City dwellers of the future: Urban heat island warming may be as large as doubling CO2
Monday, April 19th, 2010
I remember driving on a freeway in Phoenix after midnight in 1990. The temperature was a cool 102 degrees F after breaking the all-time heat record of 126 F that day. Deserts are good at cooling off at night. But with all of the built environment in Phoenix storing heat from the day, the sidewalks, roads, and even swimming pools felt like they were being heated.
We all have probably experienced urban heat islands—the mass of dark asphalt and concrete absorbing solar radiation and radiating it back to space as heat. The lack of water exacerbates the situation because there is little-to-no evaporative cooling. Waste heat from cars, machines, air conditioners, and even human bodies also heat up the air. And the warmer it gets, the stronger the tendency to crank up the air conditioners, generating even more waste heat.
The problem is potentially large in areas like the Middle East, India, parts of Africa, and the American Southwest, where rapid urbanization in warm, dry environments has the potential to make some urban areas much warmer at night than surrounding rural areas.
In a forthcoming article in Geophysical Research Letters1, Mark McCarthy and colleagues at the Met Office, Hadley Centre, UK used a climate model that examines what climate might look like in a doubled CO2 world and calculates the added warming caused by urbanization and wasted heat.
Their results were eye-opening:
- Urban regions in places like the Arabian Peninsula, Iran, and India may experience night time warming by as much as 3-5 degrees C above and beyond that caused by doubled CO2 alone.
- The number of hot nights per year (defined as temperatures in the 99th percentile of nonurban areas) increase in the following cities:
- London: 1-2 hot nights now vs. up to 10 hot nights in 2050
- Sydney: 1-2 hot nights now vs. up to 15 hot nights in 2050
- Delhi: 5-10 hot nights now vs. up to 30 hot nights in 2050
- Beijing: 3-6 hot nights now vs. up to 50 hot nights in 2050
- Los Angeles: 8-12 hot nights now vs. up to 40 hot nights in 2050
- Tehran: 20 hot nights now vs. up to 60 hot nights in 2050
- Sao Paulo: <5 hot nights now vs. up to 80 hot nights in 2050
- Lagos (Nigeria): <5 hot nights now vs. up to 150 hot nights in 2050
As mentioned in an earlier post, we only need to remember Chicago in 1995 to recall the deadly impact that heat waves can have on urban people. And as we saw in that unfortunate example, the victims were disproportionately the elderly and African American.
Although we may not be able to mitigate this warming, basic adaptation steps should be set into motion, including re-thinking urban design, making cities more resilient to hot environments, developing better energy and technology solutions (including cooling), installing green roofs, and putting into place emergency disaster plans and social safety nets for vulnerable populations.
1Mark McCarthy, Martin Best, and Richard Betts (2010). Climate change in cities due to global warming and urban effects Geophysical Research Letters : 10.1029/2010GL042845
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3 Responses to “City dwellers of the future: Urban heat island warming may be as large as doubling CO2”
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Look forward to reading the article when it comes out. Having been in Paris during the heat wave in 2003, this is a topic that’s near and dear to me. (More people died in Italy than France that year, but the French got all the publicity for neglecting old people while they vacationed on the beach. A year later Spain had it’s own “through the roof” heat wave.)
It’s also a learning opportunity; the incoming, short wave UV and visible energy isn’t changing, but the outgoing, longer wave infrared heat is increasing… with more of it being trapped by increased GHG… including all the water vapor being thrown into the atmosphere to cool things down (evaporative cooling is only a temporary solution, after all…).
I remember being amazed at the amount of heat being radiated from the buildings and sidewalks in Paris throughout the night… it never really cooled down. Buildings were literally sweat boxes. And these sorts of heat waves are just the beginning….
[...] and urban effects, Geophys. Res. Lett., 37, L09705, doi:10.1029/2010GL042845. [tiivistelmä] “City dwellers of the future: Urban heat island warming may be as large as doubling CO2″… Aihe(et): Ilmastouutiset. Jätä kommentti [...]
I wonder If you have studied the effects of traffic derived ozone in very high
temeperatures on mortality.This may be of more relevenace to urban dwellers,who
are surrounded by daytime air pollution.They die within the next seven days of a
peak.The effects are very geographical (city local topography has profound effects
on concentrating or diluting ozone..eg. Bordeaux low,Toulouse high),and mortality
rises with temeperature at any given ozone level, and with ozone levels at any
given temperature.