Science

Extreme temperatures in major Latin American cities could be linked to nearly 1 million deaths

In mid-January, the southern tip of South America suffered its worst heat wave in years. In Argentina, temperatures in more than 50 cities rose above 40°C, more than 10°C warmer than the typical average temperature in cities such as Buenos Aires. The scorching heat sparked wildfires, worsened a drought, hurt agriculture, and temporarily collapsed Buenos Aires’s electrical power supply. It also killed at least 3 people, although experts estimate the true number might be much higher.

With climate change, heat waves and cold fronts are worsening and taking lives worldwide: about 5 million in the past 20 years, according to at least one study. In a new study published today in Nature Medicine, an international team of researchers estimates that almost 900,000 deaths in the years between 2002 and 2015 could be attributable to extreme temperatures alone in major Latin American cities. This is the most detailed estimate in Latin America, and the first ever for some cities.

Most studies that link extreme temperatures with mortality in cities have been done in North America, Europe, and China. “There’s relatively little locally generated knowledge that’s specific to the Global South,” says Ana Diez Roux, an epidemiologist at Drexel University who co-authored the new study. “Latin America, in particular, is a region that has not received a lot of attention.”

And the new paper has a much better representation of urban areas in Latin America than previous studies in the region, says Antonio Gasparrini, an environmental epidemiologist at the London School of Hygiene & Tropical Medicine. “So, this is already an improvement.”

To estimate how many people died from intense heat or cold, researchers with the Urban Health in Latin America project—which studies how urban environments and policies impact the health of city residents in Latin America—looked at mortality data between 2002 and 2015 from registries of 326 cities with more than 100,000 residents, in nine countries throughout Latin America. They calculated the average daily temperatures and estimated the temperature range for each city from a public data set of atmospheric conditions. If a death occurred either on the 18 hottest or the 18 coldest days that each city experienced in a typical year, they linked it to extreme temperatures. Using a statistical model, the researchers compared the risk of dying on very hot and cold days, and this risk with the risk of dying on temperate days. They found that in Latin American metropolises, nearly 6%—almost 1 million—of all deaths between those years happened on days of extreme heat and cold. They also created an interactive map with the data for individual cities (see maps, below).

When the team analyzed the specific cause of these deaths in the registries, they found—consistent with previous studies—that extreme temperatures are often linked to deaths from cardiovascular and respiratory diseases. Extreme heat makes the heart pump more blood and causes dehydration and pulmonary stress. Extreme cold, on the other hand, can make the heart pump less blood and cause hypotension and, in some cases, organ failure. The team also found older adults are especially vulnerable to extreme temperatures, with 7.5% of deaths among them correlated to extreme heat and cold during the study period. Although the numbers varied from year to year, in 2015, for instance, more than 16,000 deaths—out of nearly 855,000—among people ages 65 or older were attributable to extreme temperatures. Latin America’s aging population is projected to rise more quickly than other parts of the world—from 9% in 2020 to 19% in 2050, by some estimates.

An aging population combined with Latin America’s high urbanization (more than 80% of the population lives in cities) and worsening climate change impacts “make extreme temperatures a really alarming or dangerous hazard for Latin American cities, [particularly] in the 21st century,” says Josiah Kephart, an environmental epidemiologist at Drexel, who led the new study.

Although deaths on extremely cold days—about 785,000—were much higher than those on extremely hot days—about 103,000—overall there were more days with intense cold, which could explain this difference. But for some cities, such as Buenos Aires, Rio de Janeiro, and Mérida, heat is more deadly than cold: The researchers estimated that on very hot days, the chance of dying increases by 5.7% for every 1°C increase in temperature. “It’s very alarming how quickly the risk of mortality increases at hot temperatures by even 1°,” Kephart says.

Rosana Abrutzky, a sociologist at the University of Buenos Aires’s Gino Germani Research Institute, knows this too well. “During the summer is when the temperature changes have the strongest and most immediate impact,” she says. “There’s no quick way to escape [high] temperatures.” In a 2019 study, she and her colleagues determined that daily deaths increased by 43% during a December 2013 heat wave in Buenos Aires. About the current study, Abrutzky says getting this kind of comprehensive data is not easy. Although the regional trends—such as how vulnerable the elderly are to extreme temperatures—are valuable, no specific reasons behind the deaths can be established from this study, she adds. “Everything depends not only on the different climates, but also on the different characteristics of the population [of each city],” she said.

Latin America has high levels of inequality, Diez Roux says, which makes marginalized groups more vulnerable to health impacts from extreme temperature. For many people, she says, air conditioning and heating are a luxury.

The team is now working to untangle how certain inequalities, such as housing conditions and access to green spaces, affect deaths that happen on hot or cold days. In the coming decades, Latin America is projected to experience a substantial increase in the frequency of heat waves, so the team is also looking into temperature projections in these cities 50 years from now to estimate how these deaths will increase and which cities will be hardest hit. Since 2018, researchers—including Abrutzky—have teamed up with local agencies in Buenos Aires and the city’s meteorological service to have an early warning system for extreme temperatures, allowing citizens and health services to be prepared for casualties. In the past year, she says, they’ve been working to replicate this to other cities in the country.

Diez Roux hopes these new city-level results can empower local and national governments to put mitigation and adaptation strategies in place; many of these are the same tactics applied to mitigate climate change. “We’re hoping that making this issue visible for the region with this local information will increase awareness,” Diez Roux says, and “a sense of urgency about addressing climate change in our countries and in our cities.”

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