If the world does not curb the rate at which it spews out climate-warming greenhouse gases, the death toll from extreme heat could nearly meet the current death rate of all infectious diseases combined, according to a new study from Climate Impact Lab, published by the National Bureau of Economic Research on Monday.
Heat waves are the deadliest form of extreme weather on the planet. Yet because individual deaths are infrequently attributed to surging temperatures, their impact is far less widely recognized than that of hurricanes or tornadoes.
To better illuminate the relationship between temperature and mortality, the researchers distilled 399 million death records from 41 countries, accounting for 55 percent of the global population.
The researchers found that death tolls due to the direct effects of high temperatures, including heat stress or heat stroke, account for only a small portion of heat-related fatalities. A larger portion comes from indirect impacts, such as increased heart attacks amongst people who already have underlying cardiovascular issues.
“People who are older and have underlying conditions are very susceptible to these - your body starts pumping more blood around, trying to stay cool and it puts extra stress on your system,” Amir Jina, environmental and development economist at the University of Chicago and co-author of the study, told Earther in an email. “It’s these ‘indirect’ deaths that we can only really observe and attribute after the fact when looking carefully at the data and controlling for all the confounders with statistical models.”
Based on their studies of extreme heat’s effects on mortality rates, the researchers found that if world leaders do nothing to curb greenhouse gas emissions (a scenario known as RCP8.5), heatwaves will kill an additional 73 people per 100,000 by 2100, compared to a world with no additional warming. That’s nearly the same number of fatalities as those caused by all infectious diseases—including HIV, malaria, and yellow fever—combined.
As the world warms, the impacts will be felt disproportionately. The researchers expect that populations in the world’s warmest regions of the global south will see the highest death tolls. In those areas, such as Bangladesh, Pakistan, and Sudan, the authors found the mortality rate could exceed 200 deaths per 100,000. That’s not only because those regions are already hot—it’s also because they’re poorer.
“Economic development is really crucial—wealthier locations are much less affected by these impacts in the future,” Jina said. “Being richer clearly helps - people are able to invest in better infrastructure or technologies like air conditioning.”
A major factor in individual nations’ ability to prevent these deaths will be their capacity to invest in adaptation measures, such as building cooling centers.
“The poorer locations are...unable to spend as much to adapt,” said Jina. “Essentially, it appears that wealthier places pay for climate change impacts with money, and poorer places pay with their lives.”
Within individual countries, this devastation also won’t be spread evenly. Poorer people who have less access to cooling technology and health care will be hit hardest. Age will also be a major factor: People over the age of 65, who are more likely to have underlying conditions which can be aggravated by extreme heat, are set to suffer most.
The financial toll of all of this mass death will also be severe. The researchers predict that if emissions are not constrained, the cost of heat-related deaths will consume 3.2% of the world’s global economic output by the end of the century. They found that each ton of carbon dioxide the world emits will cost $36.60 in damage.
Crucially, this level of mass death is far from unavoidable. If civic leaders begin taking the climate crisis seriously and take steps to rapidly draw down greenhouse gas emissions, meeting a scenario known as RCP4.5, heat-related deaths will increase by less than a third of the projected increase of the most severe RCP8.5 scenario. But the pattern of inequality would still remain.
“The poorer locations are the ones that have had the lowest contribution to climate change but will experience more of the impacts,” said Jina.
The study highlights the need to not only curb global warming, but also the need to tackle economic inequality. Richer, higher-emitting countries could do so by taking the lead on climate action and investing in other countries’ adaptation plans. That’s particularly true for the U.S., which is the largest historical emitter of greenhouse gases.
The time to start is now. Just last week, Iraq saw temperatures exceed 127.4 Fahrenheit (53 degrees Celsius). There’s a lot more of that in the future if we don’t change course.