Bad news for climate change
In August alone, loggers and farm interests leveled 300 square miles of Amazon rainforest, the Brazilian government reports (via AP).
That’s a land mass larger than greater Chicago — taken out in the span of a single month. It also represents a leap of 228 percent over August 2007’s destruction.
1) Higher soy prices accelerate Amazon clearance (see Searchinger, et al, "Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change" [PDF].) And soy prices have been pushed up by U.S. and European biofuel mandates.
2) The Amazon rainforest anchors global climate stability by storing vast amounts of carbon; destroying it releases carbon and accelerates climate change. In an article in The New York Review of Books last year, Duke ecologist John Terborgh explains why piecemeal deforestation leads to feedback loops that could eventually destroy the rainforest wholesale. In the Amazon region, writes Terborgh,
[l]and clearing and the transformation of the landscape by fire act synergistically to alter the local microclimate and hydrological cycle. Much of the solar energy that falls on a natural forest is dissipated high in the tree canopy through "transpiration," the evaporation of water transmitted from the soil through the roots, stems, and foliage of plants, a process that consumes solar energy and cools the environment. When the forest is largely cut down, less solar energy is intercepted by foliage and more reaches the ground where it is absorbed and heats the surface to stifling temperatures. Reducing the vegetation that covers the ground alters the hydrologic cycle as less moisture is returned to the atmosphere through transpiration and more flows directly into streams and rivers, accelerating erosion.
As the agricultural frontier extends northward into the Amazon region, climate scientists fear that a "tipping point" will be reached at some as yet unknown level of deforestation. The argument runs like this. Nearly all the water that falls as rain in the Amazon derives from the Atlantic Ocean, where it evaporates and is carried onto land by easterly trade winds. The isotopic content of evaporated seawater possesses a distinctive character or "signature" that is altered when rainwater is transpired through the leaves of trees and plants. (The ratios of isotopes of hydrogen and oxygen change with evaporation and transpiration because the heavier isotopes do not evaporate as readily as their lighter counterparts.) The Brazilian atmospheric scientist Eneas Salati showed many years ago that the signature of rainwater varies systematically from east to west across the Amazon basin in a way consistent with the idea that much of the water originally derived from the ocean off the eastern coast is recycled through plants in passing over the Amazon basin. Salati estimated that three quarters of the rainwater falling in western Amazonia is recycled water. When deforestation reduces the amount of rain that is recycled to the atmosphere via transpiration, there will be less water available to fall as rain in the downwind direction, that is, to the west.
Concern that the crucial recycling mechanism will be disrupted by deforestation in the eastern Amazon is widespread in the scientific community. Most climate models agree in indicating a tipping point beyond which parts of the Amazon will become significantly drier. Less rain implies longer, more severe droughts and increased incidence of fire. Carlos Nobre, Brazil’s most distinguished climate scientist, talks of the "savanaization" of the Amazon region, i.e., its reduction to grasslands. A major alteration of the Amazon’s hydrological cycle could have global consequences, but current climate models disagree about what the consequences would be.
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