White roofs might cool a city, but hardly the globe

Brian Rudman, in White roofs are good for society, in the Herald last Wednesday, dredges up Professor Steven Chu’s wacky idea from last May to paint our roofs white, reflect more sunlight and thus temper the severe global warming presently afflicting us.

Professor Chu, US Energy Secretary and Nobel-prize-winning physicist, said lightening roofs and roads in urban environments would offset the global warming effects of all the cars in the world for 11 years.

He doesn’t tell us how long everything must remain painted white to earn those 11 years, or how much we’d need to pay for all the paint.

We can tell him, however, that it wouldn’t make any difference to global warming, although it might reduce the urban heat island (UHI) effect.

How does the UHI work? Well, roads and buildings absorb heat from the sun more than trees or grasslands do. So, as a village becomes a town and the town grows into a city, adding more and more roads and buildings, average temperatures climb, especially at night. This happens in both hot places and cold places, it makes no difference; if you build a city, you raise the temperature.

But if more surfaces were light-coloured instead of dark, more sunlight would be reflected and downtown wouldn’t get so hot.

The trouble is, it’s just not enough to combat global warming. With only about 0.1% of the sun’s energy being reflected away even if every road and building in the whole world was painted white (which would be a miraculous feat of co-operation), we wouldn’t see any change in the global average temperature, which might go down by about 0.1°C.

So we’d pay trillions to keep our parts of the world painted and we wouldn’t see any result for it.

The irony of this proposal is that the US-managed global surface temperature record is contaminated by the UHI effects from urban weather stations all over the world, since so many of them are in towns and cities. Anthony Watts, at Watts Up With That, has gathered evidence of this and for years has been lobbying to have adjustments made to the dataset to remove the spurious UHI warming and see whether we really do have global warming.

There is strong evidence that if this was done most of the surface “warming” recorded over the last part of the 20th century would simply disappear.

How ironic that Rudman picks up on a solution incapable of solving a problem that doesn’t exist, but whose effect could be to remove evidence of the problem.

Uh, so it will solve global warming! White paint, anyone?

By the way, it’s important to remember that this solution only makes sense in low latitudes (closer to the equator), where cooling your building is sensible. In higher latitudes (closer to the poles), where it’s already colder, you must heat the building and you really want darker colours to warm it a bit and save that heating money. So you can’t really paint all the buildings white, only those in the warmer places. And you don’t want to paint the colder roads white, since they ice up more readily.

What a pity. It was such a good idea.

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