Forests are more important for the climate than we think
New discoveries show treetops bring cooling clouds that reflect sunlight
Most of us took science class in high school. When our teacher stood at the front explaining how things worked, we assumed they were right. After all, it was science. But with time we learned that science constantly evolves, building on each new idea or discovery. (That hit home when I realized the Solar System no longer has nine planets!)
What is known about the links between forests and climate is also changing. The old view was that vegetation is determined by the climate, now we know that it is also the other way around: vegetation also influences the climate.
Scientists have long recognized the importance of plants sucking carbon dioxide out of the air. But they have only recently realized how much plants influence the amount of sunlight the earth absorbs and how much water vapor, hot air, dust, and other particles and chemicals rise to the sky. These factors have a huge influence on temperatures and rainfall, not only locally but also hundreds of miles away.
That means losing trees and forests can greatly change the climate. It can make cities unbearably hot, cause crops to fail, spark wildfires, and dry up urban reservoirs.
What scientists discovered
Why did it take so long to understand the links between forests and the climate? People have speculated on forests’ effects on the climate for centuries. But without remote sensing, big data, artificial intelligence, and flux towers, scientists lacked the tools to disentangle all the different pieces. Even today, this is right on the cutting edge. Almost every week new studies come out that make us rethink our preconceptions.
Two such studies hot off the press highlight how forests cool the planet by creating more clouds. Gregory Duveiller and his team published “Revealing the Widespread Potential of Forests to Increase Low Level Cloud Cover” in Nature Communications on July 15th. Then the Proceedings of the National Academy of Science came out with “Cloud Cooling Effects of Afforestation and Reforestation at Midlatitudes” by Sara Cerasoli, Jun Yin, and Amilcare Porporato three weeks later.
The Duveiller et. al. study used high resolution satellite data and sophisticated statistical analysis to assess how different types of vegetation affects low cloud cover; something practically impossible until recently. They found that in most tropical, temperate, and arid regions forests increase low cloud cover, sometimes by as much as 15%. Unlike high clouds, which tend to warm the earth, low level clouds usually cool it. That is because high clouds let the sunlight get through and then trap the heat below, while low-level clouds reflect most of the rays back into the sky. In some regions, including the tropics, low clouds also bring more rain.
The Cerasoli, Yin, and Porporato study looked at the same issue, using a slightly different method. They were particularly interested in whether more trees would help cool the Earth in mid-latitude areas in North America, Europe, and China. Many scientists believe that planting trees in these areas raises temperatures since forests absorb more sunlight than grass, shrubs, or crops because they are darker. (Like dark clothing in the sun makes you hotter). These scientists assume forested areas will absorb heat, but they do not consider cloud formation. It turns out that, in these areas, extra clouds forests create block enough sunlight to compensate for the darker cover.
Why this matters
Forests and trees usually help us to keep the earth cool and avoid drought, often in ways we have never heard of. If we lose them, climate change will hit us even harder — and it is not just because trees suck up carbon. We are constantly learning new reasons to keep forests standing.
There’s a lot yet to learn about how vegetation affects the climate. So, we cannot say exactly how losing so much forest will affect our local (and global) climate. But with this growing body of research, we now have even more evidence to prove that destroying forests is not a good idea.
Read the research:
Revealing the Widespread Potential of Forests to Increase Low Level Cloud Cover: https://www.nature.com/articles/s41467-021-24551-5
Cloud Cooling Effects of Afforestation and Reforestation at Midlatitudes: https://www.pnas.org/content/118/33/e2026241118
Satellites reveal how forests increase cloud and cool climate:https://phys.org/news/2021-08-satellites-reveal-forests-cloud-cool.html
