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Environment - atmosphere

The climate equation

Study evaluates the real impact of native and cultivated plants in the Americas on global temperatures

John Lee / Getty images

Amazon Rain Forest: greater effect than had been estimated before the climate regulation servicesJohn Lee / Getty images

Determining the real effect of deforestation and agricultural activities on the planet’s average temperatures is the main result of research conducted by Brazilian and American researchers. The results were published in the March issue of the journal Nature Climate Change. Better knowledge of the impact of the earth’s ecosystems on the climate has now become possible because researchers have included two previously disregarded phenomena in their calculations: evapotranspiration (the loss of water by evaporation and plant transpiration) and the absorption of solar energy by vegetation. These phenomena of a biophysical nature regulate the local climate and affect the global climate. Previous projects, used to establish environmental protection policies, only included data on the absorption or release of greenhouse gases, the so-called biogeochemical mechanisms, which have global effects.

In the Nature Climate Change article, the researchers showed that they had been able to condense the biophysical and biogeochemical effects into a single, broad index, named climate regulation values (CRV). “This index counts the carbon inventory and the exchange of carbon dioxide in the ecosystems, the emission of nitrous oxide and methane and, in addition, also considers the evapotranspiration and solar energy absorption associated with each type of vegetation,” explains Santiago Cuadra, a researcher from the Celso Suckow da Fonseca Federal Center for Technological Education of Rio de Janeiro (Cefet/RJ), one of the authors of the paper.

The results of the new index reinforce the importance of protecting tropical forests. They also show that boreal forests produce a relatively insignificant effect on the planet’s average temperature. In addition, these results indicate that the crops for the production of bioenergy – such as sugarcane, corn and the Miscanthus giganteus and Panicum virgatum grasses, used to generate ethanol – might have a positive impact on the climate, when considering such issues as water loss, which reduces the temperature of the places where these plantations are cultivated, and the absorption of solar energy by the plants. “It is important to point out that, in general, native forests have a cooling power close to the soil that is stronger than that of agricultural and bioenergy crops,” explains researcher Marcos Heil Costa, from the Federal University of Viçosa (UFV), one of the other authors of the paper. “The best-known exception concerns Canadian pine trees, because, despite the huge amount of snow in this region, the existence of trees tends to warm the region instead of cooling it.”

Forests and plantations
This paper complements a previous one. In an article published in 2000, the researchers had shown that in areas of intense deforesting, such as the Amazon Region, the warming caused by less water being released and by the absorption of solar radiation is several times higher than that caused by the increase of greenhouse gases released into the atmosphere. “Other authors have confirmed these results for several types of changes in land use,” says Costa. “The discussion has evolved to the point of proposing in this article that CRV be applied to natural and agricultural ecosystems, which is compatible with the index of carbon dioxide that is equivalent to that of the greenhouse gas effects.”

The CRV demonstrates the increase of greenhouse gases in the atmosphere and to what extent the temperature closer to the surface of the ground may be changed because of water loss and the absorption of solar energy by plants. This has led to a comparison of how different plants (natural and agricultural) influence the climate and which plants are more efficient at reducing climate change.

The study evaluated the impact of 18 ecosystems in the Americas: 12 of them natural ecosystems and six are agricultural ones with potential for biofuel production. Among them are the Amazon Rainforest and the cerrado (Brazilian savanna) regions and the deciduous tropical forests (that shed leaves in autumn) of South America. The United States included the temperate pine forests from the mountains in the West and on the Northwest Coast, the temperate deciduous forests in the East, and the mixed forests in the Northeast, in addition to forests in the Desert of the Southwest, the forests on the Midwest prairies, and the chaparral (shrubbery) vegetation of California. In Canada, the study analyzed the mixed forests in the southeast, as well as the boreal forest and the tundra.

The following bioenergy-producing crops were analyzed: sugarcane in Brazil and soybeans in Brazil and in the United States. Two types of grasses were analyzed in the United States: Miscanthus giganteus and Panicum virgatum, used for making biofuels. All 18 ecosystems were compared to a barren surface that was used as a reference.

The group evaluated how much each system would contribute to increasing the atmosphere’s temperature over a 50-year period. The results showed that, for most of the ecosystems, water loss and solar energy absorption increase the value of the CRV. This means that the removal of the plant coverage of those ecosystems increases the temperature of the atmosphere because of greenhouse gas emissions and also because this reduces the cooling effect provoked by the existence of vegetation.

“There was a 12% increase in the case of the Amazon Rain Forest,” says Kristina J. Anderson-Teixeira, of the University of Illinois, the main author of the article. “In the case of the cerrado region, the increase was 9%. In the case of some ecosystems, however, they reduced the total value of the service. This was the case, for example, with the boreal forests in Canada (-115%) and in the desert in the Southeast of the USA (-123%).”

Scientific article
ANDERSON-TEIXEIRA, K.J. et al. Climate-regulation services of natural and agricultural ecoregions of the Americas. Nature Climate Change. 8 Jan. 2012.