A new study led by NASA and the National Center for Atmospheric Research (NCAR) shows that tropical forests may be absorbing far more human-emitted carbon dioxide than many scientists thought. The study estimates that tropical forests absorb 1.4 billion metric tons of carbon dioxide out of a total global absorption of 2.5 billion, in response to rising atmospheric levels of the greenhouse gas.
This means, if left undisturbed, the tropical trees should be able to continue reducing the rate of global warming.
“This is good news, because uptake in northern forests may already be slowing, while tropical forests may continue to take up carbon for many years,” said David Schimel of NASA’s Jet Propulsion Laboratory in Pasadena, California.
Schimel is lead author of a paper on the new research, appearing this week in the Proceedings of National Academy of Sciences.
The question of which type of forest is the bigger carbon absorber “is not just an accounting curiosity,” said NCAR scientist Britton Stephens, a co-author on the paper. “It has big implications for our understanding of whether global terrestrial ecosystems might continue to offset our carbon dioxide emissions or might begin to exacerbate climate change.”
Forests and other land vegetation currently remove up to 30 percent of human carbon dioxide emissions from the atmosphere by absorbing carbon dioxide during photosynthesis. If the rate of absorption were to slow down, the rate of global warming would speed up in return.
The new study is the first to devise a way to make apples-to-apples comparisons of carbon dioxide uptake estimates from many sources at different scales: computer models of ecosystem processes, atmospheric models used to deduce the sources of today’s concentrations (called atmospheric inverse models), satellite images, data from routine and experimental forest plots, and more. The researchers reconciled these analyses and assessed the accuracy of the inverse models based on how well they reproduced independent, airborne and ground-based measurements. They obtained their new estimate of the tropical carbon absorption from the weighted average of atmospheric, ecosystem model, and ground-based data.