Tropical forests may be absorbing more carbon dioxide than previously believed in reaction to the increasing atmospheric level of the heat-trapping greenhouse gas, research led by NASA scientists shows.

The study, which was published in the Proceedings of the National Academy of Sciences on Dec. 29, reveals that while some of the carbon dioxide is absorbed by forests in Siberia, Canada and other ice-covered northern regions known as boreal forests, 1.4 billion metric tons of carbon dioxide are estimated to be absorbed by tropical forests per year, a significant chunk in the total global carbon dioxide absorption of 2.5 billion metric tons.

"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 study lead author David Schimel from NASA's Jet Propulsion Laboratory.

For 25 years, climate scientists believed that the northern forests take in more carbon dioxide than the tropical forests, based on understandings of global air flow and the notion that massive deforestation in the tropics was causing tropical forests to emit more carbon than they were storing.

New studies, however, show that current climate models underestimate the carbon absorption of tropical forests.

The Earth's wooded areas play a crucial part in slowing the impact of the increased human emission of carbon dioxide, which is attributed as the primary contributor of climate change. Forests and other land vegetation take care of about 30 percent of human carbon emissions through photosynthesis, during which plants store some of the greenhouse gas in their wood and leaves then transfer some of these to the soil through the roots.

There are, however, concerns that should the rate of absorption slow down, the process could exacerbate and speed up global warming, making the Earth more inhospitable and causing unwanted and potentially deadly consequences such as extreme weather events, drought and the displacement of human and animal populations.

Study researcher Britton Stephens from the National Center for Atmospheric Research said that knowing which type of forest absorbs more carbon does not only serve accounting purposes. It also has implications that could shed light on whether terrestrial ecosystems worldwide would continue to offset the carbon dioxide in the atmosphere or worsen climate change.

It appears that, as more carbon dioxide is released into the atmosphere due to human activities, forests worldwide respond by using these to grow faster, reducing the amount of carbon that remains airborne, an effect known as carbon fertilization.

"All else being equal, the effect is stronger at higher temperatures, meaning it will be higher in the tropics than in the boreal forests," Schimel said.

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