The travel writer Bill Bryson once said the most striking thing about the British weather is that “there isn’t very much of it.” No tornadoes, no monsoons, virtually no raging blizzards. Britain was a land where you did not need air conditioning, where you could wear the same type of clothing every day of the year, where you would not perish unless you went “walking up Ben Nevis in carpet slippers in February”, the Iowa-born author wrote.
We Britons didn’t see ourselves as having a Goldilocks climate. We complained daily about the weather. To be fair, we lived with the knowledge that it would rain on whatever outdoor occasion we held dear. But Bryson was right. Britain could be a nation of gardeners, partly because it was never too dry or too cold to grow things.
Heat — real heat, the type that forced you to cross the street for shade or to keep your dog indoors — was something foreign. It was associated with places we had conquered, as colonisers or tourists. As Rudyard Kipling wrote in a short story about Lahore: “The heat in the built-in street is fearful. Inside the shops it must be almost unendurable.” In EM Forster’s A Passage to India, a British expat is “invaded” by the heat; the air feels “like a warm bath into which hotter water is trickling constantly”.
But as this summer came to a close, Britons’ sense of what was normal changed. For three months, heat was a regular curse, not an occasional blessing. Our green and pleasant land turned yellow and unpleasant. It has been England’s warmest summer on record (tied with 2018), featuring its highest ever temperature. For decades, if not centuries, the British mocked the Spanish siesta. Now, with our summers turning Mediterranean, we may learn to crave the afternoon nap.
The implications didn’t dawn immediately. As Britain teetered on the verge of its first recorded 40C (104F) day — nearly double the average maximum for July — then-deputy prime minister Dominic Raab shrugged, “We ought to enjoy the sunshine.” After the Met Office issued its first “red warning” for exceptional heat, TV presenter Jeremy Clarkson tweeted: “It’s very hot in the south of France but so far as I know, there’s no DefCon 8 level 3 killer death heatwave warning in place.” The Daily Mail mocked health fears: “Sunny day snowflake Britain had a meltdown,” it thundered on July 19, praising Prince Charles (as he was then) for wearing a jacket and tie.
Reality came at the newspaper fast: the next day, after parts of London had burst into flames, the Mail’s front page lamented: “Nightmare of the wildfires”. It turns out that the melting point of a stiff upper lip is about 40C. The satirical website The Beaverton summed up our distress: “British Empire begs Sun to set on it.”
Like many Britons, I found that the past summer was the first time that heat played a major factor in my scheduling. It was too hot to meet up with friends in the park. It was too hot to play tennis. It was too hot to work in my (un-air conditioned) home, yet also too hot apparently for the train to take me to the office given the chance of the tracks buckling. I never particularly wanted to live in a hot country, but I seemed to have ended up in one. As I dripped my way around north London, a flyer from the British campaign group Just Stop Oil merrily warned: “40C is just the beginning.”
The UK’s discomfort is mild compared with the challenges faced by other regions as the climate warms. In many places, record heat is throwing old certainties into question. Californians, who thought they had the perfect climate for outdoor living, faced devastating wildfires and narrowly avoided electricity blackouts in recent weeks. Ethiopian nomads, who long lived near the limits of possibility, find themselves pushed to the precipice. A meme, adapted from The Simpsons, is again doing the rounds: “This is the hottest summer of my life,” says Bart. “This is the coldest summer of the rest of your life,” corrects Homer. We have changed the temperature. How will it change us?
At Brunel University in west London, Pascale Kippelen asks a young woman to go into a 3-metre cubed chamber and walk for an hour on a gently inclined treadmill. The chamber looks like the child of a Portakabin and a sauna: it is heated to 35C, and Kippelen, a respiratory physiologist, wants to use it to examine what happens to our breathing in hot conditions.
