If It’s Not Hot Enough For You, It Will Be Soon Enough

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When I woke up today at my apartment in upper Manhattan, it was nearly 80 F. It’s nearly 90 F right now, and it will likely scrape 100 F before the day is blessedly over. On a weather map, the entire broiling eastern half of the U.S. looks like it has a bad Memorial Day early summer sunburn. It’s hot, it’s staying hot and it’s really uncomfortable.

No surprise there. Heat waves are a part of life in the urban Northeast—a part of life that has gotten a lot easier to manage since the ubiquity of air-conditioners in homes, businesses and even the occasional subway car. The record high for June 9 in New York City is 96 F, recorded during a nasty heat wave in 1984—but fingers crossed, I think we’re going to bust it.

But a heat wave that feels nigh unbearable today might count as a cool weather in the future. According to a forthcoming study in the journal Climatic Change Letters by a pair of Stanford researchers, the tropics and much of the Northern Hemisphere are likely to experience an irreversible rise in summer temperatures over the next 20 to 60 years, assuming greenhouse gas emissions continue to rise. Says Noah Diffenbaugh, an assistant professor of environmental Earth system science and the study’s lead author:

According to our projections, large areas of the globe are likely to warm up so quickly that, by the middle of this century, even the coolest summers will be hotter than the hottest summers of the past 50 years.

So it can get much worse. Diffenbaugh and his co-author Martin Scherer analyzed more than 50 climate model experiments, including simulations of a 21st century where the world fails to curb carbon emissions, and simulations that accurately predicted climatic changes over the course of the 20th century. They concluded that it won’t be long before the coolest temperatures in future summers exceed the warmest days experienced today. They also found that the first evidence of extreme heat is already beginning to emerge today—although, as is the case with storms and other forms of extreme weather, the system is still too noisy to be certain current heat waves are a result of climate change.

Such prolonged summer heat waves could put a crimp in global agriculture—especially in the super-hot tropics, as another recent study predicted. And cities that fail to adapt to extreme heat won’t just be highly uncomfortable—they could also be deadly. A recent study by scientists at Harvard’s School of Public Health and the Johns Hopkins Bloomberg School of Public Health estimated that the city of Chicago could have between 166 to 2,217 additional deaths each year due to heat waves in the years 2081-2100. Heat waves—especially in old urban cities that experience high humidity and where air conditioning isn’t yet the norm—can be incredibly deadly, with the Red Cross estimating that extreme heat has caused more excess deaths in the U.S. than any other weather event, including floods and tornadoes. During the great Chicago heat wave of 1995, the high temperatures caused an estimated 700 excess deaths in the city in one week—more than all the Americans who have died so far from the record-breaking tornadoes of 2011. The record European heat waves of 2003 caused an estimated 40,000 excess deaths. Said Francesca Dominici of Johns Hopkins, a lead author on the paper:

Our results show that for a major U.S. city, the impact of future heat waves on human health will likely be profound.

Of course, it’s not the heat, it’s the adaptation (and the humidity)—otherwise Phoenix, with its average June high of 103 F, would be far more deadly than Chicago, with its average June high of 79.2 F. As air-conditioning becomes cheaper and more common—and cities get better at dealing with the heat—we should be able to live with even hotter summers, at least in the rich world. (The poor places, as the song goes, won’t be so lucky.) If hotter summers mean warmer winters, that could blunt deaths that occur during the coldest months of the year. But however much we adapt, those future summers in the city are not going to be pleasant.

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