The secret to preventing killer heatwaves isn’t what you think

2nd September, 2021

In July 1995, a hot, humid, slow-moving mass of air rolled over Chicago and stayed there for a week. Roads and railway tracks buckled. Lifting bridges were hosed down to prevent thermal expansion from locking them in place. Shops sold out of air conditioners. Demand for electricity led to blackouts. Then people started to die, simply unable to cope with the humidity and the heat day after day.

There is no official estimate for the death toll, but it is often reckoned to be more than 700 people. As with Covid-19, most were elderly, but epidemiologists later estimated that the majority of those older people were not otherwise in imminent danger of death.

The disaster received far less attention than, for example, the 1989 earthquake, which killed less than a tenth as many people in San Francisco and Oakland. This is not surprising. Heat does not look impressive on television. That said, the world did take notice of the refrigerated trucks sitting in the parking lot of the Cook County medical examiner’s office. They had been volunteered by a local meatpacking firm to help cope with the overflow of bodies from the morgue.

Heat continues to be a killer. The World Health Organization estimates that, between 1998 and 2017, 166,000 people died owing to heatwaves, a total that eclipses many more photogenic natural disasters.

Extreme heat is becoming more common. Professor Peter Stott of the Met Office in the UK told me that the recent heatwave in North America, when temperatures came close to 50C in Canada, could have been expected roughly every 60,000 years in the pre-industrial climate. In the modern world, warmed by many decades of greenhouse gas emissions, it could be expected once every 15 years or so.

We are going to have to get used to scorching temperatures and smothering humidity. Which makes it all the more important to understand what happened in Chicago a quarter of a century ago. Researchers from the US Centers for Disease Control and Prevention studied the problem carefully and concluded that “those at greatest risk of dying from the heat were people with medical illnesses who were socially isolated and did not have access to air conditioning”.

That’s not wrong, but neither is it especially helpful. Why did people have no access to air conditioning? The city was full of air-conditioned spaces, many of them — such as libraries and shops — open to anyone, free of charge. And why were people so cut off, even in a crisis? As the great urban observer Jane Jacobs told the Chicago Sun-Times back then, “It took a lot of effort to make people this isolated.”

In his 2002 book Heat Wave: A Social Autopsy of Disaster in Chicago, the sociologist Eric Klinenberg went beneath the surface of the catastrophe. The CDC analysis had compared pairs of individuals, contrasting those who had died with apparently similar individuals who had not. Klinenberg compared two adjacent Chicago neighbourhoods: North Lawndale and South Lawndale.

North Lawndale had a heatwave death rate 10 times higher than South Lawndale. Why? Both neighbourhoods had plenty of poor elderly people living alone and both were overwhelmingly non-white. But in other ways they were different.

North Lawndale was depopulated, an urban desert with vacant lots. Gangs used it as a convenient place to sell drugs. “We used to sit outside all night and just talk,” said one resident. But with bullets flying, that became impossible. Big employers such as International Harvester, Sears Roebuck and Western Electric had moved away and shops had closed. People didn’t leave their apartments because they were afraid of being mugged or burgled. They weren’t used to walking to local shops — and there weren’t many local shops to walk to.

South Lawndale, by contrast, was overcrowded, but as a result it felt bustling — and safe. (The area is now known as “Little Village”.) You could step outside your door any time and there would be folk around. When the heatwave struck, elderly residents were happy to walk into an air-conditioned store nearby and hang out. They felt safe leaving an empty apartment behind. When at home they felt safe opening their doors to the people who came to check on them. In a heatwave, lively streets save lives.

Neighbourhoods can also be heatwave-prone or heatwave-resistant in more literal ways, as a recent article in Nature argues. A city block with tarmac and concrete, little shade and rapid drainage of water can be several degrees hotter than one with the shade of trees or patches of vegetation that catch water and let it evaporate. It will surprise no one that leafy, richer neighbourhoods tend to be cooler.

The effect is large. A recent study in the journal Climate found that historically “redlined” areas in US cities — mostly African-American, denied federal mortgage support in the 1930s and long marginalised afterwards — are an average of 2.6C warmer.

It is all rather depressing, but there is an opportunity too. It is inevitable that we will have to adapt to climate change, and adaptation is often thought of as an expense: vast dykes, flood barriers and weatherproofing. But if adaptation to climate change means supporting vibrant neighbourhoods, planting trees, reducing crime and encouraging local businesses, that is something we would surely want to do, regardless of what the climate holds.

Written for and first published in the Financial Times on 30 July 2021.

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