Sitting in the air conditioning, I stare out the window and smile as the dogs being walked crumble in the shade of my Norway maple. And who could blame them? Would any of us want to go out in this scorching heat with a fur coat on?
It was one of the rare times when I was thankful for not being in Paris. That’s because, although much of Europe is baking, Paris is still suffering more than cities like London, where the temperature has exceeded an unheard-of 100 degrees Fahrenheit.
Climate change is happening everywhere, but why is Paris doing worse than elsewhere? Not enough trees.
Trees provide shade, which cools the sidewalk below. They also increase water evaporation, another heat moderating factor.
Concrete, metal and asphalt in cities absorb heat and release it. Without much greenery to offset some of it, Paris has become a textbook case of “urban heat islands”. That is, parts of the city were nearly 20 degrees warmer than nearby areas.
The preferred French word for heatwave is “canicule”. Translation: “dog days.”
Noting that a green umbrella helps lower temperatures, MIT’s Senseable City Lab has put together a “Treepedia” that compares tree cover in a number of cities. The researchers based the calculations behind their “green view index” on panoramas from Google Street View.
Paris has arrived at the bottom. Its canopy covered only 8.8% of the city. In contrast, London lost 12.7%. In Los Angeles, trees shaded 15.2% of the city from the sun. It should come as no surprise that Seattle’s tree cover reaches an admirable 20%.
Interestingly, New York’s “green view index” reached a respectable 13.5%. Gotham isn’t all “concrete canyons,” as tradition would have it.
Competition for limited space complicates cities’ efforts to plant more trees. For example, Athens has long been a hot, cobbled city. But tree-planting proposals must contend with the demand for parking spaces. It’s necessary to choose.
The heat problem has economic implications. By 2050, “urban heat stress” could reduce a person’s ability to work by around 20% during hot months, according to a United Nations report by leading climate experts. Overheated human beings are more likely to suffer from exhaustion, dizziness and even organ failure.
Trees, of course, play an important role in the global warming crisis. Wherever they are, trees store carbon dioxide which warms the earth’s atmosphere. They also release water vapor which helps form clouds. Thus, massive deforestation in the tropics harms the quality of life in remote places, including urban centers in the north.
The science here isn’t straightforward, however. Some effects of climate change may actually moderate the warming trend. As the Arctic melts, reports Science magazine, trees are growing in areas where ice was prevalent. In parts of Alaska where there used to be only moss and lichen, spruce trees grow.
The bare tundra of northern Siberia gives way to bushes and willows. Such development, if continued, would not create a small forest. The Nenets Autonomous District alone is the size of Florida.
In arid regions with milder climates, increased carbon concentrations allow 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, multi-billion dollar things can be done to insulate buildings and retrofit urban infrastructure to absorb less heat. But trees cost so little, don’t require new technology, and look beautiful too.
The trees don’t stay there. They can help beat the heat and may end up saving civilization. The dogs already know this.
Follow Froma Harrop on Twitter @FromaHarrop. She can be contacted at [email protected]