The Amazon has long done its part to balance the global carbon budget, but new evidence suggests the climate scales are tipping in the world's largest rainforest. Now, according to a study published July 14 in Nature, the Amazon is emitting more carbon than it captures.
This study is the first to use direct atmospheric measurements, across a wide geographic region, collected over nearly a decade that account for background concentrations of atmospheric gases.
These results have important implications for policy initiatives such as REDD+ that rely on forests to offset carbon emissions. Because different regions of the Amazon differ in their ability to absorb carbon, schemes that use one value for the carbon-capturing ability of the whole Amazon need to be reexamined, scientists say.
"The Amazon is a carbon source. No doubt," Luciana Gatti, a researcher at Brazil's National Institute for Space Research (INPE) and lead author of the study, says. "By now we can say that the budget for the Amazon is 0.3 billion tons of carbon per year [released] into the atmosphere. It's a horrible message."
Southeastern Amazonia, in particular, switched from being a carbon sink to a carbon source during the study period. Emissions were high in 2010 because of a dry El Niño year, Gatti says, and she expected to see emissions return to normal afterward. But this never happened. The reason: emissions from fires.
In the Amazon, forests are often cut during the wet season and burned during the dry season to make way for agribusiness, particularly cattle pasture. According to the study, fire emissions in the southeastern Amazon are three times larger than the net biome exchange (NBE), a measure of the forest's carbon uptake plus all emissions from decomposition and human sources such as burning fossil fuels.
Without emissions from fires, Gatti says, the Amazon would be a carbon sink. "In other words, the Amazon is a source because of biomass burning."