When bad things happen, they happen more in cities than anywhere else. Diseases spread faster, waste piles up more quickly, and food shortages go from bad to terrible in a much shorter space of time. As it turns out, the same goes for climate change.
Cities are already hotter than their surrounding areas, due to human activities like pollution, industrial production and, well, heating. This is generally known as the “urban heat island effect” (it also, incidentally, may be making city spiders bigger).
According to a new report from Climate Central, however, climate change is intensifying this effect in US cities. As a result, temperatures in cities could reach levels that “threaten human health, strain energy resources, and compromise economic productivity”.
Here’s a graph from the report showing the late afternoon temperatures in and around an urban heat island:
In an analysis of 60 large US cities, the researchers found that every one of them averaged at least 8 more days over 90°F (32°C) per year than surrounding rural areas. In two thirds of the cities, the combination of climate change and urbanisation seemed to be increasing summer temperatures faster than climate change alone: summers are getting hotter at a faster rate than is typical in their region. In 12 of the cities, summers were getting hotter at least twice as fast as the average for their area.
The heat island effect was most intense in Las Vegas, which on average was 7.3°F (4°C) hotter than nearby rural areas during the day and 10.3°F (5.7°C) hotter at night. (At least it’s nice and mild if you’re hopping between all-night casinos.)
The biggest problem with these higher temperatures is ozone pollution. That happens when pollutants like from burning gas and coal react with oxygen in strong sunlight or high temperatures – so hotter cities can mean more ozone in the air. That, in turn, can cause respiratory problems and even heart attacks.
There is, however, some good news on the air pollution front: the Environmental Protection Agency announced last week that the air in US cities is, in general, cleaner than it was 25 years ago. Since 1990, apparently, the mercury from human sources in the air has fallen by 60 per cent, while lead has fallen by 84 per cent. Let’s hope they can find a way to do the same for ozone.
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