Planting Trees Encourages Cloud Formation—and Efficiently Cools the Planet

New study examines cooling effect of clouds produced by deciduous forests under pressures of climate change

Reforestation
The creation of clouds over forested areas shows that reforestation would likely be more effective at cooling Earth’s atmosphere than previously thought, a Princeton study says.

A new study shows that reforestation does more than shield the Earth with green leaves—it produces clouds that also protect the planet from the sun’s rays. It seems like a no-brainer, but if we plant forests, it could cool the climate—more than previously thought.

Researchers at Princeton University discovered that many climate models don’t take into account the clouds produced by forested areas, resulting in cooler temperatures. Other scientists were concerned that trees in midaltitude regions—temperate areas between the tropics and polar zones—would not be effective in controlling the climate when they lost their leaves in winter, reports Gustaf Kilander for the Independent.

“We show that if one considers that clouds tend to form more frequently over forested areas, then planting trees over large areas is advantageous and should be done for climate purposes,” co-author Amilcare Porporato, a civil and environmental engineer at Princeton, says in a statement.

Some scientists questioned the benefit of replanting forests in midaltitude regions because of albedo—the ability of the Earth’s surface to reflect sunlight—when deciduous trees lose leaves during cold seasons, reports Martin Woolridge in the Daily Guardian. The Princeton researchers point out that theory ignores an important consideration.

Published in the peer-reviewed journal Proceedings of the National Academy of Sciences, the study shows that reduced albedo is more than offset by the considerable clouds created by these forests when leafed trees release moisture into the atmosphere.

“The main thing is that nobody has known whether planting trees at midlatitudes is good or bad because of the albedo problem,” Porporato says.

As clouds pass between the sun and Earth, they produce a cooling effect on temperatures. According to this research, clouds have a high albedo—similar to snow and ice—but have been largely discounted in many studies examining natural mitigation of climate change.

Porporato and fellow researchers Sara Cerasoli and Jun Ying combined satellite data of clouds with models estimating the interaction between plants and the atmosphere. The team learned that cooling clouds and increased absorption of carbon dioxide were more beneficial than the solar radiation absorbed by forested areas.

The authors urged caution when considering reforestation for a particular area. Further research is needed to determine how and what needs to be done to a region before tree planting begins.

“We can’t just consider climate change, but must also consider other factors, such as biodiversity and the fact that land is also needed for food production,” says Cerasoli, a Princeton graduate student. “Future studies should continue to consider the role of clouds, but should focus on more specific regions and take their economies into account.”

“So many things are connected in the earth system,” adds Porporato. “The nature of interactions between, for example, the water cycle and climate mean that if you change one thing, it’s very difficult to predict how other parts of the system will be affected.”