At a comfortable temperature, using just over half their maximum oxygen intake, a person will typically reach a steady rhythm of breathing after a few minutes. But here, in the heated chamber, the young woman continues to take more and more breaths. This is less logical than it sounds. Intensified breathing does not help humans get rid of excess heat. It does, however, remove carbon dioxide from the body, and the resulting change in the blood may cause dizziness. “We don’t know what the body is trying to do,” says Kippelen. Breathing problems are one of the major causes of death from heat.
Kippelen wants to understand why older women are more likely than older men to die from heat. Much laboratory research on how it affects the body has been done on men; one reason is that the menstrual cycle was assumed to complicate results from women, she says. Our knowledge about how heat affects the body comes partly from studies like Kippelen’s, and partly from large-scale epidemiological analysis. What is clear is that a brief period of heat is not the problem. Many people find saunas refreshing. (At the 2010 World Sauna Championships, one of the finalists died after six minutes of 110C heat, but the cause of death was listed as burns derived from the sauna’s humidity. The event has not been held since.)
The problem is the accumulation of heat in the body. Our proteins work in a very narrow range of temperature, beyond which they lose their shape, says Abderrezak Bouchama, an expert on heat at Saudi Arabia’s King Abdullah International Medical Research Center. Humans maintain their core body temperature around 37C; our skin is cooler, at 33-35C. To avoid overheating, our blood transfers heat to the skin, where it diffuses. When the air is hotter than the skin, humans can still cool by producing sweat, which takes heat away as it evaporates. Humans can sweat up to 20 litres a day, each litre taking away 580 calories of energy when the air is dry.
When humidity is low, sweating works. But when heat and humidity are both high, the body cannot keep losing heat through sweat. One way of measuring risk is the “wet bulb temperature”: a combination of heat and humidity that indicates a body’s evaporative capacity. Thermodynamics suggests that humans cannot survive in areas where the wet bulb temperature exceeds 35C for several hours. That threshold, long seen as theoretical, has now been exceeded briefly in places including the Gulf. Within decades, parts of the world, including heavily populated western China and some cities in Australia, could be unlivable.
When the body is no longer able to regulate its temperature, heat exhaustion and, more seriously, heatstroke, can strike. One sufferer describes heat exhaustion feeling “as if your whole body is made from very thin, brittle glass”. Heatstroke, where the body reaches 40C and blood is diverted from key organs, can kill. “One of the first symptoms of heatstroke is that you get confused. Being confused doesn’t necessarily tell you you’re getting into trouble with the heat,” says Kristie Ebi, professor of global health at the University of Washington. “Nobody thinks they are at risk.” Although most people survive, some may suffer enduring effects. The few studies that exist conclude that “almost a third of heatstroke survivors will have long-term brain damage”, says Bouchama.
Even when it is possible, regulating heat puts our bodies under strain: more blood flows to the skin, rather than other organs. For athletes, this leads to reduced performance. For those with cardiac problems, the strain can be fatal. Older people, who are particularly at risk from heart and lung problems, also have a reduced sensation of thirst, so risk dehydration. The 2003 European heatwave — until this year the hottest on record, with wet bulb temperatures of 28C — caused more than 70,000 excess deaths, mainly people aged 65 and over. Among pregnant women, heatwaves are associated with a 16 per cent rise in the chance of preterm birth.
Highest recorded temperature in the UK, July 2022, Coningsby, Lincolnshire
Hotter temperatures seem to also affect mental health and cause an increase in suicides. Hospital admissions in 1993 and 2006 for mental and behavioural disorders in Adelaide, Australia, rose when temperatures went above 26.7C. A study last month showed the number of hateful tweets increased on hot days (and on very cold days). Hot nights lead to poorer sleep, which is detrimental to our health in almost every way. “We are designed to shed heat from the body core at night,” says Colin Espie, professor of sleep medicine at the University of Oxford. This is a particular problem in cities, where the urban heat island effect means heat is absorbed by buildings and roads during the day, then released at night.
