Tuesday, October 19, 2021

Vox and PBS Terra examine planting trees to fight climate change

I tell my students that income inequality is visible from space. That's because of the relative density of trees, with wealthier neighborhoods having more tree and poorer ones having fewer, which satellites can photograph from orbit. That has important environmental effects, as Vox depicts in How America's hottest city is trying to cool down.

Can trees help save Phoenix from extreme heat?
It’s time to stop looking at trees as a form of “beautification.” They are, instead, a living form of infrastructure, providing a variety of services that include stormwater management, air filtering, carbon sequestration, and, most importantly for a city like Phoenix, Arizona, they cool the environment around them.

Trees can lower neighborhood temperatures in three ways:
1) Their shade prevents solar radiation from hitting paved surfaces like concrete and asphalt, which absorb energy and rerelease it into the air as heat.
2) Their leaves pull heat from the immediate area in order to evapotranspirate water that’s drawn from the soil.
And, 3) If you’re standing under one, a tree protects your body directly from the sun’s rays. If you’ve ever made a summer visit to a dry, hot city like Phoenix, you’ll know how important shade is for making any outdoor experiences tolerable.

As Phoenix deals with a rising frequency of extreme heat waves — which aren’t only deadly, but also cause worrisome spikes in energy demand — the city is looking to trees as part of its heat mitigation strategy. Phoenix isn’t devoid of trees, but they’re distributed unevenly across the city. A quick glance at a satellite image of the metro area reveals substantial green splotches in the north and east and brown ones in the south and west, where many lower-income neighborhoods are located.

So Phoenix recently pledged to reach “tree equity” by 2030, under an agreement with American Forests, a national tree organization. I visited Phoenix recently to take a look at the current state of the city’s urban forest. In this video, we use drone imagery and thermal cameras to understand how the urban design of the city contributes to extreme heat, and what it can do to cool down.
I wish Phoenix luck in achieving "tree equity." They'll need it, especially with the challenges of drought and aridification working against the effort.

PBS Terra also examined planting trees as a method of carbon capture in The Surprising Truth Behind Planting Trees.

For decades we’ve been planting trees in hopes of reducing carbon pollution. But when it comes to carbon sequestration, have we actually been getting it all backward?

As the UN Climate Conference (COP26) approaches this November, the topic of carbon capture and storage will be hotly debated. In this episode, we travel to the Pacific Northwest forests of Oregon to see what we can learn about forest carbon sinks from Beverly Law and her groundbreaking research with Oregon State University’s Department of Forestry.

What do you think about planting trees and forest carbon storage? Let us know in the comments!
Planting trees serves as an example of "Nature knows best" for sequestering carbon, but this video shows it's not a good short-term solution. Another PBS Terra video shows one possible technique, but I'll save that for another video. Stay tuned.

Both of these are great videos to show my students. I'll be sure to find places in my curriculum to do so.

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