Abnormal hot and cold temperatures account for more than 5 million excess deaths a year across the world, according to a new study – the largest of its kind to date on the link between global climate and mortality rates.
The study looked at "non-optimal ambient temperatures", referring to exposure to abnormal hot and cold temperatures above and below an accepted range. These ranges and mortality rates were localized for each of the 750 locations around the globe studied to estimate additional deaths.
Mortality and temperature data was analyzed across the years 2000 to 2019, with global temperatures shifting upwards by an average of 0.26 degrees Celsius per decade across that time, and models used to extrapolate the figures.
"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," says environmental epidemiologist Yuming Guo from Monash University in Australia.
"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."
The statistics from the study make for grim reading, with 9.43 percent of global deaths attributed to cold and hot temperatures. A previous study using a less comprehensive dataset put that figure at 7.71 percent.
Right now, around 9 out of 10 of these excess deaths are due to the cold, but that will change as the planet warms up – and we also know global warming leads to spells of extreme cold as well as extreme heat.
Asia and Africa carried the heaviest burden of cold-related deaths, with 2.4 million and 1.18 million deaths respectively every year, on average.
When it comes to heat-related deaths, the highest figures came from Asia with 224,000, and Europe with 178,700. Europe was the only continent where deaths linked to both cold and heat were higher than the global average.
Overall, climate-related mortality went down over the study period, but the trends are worrying. Deaths linked to the cold dropped 0.51 percent from 2000 to 2019, while deaths related to the heat rose 0.21 percent.
To put the statistics another way, we're talking about 74 excess deaths for every 100,000 people across the world. With deaths related to non-optimal temperatures currently one of the top 10 causes of mortality worldwide, this is already a major problem.
It's not just mortality rates that rising temperatures can affect. As the planet heats up we're going to see certain areas become inhospitable or useless for growing crops, while the animals we share Earth with are also under severe threat too.
On the positive side, having more data and better estimates on the impacts of climate change can only be helpful: by making significant changes across everything from government policies to individual behaviors, we might be able to get closer to whatever the best-case scenario looks like.
"Because of the inevitability of climate change, it is urgently important to provide a global view of the relevant mortality burden and to push and develop intergovernmental strategies against the health impacts of temperature events," the researchers write.
The research has been published in The Lancet Planetary Health.