Our cognitive abilities seem to falter in the heat too. A study in Iran found that hospitalisations from motorcycle crashes increased during heatwaves. Overall, around one in 10 hospitalisations from motorcycle crashes were attributed to extreme cold or heat. “Being exposed to heat for long periods probably affects our ability to drive,” says Antonio Gasparrini, who co-authored the study.
Hot summers are associated with a rise in violent crime (though when it gets really hot, violence may go down) and a fall in productivity. In one of the few controlled studies of labour performance, seven male volunteers were confined to a Slovenian hotel for 10 days. The temperature was set at up to 35.4C to simulate the 2003 Paris heatwave. The men were given the task of inspecting circuit boards. As the heat kicked in, they made 35 per cent more errors and took more toilet breaks. Performance improved a little as they acclimatised.
For ethical reasons, the participants were young and healthy. “We don’t know what would have happened with older, obese people,” says Leonidas Ioannou, one of the researchers. In another study, grape pickers in Cyprus were filmed, under the pretence of a documentary. When the air temperature went much above 25C (or much below 10C) productivity fell substantially. “Fifteen degrees is the optimum temperature for someone to work, at least in agriculture,” says Ioannou.
In the US, only 700 deaths a year are attributed to heat, as are about 3,400 workplace injuries and illnesses requiring days off work. But both of these figures are seen as large underestimates. “When somebody dies from heat, it’s very hard to diagnose,” says Ioannou. As the Global Heat Health Information Network, a group of scientists and policymakers, warns: “Extreme heat is an invisible disaster.”
One morning in mid-August, Ryan, a fit Londoner in his late forties, went for a routine gym session. He then hit some golf balls on the driving range. The air temperature was in the high twenties. Out of caution, Ryan (not his real name) stayed in the shade and drank two litres of water.
He noticed his golf game was not going well. On the way home, he found himself in a “near-fury”, getting worked up about the quality of his shots. It was unusual, but he pressed on to the hairdresser. By the time he came out, he had stomach cramps and was struggling to walk. The air temperature was now 34C. “Is this the heat?” he asked himself.
Ryan bought a can of 7UP from a shop, but had to force himself to drink even half. He shuffled home so erratically that he worried that anyone watching would assume he was drunk. Back in his flat, he felt close to throwing up. He couldn’t drink. He recoiled from the cold water in the shower. Even after taking a sleeping pill, he struggled to sleep. Around 5am, he woke up convinced his bed was shaking. He logged on to an online earthquake map, waiting for the tremor to show up. It never did, because it existed only in his body. Looking back, his behaviour that day “just seems surreal.” He now believes he was suffering from heat exhaustion, and that his reaction may have been exacerbated by his ADHD medication, which can raise core body temperature.
Because of differences in humidity, underlying health conditions and the way our bodies adapt to heat over time, it is possible for some people to play golf happily in 46C in Saudi Arabia (as Bouchama does), but for others to suffer heat exhaustion at 34C in London. The real implications of hotter summers in Britain will depend on how willing we are to change our ways.
The idea that climate could shape who we are dates back at least as far back as the fifth century BC and includes some fundamentally racist tropes. Hippocrates, the father of medicine, argued that people from Asia were “more gentle and affectionate”, because of their milder climates. Centuries later, the French philosopher Montesquieu suggested that, because the cold quickened blood flow, people in cold regions were more suited to war, whereas those in hot climates were more suited to philosophy, hence the ancient Greeks.
Montesquieu retained a place for free will, says Sara Miglietti, a senior lecturer at the Warburg Institute. His driving idea was that humans could find forms of government that worked for different climates. Those in hot climates were more prone to allow despots to rise, he argued, whereas those in cold climates were more likely to guard their liberty, hence England’s curbed monarchy.
When European colonialists expanded across the globe in the 19th century, some thinkers took an even uglier stance: they wove together racial and environmental differences and argued that climate was destiny. The perceived “backwardness” of colonised people was explained in part by their climate, which was said to induce laziness. One persistent idea was that temperate regions required societies to plan for winter, whereas people in the tropics could live from the land throughout the year. “The whole idea that Europeans had a responsibility for the tropical world was frequently attributed to climate,” says David Livingstone, a geographer at Queen’s University Belfast.
