Zee Media Bureau/Salome Phelamei
Pasadena, CA: In a finding that is seen as a significant factor in reducing global warming, a new NASA-led study confirmed that natural forests in the Amazon remove more carbon dioxide from the atmosphere than they emit.
The seven-year study, which was led by Fernando Espírito-Santo of NASA`s Jet Propulsion Laboratory, resolves a long-standing debate about a key component of the overall carbon balance of the Amazon basin.
While living trees take carbon dioxide out of the air as they grow, dead trees put the greenhouse gas back into the air as they decompose.
The new study that included scientists from US, UK, Brazil, Peru and Australia is the first one to measure tree deaths caused by natural processes throughout the Amazon forest, even in remote areas where no data has been collected at ground level.
To analyse satellite and other data, scientists created new techniques and they found that each year, dead Amazonian trees emit an estimated 1.7 billion metric tons of carbon to the atmosphere. To compare this with Amazon carbon absorption, the researchers used censuses of forest growth and different modelling scenarios that accounted for uncertainties.
In every scenario, carbon absorption by living trees outweighed emissions from the dead ones, indicating that the prevailing effect in natural forests of the Amazon is absorption.
Till date, scientists had only been able to estimate the Amazon’s carbon balance from limited observations in small forest areas called plots. On these plots, the forest removes more carbon than it emits, but the scientific community has been vigorously debating how well the plots represent all the natural processes in the huge Amazon region. That debate began with the discovery in the 1990s that large areas of the forest can be killed off by intense storms in events called blow-downs.
Espírito-Santo said that the idea for the study arose from a 2006 workshop where scientists from several nations came together to identify NASA satellite instruments that might help them better understand the carbon cycle of the Amazon.
“It was a difficult and audacious study, and only Espírito-Santo’s dedication made it possible,” said Michael Keller, a research scientist at the US Forest Service and co-author of the study.
Correlating satellite and airborne-instrument data with ground observations, Espírito-Santo and his colleagues devised methods to identify dead trees in different types of remotely sensed images. For example, fallen trees create a gap in the forest canopy that can be measured by lidar on research aircraft, and dead wood changes the colours in a satellite optical image. The researchers then scaled up their techniques so that they could be applied to satellite and airborne data for parts of the Amazon with no corresponding ground data.
This study looked only at natural processes in Amazonia, not at the results of human activities such as logging and deforestation, which vary widely and rapidly with changing political and social conditions.
The new study is published in Nature Communications on March 18.