A devastating heat wave swept across Europe in 2003, killing tens of thousands of people, scientists estimate. Many were elderly, with limited mobility, and some already suffered from chronic diseases. But climate change is making such extreme weather more common—and the effects will not be limited to the old and sick. Warming temperatures do not only threaten lives directly. They also cause billions of hours of lost labor, enhance conditions for the spread of infectious diseases and reduce crop yields, according to a recent report.

The report, published last December in the Lancet, represents the latest findings of the Lancet Countdown—a coalition of international research organizations collaborating with the World Health Organization and the World Meteorological Organization. The group tracks the health impacts of—and government responses to—climate change.

“It affects everyone around the world—every single person, every single population. No country is immune,” says Nick Watts, executive director of the Lancet Countdown and one of many co-authors of the report. “We've been seeing these impacts for some time now.”

Credit: Amanada Montañez; Source: “The 2018 Report of the Lancet Countdown on Health and Climate Change: Shaping the Health of Nations for Centuries to Come,” by Nick Watts et al., in Lancet, Vol. 392; December 8, 2018

The report found that millions of people worldwide are vulnerable to heat-related disease and death and that populations in Europe and the eastern Mediterranean are especially susceptible—most likely because they have more elderly people living in urban areas. Adults older than 65 are particularly at risk, as are those with chronic illnesses such as heart disease or diabetes. Places where humans tend to live are exposed to an average temperature change that is more than twice the global average—0.8 versus 0.3 degree Celsius (graphic). There were 157 million more “heat wave exposure events” (one heat wave experienced by one person) in 2017 than in 2000. Compared with 1986 to 2005, each person was exposed to, on average, 1.4 more days of heat wave per year from 2000 to 2017. That may not seem like a lot, but as Watts notes, “someone who is 75 and suffers from kidney disease can probably survive three to four days of heat wave but not five or six.”

Sweltering temperatures also affect productivity. A staggering 153 billion hours of labor—80 percent of them in agriculture—were lost to excessive heat in 2017, the new report found, with the most vulnerable areas being in India, Southeast Asia, sub-Saharan Africa and South America. The first stage of heat's impact is discomfort, says report co-author Tord Kjellstrom, director of the Health and Environment International Trust in New Zealand and a consultant on environmental and occupational health. But there comes a point at which it is simply too hot for the body to function. For example, sweating heavily without replenishing water can result in chronic kidney disease, Kjellstrom notes. News reports have documented farm workers in Central America dying from kidney problems after years of working in the hot fields. Richer countries such as the U.S. may avoid the worst effects because of better access to drinking water and, in the case of indoor work, air-conditioning. But these solutions can be expensive, Kjellstrom says.

Then there are indirect effects. For example, warmer temperatures have increased the geographical ranges of organisms that spread dengue fever, malaria and cholera. The “vectorial capacity”—a measure of how easily a disease carrier can transmit a pathogen—of dengue virus, which is spread by the Aedes aegypti and Aedes albopictus mosquitoes, reached a record high in 2016. The percentage of coastline suitable for bacteria in the Vibrio genus (which includes the species that causes cholera) increased from the 1980s to the 2010s in the Baltic region and northeastern U.S. by 24 and 27 percent, respectively. In Africa's highlands, environmental suitability for the malaria-causing Plasmodium falciparum parasite increased by nearly 21 percent from the 1950s to the 2010s.

Climate change also threatens food security. Our planet still produces more than enough food for the world, but 30 countries have seen crop yields decline as a result of extreme weather, the report found.

“Overall, the report does suggest very serious concerns about the way in which climate change is evolving and its potential implications for human health,” says Andy Haines, a professor of environmental change and public health at the London School of Hygiene & Tropical Medicine, who was not involved in the 2018 report but has co-authored previous Lancet Countdown assessments. “One of the problems is that we don't have enough data on the actual impacts, particularly in the low-income countries,” which will likely be most affected, he says.

The report did find some bright spots: in 2015, 30 of 40 countries surveyed by the WHO reported having climate change health adaptation plans, and 65 percent of cities have undertaken (or are undertaking) risk assessments that address threats to public health infrastructure. But worldwide spending on health adaptation is still under 5 percent of all climate adaptation spending. And funding has not matched that pledged in the Paris Agreement, the global climate accord that is set to take effect in 2020.

Among the biggest steps countries can take to mitigate these health effects are phasing out coal-fired power and shifting to greener forms of transportation, Watts says. Electric vehicles are making inroads in places, he notes—and “active” transport, such as walking or cycling, is also important. Tallying up the costs of climate change, Watts says, makes it clear that “our response or lack of response is going to determine our health over the next century.”