Paint your roof white, Marty G urges, and save the planet:

Just painting the dark roof of a 100m2 house white offsets 10 tons of carbon emissions – over half of average annual emissions per person.

If only it were that easy. Partly it is, of course – some of the gain comes from the heat being directly reflected back, and that bit still holds. But the paper refers to carbon emissions saved from people in white-roofed houses not needing to run air conditioners. That might be fine in Texas or California, or Australia but in NZ the problem set is completely different. Most people don’t have aircon, beyond the windows. Those who do probably use it for a couple of months a year, at most. A much greater problem in NZ is heating – so in NZ we should be painting our roofs dark in order to save on heating, right?

Perhaps what we need is a switchable system which can be dark or light when needed. But the lesson is a much more elementary one – house design should suit the locale.

Eagerness, again, is no substitute for thought.

L