Tropical forests have emerged as a crucial factor in the fight against climate change, according to a new NASA-led study published Friday which finds that they are absorbing carbon dioxide at a far higher rate than previously thought.
As atmospheric levels of greenhouse gases have continued to rise, tropical forests, like those found in Malaysia, have been absorbing roughly 1.4 billion metric tons of carbon dioxide out of a total global absorption of 2.5 billion, NASA found. Those rates are not only higher than previously estimated, they are also higher than those of the vast boreal forests found in northern regions like Canada and Siberia—which are diminishing.
"This is good news, because uptake in boreal forests is already slowing, while tropical forests may continue to take up carbon for many years," said Dr. David Schimel, NASA Jet Propulsion Laboratory senior research scientist and lead author of a paper on the study.
Forests use human-made emissions to grow faster, which in turn reduces the amount of carbon dioxide in the atmosphere—an effect known as carbon fertilization. They also remove up to 30 percent of airborne human emissions through photosynthesis. If those processes slowed down, the rate of global warming would increase.
Why was it important to determine which kind of forest are more adept at that process?
Because the answer "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," said Britton Stephens, co-author of the study and a scientist at the National Center for Atmospheric Research.
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Schimel added, "All else being equal, the effect is stronger at higher temperatures, meaning it will be higher in the tropics than in the boreal forests."
The problem lies in other harmful impacts of climate change that also affect forests. Warming temperatures decrease water availability and increase larger and more frequent wildfires—which, in turn, release large amounts of carbon into the atmosphere.
Still, NASA's discovery is largely auspicious. "What we've had up till this paper was a theory of carbon dioxide fertilization based on phenomena at the microscopic scale and observations at the global scale that appeared to contradict those phenomena," Schimel said. "Here, at least, is a hypothesis that provides a consistent explanation that includes both how we know photosynthesis works and what's happening at the planetary scale."
The study is groundbreaking in its methodology, as it is the first to use a variety of models, technology, and data to create an "apples-to-apples" comparison carbon dioxide estimates between forests, NASA explained.
By using computer models of ecosystem processes, inverse models of atmospheric concentrations, satellite images, and other data and analysis, the researchers were able to determine the accuracy of their results "based on how well they reproduced independent, ground-based measurements."