Death Valley, Calif., recently recorded its hottest nighttime temperature ever as extreme heat blankets the globeDeath Valley, Calif., just recorded the world's hottest month ever as extreme heat spread misery around the globe. Photo credit: David McNew/Getty Images

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By Dana Drugmand

The blistering heat currently scorching much of the planet—from Japan to Europe to the United States—is the climate change impact that scientists can most definitively link to global warming. But unlike hurricanes or wildfires that mostly damage property, the costs of those heat waves are much harder to quantify because the impacts are absorbed primarily by people and not by property.

Understanding those costs, however, is crucial for cities and states trying to protect their residents from climate impacts. They are working to calculate the toll of extreme heat, from decreasing outdoor worker productivity, to crop failures, cancelled flights and students’ decreasing ability to learn.

Many of the estimates come from cities that have filed climate liability suits, seeking to hold the fossil fuel industry accountable for those costs. New York City, for one, estimates in its complaint that its heat mitigation initiative, Cool Neighborhoods NYC, will cost more than $100 million and it tallies another $100 million in related public health care costs.

The Environmental Protection Agency estimates that heat may cost 1.8 labor hours per person across the U.S. workforce by 2100, which equates to $170 billion in lost wages. Millions of Americans have jobs that require outdoor work, which leaves them vulnerable to intense heat.

For those fortunate to work and live in air conditioned offices and homes, the costs of keeping them cool will rise as temperatures soar. According to the Energy Information Administration, residential air conditioning accounted for 12 percent of household energy expenses in 2015, an average cost per year of $265. The EIA also calculated that Americans spent more than $27 billion on home cooling in 2015. Another study published in 2017 projected that energy use from air conditioning would rise 2.8 percent by the end of the century, and peak demand during extreme heat would rise 7.2 percent.

Agriculture could also take a big hit from rising temperatures and its sister climate impact: drought. While warming may facilitate crop growing in some areas, it could damage crops in many others and accompanying droughts threaten agriculture on a wide scale, according to the EPA. Heat stresses livestock and fisheries, helps the spread of weeds, pests and fungi that farmers spend large amounts to battle, and high nighttime temperatures lower crop yields. A warm winter in 2012 caused Michigan cherry trees to bloom early and cost that industry $220 million.

The most tragic, but hardest to quantify, impact is in the loss of human life. Japan’s current heat wave has killed nearly 100 people. A new study published in PLOS Medicine warns that unchecked greenhouse gas emissions could cause warming that leads to five times more heat wave deaths in the U.S. Heat and humidity already kills an average of 1,300 people in the U.S. each year

One study that looked at total health costs (including premature deaths) from six climate-driven events from 2000 to 2009 found that a deadly 2006 heat wave in California cost roughly $5.3 billion. Most of that cost is associated with premature mortality.

Dr. Kim Knowlton, senior scientist at Natural Resources Defense Council and one of the authors of that 2011 study, said more studies are needed to understand the health-related costs of heat, which often get overlooked.

“We’re going to update the 2011 work and look at other heat waves since then that have been well-documented,” she said. “We hope that a year from now we’ll have another array of valuation studies to look at. We think it’s very important to keep this work going.”

Another study published last week from researchers with the Climate Impact Lab is the first of its kind to use comprehensive data on mortality, income, climate and historical temperature to estimate the mortality cost of extreme heat. According to the study, the median mortality risk cost is roughly $39 per metric ton of carbon emitted today. This value accounts for lives lost to extreme heat, lives saved due to less extreme cold, and net costs of adaptation to withstand temperature extremes. The estimate comes from historical data covering 399 million deaths globally over the past several decades, and modeling future scenarios for population, income and emissions.

Overall, the study concludes that if past emissions trends continue, the global mortality damage from climate change will equate to about 3.7 percent of worldwide GDP by the end of the century.

Cities Filing Climate Suits Have Done Some Accounting

In terms of costs, heat-related climate impacts are likely to be in the billions of dollars, considering risks to health and mortality, economic disruption, and cooling expenses. Currently these costs are shouldered solely by taxpayers, but the climate liability lawsuits targeting the fossil fuel industry are trying to shift that burden.

New York quantified its costs in its complaint against five major oil companies—recently dismissed by a federal judge but the city says it will appeal—as it faces skyrocketing costs related to heat.

“Heat kills more New Yorkers than any other natural hazard and disproportionately impacts communities of color and the elderly, which is why the City is tackling this challenge with unprecedented investments in heat mitigation and adaptation programs,” said Jainey Bavishi, director of the Mayor’s Office of Recovery and Resiliency.

According to the city’s complaint, if emissions are not significantly reduced, scenarios project temperatures at or above 90 degrees F for 33 days per year by the 2020s, 57 days per year by the 2050s, and 87 days annually by the 2080s. In other words, “by the 2050s, today’s worst heat waves are expected to become ordinary summer days.”

“Without mitigation, hotter summers projected for 2020 could cause an estimated 30 percent to 70 percent increase in heat-related deaths, or about 110 to 260 additional heat-related deaths per year on average in New York City,” the complaint states.

New York City, of course, is not unique in its heat projections. Most of the U.S. could swelter with temperatures above 90°F for 20 to 30 more days annually in the coming decades, according to  a new analysis from the Union of Concerned Scientists.

The complaint filed by three Colorado communities—Boulder, Boulder County and San Miguel County—against two oil companies, Exxon and Suncor, highlights heat as a major threat to their citizens. As the first inland municipalities to seek compensation from fossil fuel companies, they know the costs extend far beyond showier impacts like more intense hurricanes and sea level rise.

“Warming temperatures and heat waves caused and contributed to by the levels of Defendants’ fossil fuel activities are a threat to health, property and infrastructure,” the communities wrote in their complaint. “Medical studies have linked heat waves to increases in premature deaths, and adverse economic impacts have been documented on extreme heat days, with particularly large effects on outdoor labor productivity in sections such as construction, transportation and agriculture. The levels of Defendants’ fossil fuel activities has thus already contributed to substantial economic losses in the Plaintiffs’ communities.”

Whether courts will hold fossil fuel companies liable for these losses remains to be seen. In the meantime, the tab will continue to rise as the mercury does.