- News Home
12 December 2013 1:00 pm ,
Vol. 342 ,
In an ambitious project to study 1000 years of sickness and health, researchers are excavating the graveyard of the now...
Stefan Behnisch has won awards for designing science labs and other buildings that are smart, sustainable, and...
The iconic 125-year-old Lick Observatory on Mount Hamilton near San Jose, California, is facing the threat of closure...
Recent results from the Curiosity Mars rover have helped scientists formulate a plan for the next phase of its mission...
A new, remarkably powerful drug that cripples the hepatitis C virus (HCV) came to market last week, but it sells for $...
In pretoothbrush populations, gumlines would often be marred by a thick, visible crust of calcium phosphate, food...
Evolutionary biologists have long studied how the Mexican tetra, a drab fish that lives in rivers and creeks but has...
Victorian astronomers spent countless hours laboriously charting the positions of stars in the sky. Such sky mapping,...
- 12 December 2013 1:00 pm , Vol. 342 , #6164
- About Us
Amazon's Carbon Sink Under Threat
5 March 2009 (All day)
Researchers monitoring the long-term health of the Amazon tropical rainforest have made a startling discovery. A severe drought in 2005 not only restricted the rainforest's ability to absorb carbon dioxide from the atmosphere but also, in some cases, killed off so many trees that it made areas net CO2 emitters. The findings, to be reported in tomorrow's issue of Science, suggest that not even rainforests can be considered fail-safe when it comes to sequestering greenhouse gases.
When the world's tropical rainforests are growing, they can absorb a huge amount of CO2 from the atmosphere--on the order of 1.8 billion metric tons annually, or nearly one-fifth of global emissions from fossil-fuel combustion. But when trees are not healthy, they don't use nearly as much CO2, and in some cases they can even be a net emitter.
RAINFOR, a team of scientists from 13 nations, has been tracking forest health in the Amazon for the past 25 years by surveying 136 plots scattered across 44 sites in the region. When the drought struck in 2005, the researchers raced across the Amazon Basin to assess the potential damage. They managed to remeasure 55 of the plots that year. Before the drought, trees on 76% of those plots had been sequestering about 0.5 tons of carbon per year per hectare, while the remainder were growing less rapidly and therefore packing away less carbon. During the drought, however, only 51% continued to sequester carbon, while the rest lost carbon--as much as 6 tons per year per hectare--the result of rot and digestion by soil microbes.
"We found the Amazon surprisingly sensitive to drought," says ecologist and lead author Oliver Phillips of the University of Leeds in the U.K. The 2005 event "was strong enough to switch the forest from being a long-term absorber of CO2 ... to being a temporary source of CO2." Because some climate models point to increased incidences of drought in the Amazon Basin this century, he adds, the loss of tropical rainforests as a carbon sink could cause CO2 levels to rise even faster.
Ronald Neilson, a bioclimatologist with the U.S. Department of Agriculture's Forest Service in Corvallis, Oregon, says the study shows that drought in the rainforest "can have a very significant impact on the planetary carbon balance." But he points out that because droughts tend to produce fewer cloudy days, increased sunlight may encourage growth even in dry weather.