Normal Temperatures Have Lost Their Meaning

In September 2020, the United Kingdom’s Meteorological Office published a hypothetical weather forecast for a mid-July day in the year 2050. Forty degrees Celsius in London. (That’s 104 degrees Fahrenheit.) Thirty-eight in Hull (100 degrees F). Thirty-nine in Birmingham (102 degrees F). These were preposterous numbers, never before seen in U.K. weather forecasts, much less felt in reality—until last week. On Friday, the Met Office published an actual forecast for Tuesday that, as several observers noted, looked scarily similar to its 2050 projections. And today, as predicted, the U.K. smashed its previous heat record, registering a provisional reading of 40.3 degrees C, or 104.5 degrees F, in a small village near the eastern coast. From speculative fiction to nonfiction in less than two years.

When I asked Simon Lee, an atmospheric scientist at Columbia University, just how unusual this heat is, he explained that the question is, in one sense at least, all but impossible to answer. Compared with the past? Clearly unusual. In the context of our present climate? To establish the baseline we’re measuring against, Lee said, we would ideally rely on years of somewhat consistent observational data. But the climate is simply changing too rapidly. How do you ascertain what is unusual when you can’t even get a grip on what is usual? “It’s like trying to go to every restaurant in New York City—you can’t,” Lee said. “You’re never able to get to all the restaurants and say, ‘I’ve eaten at every restaurant,’ because there’s always new ones opening.” Earlier this year, the U.K.’s Met Office had to update its definition of a heat wave because climate change had rendered the old definition obsolete: Heat waves would now be so common as to have lost their meaning.

It’s not just the U.K. Now everywhere is hot. More than 100 million Americans are currently under heat advisories or warnings. In India, a record-breaking heat wave has only recently given way to the monsoon. Parts of Central Asia are still seeing temperatures as high as 115 degrees F. And the damage done by overlapping disasters doesn’t merely accrete linearly; it compounds. Over time, climate change has made these concurrent extremes more and more common, Kai Kornhuber, a climate scientist at Columbia, told me. Since the late ’70s, concurrent major heat waves have grown six times more frequent in the Northern Hemisphere, Kornhuber and several colleagues found earlier this year. “What we’re seeing now is a situation where the overall warmth of the climate is higher, which puts us intrinsically closer to those extreme-heat thresholds,” Alex Ruane, a climate scientist at NASA, told me.

There is also the possibility, Kornhuber said, that beyond simply warming the planet as a whole, climate change could be changing the way weather systems move around the globe so as to make concurrent heat waves more likely. Under one hypothesis, the rapid warming of the poles compresses the temperature gradient between the poles and the equator. This, in turn, slows the equatorial jet stream (which you can basically think of as the giant wind highway along which lots of weather travels), causing heat waves to linger longer than they otherwise would. This hypothesis, though, is just that—a hypothesis. Scientists disagree about how much, if at all, this mechanism contributes to the growing prevalence of extreme heat.

At some level, the mechanics don’t really matter. Whatever they are, the story is this: Heat waves are getting hotter and longer and more frequent, and that is very bad news indeed. For anyone who aspires to be alive for several more decades, “the simple laws of physics mean this will likely be one of the cooler summers of our lifetime,” Daniel Horton, a climate scientist at Northwestern University, told me.

As a co-author of the Intergovernmental Panel on Climate Change’s 2021 report on the physical science behind climate change, Ruane helped model exactly how this future might play out. In a scenario in which we limit warming to 1.5 degrees celsius, we could expect to see a heat wave that would have occurred once every 50 years in the late 1800s climate happen about nine times as often. That scenario is pretty much already an optimistic fantasy. In the worst-case scenario the report considered, we would see a once-every-50-years heat wave 40 out of every 50 years. It’s easy to forget, when imagining such hypothetical futures, that when the extremes of the present become the norms of the future, that also entails the emergence to new extremes. And according to the IPCC report, those new extremes could approach 10 degrees F hotter than they are at present.

To an extent, we can adapt to our warming world, but “our ability to adapt is not infinite,” Ruane said. And we are already pressing up against its limits. More than 1,700 heat-related deaths have been reported this month in Spain and Portugal alone. Runways are melting and delaying planes. Tracks are warping and delaying trains. Surgical procedures are being canceled because of overheated operating rooms. Also, sharks.

When we note the eerie resemblance between this week’s U.K. weather forecast and the hypothetical 2050 forecast published two years earlier and say that the current heat wave is a glimpse of the future, we are in a way eliding the real question. Which is: What part of the future are we glimpsing? A true outlier? Or a pretty hot summer? Or four years out of every five? “The answer,” Ruane said, “is, it depends on what we as a society choose to do.”  That could be heartening. But the way things are going, it’s not very heartening at all.