Nearly 1 million deaths in Latin America thought to be linked to extreme temperatures in major cities

In mid-January, the southern tip of South America was hit by the worst heat wave in years. In Argentina, temperatures rose above 40 degrees Celsius in more than 50 cities, more than 10 degrees Celsius above typical average temperatures in cities such as Buenos Aires. The searing heat sparked wildfires, exacerbated drought, damaged agriculture and temporarily crippled Buenos Aires’ electricity supply. It also killed at least three people, although experts estimate the true number could be much higher.

In a new study published today in Nature Medicine, an international team of researchers estimates that extreme temperatures in major Latin American cities alone could have killed nearly 900,000 people between 2002 and 2015. This is the most detailed estimate for Latin America and the first of its kind for some cities. To estimate how many people died from the heat or cold, researchers from the Latin American Urban Health Project looked at death data from 2002 to 2015 from death registries in 326 cities with more than 100,000 residents in nine countries throughout Latin America.

They calculated average daily temperatures and estimated the temperature range for each city from a public dataset of atmospheric conditions. They linked each city to temperature extremes if the death occurred during the hottest 18 days of the year or the coldest 18 days of the year. Using a statistical model, the researchers compared the risk of death on very hot and very cold days, and that risk with the risk of death on temperate days. They found that nearly 6 percent, nearly 1 million, of all deaths in Latin American metropolitan areas occurred on very hot and very cold days.

When the team analyzed the registry for specific causes of these deaths, they found that extreme temperatures were often associated with deaths from cardiovascular and respiratory disease. Extreme heat causes the heart to pump more blood and leads to dehydration and lung stress. Extreme cold, on the other hand, causes the heart to pump less blood, leading to low blood pressure and, in some cases, organ failure. The team also found that older adults are particularly vulnerable to temperature extremes, with 7.5 percent of their deaths during the study period linked to extreme heat and cold. While the numbers vary from year to year, in 2015, for example, more than 16,000 deaths among people aged 65 or older were caused by extreme temperatures, and that number was closer to 855,000.

An aging population combined with Latin America’s high level of urbanization, with more than 80 percent of the population living in cities, and the worsening effects of climate change make extreme temperatures a truly alarming or dangerous hazard in Latin American cities.