Heat waves are invisible. But we need to see them for what they are

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Sam Anderson is a postdoctoral research fellow at Simon Fraser University and a hydrologist at Northwest Hydraulic Consultants. He is writing a book about climate extremes in Western North America.

Heat waves are unique among natural disasters because they are invisible. They don’t have names and categories like hurricanes, nor do we quantify them with numeric scales like tornadoes. Their invisibility makes it difficult to grasp from outside of the heat’s dome: there are no satellite images like a hurricane barrelling toward an unprotected coast; there are no aftermath photos of homes razed and streets filled with debris. If we see them reported on the news, they’re usually accompanied by images of beaches and of playing in water, or by unfeeling statistics and maps painted red.

For the task of describing these disasters, we are left with a bag of exasperated adjectives that sound hyperbolic until you experience the heat yourself: jaw-dropping, eye-popping, heart-stopping. And the result is that extreme heat becomes easy to ignore, if it isn’t actively searing your skin.

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For Canadians hearing reports of the record-shattering spring heat that broiled much of the U.S. in March, it is easy to tune out and look away. Heat waves can be easy to forget, too, for the same reason, even when they leave physical scars; this summer will somehow mark five years since the unprecedented heat wave of June, 2021, killed hundreds of Canadians and burned the village of Lytton, B.C., to the ground.

But this must be a moment to stare climate change head on, and to clearly see the shape and scale of the crisis we face. We can strip heat waves of their invisibility by understanding the crucial difference between record-breaking and record-shattering heat, and by seeing how they affect water – our most valuable resource, and one of the most visible, too.

Record-breaking temperatures are a relatively normal feature of living on a planet that spins and has land, ocean and atmosphere. On-the-ground temperatures are the result of complex interactions amongst a vast and swirling sky, and so the temperature of any given day is a sample of what these interactions add up to. The longer you observe, the greater the number of conditions you are sampling, and so the harder it is for any day to break a record: There are simply a greater number of other days with which it is competing. Given time, records should be broken less frequently, and the margins by which old records are broken should shrink – fractions of a degree or less.

A shattered record is a categorically different phenomenon, and one that has distressingly become a part of the modern climatologist’s lexicon. A shattered record is one where the margins of a broken record are large – on the order of several degrees – even against a long observational backdrop. A broken record is a javelin thrown to new lengths, piercing the soil in the middle of an Olympic field; a shattered record is a javelin thrown so far that it flies beyond the field and pierces those in the crowd. It’s so far beyond any prior observation that it begs the question: How was that even possible? They’re the sign that something fundamental has changed.

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In the Western U.S., many weather stations have recorded more than a century of observations. So it is no small feat that the recent heat wave shattered just about every metric you can come up with: It produced the hottest March day ever recorded in the U.S. (with many locations even exceeding all-time highs for April, too), and set more than 1,500 temperature records across 11 states. As a climate scientist, this is the kind of weather that I watch with fear and awe, with mind-melting Lovecraftian horror rather than with a clinical eye. It makes me ask, as a 31-year-old, how I’m supposed to survive another few decades on this planet. By shattering records and not just breaking them, such heat waves reveal themselves as more than a leading signal of climate change: they tell us that the atmosphere has changed not just incrementally, but fundamentally.

Heat waves reveal themselves in water, too. They play with the phases of water like a cat with a mouse: amplifying melt, drying soils, and rerouting storms. In the Colorado River Basin, for example, what was already a record-low snowpack is undergoing rapid melt at time when the snowpack is normally still growing: from record low, to record lower, to record lowest. At the same time, heat drives evaporation from exposed soils and transpiration from plants in areas without shielding snowpack, and although such observations have not yet been published from the March heat wave, we can expect that enhanced atmospheric thirst will continue to dry out an already dry West. And finally, when a mid-March atmospheric river took aim at the west coast of North America, it was routed by the heat wave’s high-pressure ridge clockwise around the dome, and aimed directly at the southern coast of British Columbia. Flood and fry: Heat waves do it all. The U.S. heat wave may now be moving on, but its effects on water will last through the summer, with less snow and more drought on the continent than we otherwise would have.

I lived in Vancouver through the record-shattering heat wave in June, 2021, and after it ended, I wondered if the event was a one-off, or the type of thing that I was going to need to get used to if I wanted to continue building my life here. Looking now at what’s happening across the U.S., I take no comfort in knowing that the heat wave just narrowly missed my West Coast home. Heat waves have boundaries, but climate change does not; the recent heat wave does not mean that we Canadians have evaded the consequences of our fossil-fuel-filled sky. It just means that the ferocious heat that came to feast in 2021 was not satiated, and so has decided to stay. Let’s be courageous enough to look that fact in its fearsome face.