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We Made This Heat, Now We Cool It

We Made This Heat, Now We Cool It

Just how hot can the Earth get before our ongoing mass-extinction event hammers humans in unbearable ways? An initial estimate scientists made in the mid-1990s called for keeping the rise in global average temperature below 2C. This summer finds us approximately halfway there, and even closer to a revised safety threshold of 1.5C.

There’s another way to think about this, an angle that tends to attract experts in economics and other social sciences: Since apparently we are going to heat the world well beyond the level scientists advise, perhaps even as far as 3C, humans will simply adapt as we always have. What must be done can be done.

But an adaptation optimist needs to account for the fact that heat kills. We are pretty resilient in dry heat. My mom used to say, “It’s not the heat, it’s the humidity.” Like most folk sayings, this isn’t quite right: It’s the combination of heat and humidity that kills.

Humans evolved to dissipate body heat mostly by sweating, but when the air is extremely humid, sweat stops working. Even if you were in the shade, unclothed, with a fan blowing on you, the weather would kill you. You’d be parboiled in your own sweat, and death by heat stroke would follow. Only air conditioning could save you at that point. But you can’t always count on the power supply, especially in times of emergency. What we’ll need isn’t the air conditioning of rooms but the air conditioning of the entire planet: We will have to decarbonize the atmosphere.

There are indexes that combine heat and humidity into a single number, just as wind chill factor accounts for cold and wind to gauge their combined impact. One of these, the heat index, ought to be familiar enough from TV meteorologists and weather websites. For purposes of figuring out how much heat we can withstand, it helps to use another: wet bulb temperature, which shows when evaporative cooling becomes completely inoperative. A wet bulb reading of 35C is quickly fatal for human beings.

In a warmer world we will see this kind of heat—and this kind of death—much more often. Forty years ago, wet bulb temperatures of 33C happened four or five times per year worldwide; now they happen 25 to 30 times each year. The fatal 35C wet bulb threshold wasn’t supposed to occur with regularity until around 2050, based on projections from climate models. But some weather stations are hitting “wet bulb 35” right now. That’s the finding from a recent analysis published by Colin Raymond of NASA’s Jet Propulsion Laboratory and two colleagues, who determined through meteorological data and modeling that there are already highly vulnerable areas in the Middle East, southern Asia, equatorial Africa, South America, and the U.S. Gulf Coast.

An adaptation optimist might still assert that we can simply adjust to these fatal heat waves, and those of us living far from the equator might imagine the wet bulb extremes will mostly happen to people in the tropics. But in fact many regions are susceptible to humid heat waves, and those that aren’t won’t be able to support the 2 or 3 billion people who might try to escape the killing heat.

Easy talk of adaptation ignores the realities of biology. If we’re to avoid mass disruption and mass death, we have to decarbonize our technologies and our planet’s atmosphere as quickly as we can. This coming era of killer heat waves isn’t inevitable—at least not yet. The overriding project for civilization in this century will have to become designing, building, and paying for the rapid decarbonization of our technological base and our atmosphere. We can do that.

This is what our global civilization has to organize itself to do. We could become a carbon-negative civilization in a couple of decades. Many methods for decarbonization already exist, and what can be done must be done, because the alternative is too dire.

Getting back into that zone of livable temperatures will take a monumental effort, achieved only by deliberate coordination—full social, governmental, and business support for every action that can help forward the cause of cooling.

Two broad areas of effort will be key. The first is carbon drawdown by biological means. Changing our relationships with the Earth’s land includes agriculture and forestry, of course, but cooling also requires revising city design and wildlife management. We need to leave a good share of our landscape open to the other animals and the ecological communities that would naturally thrive there. This turns out to draw down carbon faster than anything else we can do, and it also protects us from being physically overwhelmed in heat waves.

Secondly—because this first measure, even at its best, won’t be sufficient to do the job—we’ll need to master technology-driven carbon capture, often referred to as direct air capture. This means building machines to suck carbon dioxide out of the air and store it, or else render the captured carbon for use as a building material that can replace energy-intensive concrete and steel.

This summer in Iceland, in an example of what’s to come, a startup specializing in direct air capture has teamed up with another that can safely store carbon. The main backers, ClimeWorks and Carbfix, claim the project will be able to remove 4,000 tons of CO2 from the atmosphere per year, all powered by Iceland’s abundant and clean geothermal energy. The experimental technology even looks like an array of air-conditioning vents.

We’re not doomed. The devastation we’re hurtling toward can be avoided. We will have to train ourselves, and pay ourselves, to do all these things. Because we’re in an all-hands-on-deck moment.

It’s meaningful work, so there’s no cause for despair. Meaningful work is cool.

Robinson writes science fiction in Davis, Calif. His next novel, The Ministry for the Future, will be published in October.

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