This month, the Intergovernmental Panel on Climate Change (IPCC) completed a year-long release of its fifth major climate change assessment by issuing a synthesis report that pulls together the key findings of the three large volumes published earlier in the year. Among those key findings is some good news—we've made tremendous progress in the science of climate change, and there are clear paths we can follow to mitigate and adapt to our changing environment. The major bad news won't surprise anyone: We face dire consequences by mid-century if we don't act very soon. But there is other bad news, not quite as dramatic as the worrisome future scenarios described in the report, but much more immediate: Climate change is already killing us.
It's killing us in ordinary ways and in relatively small numbers at this point, so it's hard to notice. As the IPCC report describes it: "Until mid-century, projected climate change will impact human health mainly by exacerbating health problems that already exist (very high confidence)." In other words, in the near future a warming world will threaten our health in familiar ways. People would still die from heat waves and other extreme weather events, food-borne illnesses, air pollutants, poor water quality, under-nutrition, and infectious diseases even in the absence of climate change—but not as many. Much of the illness and death due to these causes is preventable, and over the past century, we've made such impressive progress in preventing them that, at least in wealthier countries, we rarely think about them. Now that progress is being undone.
"Climate change poses the same threat to health as the lack of sanitation, clean water, and pollution did in the early 20th century."
The most direct way that global warming is killing us is by heat. Heat waves kill more than any other weather-related event. One study cited in the IPCC report found that there were 70,000 additional deaths during the brutal European heat wave of 2003. Not all heat waves are so lethal; during a subsequent heat wave in Europe, countries like France were more prepared and fewer people died. Compared to leading causes of death in the United States and Europe, such as heart disease and cancer, 70,000 deaths is not an especially large number. But the risk is growing—the likelihood of extreme summer heat has quadrupled in Europe since 1998.
Fires are another way that climate change is already killing us. After one of its "most severe and prolonged heatwaves," Australia suffered an unusually intense set of wildfires on February 7, 2009, that killed 173 people. Worldwide, smoke from wildfires is surprisingly damaging. As the IPCC report notes, wildfires "release particulate matter and other toxic substances that may affect large numbers of people for days to months," which is obvious to anyone who has lived in a place like Denver, Salt Lake City, or San Diego during or after a large fire. A 2012 study found that smoke from wildfires is responsible for almost 400,000 annual deaths, which occur overwhelmingly in sub-Saharan Africa and Southeast Asia, but also the U.S. The U.S. National Climate Assessment reports that the U.S. area burned by wildfires has grown substantially, and that climate is the dominant factor—meaning that more people are now at risk.
In addition to the heat and the fires, climate change is killing people with water. Heavier rainfalls are becoming more frequent in many regions. Those rainfalls lead to contaminated water, which then spreads disease, particularly among children. Near my home in St. Louis, there's a park with a creek running through it. The kids like to play there—right next to the large EPA signs warning about a possible sewage overflow. St. Louis is beginning a two-decade-long effort to upgrade its century-old wastewater infrastructure, so that raw sewage will no longer flow into local creeks and rivers after a downpour. This problem is now exacerbated by climate change, and it's not just limited to St. Louis—many other cities are also struggling with aging and inadequate infrastructure. A recent study conducted in northern and central Wisconsin found that increased precipitation was followed by an increase in gastrointestinal illness in young children. And while these illnesses are rarely fatal in the U.S., world-wide they are responsible for more than a million deaths each year.
The list of ways that climate change is already killing us goes on: Hot summer days increase ground-level ozone to dangerous levels in U.S. cities. The shifting ranges of disease-carrying insects lead to a wider distribution of Dengue and Chikungunya in the Americas and Europe, Lyme disease in Canada, and schistosomiasis in China. Pathogen damage to food crops exacerbates malnourishment. More speculatively, there are even mental health effects, those that come in the aftermath of natural disasters like hurricanes. One recent study found a link between high temperatures and suicide in Japan. And this list is far from exhaustive.
Climate change is already killing us—at the margins, for now. The present impact of climate change on human health is not cataclysmic, and therefore it's easy to ignore. But it exists, and it's eating away at the last century's stunning progress in reducing deaths by preventable causes. As a recent comment in the Journal of the American Medical Association put it: "Climate change poses the same threat to health as the lack of sanitation, clean water, and pollution did in the early 20th century." The good news is that there is much we can do to mitigate this threat. But first, we need to acknowledge that it exists.