Coyote Blog

For most city dwellers, the temperature increase in the summer time from the urban heat island effect (UHIE) dwarfs any temperature increase from global warming.  UHIE is the result of high population density, with lots of cars and equipment that generate heat and buildings and roads that seem to hold it in.  Many cities are several degrees warmer than the surrounding countryside.  The effect is so dramatic that correcting for this effect is a big part of the uncertainty in answering seemingly simple questions like "how much has the earth warmed in the last 100 years?"

Apparently, UHIE is a big problem in one of the world's densest cities, Tokyo.

The gleaming high rise buildings that crowd the
cityscape may symbolize Japan's economic recovery but they have also
converted this priciest of human habitats into vast heat-trapping
canyons in what is known as the urban heat island (UHI) effect.

Heat churned out by air-conditioners, automobiles and human activity
finds no escape, causing ambient temperatures, especially in the summer
months, to rise by several degrees and forcing authorities to
constantly look for newer ways to cool down a city on the boil....

A report released by the Tokyo Metropolitan government this
year shows that average temperature rise in the capital over the course
of the 20th century has been 3 degrees C....

Yamaguchi also told IPS that the number of days recording temperatures
of over 35 degrees C has gone up to more than 35 days a year,
concentrated around the three summer months between July and September.
That contrasts with the 14 days recorded in 1975....

Tellingly, most of the deaths from the European heat wave several years
ago where in cities, which tells me that UHIE had a contributing role
more than global warming.  This is actually something we argue about
from time to time in Phoenix.  Ocasionally the city considers
steps to lower our albedo, such as requiring white (rather than black)
roofs and looking at alternatives to dark asphalt for roads.

This has never been a big environmentalist issue.  My guess is that
this is because environmentalists, at least in the US, have adopted a
goal of increasing urban concentration and population densities.  I
suppose it might be embarassing for them to admit the warming they are
trying to get city dwellers to blame on CO2 may in fact be largely due
to the environmentalists own urban planning approaches.