Amazon Forest Drought Corrects Global Warming Model

A prominent global climate model predicts that the Amazon forest would begin to "brown down" after just a month of drought and eventually collapse as the drought progressed, but according to the University of Arizona (UA), drought-stricken regions of the Amazon forest grew particularly vigorously during the 2005 drought.

This counterintuitive finding contradicts expectations. Scott R. Saleska of the University of Arizona, who is the author of the new research paper, says that it is a very interesting and surprising result. "Instead of 'hunkering down' during a drought as you might expect, the forest responded positively to drought, at least in the short term."

Researchers already knew the Amazon forest takes advantage of annual dry seasons to absorb sunlight, which is unimpeded by clouds, and grow. The UA scientists and some other researchers had conducted previous research using satellite data in combination with field measurements and learned that intact Amazon forest increases photosynthesis, actually "greening up," during the dry season.

Current global climate models predict that the Amazon forest would quickly cut back photosynthesis when a drought starts. That slowdown in plant growth would create what is known as a positive feedback loop -- as the forest processes less and less photosynthesis, it removes less and less carbon dioxide from the atmosphere. According to the model, the CO2 ordinarily sequestered by growing trees would remain in the atmosphere, increasing global warming and further accelerating the forest's decline and additional CO2-fueled warming.

Saleska, a UA assistant professor of ecology and evolutionary biology, and his colleagues at the UA and at the University of São Paulo in Brazil used data from two NASA satellites to discover that in the 2005 drought undisturbed Amazon forest flourished as rainfall levels plummeted.