Editorial NexoScience
The deadliest weather disaster of this century in Brazil came with no emergency declaration and barely a trace in the news. It killed more than twenty times as many people in the country’s largest urban areas as landslides did nationwide over the same years, and the official surveillance system never registered a single one of the worst episodes. That is the picture drawn by an analysis of death records and temperature series published in PLOS ONE.
The toll was counted from death certificates, not from models. The researchers compared the deaths registered during each heat wave with deaths in equivalent periods of the same time of year without one, across the fourteen most populous metropolitan regions of Brazil, home to roughly one in three Brazilians. Between 2000 and 2018 that gap added up to 48,075 excess deaths, more than twenty times the country’s landslide deaths over the same period. Put another way, the population of a mid sized Brazilian city died of heat across those years without any of it entering the ledger of catastrophes.
The deadliest heat waves were not the most extreme ones. The events with the largest relative jump in mortality in each metropolitan region were mostly short, often under a week, and fell into the mildest category of the index the study used. In all but three of those regions, the worst event on record happened in the final five years analysed, and most of them arrived less than a month after a previous heat wave.
Old age multiplied the risk far beyond its weight in ordinary mortality. People over sixty five accounted for between 75 and 94 percent of the excess deaths, while that same group makes up less than 60 percent of all natural deaths registered in those cities. Women came out worse than men in every metropolitan region, with the widest gaps in places such as Porto Alegre, São Paulo and Rio de Janeiro.
Skin colour and years of schooling changed the odds more than the map did. Among people over sixty five, mortality during heat waves rose more for those with the least schooling in the cities where the comparison held up statistically, among them Belém, Recife, São Paulo and Rio de Janeiro, and in Recife the excess mortality of the least educated men was nearly double that of the most educated. In Cuiabá, the rise in deaths among women went from 1.60 times the expected number among white women to 3.25 times among Black and brown women. In none of the fourteen regions did the increase among white people exceed the increase among Black and brown people. The authors name that pattern environmental racism, the concentration of environmental harm on the groups already worst served by housing, income and health care.
Heat does not only stop hearts. Circulatory diseases, respiratory diseases and cancers together accounted for roughly half to two thirds of the excess deaths, depending on the city. But the sharpest relative increases showed up in conditions that almost never appear in a heat advisory, such as diseases of the skin, of the nervous system and of the genitourinary tract.
The system meant to catch this saw nothing. The team ran the World Health Organization’s event based surveillance tool over the same years, searching news and social media for heat related signals in Brazil. It returned only a few dozen mentions, none before 2014, and not one of them coincided with the heat waves that actually drove mortality up. Extreme heat, the authors write, remains “a neglected disaster in Brazil”.
What the study can show, and what it cannot. This is an observational analysis of administrative records, mortality registries on one side and weather stations on the other, not an experiment, so it establishes an association between heat waves and deaths rather than proving that each of those deaths was caused by heat. The authors list the limits themselves. A single weather station stands in for each metropolitan region, the death registry carries few socioeconomic variables, and the analysis includes no delayed effect even though mortality keeps rising for days after an episode ends, which they say makes the real toll probably larger than the one they publish. They also cannot separate the effect of heat from simultaneous droughts, pollution episodes or dengue outbreaks, and the fourteen regions studied cover about a third of the population, heavily weighted towards the southeast, so the results should not be stretched to the whole country.
The fix the authors propose is not only meteorological. They argue that warning systems in Brazil need to be rebuilt around the events that actually kill there, short and unspectacular heat spells rather than the long severe ones the classification was designed for, and that the most effective heat policy may be the least climatic one: stronger primary health care and narrower gaps in income, education and race.
The study, Twenty-first-century demographic and social inequalities of heat-related deaths in Brazilian urban areas, was published by Djacinto Monteiro dos Santos, Renata Libonati, Beatriz N. Garcia et al. in PLOS ONE. DOI: 10.1371/journal.pone.0295766.
