Most people in reasonable health could probably complete a 100m run without serious ill effects. However, get them to jog non-stop for 24 hours and they might be in serious danger.
That is a useful way to think about how urbanization on our rapidly warming planet is risking the well-being of billions of people.
We are used to measuring dangerous heatwaves in terms of daytime highs, such as the scorching 48.2°C in a town in India’s Uttar Pradesh province last month. We should probably be more worried about the 32.5°C nighttime low in Delhi the following week, though. The sprint of one sweltering afternoon is survivable for most people. The marathon of days on end with no nighttime respite can be fatal.
Illustration: Louise Ting
Scientists are only just starting to understand this phenomenon, and data on the subject is still sparse. However, it is all pointing in one direction. A 2023 study of 25 million deaths in Japan between 1973 and 2015 found that mortality was as much as 10 percent higher on hot nights, even after controlling for daytime heat. Another found that such conditions raised the risk of death in parts of Switzerland by as much as a third. The same effects have since been observed in the US and 28 East Asian cities. When daytime and nighttime heatwaves coincide, leaving no opportunity to cool down, the effects could be even worse.
The comparison with endurance athletes is not a flippant one. The toll on the body of heat and exercise is quite similar: sweating increases, the skin flushes, blood vessels dilate, the heart beats faster and dehydration accelerates as our systems work to dump excess internal warmth into the atmosphere.
Like an endurance athlete deprived of recovery time, a person exposed to constant high temperatures without the opportunity to cool off during sleep finds their reserves run down, day after day. As the cardiovascular system weakens, the chances of stroke or heart attack rise markedly.
The risk is greatest in the burgeoning megacities of South Asia, Southeast Asia and Africa, where urban populations are set to grow by about a billion people over the coming decades.
In the tropics and hot subtropics, overnight temperatures are already high and set to get higher. Worse still, cities are growing fastest where incomes are lowest. New housing is not going to be built to the best standards of well-ventilated, sun-shaded passive cooling, let alone come with air conditioners installed.
Take India’s Ahmedabad, where one notorious 2010 heatwave killed at least 1,300 people. The city has pioneered painting roofs white, a cheap technique that can lower indoor temperatures several degrees Celsius by reflecting the sun’s rays away. However, even that simple expedient only appears to have been implemented on a minority of roofs.
Worse still is the way that urbanization itself is exacerbating the problem. Cities in the developing world typically expand by absorbing neighboring farmland: felling trees, filling in wetlands and paving soil and then progressively building over even the small pockets of nature that remain. Bengaluru was once famed for its lakes and water tanks, essential infrastructure for millennia in Indian cities that can go through months without rain. Since the 1970s, about 80 percent have disappeared, to be replaced by stadiums and bus terminals. Nowadays, as much as a quarter of the population depends on water tankers to meet their daily needs.
That process eliminates areas that can act as temperature regulators and replaces them with concrete and asphalt. These hard surfaces suck up solar radiation during the day and then act as immense radiators overnight, flooding homes and streets with heat just when people need a reprieve.
Air conditioners fix the problem for those who can afford them, but dump further excess warmth on those who cannot. In India, the unfortunate latter group comprises about 90 percent of the population.
It is not too late to mitigate the problem. The greening of global cities has been going on since the 19th century, when London, Paris and New York made building city parks and tree-lined boulevards fundamental elements of urban development. More recently, Curitiba in Brazil and Shenzhen in China made parklands central to their development plans, while Medellin in Colombia, Seoul and Singapore have managed to claw back green space from already built-up urban fabric.
Doing the same to the next wave of megacities is going to require levels of civic ambition that are all too rare in emerging Asia and Africa, however.
Delhi, the largest city in the most populous country, cannot even protect its 30 million people from choking pollution caused directly by human activity in and around the city itself. What hope is there that the same politicians would tackle the more insidious threat from a whole planet dumping carbon dioxide into the atmosphere? If you think of the future of night in the city, do not think of peace. Think instead of sweats, sleeplessness and a racing heart rate.
David Fickling is a Bloomberg Opinion columnist covering climate change and energy. Previously, he worked for Bloomberg News, the Wall Street Journal and the Financial Times. This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.
The White House’s decision to take a 9.9 percent stake in Intel Corp is looking like very shrewd business indeed. Since the government bought in at US$20.47 a share last August, the US chipmaker’s surging stock price has delivered the US a US$43 billion return. One of the reasons the investment has so far proved so sound is that the White House has made sure of it. According to The Wall Street Journal, Howard personally pushed deals on Intel’s behalf with some of the most lucrative clients imaginable. They include Nvidia Corp, the company at the heart of the AI
A single photograph can cut through a lot of noise, but it can also be used to misrepresent the truth. At the very least, it can concentrate the mind on something that requires further investigation. On Monday last week, Ma Ying-jeou Foundation CEO Tai Hsia-ling (戴遐齡) and former National Security Council secretary-general King Pu-tsung (金溥聰) held a news conference in which they showed a photograph of former foundation CEO Hsiao Hsu-tsen (蕭旭岑), now Chinese Nationalist Party (KMT) deputy chairman. In the image Hsiao is seated next to Xiamen Taiwan Businessmen Association chairman Han Ying-huan (韓螢煥). The two men were holding
I first met Professor Ray Jiing (井迎瑞) as a film and documentary student at Shih Hsin University’s (SHU) Department of Radio Television and Film in 1988. The following year, he went on to become the director of the Chinese Taipei Film Archive — forerunner of the Taiwan Film and Audiovisual Institute (TFAI). Over his eight-year tenure, Jiing rescued and restored over 200 classic Taiwanese films. In 1997, he established the Graduate Institute of Studies in Documentary and Film Archiving at Tainan National University of the Arts (TNNUA), and I joined the program in his third cohort of students. Beyond a
A recent report concerning a student who is suing his teacher posed the question in its headline: Does failing a student in two subjects constitute bullying? The college student in Chiayi County apparently sought NT$2 million (US$63,603) in state compensation, but a court dismissed the case. The first reaction of many might have been to ask: What has happened to students nowadays? Some say that teachers have lost their authority, while others say students are overindulged. Some even start reminiscing over the days when “whatever the teacher says goes.” However, the real issue might be overlooked if emotional reactions like that are the
RSS