A Primer on the Relationship Between Deforestation and Global Warming
written by: Don Shepard•edited by: Sarah Malburg•updated: 1/12/2010
The relationship between deforestation and global warming is both straightforward and complex. Here is a description of how trees fight climate change. Included are ways trees directly and indirectly affect the atmosphere.
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Trees: Climate Change Soldiers
Standing swaths of forests have always been valued by those who care about our environment, though the need to protect them is magnified with the high stakes issue of climate change taking front and center. The relationship between deforestation and global warmingis drawing much attention from the research community as there is still more to be learned about this correlation. While some processes are well understood, the implications from feedback within the climate system may not be.
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Carbon “Sink" Description
The biggest role trees play in mitigating atmospheric carbon and associated climate change is “fixing" of carbon. This takes place mainly through photosynthesis. The reverse of photosynthesis is plant respiration where carbon dioxide is released back into the atmosphere. This results in seasonal fluctuations of carbon dioxide in the air. The real climate change mitigation happens as a result of long term cycles that result from this process. As pointed out by NASA’s Earth Observatory, plants increase soil weathering, which leads to “long-term—but slow—uptake of carbon dioxide from the atmosphere."
Forests are the second largest carbon reservoir on the planet, trailing only oceans. Tropical rainforests are the biggest contributor to this reservoir. According to Michigan State University’s Rain Forest Report Card, “Each acre of tropical forest stores about 180 metric tons of carbon." Deforestation releases this carbon all at once.
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Trees affect albedo rates of the earth’s surface. Albedo is defined by The Free Dictionary as: “The fraction of incident electromagnetic radiation reflected by a surface, especially of a celestial body." An example of a high albedo surface is land covered with snow. Basically, more of the sun’s radiation is reflected with snow on the ground, resulting in less warming.
It is generally accepted and portrayed by general circulation models (GCM’s) that deforestation decreases the albedo rate of the land. Decreasing the albedo further contributes to the problem of equatorial warming. So a subversive way trees fight climate change is through increasing, or maintaining, albedo rates.
Tress can creates thick cloud cover, as famously portrayed in Amazon rainforest images. Deforestation can cause decreases in humidity and its’ associated clouds. This sets off many reactions that have varying effects on global climate change.
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Beware Unintended Consequences
When planting trees to fight global considerations such as previous land uses, the trees' nativeness and soil types should be considered. Planting trees in an area of native grassland is not always a good idea. Reasons for this vary and can get complicated, though the basic reason is that the introduction of non-native plants changes natural cycles. These include the cycles of water, carbon and nitrogen. This can do things such as disrupt the carbon storage capacity of the soil, increase nitrogen runoff into a nearby stream, and introduce other environmental problems.
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The relationship between deforestation and global warming can be compared to many envrionmental issues. The interruption of natural cycles can cause changes which permeate the biosphere. The abrupt landscape change brought about by clear cutting trees is an example of such an interruption on a large scale.
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Michigan State University. Rainforest Report Card: Deforestation of Tropical Rainforests. http://www.trfic.msu.edu/rfrc/status.html (accessed January 11, 2010).
NASA. The Carbon Cycle. January 11, 2010. http://earthobservatory.nasa.gov/Features/CarbonCycle/carbon_cycle2.php (accessed January 11, 2010).
TheFreeDictionary. TheFreeDictionary. 2010. http://www.thefreedictionary.com/albedo (accessed January 11, 2010).