Long Hot Summers

Well, this is interesting. . . according to the excellent Climate Central web site, computer models and scientific literature suggest that across a large number of U.S. cities, the average number of days in August with temperatures over 95 degrees Fahrenheit could nearly triple by 2050, and the average number of days over 100 degrees could nearly double.

Here in Atlanta, for example, we typically experienced 11 days in August during the 1980s and 1990s with temperatures over 90°F and 2 days with temperatures over 95°F. By 2050, however, the computer models predict that the number will increase to 25 days each August with temperatures over 90°F and 14 days each August with temperatures over 95°F. And while we typically had no days in August with temperatures over 100°F (our hottest month is typically July), by 2050 we should average 3.

In other words, by 2050, Atlanta's heat will be more like Dallas's now.

By comparison, Boston currently averages 3 days per August with temperatures over 90°F and 0 days with temperatures over 95°F. By 2050, the computer models predict that Boston will be hotter than Los Angeles is today, with 8 days over 90°F and 3 over 95°F.

I'm usually leery of such specific weather predictions. Climate can reasonably be predicted out over centuries and decades, but tomorrow's weather is generally anybody's guess. But Climate Central’s Ben Strauss emphasizes that the numbers are not predictions. “We’re talking about best estimates and averages,” he says. “No matter how close the projections turn out to be, some years will have more hot August days, and others will have fewer.”

Staff scientists drew on regional scenarios from a dozen highly sophisticated computer climate models. The bottom line is that locations across the nation are likely to experience significant jumps in the number of extreme hot days in August and other summer months, from New York to Los Angeles, and from Florida to the Midwest to Seattle, which just experienced an unusual heat wave earlier this summer.

Since 1995, tens of thousands of people worldwide have died in heat waves. Other important impacts include increases in demand for energy (particularly electricity for cooling), and increases in urban and agricultural water demand.

The severity of increases in extreme heat and their impacts will depend on the extent of future use of fossil fuels. We do, after all, have some choice here. How hot it will actually get will depend on the choices we make about energy and transportation in the years to come.