Some five million people die every year from exposure to abnormally hot or cold temperatures related to climate change, a number that accounts for about 9.43 percent of global deaths, according to a first-of-its-kind study.
Heat-related deaths are increasing across the world due to human-driven climate change, even as net mortality rates are dropping as a result of decreases in cold-related deaths, which are far more deadly, reports the study, which was published on Wednesday in The Lancet Planetary Health.
While previous research has assessed the impact of high and low temperatures on global death rates, the new paper tracked these trends specifically across the 21st century, a period that has experienced temperature increases of 0.26°C per decade due to human-driven climate change.
"This is the first study to get a global overview of mortality due to non-optimal temperature conditions between 2000 and 2019, the hottest period since the Pre-Industrial era,” said Yuming Guo, a professor of global environmental health and biostatistics at Monash University and head of the Monash Climate, Air Quality Research (CARE) Unit, who co-led the research, in a statement.
"Importantly, we used 43 countries' baseline data across five continents with different climates, socioeconomic and demographic conditions and differing levels of infrastructure and public health services, so the study had a large and varied sample size, unlike previous studies," he added.
By compiling this enormous dataset, Guo and his colleagues found that deaths from heat exposure have increased by 0.21 percent since 2000, while deaths from colder temperatures have decreased by 0.51 percent. This means that while more people are dying from heat, fewer people are dying from temperature-related causes than in the past overall, though the study projects that rising heat-related mortality rates will eventually surpass declining deaths from cold.
“In the long-term, climate change is expected to increase the mortality burden because hot-related mortality would be continuing to increase,” noted Guo, who co-led the research with Shanshan Li, a senior research fellow and deputy head of CARE at Monash University, and Qi Zhao, an epidemiologist at Shandong University in China.
This worrying increase in mortality due to hot weather is already evident as summer temperature records are broken each year by severe and extended heat waves. The Pacific Northwest heatwave at the end of June killed hundreds of people, and these intensely hot periods are projected to continue as summer reaches its peak temperatures in the Northern Hemisphere over the next two months. Meanwhile, the disastrous cold wave in Texas in February, which killed over 200 people, is one recent example of how climate change can also exacerbate cold-related mortality.
As with all aspects of the climate crisis, the risks are not even distributed, with three quarters of temperature-related deaths occurring in Asia (2.6 million deaths per year) and Africa (1.2 million deaths per year). By comparison, the team estimated an annual death rate of 835,000 in Europe each year, 173,600 in the United States, and 141,000 in South America.
The vast majority of deaths in every region are a result of exposure to cold, and Sub-Saharan Africa remains particularly vulnerable to high mortality from low temperatures, according to the study.
However, rising global temperatures have caused large drops in net mortality in other regions, especially Southeast Asia. Moreover, while an estimated 657,000 people in Europe die annually from exposure to cold, the continent also had the highest excess death rate from heat exposure of any region in the study: roughly 178,700 deaths per year due to high temperatures.
The results provide a new and expanded view of how climate change is affecting mortality rates around the globe, which is essential information for researchers and activists hoping to mitigate its worst effects in the coming decades.