That’s two studies in two weeks time both stating the proclaimed phenomenon of the urban heat island effect [cities are a bit warmer, due to urbanisation their influence would increase] does not provide an alternative explanation for a measured global rise in temperatures – and is also not an important creator of heat [through albedo decline] on a global scale.

The first of the two, by Stanford University, is now actually two weeks old – but that’s the one we have not yet discussed. It states we need to stop thinking backyard-scale on all accounts. Paint your rooftop whichever colour you like, we’ve got a planetary problem to solve…

Urban climate debunking study – Berkeley

Last week we did report on a Berkeley study which had reinvestigated available land temperature data – and which received a lot of media attention in the US and elsewhere. The study used four times as much climate data but reached exactly the same conclusion as independent studies by NASA, NOAA and the Hadley Centre before – Earth is on a warming trend, average land temperatures are up 1 degree Celsius since the mid 1950s.

That study was an honest scientific attempt to closely examine the arguments of climate skeptics who argue temperature records would be flawed. The Berkeley team however could not find any scientific evidence to support that claim. About the urban heat island effect for instance it had this to say:

“The urban heat island effect is locally large and real, but does not contribute significantly to the average land temperature rise. That’s because the urban regions of Earth amount to less than 1% of the land area.”

Urban climate debunking study – Stanford

The Stanford researchers in their publication in Journal of Climate begin by even more narrowly placing cities in perspective. Big as metropolises may seem when you take a walk right in the middle of one, all urban areas combined still take up as little as 0.1 percent of Earth’s cover – and of this half is actually vegetation.

In the Stanford climate model study these urban areas did still create some heat, but no more than 2-4 percent of global warming over the next 20 years. [To be honest that surprises us as being perhaps a bit more than being ‘negligible’ if it weren’t for the fact that we’re without practical action perspective here, apart from carpet bombing random cities. The researchers think it is not a lot, although theirs is indeed slightly higher than previous scientific estimates of the urban heat island.]

Over the next 20 years, according to ther model, about 79 percent would be down to greenhouse gas climate forcing and 18 percent to soot.

Cities’ limited albedo influence works both ways

Their model also says rooftop SRM geoengineering (painting roofs white to reflect sunlight) would have little effect: “A worldwide conversion to white roofs, accounting for their albedo effect only, was calculated to cool population-weighted temperatures by ~0.02 [degrees Celsius].” That’s a bit disappointing, for a full-implementation scenario. Globally it would not prevent further temperature rise over the next two decades.

The researchers have not taken into account possible changes in energy consumption depending on roof type changes. If you live in a warm climate zone and can’t chose between a white and a air conditioning system, think of your energy bill and make the sensible choice.

© Rolf Schuttenhelm | www.bitsofscience.org