Deaths per year in the US that are attributed to heat, as are about 3,400 workplace injuries and illnesses requiring days off work. Both figures are seen as large underestimates
Climate determinism deservedly fell into disrepute in the mid-20th century, and Livingstone is wary of what he sees as attempts to resurrect it. But increasing evidence does show that climate shapes human societies. A 2015 Nature paper found that economic productivity was optimal at an average temperature of 13C. Although the US had long benefited from roughly that temperature, its average over the past decade, weighted for population, has been 14C. The three co-authors are currently updating the results. “If anything, [the effect] appears to be stronger if you add another nine years of GDP and temperature data,” says one, Marshall Burke, an associate professor at Stanford University.
There is scepticism that temperature can explain large chunks of GDP growth, and Burke’s research does not disentangle temperature itself from associated climatic changes such as fires and flooding. But he insists his findings are “consistent with the things you see going on today”. As we spoke over video in mid-August, factories in south-west China were closed because a heatwave had led to a shortage of electricity for air conditioning and fans.
When Britain hit 40C, it felt semi-apocalyptic. As summer wore on, I found myself a little less bothered. Forecasts of temperatures in the mid-thirties no longer filled me with foreboding. Research has found that individuals do adapt. Firefighters’ tolerance of heat increases in the fire season. Sports scientists now consider about 10 days of heat exposure necessary for some form of physiological acclimatisation. (In contrast, acclimatising to the cold can take years.) People who have adjusted to heat sweat sooner, sweat more and sweat out fewer electrolytes, of the type that energy drinks seek to replace. This adaptation can be retained if a person has heat exposure every three to four days, a strategy that some northern hemisphere athletes adopt.
Societies adapt too. In much of Europe, the US, Japan and Australia, the impact of heat on health has actually been falling in recent decades. High temperatures in 2006 in Spain, for example, raised the risk of death by less than in 1993. Mediterranean cities, which are more likely to have put plans in place against the heat, seem to have reduced mortality faster than northern European cities.
In India and Pakistan, where heat records were broken in April, the death toll appears lower than expected (although the data are partial and provisional). One suggested explanation is that, faced with dramatic warnings about the heat, locals took breaks in outdoor work and drank more water. France’s heatwave this summer has been linked to 11,000 excess deaths, slightly below the 15,000 recorded in August 2003, although still showing that national heat planning is “dangerously insufficient”, says Bouchama.
“Almost all heat-related deaths are preventable deaths,” says the University of Washington’s Ebi. Access to water and shade are key. The medical journal The Lancet recommends cooling techniques for extreme heat including electric fans, spraying yourself with water and soaking your clothes in water every hour, which can allow evaporative heat loss without sweating.
In Phoenix, the hottest big city in the US, residents are used to working round high temperatures. “At 4am, the hiking trails will be filled with people with lights to get their hike in,” says Jennifer Vanos, an assistant professor at Arizona State University. Preparing for unprecedented temperatures is still hard. A large proportion of reported heat-related deaths in Phoenix and Las Vegas took place among the cities’ homeless population. When a “heat dome” trapped heat over the Pacific north-west last year, authorities put people with heatstroke in body bags filled with water and ice. It was effective, but the authorities nearly ran out of ice. Another plan in Portland was for people to reach cooling centres by light rail, but the light rail system buckled under the heat.
Adaptations can’t prevent the economic hit. In what may have been a world first, Cyprus introduced a legal maximum temperature for work, of 32.2C wet bulb globe temperature, an index that includes air temperature, humidity, solar radiation and wind speed. London exceeded this threshold on two days in July. If London had the same rules as Cyprus, outdoor work would have come to a halt. Instead UK legislation simply says that hot temperatures for work should be “reasonable”, an attempt to allow work in places such as restaurant kitchens to continue.
