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Cool cities

Steven Chu is cheerleading another approach to fight global warming: Painting roofs and even pavements white to reflect sunlight. Such a measure is suggested to potentially offset 44 Gt of CO2 emissions via negative radiative forcing when implemented globally. White painting is related to a list of geo-engineering approaches, including ocean fertilization with iron and sending sulphate aerosols into the stratosphere. However, these approaches can endanger ecosystems, are potentially very limited in their efficacy, cost a lot and pose significant risks (e.g., see here for the sulphate case). It seems that white painting has less of these disadvantages, beside the need for more sunglasses.

White painting is also not an esoteric method. Precisely because is works so well, white painting is an established method all over the world. Consider the white towns in Andalusia and Nicaragua. From above, such a town - Arcos de la Frontera in Andalusia - looks like this.

Arcos de la Frontera in Andalusia. Source: Wikipedia.

Of course, the historic towns have not been built to mitigate or geo-engineer climate change. The motivation was simply to cool down the city in the summer heat. This observation is crucial to understand that climate change mitigation does not necessarily have to be conducted through the perspective of climate change. Cities may be motivated by the more direct impact of white painting, for example. The effect of white painting is double fold:

• Direct: Higher urban albedo reduces summer temperature in cities
• Indirect: Less air-conditioning is needed

Both effects mitigate climate change, benefit house dwellers, and benefit fellow city inhabitants. These co-benefits on different agent levels are pleasant from a game-theoretic perspective. Common national measures discussed in international negotiations are often framed in the context of a modified prisoner’s dilemma where national action produces costs locally but externalizes the benefits. White painting, as well as many other measures, offers a no regret options for city dwellers. Either it helps to cool the global climate or it provides proper adaptation and protection for increased global heat. White painting has another advantage: no big investments or government action is needed. Motivated dwellers can act themselves, or municipalities can initiate urban schemes. Specifically, engaged US-cities do not need to wait for reluctant Congress. Action can be incremental and action is not dependent on a huge technological breakthrough.

Urban gardening or parks are another related measure to reduce the urban heat island effect and cool down cities. It would be interesting to explore to what degree urban greening and urban whitening complement or compete against each other and where what kind of strategy is more appropriate.>.

Posted by Felix Creutzig on May 27, 2009 11:38 PM | Permalink