climate change

Paint it white – combating climate change with colour

white-roadHere’s a bizarre way to combat climate change for a friday evening: according to the report I’ve been reading this week, “whitening the pavements and roofs of the world’s largest 100 cities would offset the equivalent of 44 billion tonnes of CO2 per year, and save money through reduced air conditioner use.”

To put that it perspective, our entire worldwide fossil fuel use is responsible for 8 billion tonnes of CO2 a year, so that’s quite a lot of offsets. I’m no fan of offsetting as a long term strategy, but that sounds like a simple and ingenious way of buying us some cool while we bring our emissions under control.

It works because dark colours absorb heat, while light colours reflect it. If we can increase the reflectivity, or albedo, of our cities, they will be cooler. More sunlight will be reflected back from the earth, rather than being absorbed into the urban ‘heat islands’ that tend to be a feature of our built-up areas. Since cities will be cooler, we can switch off the air conditioning, one of our more disastrous inventions when it comes to climate change.

We actually operate this principle with our cars already in some parts of the world – check out the ratio of white cars to non-white cars in this Kenyan traffic jam. If you’ve climbed into a black car in a tropical country, you already know all about albedo.

So, let’s get the white paint out and get started. I’m imagining roads that are white with black lines, rather than the other way round, and it all sounds a little ridiculous. But, if we learned to lay lighter coloured concrete when pouring a parking lot, or used shiny corrugated iron roofing more, or painted our shingles white, we’d make a considerable difference to the heat of our cities.

  • , from the Lawrence Berkeley National Laboratory, USA (pdf)
  • – being somewhat intrigued, I wrote a bunch more on this for Celsias.

5 comments

  1. The figure of 8 billion tonnes is for carbon only, the CO2 figures is 3.7 times this (the difference in weight between a carbon atom and a carbon dioxide molecule).

    Which makes global emissions around 30 billion tonnes of CO2… although if you check the global carbon project figures they are higher…

    Richard

  2. Thanks for the clarification Richard, that makes more sense.

    Thanks for a great report too. It’s given me a lot to think about, and my broader thoughts on it should appear on Celsias some time this week.

  3. yes you are correct

    when the suns light falls on white roofs it reflects most of it back into space.

    it is only when the suns light strikes non white objects that the object re emits infra red light which is absorbed so well by the earths atmosphere.

    the sooner we paint roofs white the sooner we will cool the planet closer to normal values. we need to stop creating houses which have black roofs or roads that are jet black, they are turning the planet into a griddle.

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