[#11] Web Bulbs, Bodies and Heat

[Excerpt from upcoming book — It’s Getting Hot in Here: Reflections of a climate hawk grappling with the inevitable]

You know we’re in trouble when ‘wet bulb temperature’ is trending ...

Imagine someone who sits in the shade, naked as the day they were born, misted with water while a fan blows air across their skin. The water sucks heat from their body as the fan maximizes evaporation. That person does no work - no walking, moving or even flipping the pages of a book. Instead, they sit quietly. They breathe, digest, just be. Their body expends energy only to keep critical systems going. An economist would never call that ‘work’, but it certainly is to a physicist: normal, baseline physiological activity creates heat.

Now imagine temperature, humidity - or both - slowly increase. There comes some combination of heat and humidity where their body can’t reject its own heat into the surrounding air. What happens next? It’s got complex physiological underpinnings, but a simple description: they die.

The technical definition of ‘wet bulb temperature’ is: adiabatic saturation – a fancy way of saying the temperature of a wet thermometer with maximum evaporation (like sweat removing heat). ?So it’s a measure of heat and humidity since more humidity means less water evaporates (with associated heat loss). Colloquially: “it’s not the heat, it’s the humidity!” As climate warning: once wet bulb temperatures hit 30C, outdoor work is impossible even with limitless water breaks. Near 32C, we can’t do much more than sit still - in the shade. Anything close to 35C and we die. Doing nothing.

I first encountered the term researching climate models for my book Waking the Frog a decade ?ago. Frustrated with the narrow probability curves that dominated late-century warming models – and eliminated the odds of catastrophic warming with no empirical basis – a few climate-savvy economists (eg the late, great Martin Weitzman) proposed alternates. ‘Fat tails’ widened temperatures distribution curves[1] to include small (but real) probabilities of mind-numbing warming of 4, 6, even 10C[2] . There aren’t many ways to express those temperatures other than yelling: ‘Mad Max’ (a lazy habit of mine). But Weitzman used wet bulb temperature to capture the absurd risks we’re taking in a simple way: at 10C of warming, most of the world becomes literally unliveable for part of the year since the wet bulb temperature will exceed 35C and “death from heat stress would ensue after about six hours of exposure” even if the person is “out of the sun, in a gale-force wind, doused with water, wearing no clothing and not working.”[3]

?

We don’t need to hit 10C to experience these conditions. We’ll see it a lot under Bad Warming. The Mideast and Africa are in most danger, but places from Houston to Delhi and Atlanta to Rome will cross these thresholds. Indeed, it’s already started. Who knew such a nerdy-cum-scientific term would become part of popular culture in 2023? Google it to find news reports across the world sounding like a university science class in thermodynamics, and surreal video of TV weather personalities struggling to explain a picture of a thermometer wrapped in wet gauze.

I can hardly imagine a more stark climate-driven class confrontation: the well-off in air-conditioned condos frustrated they can’t order Uber Eats because the delivery workers keep passing out from heat stroke. Or construction bosses in wealthy countries losing profit as timetables slip because workers drop like flies in the heat. It’s happening now: thousands of migrant workers died from heat stroke building World Cup infrastructure as ?wet bulb temperatures approached 32C[4] . Labour laws, reformed in 2007, couldn’t keep up as climate conditions advanced. The rich get air conditioning, and the poor get a hat and bottle of water.

Sure, we can move jobs inside. Maybe deliver Uber Eats by drone. And give lots of water breaks for those forced to be outside. But the onset of literally unliveable outdoor conditions is as distopian as it comes. When ‘wet bulb temperature’ becomes a meme, you’re know we’re in for a hell of a ride.

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[1] For the technically minded: Bell curves are normal distribution curves that model lots of phenomenon from exam marks to body height. It has a particular shape associated with how fast the curve drops off on either side from its peak (the ‘norm’). A Pareto curve is the same thing, but with widened ‘shoulders’ – ie, the probability of events further away from the norm are increased. No-one has any idea what shape climate sensitivity curves (warming from a doubling of atmospheric ghg) should have.

[2] Under a Pareto Curve, we have a one-in-twenty chance of hitting 10C at a ghg concentration of 800 ppm of CO2 equivalent. This is not a bet we want to make.

[3] Weitzman, Fat-Tailed Uncertainty, pg. 10.

[4] See Thousands of Migrant Workers Died in Qatar’s Extreme Heat. The World Cup Forced a Reckoning, Time Magazine, Nov 3, 2022