Tropical Forests

According to New Study, Tropical Forests Capacity to Absorb Carbon is Diminishing Fast

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In simple terms, tropical forests’ ability to capture carbon has already passed its peak. These forests, in the words of environmental scientists, are increasingly becoming “carbon saturated”. 

Tropical forests are capturing less and less carbon dioxide from the atmosphere, thereby significantly reducing their capacity to act as ‘carbon sinks’, and this could have a serious impact on the global efforts to fight climate change, a study found.

The international study was conducted by dozens of researchers and was featured on the cover of the current edition of the journal Nature.

One of the study’s authors, University of Toronto’s Sean Thomas, who is a professor of forestry at the John H. Daniels Faculty of Architecture, Landscape, and Design, has found out that “intact tropical forests have been offsetting global carbon dioxide emissions, [but] that’s going to go away”.

Through his experiments, in what is now the Democratic Republic of Congo (DRC), in the mid-1990s, Thomas had assisted in establishing nearly four 10-hectare research plots in the Ituri Rainforest in the region. This dense forest, home to small forest antelope, monkeys, and the occasional zebra-striped okapi, served as living laboratories that, a quarter-century later, yielded key data for the global study led by researchers at the University of Leeds.

Tropical Forests
Sunset on the Tapajós River, deep in the Amazon rainforest, in Brazil. (Source: The New York Times)

Study authors, using tree measurements from Thomas’ research forests in DRC combined with similar measurements from several other tropical forests in South America and Africa, have concluded that the absorption capacity of tropical forests are decreasing and reaching a saturation point where they can no longer absorb and will only release back carbon once the trees die.

To elaborate more on the findings, Thomas and study researchers have said that “intact tropical forests – that is, those that haven’t been logged or otherwise commercially exploited – absorbed only about six percent of man-made carbon emissions by the 2010s. That’s compared to 17 percent in the 1990s.”

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“That makes the problem of achieving the goals of the Paris Accord and stabilizing temperature increases much more difficult,” said Thomas. The study further states that over a period of time, the forests’ capacity to “remove carbon will keep declining in the future”.

In simple terms, tropical forests’ ability to capture carbon has already passed its peak. These forests, in the words of environmental scientists, are increasingly becoming “carbon saturated”.

The logic behind trees serving as carbon sinks is this: Trees absorb carbon by absorbing carbon dioxide from the atmosphere and this goes through a process of chemical transformation via photosynthesis and converts it into the complex sugars that fuel tree growth. But when a tree dies, the exact opposite takes place: it releases carbon back into the atmosphere as it decomposes.

This study essentially upends the long-held assumption by scientists that tropical forests which are wholly intact are absorbing more carbon than they’re releasing, essentially cleansing the environment of human-induced pollutants.

But Thomas and his co-authors have now concluded that this positive process is not happening anymore in South America and Africa as many trees are dying. They say climate change is likely to blame, while not completely. This is decreasing the tropical forests’ capacity to absorb more carbon than they produce.

What’s more worrying, Thomas opines, is that the “amount of carbon released into the environment from decaying plants will be greater than the amount of carbon absorbed by living plants”.

“That point of diminishing returns has been thought to be not for a long while, maybe 100 years away,” he says. “Now we know that it’s already here, or imminent.”

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