Heat in the Southeast

A post by Anne JeffersonHere in Charlotte we had a hot summer. We barely escaped the dubious distinction of hottest summer on record, with an average temperature of 81.1° F (27.3 ° C) between 1 June and 31 August. The record had been set in 1993, when Charlotte recorded an average temperature of 81.5° F (27.5 ° C). In terms of record breaking heat, we actually fared better than many parts of the east coast, where temperature records from New York City to Greenville-Spartanburg, South Carolina were broken. Below there’s a nice map from NOAA of how far average temperatures deviated from the 30-year climate normal period (here, 1966-1996).

U.S. surface temperature departure from average (°C), June 1 to August 31, 2010, from NOAA/ESRL Physical Sciences Division, Boulder Colorado

U.S. surface temperature departure from average (°C), June 1 to August 31, 2010, from NOAA/ESRL Physical Sciences Division, Boulder Colorado

Of course those average temperature records belie the minima and maxima experienced by each place over the course of those three summer months, so there’s another statistic that I’m finding even more interesting: the number of days where maximum temperatures exceeded 90° F (32.2 ° C). I think of it as Anne’s index of intolerable heat, especially when combined with the Southeast’s oppressive humidity. In Charlotte, between 1 June and 31 August, we had 67 days that exceeded 90° F. That means that 73% of days this summer were intolerably hot (at least for me). Also, that’s only counting the days in the climatological summer. We had 90+° F degree heat in early April, some in May, and we’ve already had some in September, with more in the forecast this week. I suspect that by the time the year is out, our total days above 90° F will be something around 80, if not more.

The long-term predictions for the index of intolerable heat look grim for Charlotte and the rest of the southeast. The image below shows historical and modeled days with peak temperatures exceeding 90° F. By the end of the century, at least under a high emissions scenario, 80+ days of intolerable heat will be considered a cool summer in North Carolina. We’re heading towards 120 days or more of hot, hot weather, a doubling of our historical average. In parts of Florida and Texas, more than half the year will be hotter than 90° F. Yuck. Glad I won’t be around here then.

Historical and predicted days with peak temperatures above 90 degrees Fahrenheit

These temperature trends are not just bad news for people who like to play (or do field work) outside in the summer, but are too wimpy to drop bucketloads of sweat. Hotter average temperatures and more days with ridiculous heat have real health consequences. On hot days, the chances go up that people playing outside end up with heat exhaustion or life-threatening heat stroke. People without air conditioned homes or workplaces, people too poor to pay tremendous energy bills for air conditioning, or people who just happen to have their AC break do not even need to play outside to be at risk of heat related illness or death. About 700 people already die each year from heat-related causes, and the elderly are a disproportionate share of the victims. Those with cardiovascular disease are also at substantially increased risk of heat-related mortality.

And it’s not the heat alone that spells bad news for the Southeast. With hotter temperatures come increasing rates of photochemical reactions…such as the production of ground-level ozone from nitrous oxides and volatile organic compounds released by car exhaust, power plants, and natural sources. The chemistryof photochemical ozone production is pretty complex and we don’t have a fantastic handle on how coming climate changes will impact the percent of hot days with sun versus clouds, but if the number of hot sunny days increases, it is likely that ozone production will increase too. Ozone brings its own host of adverse health effects, particularly respiratory problems, so even if you don’t mind the heat, running around outside on hot, sunny days can be a bad idea. Once again, children, the elderly, and those with asthma and other respiratory problems are most at risk on high ozone days. Such days, labeled as orange alerts, occur sporadically thoughout the summer already. In Charlotte, we’ve had 13 days with air quality in the orange category since May 1 this year. On those days, people at risk are encouraged to avoid outdoor exercise, and daycare centers limit the time kids spent playing outside. Some days, the air quality is bad enough (red alert) that even healthy adults are encouraged to avoid to outdoor exercise. That’s happened once this year in Charlotte.

As Charlotte and other parts of the southeast move towards one-third of their days in the intolerably hot range, with the probable added bonus of worse air pollution, it will be interesting to watch the societal shifts in attitudes toward the climate. Will Southerners get serious about reducing emissions from cars? Will Charlotteans end their love affair with sprawl in order to improve air quality? Will the Southeast be depopulated of Yankee transplants like me, who finally decide that they can’t take the heat? Or will we just stay inside and crank up the air conditioning units and complain about the weather?

Categories: by Anne, climate science
Tags: , , , ,

Comments (9)

  1. Good day Anne,

    Fine article indeed! Note that here in Raleigh, we are at 77 days of 90+, with the all time record being 80 such days in a calendar year. We should break that record this week.

    Indeed, I have noticed day after day, week after week, that we are nearly always above normal (30-year-climate-mean) on the high temperatures, rarely below. This labor day weekend we were closer to normal, but still above – and it felt cool.

    As for the sprawl issue – I think we have you beat here in Raleigh. Charlotte, at least, has an urban core that you can rally around with mass transit. Here, with four or five core areas, all about 10 miles apart (Raleigh, Durham, Chapel Hill, Cary and RTP) we are designed to BE sprawling.

    That said, we do make use of the pool a lot as a result of the heat.

    Thanks again for the good posting!

  2. jaycubed says:

    Here in northern California it has been an absolutely perfect year (and No, I never once complained about the rain all winter & spring). At most we have had two weeks worth of +90?temps all summer. Beautiful!

    I just love it when the Pacific High gets stalled off the coast.

  3. Silver Fox says:

    I thought it was cooler this summer in eastern Nevada, but apparently it was just about average or slightly warmer, and I was thinking mostly of the cooler-than-usual May. We had 29 days above 90 from June1 through Aug31. Your 67 days sounds nasty.

  4. Chris Rowan says:

    Rather amusingly, the closest weather station to me in Edinburgh, at the Botanic Gardens, claims that the highest temperature ever recorded there was 30 Celsius – 86 Farenheit on 5th August 1975. The average for this summer has been more like 18 C (64 F). So Scotland does pretty well on your intolerability index!

  5. Alan Kellogg says:

    Two things are going to have to change in the American south-east with more hot and humid days, architecture and clothing. More open architecture so breezes can make it through each structure, and lighter clothing, and less of it, to allow the skin to breathe.

    There are other ways of adapting to the heat, but my brain is refusing to cooperate and detail what I’m thinking about. One thing I can relate has to do with plants and how stands of trees and shrubbery can cool the air.

  6. The Northeast had a record hot spring and summer at a majority of stations from Northern Virginia northward through Maine.

  7. Ryan Brown says:

    According to the Oregon Meteorological Society, Portland just finished it’s coolest summer in 17 years. I don’t think we hit above 90 till after the first of July. And even then it was only for a couple of days before dipping backing into the low 70’s for most of the summer. It was slightly ridiculous.

  8. Dan McShane says:

    I like the pick of 90 degrees to measure comfort. In Seattle, Cliff Mass uses 70 degrees as a measure of warmth. Using that method, he concluded that this was the coolest summer in Seattle since 1980.

  9. sean gray says:

    i live in gaston south carolina 25 miles south of colmubia. i saw only 17 days from june1 to aug31 that where under 90. and the lowest of thoses temps where 87 but with the heat index it felt in the mid 100’s. and on the 22,23,24 of september the start of fall it was 98 or above. its hot when it is 93 outside and it feels cool. bring it on i love it!!!