Wednesday 13 October 2010
MEDIA RELEASE
Hot cities
If you thought our cities are getting warmer, you're right.
Bureau of Meteorology researchers have found that daytime temperatures in our cities are warming more rapidly than those of the surrounding countryside and that this is due to the cities themselves.
Bureau climate scientist, Belinda Campbell, said "we've known for a while that city night time temperatures have been warmer because the heat's retained after sunset just that much longer than the countryside, and that city daytime temperatures have been warming too."
"But what we didn't know was whether city day time temperatures were also warmer because of the urbanisation or whether it was due to the overall warming of the planet associated with the enhanced greenhouse effect."
"We can now confidently say that the reason our cities are warmer and warming faster than the surrounding countryside during the day is because of the urbanisation, the fact that all those offices, houses and factories absorb the heat and retain it a little bit longer," Ms Campbell said.
On average, the enhanced greenhouse effect is responsible for about 0.5 to 1.0 degree of observed warming around the globe (more in some areas, less in other areas).
The additional effect of urbanisation on warming varies from city to city (depending on the buildings and open parkland close to the observation site).
The research team analysed data from 70 sites in the Bureau's meteorological data archive in order to quantify how much the increases in daytime temperature can be attributed to urbanisation and how much to the enhanced greenhouse effect.
The sites were mostly from towns with populations ranging from 500 to 100,000, with a handful being either in cities with more than 100,000, or in isolated locations with hardly anybody for hundreds of kilometres.
Ms Campbell is presenting the results of the team's work at the Australia - New Zealand Climate Forum in Hobart on Thursday (14 October, 2010).
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