By Sid Perkins
A new computer model that includes a forest’s effect on regional climate shows that the Amazon rain forest could disappear much more rapidly than previously expected.
Rain forests depend on large amounts of precipitation to remain lush. Much of the moisture taken in by a trees’ roots returns to the atmosphere through the leaves in a process called transpiration. In the rain forest, this process has a significant effect on local and regional climates, says James E. Alcock, an environmental scientist at Pennsylvania State University’s Abington College in Abington.
Logging and burning for agriculture currently claim about 1 percent of the Amazon rain forest per year. Alcock says that this large-scale deforestation substantially alters the rate of transpiration.
After farmers and loggers cut and burn broad swaths of rain forest, more precipitation runs out of the area via the rivers. This leaves less moisture to return to the atmosphere–and that means, in turn, less rain. As a result, forest areas that people have cleared don’t grow back as quickly. Meanwhile, the decrease in precipitation slowly transforms the remaining stands of trees into a different type of forest.
Because large-scale deforestation of the Amazon River basin began in the mid-1970s, a simple calculation that accounts for regrowth predicts that the rain forest there will last only until 2150 or so.
However, Alcock says that when mathematical models also include the effects of decreased transpiration on regional climate, the forest disappears much faster. Such an analysis suggests that the Amazon rain forest could disappear sometime between 2020 and 2030, he notes.
