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).
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.
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.
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.
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 Communications, 12(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 Sciences, 118(33), e2026241118. https://doi.org/10.1073/pnas.2026241118
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 Climate, 32(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