This summer, the world is experiencing record hot temperatures: June continued a 2020 streak, ranking among the warmest months in history. A weather station in Death Valley, California, clocked a scorching 53.3°C /128°F in July, one of the hottest temperatures ever observed on Earth. Officials from Delhi to Tokyo to Lagos, cities where past heat waves have claimed hundreds of lives, are bracing for dangerously hot periods. Simultaneously, the coronavirus pandemic’s devastating mortality impact and economic fallout are demanding society prioritize public health like never before.
How much is temperature to blame when hospital visits surge during heat waves and cold spells? What role might adaptations like indoor heating and cooling systems play in blunting those effects? And, at what cost? A new working paper from the Climate Impact Lab, published by the National Bureau of Economic Research, takes on these questions and finds that in a world with continued high fossil-fuel emissions, warmer temperatures will rank among the world’s most significant public health threats by the end of the century.
Specifically, the study projects that climate change’s effect on temperatures could raise global mortality rates by 73 deaths per 100,000 people in 2100 under a continued high emissions scenario, compared to a world with no warming. That level is roughly equal to the current death rate for all infectious diseases—including tuberculosis, HIV/AIDS, malaria, dengue, yellow fever, and diseases transmitted by ticks, mosquitos, and parasites—combined (approximately 74 deaths per 100,000 globally).
“Our data indicate that with the continued growth of greenhouse gas emissions, the temperature effects of climate change are projected to be five times deadlier than recent U.S. flu seasons. In poor hot countries, the heat may be even more threatening than cancer and heart disease are today,” says Michael Greenstone, the Milton Friedman Distinguished Service Professor in Economics at the University of Chicago.
In the worst-hit countries, including Ghana, Bangladesh, Pakistan and Sudan, climate change could be responsible for an additional 200 or more deaths per 100,000 by the end of the century, the research shows. The study comes from the interdisciplinary Climate Impact Lab, which has developed a new approach that uses real-world data to understand the impacts of climate change. Researchers reveal the role of higher incomes in reducing heat’s health threat and the significant costs of adapting to rising temperatures, clearing a major hurdle that to-date has stymied researchers in this field. Under a scenario of continued high emissions, the researchers estimate that climate change’s impact on mortality will cost the world roughly 3.2% of global economic output in 2100.
To uncover the relationship between temperature and mortality, the team distilled 399 million death records across 41 countries, accounting for 55 percent of the global population. They summarized this complex calculation into a single value representing projected spending to adapt to rising heat, like installing air conditioning, plus the value of life-years lost. The results, which also quantify uncertainty, can be used by decision-makers to weigh the benefits of reducing emissions: emitting one additional ton of CO2 today costs ourselves and future generations a total of $36.6 under a continued high emissions scenario and $17.1 under a moderate emissions scenario.
“This means an average American imposes about $575 worth of unpaid-for death-related harm on the world each year by emitting 15.7 tons of CO2. By comparison, the entire foreign aid budget of the US amounts to about $150 per person,” notes Robert Kopp, director of the Rutgers Institute of Earth, Ocean, and Atmospheric Sciences at Rutgers University.
The authors emphasize that the victims of climate change in their analysis are no longer an abstract and distant generation.
“We are studying the risk of death faced by our own children. Today’s ten-year-old fifth grader will turn 65 in 2075, facing mortality risks from climate change every year of their retirement. Failing to address climate change is not that different from driving your kids around without a seat belt: you are putting their lives at risk,” says Solomon Hsiang, the Chancellor’s Professor of Public Policy at UC Berkeley.
Age and income are especially significant predictors of the mortality risk associated with climate change, the findings show. More frequent hot days prove deadliest for elderly populations, but those living in wealthier locations are better protected. The study also accounts for climate change’s potential to reduce the frequency of life-threatening cold days. By the end of the century, damages to society grow significantly with death rates increasing most among today’s poorest populations—exacerbating existing inequalities.
“The data show that poor communities don’t have the means to adapt, so they end up dying from warming at much higher rates,” says Tamma Carleton, an assistant professor at the Bren School of Environmental Science and Management at the University of California, Santa Barbara. “Rich communities are likely to spend a lot of money to protect themselves, resources that they would be able to spend elsewhere if they didn’t have to spend it coping with the heat.”
By dividing the globe into 24,378 regions, the findings identify which places will bear the greatest burden. A more granular view of the findings is available at http://www.impactlab.org/map/. The Lab’s Impact Map shows estimated mortality costs for three future time periods under two emissions scenarios, country-by-country around the globe, and at the state level for the U.S.
Communities that have been exposed to hot climates for a long time are better adapted, the study shows. For example, in the wealthy and warm city of Houston, Texas, the impact of a single hot day above 35°C /95°F on the annual mortality rate is half the size of the effect of the same 35°C/95°F day in the comparably wealthy but colder city of Seattle, Washington. In the warm but poorer city of Delhi, India, the rate is also double that of Houston, largely because Delhi’s population hasn’t had the means to adapt. But Delhi fares worse than both Seattle and Houston, with many more of these hot days every year resulting in more lives lost to heat. Similarly, Accra, Ghana, faces an increase from one to 102 days per year above 32°C/90°F by the end of the century under continued high emissions, projected to increase the city’s mortality rate about 19 percent.
“Just as countries are impacted in different ways by extreme temperatures today, we find that the trend will continue and perhaps even intensify into the future as adaptation becomes more and more critical to people’s survival. Indeed, some will need to choose between paying a high cost to adapt and death,” says Amir Jina, an assistant professor at the University of Chicago Harris School of Public Policy.
A key finding is that although adaptation is expensive, it is a powerful way to reduce the mortality impacts of high temperatures. Globally, elderly populations in the richest third of locations are less vulnerable than those in the poorest third of locations, with a hot day above 35°C/95°F causing 5 fewer deaths per 100,000 in the wealthier parts of the world.
The researchers find that there are very high returns to lowering emissions. Even moderate mitigation of emissions that falls short of the Paris Agreement’s long-term targets would cut the projected mortality impacts of climate change by about 84 percent at the end of the century, relative to a scenario of continued high emissions. Under this moderate emissions scenario, projections show climate change could be responsible for 11 additional deaths per 100,000 by 2099—on par with the current fatality rate from auto accidents in the U.S. of roughly 12 deaths per 100,000.
“Fortunately, the world can still change course by aggressively reducing emissions, and in doing so has the potential to deliver some of the most significant public health gains in human history,” says Trevor Houser, a partner at the Rhodium Group.