It’s one of the scariest questions facing billions of humans on a hotter planet: How many of us will die from extreme heat in the decades ahead?
Your future risk of dying from heat will be determined more than anything else by where you live and the local consequences of today’s economic inequality. That’s the conclusion of a major paper released today by the Climate Impact Lab, a research consortium that spent years mapping the relationship between temperature, income, and mortality. People in poor regions who benefit less from investment in air conditioning, protective infrastructure, and elder care will die from extreme heat at much higher rates, even compared to wealthier peers who experience similar hot temperatures.
The researchers from the Climate Impact Lab determined that the toll from future heat will be far worse than expected, with the global annual mortality rate at the end of this century rising by 73 deaths per 100,000 people solely from excess heat. That’s a death rate comparable to the 79 per 100,000 that New York State has seen from Covid-19 since January. “The mortality risks from climate change are about an order of magnitude larger than previously understood,” says Michael Greenstone, an economics professor at the University of Chicago and a co-director of the Climate Impact Lab. “I really think that shouldn’t be missed.”
The results emphasize the life-saving power of income growth that drives investment into climate adaptation. Economic development can reduce projected mortality from extreme heat at the century’s end by about 60%, according to the Climate Impact Lab, a finding that translates into the possibility of saving millions of lives.
This means we can’t understand life and death on a hotter planet without first understanding inequality.
The impact of heat on the human body is an important part of the equation. Global average temperatures are already 1° Celsius warmer than previous centuries, and many studies project a catastrophic rise of 3°C by 2100.
An average doesn’t speak to what will be a dramatically unequal experience of future heat. Parts of the world have already warmed by more than twice the global average today. That trend will leave more people vulnerable to extreme heat, which has been linked to a 50% increase in mortality risk from stroke, cardiovascular disease and pulmonary conditions. In some regions working outside for a few hours will eventually carry grave risk. With enough exposure to extreme heat and humidity, the human body suffocates in its own skin because the air is too water-logged for sweat to evaporate.
But the deadly consequences of extreme heat are shaped as much by economics as biology. Imagine two nations—one wealthy and technologically developed, the other poor and without resources—that are suffering through an identical heat wave. Climate Impact Lab set out to understand the expected difference in death risk, after accounting for economic growth and adaptation.