slicking me with a layer of sweat that ran. I remember how the sweat slid into my contact lenses and burned my eyes, blurring my vision while I waited for that train. At lunch, I felt an eerie sense of anguish wandering in desolate public spaces. Madison Square Park, usually packed at midday, was at half-capacity. And among those who were there, I glimpsed a shared sense of uneasiness. What were any of us doing, after all, outside in these conditions? Heat stretches the limits of imagination because imagination is so often visual, and the visuals of heat are often images of absence: people not outside, events not attended, deaths not recorded. We often depict heat by showing the means by which people evade it. Look at the children splashing in the spray of fire hydrants; look at the families dipping into pools; look at the young women sunbathing. The dangers of visualizing extreme heat in these ways have been the focus of advocacy campaigns like one by Climate Outreach, which begins with the assertion: “Heat is Not Fun.”

It’s anachronistic and harmful for us to ascribe carefree images and language to heat, as the Times did by invoking “sultry nights.” But what’s even more harmful is how all of us are beginning to respond to extreme heat emotionally and relationally—not through the shock or horror with which we’d respond to a hurricane, but with the silent, subconscious rewriting of social norms. This creeping, unclassified disaster reshapes us in ways we barely perceive. In asking people to adjust their behavior, we excuse the conditions for their discomfort.

I knew many people this summer who got heat exhaustion and heat stroke—all in the Northeast. One of them, a friend of my mom’s, is a neighbor I grew up with and a marathon runner who’s always been in rude health. On one of this year’s hot days, though not the hottest, she went for a run around the loop in Central Park. That evening, she came down with an illness that could not be diagnosed by her husband, a doctor, who suggested it was because she had spent three hours that day rigorously moving her body in 92-degree heat. My mom ended the story with a judgment—“So stupid, right?”

My impulse was to agree—of course, it’s insane to believe that the way you've lived your life for its entirety up until the past few years is the way you can live your life today. I spend every day steeped in climate-related content, with “heat” being my primary keyword search. But I realized that the day my mom’s friend took ill hadn’t even registered for me as a particularly bad day. In fact, on that same day, I had gone on a seven-mile walk.

My own notion of danger was in part shaped by a threshold for extreme heat I first learned about in college, when I spent a summer working on a climate adaptation plan for the city of Penang. The number I had seared into my mind then was 95°F wet-bulb, or 35°C wet-bulb—the maximum temperature at which the human body, through perspiration, can cool itself. In New York City, where the average August humidity is 70%, this would mean a temperature of 104°F—a threshold that is breached on occasion in the Northeast, though far more commonly in some of the hottest regions of the world. This upper boundary was recently thrown into question by research suggesting that 31°C wet-bulb better represents the maximum safe temperature for humans. In a New York City August, this threshold would be reached when the temperature hits 96°F—which it did, multiple times this past summer. But although this number wasn’t hit on the ill-fated day when my mom’s friend went on a run, the issue is that heat and the human body do not abide by binaries. What is safe for a 65-year-old marathon runner on a hot day is not the same as what is safe for a 25-year-old on a long walk, or an elderly person with lung disease, or an energetic child. All of us possess unique combinations of exposure risks, access to adaptive measures, and physiology. This variability begs for classification systems that are as sophisticated as they are simple.

When systems for classifying the external world fail, it is this constant recalibration of social norms that serves as a hastily constructed bulwark against external threats. We create new systems that are directed at our fellow human beings.

A close friend of mine got heat stroke in Boston this summer while moving her furniture from one apartment to another on a 90-degree day in August. She is from Karachi, where temperatures of 118°F have been recorded. And still, despite her familiarity as a climate and health professional who has first-hand experience with the dangers of heat exposure, she fell ill and was sick for three days. “Since when do people from Pakistan get heat stroke in Boston?” she asked me, incredulous. Not only do our recalibrations get redirected at others—we turn them on ourselves.

The result is often punitive. A firm line is drawn between those who are affected by heat and those who are not, between those with “common sense” and those without, which weaponizes the evolving notion that while impacts of heat exposure may be horrid, they are still avoidable, and therefore it is your fault if you fall ill. It is an ethos of individualism that pervades American culture and our historic and ongoing treatment of those who are sick, differently-abled, or otherwise fail to survive in a landscape that is less livable for some than others.

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Last summer, my grandmother died on one of the hottest days of that year. I was sitting in a stifling subway station in Downtown Brooklyn when I got the news. For some reason, her care attendant had not turned on the air conditioner that day. I still find it hard to shake that fact.

The next morning, I woke up at 5 am and marched to a bank that funds fossil fuels. With other activists in tow, we blocked people from entering the corporate headquarters for two hours. I remember standing at an entrance with my arms locked in step with another activist, preventing employees from passing as a woman who had tried to shove me to the ground five minutes earlier screamed “IDIOTS” again and again. She’d found her classification.

In that moment, she drew a boundary. Her anger, her fear, her inconvenience were real—and mine, her screams told me, were not. My body did not belong there, neither did the cresting anxiety I felt in the heat of the morning, nor the grief I carried from the day before. And so, too, was my body a boundary, one that sought not to define but reframe what constitutes violence in the age of climate breakdown. When the whole world is tropical, the only boundary left to cross will be whether we remember one another, or whether we let the heat unmake us alone. ♦