The city of San Diego is giving away free trees. It's a great idea, and I’m glad that mayor Falkner jumpstarted a program that has been languishing. Trees can take just about any urban or suburban street and make them more livable. People are more likely to walk down a street if it has trees on it. Trees buffer street noise and they give us shade. I encourage you to get your tree while they are still available. The city plans on planting 1000 trees, but they have already planted 750. So hurry up and get your tree before they are all gone. My one complaint is that, as part of the city of San Diego’s Climate Action Plan, not all the trees being offered are appropriate for the purpose of a climate response. Sure the trees store carbon, but the essential function of trees in an urban climate response is to mitigate the heat island effect. And the way they do that is by providing shade. Before I go on, here’s a brief primer on the heat island effect. Concrete and asphalt heat up more than areas covered by trees and shrubs, making cities hooter than the surrounding countryside. This raises the temperatures in cities, making summertime more unpleasant and also causing an increase in ozone and greater reliance on air conditioning. And as global warming increases, we will want to further mitigate the heat island effect. A lot of the trees offered by the city provide minimal shade. Many of the trees offered are palms, such as king palms and Mexican fan palms. Have you ever laid out a picnic under the shade of either? I didn’t think so. Compare the shade of the street on the left, which has shade trees, and the right, which is shaded by palms. Which one is going to be cooler? Providing cool streets makes them more pleasant and walkable. It also reduces or eliminates our reliance on air conditioning, something that uses a lot of energy.
Now don’t get me wrong. This is a good program. I’m just saying that it could be more helpful in reducing our heat island effect in San Diego. Have you received a tree from the city? What do you want, shade or a tropical palm?
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December 2017
CategoriesAuthorPaul Hormick is the founder of South Park Climate Solutions. He sees climate change as one of our central concerns, for ecologies as well as societies. He holds a master's degree in Environmental Science and Policy from Johns Hopkins University |