Study: Afforestation Can Lead to More Cloud Cover

Afforestation and reforestation are important components of sequestering carbon and reducing carbon dioxide levels in the atmosphere. By moving carbon into tree matter, increasing forest cover has been touted as one method of offsetting carbon dioxide levels and mitigating climate change.

Impact of Cloud Cover on Reflectance

Researchers are also looking into what affect increased forest cover has on cloud cover. Increased cloud cover can both shade and trap heat at the surface of the Earth.

Factors such as cloud reflectiveness, cloud height, and whether it is day or night impact which of those two impacts the presence of clouds will have.

Low clouds normally cool the atmosphere by reflecting energy back into space, while high clouds often warm the atmosphere by trapping and emitting radiation back to the surface (L’Ecuyer et al., 2019).

This map made using data from NASA’s Terra satellite’s CERES instrument shows how the Earth’s reflectivity—the quantity of sunlight reflected back into space—changed between March 1, 2000, and December 31, 2011. Blue hues represent areas that have reflected more sunlight over time (increasing albedo), whereas orange hues denote places that have reflected less sunlight (lower albedo). Map: NASA’s Earth Observatory.

The presence of trees can increase cloud cover through the process of transpiration. Trees and plants release water vapor as they take in carbon dioxide. Collectively this water vapor can form clouds over the forested area.

Clouds over the Amazon Forest. Source: Aqua Satellite, NASA, August 19, 2009.

How Cloud Cover Changes with Afforestation

Using remotely sensed data from satellites, researchers analyzed the presence and type of cloud cover by sample forested areas around the globe. Using records of global cloud and land-fractional cover data collected by ESA’s Climate Change Initiative to study the influence of vegetation cover transitioning to deciduous and evergreen forest.

Afforestation is the process of establishing forest cover in an area with no previous forest cover established.

A map of forest area in Europe showing increase in cloud cover during the forest months. Blue areas area increased cloud cover.
Cloud cover increased during the summer months over boreal forests in North America, Russia, and Eastern Europe. Figure: Duveiller et al., 2021, CC BY 4.0.

The study found that afforestation in 67% of the sample areas resulted in an increase in low-lying cloud cover. Cloud cover increased in temperate, tropical and arid regions, sometimes by as much as 15%. The researchers note that the increase in low cloud coverages should have a cooling effect on the region by reflecting radiation.

Cloud cover during winter and spring in Boreal regions (North America, Russia and Eastern Europe) is inverted during periods of snow cover as compared to non-forested regions. Cloud cover increases about 5% of the normal cloud fraction during the summer in these regions.

Low lying clouds cool the surface of the Earth by reflecting the Sun’s radiation back into space. Photo: John Mosesso, USGS, public domain.

Studies

Duveiller, G., Filipponi, F., Ceglar, A., Bojanowski, J., Alkama, R., & Cescatti, A. (2021). Revealing the widespread potential of forests to increase low level cloud cover. Nature Communications12(1), 1-15. https://doi.org/10.1038/s41467-021-24551-5

Satellites reveal how forests increase cloud and cool climate. (2021, August 5). European Space Agency. https://www.esa.int/Applications/Observing_the_Earth/Space_for_our_climate/Sa

Cerasoli Sara, Yin Jun, & Porporato Amilcare. (2021). Cloud cooling effects of afforestation and reforestation at midlatitudes. Proceedings of the National Academy of Sciences118(33), e2026241118. https://doi.org/10.1073/pnas.2026241118

Additional References

L’Ecuyer, T. S., Hang, Y., Matus, A. V., & Wang, Z. (2019). Reassessing the effect of cloud type on earth’s energy balance in the age of active spaceborne observations. Part I: Top of atmosphere and surface. Journal of Climate32(19), 6197-6217. https://doi.org/10.1175/JCLI-D-18-0753.1

Pearce, F. (2020, February 5). Why clouds are the key to new troubling projections on warming. Yale E360. https://e360.yale.edu/features/why-clouds-are-the-key-to-new-troubling-projections-on-warming

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Fonte : National Geographic