Amazon basin can be a carbon source

The use of carbon sinks has a prominent role under the Kyoto Protocol, point out Aurélie Botta, Navin Ramankutty and Jonathan Foley from the Center for Sustainability and the Global Environment (SAGE), at the University of Wisconsin, Madison. “Yet our current understanding of the terrestrial biosphere is far from complete, making it difficult to quantify the carbon balance on regional scales, and to predict how it may change over time,” they say. The three researchers have examined the long-term effects of climate on the carbon balance of the Amazon rainforest.

In particular, the long-term behaviour of ecosystems, which could include switching between being carbon sources and carbon sinks, is little understood, they point out. “Our current understanding of the carbon budget of the Amazon basin is based solely on short-term studies,” say the researchers.

The study focuses on the period from 1935 to 1995, and reveals that, considering variations only in climate, the Amazon was carbon neutral from the late 1930s to the late 1950s. The region was then a net carbon source during the 1960s, a net sink during the 1970s, and was back to being nearly neutral throughout the 1980s and 1990s.

“This study raises serious questions regarding our ability to use short-term observations and modelling exercises to study the global carbon cycle,” the researchers conclude. “We must ask ourselves if our observations and our models are good enough to be able to understand the long-term behaviour of the global carbon cycle.”

Last month it was revealed that water courses within rainforests give off substantial levels of carbon dioxide, also questioning the use of forests as the world’s carbon sinks (see related story).