Humanity Can Beat The Heat -- But Our Cities Need Millions More Trees

Noting that a green umbrella helps lower temperatures, MIT's Senseable City Lab has put together a "Treepedia" that compares tree coverage in a number of cities. The researchers based the calculations behind their "green view index" on Google Street View panoramas.

Paris came in near bottom. It's tree canopy covered only 8.8% of the city. In contrast, London's shaded 12.7%. In Los Angeles, trees sheltered 15.2% of the city from the sun. There should be little surprise that Seattle's tree coverage was an admirable 20%.

Interestingly, New York City's "green view index" came in at a respectable 13.5%. Gotham is not all "concrete canyons," as lore would have it.

Complicating cities' efforts to plant more trees is the competition for limited space. For example, Athens has long been a hot, paved city. But proposals there to plant trees must fight demand for parking spaces. One must choose.

The heat problem has economic implications. By 2050, "urban heat stress" could cut a person's ability to work by about 20% in the hot months, according to a United Nations report by leading climate experts. Overheated human beings are more likely to suffer exhaustion, dizziness and even organ failure.

Trees, of course, play a big-picture role in the global warming crisis. Wherever they are located, trees store the carbon dioxide gases that warm the earth's atmosphere. They also release water vapor that helps form clouds. Thus, the massive deforestation in the tropics is harming quality of life in far-distant places, including northern urban centers.

The science here is not simple, though. Some effects of climate change could actually moderate the heat trend. As the Arctic melts, Science magazine reports, trees are growing in regions where ice predominated. In parts of Alaska where there was only moss and lichen, spruce trees are rising.

The bare tundra of northern Siberia is giving way to bushes and willows. Such a development, if it continues, would create no small forest. The Nenets autonomous district alone is the size of Florida.

In arid regions with milder climates, meanwhile, increased concentrations of carbon enable plants to use water more efficiently and thrive in drier soils. Carbon dioxide also acts as a fertilizer, promoting the growth of wood and leaves.

Certainly, multibillion-dollar things can be done to insulate buildings and retrofit the urban infrastructure to absorb less heat. But trees cost so little, do not require new technology and look nice, too.

Trees don't just stand there. They can help beat the heat and may end up saving civilization. Dogs already know this.

Follow Froma Harrop on Twitter @FromaHarrop. She can be reached at fharrop@gmail.com. To find out more about Froma Harrop and read features by other Creators writers and cartoonists, visit the Creators webpage at www.creators.com.