This summer it was left for individual employers to define what this meant. Royal Mail told its workers not to deliver the post in temperatures above 35C, but construction work continued. After the hot summer of 2021, Joe Biden directed the federal safety agency to draft heat rules for US workers, but the initiative faces industry opposition. One employer to take heat seriously is the military. “Somewhere over 90 per cent of the funding of all research into heat and the human body in the US has come from the American military,” says Douglas Casa, a professor at the University of Connecticut.
In Britain, as across Europe, people spend at least 90 per cent of their time indoors. The easiest way to adapt to the heat would be through air conditioning. One study concluded that increased deaths from hot days fell three-quarters in the US in the 20th-century — a trend explained entirely by the spread of air conditioning after 1960. AC tamed the American west. As of 2007, only 2 per cent of people in the UK and 5 per cent in France had air conditioning, compared with 38 per cent in Spain.
Air conditioning fixes many of the problems of heat, but not all of them. The US has widespread AC, and “we’re absolutely not immune to climate effects,” says Stanford’s Burke. Many households overheat even though they have AC available; one possible explanation is that the running costs are prohibitive. Burke’s research says that AC does not appear to affect the suicide rate. Nor does it nullify the effect on productivity, as he himself experiences at Stanford. “Even when the AC is working, I’m hot for hours after biking into work. We’re not saying productivity goes to zero. It goes down by a few percentage points, but aggregate that over all the workers in an economy and you see . . . effects that are quite large.”
Moreover AC comes at a huge cost. It accounts for nearly one-third of US electricity use in peak times. It uses so much energy that it worsens the climate problem it seeks to address. The units also generate so much heat that they warm up cities. Paris could be up to 2C warmer at night if AC use doubled.
Stan Cox, a researcher at the Land Institute in Kansas, is an AC objector. He sighs at nearby houses that almost never open their windows to take advantage of natural cooling. “They either have heat or air conditioning on almost all year round.” Cox argues that rich countries should emphasise fans, better ventilation, siestas, less formal dress codes and “month-long closings” in summer. Green roofs, made of grass or even crops, could help cool cities. His own house has AC; he turns it on a couple of days of year, partly to check it still works. In his vision, AC should be focused on hospitals and cooling centres for vulnerable people. “I’m not saying that we shouldn’t have air con. I’m saying that we should be reducing our dependence on it,” he tells me, while conceding: “I haven’t really convinced a large number of people.”
Given theories of how temperate climates created more prepared societies, the irony is that Britain’s moderate climate has meant we haven’t had to prepare for very much. The Victorians, insisting on their conservative clothing, were almost comically maladapted to the climates of the lands they ruled. “In their tropical possessions [they] must have been fearfully hot and sticky,” the historian Jan Morris wrote.
We have moved on from Victorian dress codes, but not from their building techniques. Our homes are the worst insulated in Europe. They don’t have cooling features like the exterior shutters common in the Mediterranean. When the heat struck this summer, many Britons opened their windows, when it would have been better to close the curtains. Now that the weather has cooled, how many of us are preparing for the next heatwave?
Changing our approach to heat will take more than one summer. We are still inclined to compare our air temperatures with those in the Med, not realising that because our humidity is higher, the combined effect is stronger. Perhaps in 20 years, small talk about the weather will be newly sophisticated, featuring the wet bulb temperature, combining heat and humidity. Perhaps we will redesign our homes, cities and our schedules. Or perhaps we will muddle on, shaking our fists at the lack of clouds.
By the end of this summer, the consensus among people I spoke to in London was that it had been hot enough. We are not boiling frogs, oblivious to our fate. This year will be remembered as the end of an era in Britain, due to the passing of Elizabeth II. But the heatwave that preceded her death also marked the end of an era of moderate climate that seemed to sum up our moderate national character. We complained for years about our unreliable, unremarkable weather. One day not far from now, we will want it back.
Henry Mance is the FT’s chief features writer
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