Trees Grow into the Job
As trees in tropical forests grow bigger, they absorb more carbon than prevously thought, heightening their role in mitigating climate change.
An international team of scientists including researchers from the Center for International Forestry Research (CIFOR) have discovered that rainforest trees are getting bigger, sequestering more carbon from the atmosphere and slowing climate change.
"Tropical giants", such as this Moabi tree (Baillonella toxisperma) in Gabon, are collectively absorbing up to a fifth of the carbon dioxide released by fossil fuels. Photo: Terry Sunderland, CIFOR.
According to the findings, tropical trees in undisturbed forests around the world are absorbing nearly a fifth of the carbon dioxide (C02) released by fossil fuels. That is significantly more than the greenhouse gas emissions produced by the world’s transport sector. The researchers estimate that remaining tropical forests remove a massive 4.8 billion tons of CO2 from the atmosphere each year. This includes a previously unknown carbon sink in Africa that mops up 1.2 billion tons of CO2 annually.
Published in Nature earlier this year, the 40-year study of African tropical forests, which account for one third of the world’s tropical forest, shows that each hectare of intact African forest has for decades trapped an additional 0.6 tons of carbon per year. Combined with data from South America and, to a lesser extent, from Asia, the study’s analysis of the records of 250,000 trees reveals that, on average, the remaining undisturbed forests trap carbon and thus constitute a globally significant carbon sink.
According to the report’s lead author, Simon Lewis of the University of Leeds, "Tropical forest trees are absorbing about 18% of the CO2 added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of climate change."
The reason why the trees are getting bigger and absorbing more carbon is unclear. A leading suspect is the extra atmospheric CO2 itself, which may act as a fertilizer. However, Lewis warns, "Whatever the cause, we cannot rely on this sink forever. Even if we preserve all remaining tropical forest, these trees will not continue getting bigger indefinitely."
The Intergovernmental Panel on Climate Change reports that human activity emits 32 billion tons of CO2 each year globally, but only 15 billion tons actually stays in the atmosphere and contributes to climate change. The new research shows where some of the “missing” 17 billion tons per year has gone.
One of the report’s co-authors, Douglas Sheil of CIFOR and Uganda’s Institute of Tropical Forest Conservation, says he was previously unconvinced of the role that forests play in removing CO2
from the atmosphere.
“Prior to working on the report, I was like many scientists who used to dismiss the campaigners’ slogan that forests are the lungs of the world,” Sheil recalls. “We believed that forests were basically in equilibrium with the atmosphere, neither adding to nor subtracting from its gaseous composition. Our findings give the lungs metaphor a basis after all.”
CIFOR colleague and fellow co-author Terry Sunderland adds that, while there is no question rainforest trees are getting bigger and storing more CO2, it is vital that more carbon uptake studies like those in Africa and South America be carried out in Asia.
“Indonesia is deeply interested in REDD and carbon payment schemes, yet deforestation in Indonesia is contributing to the country’s status as the world’s third largest emitter of greenhouse gasses,” he reports, referring to the United Nations Framework Convention on Climate Change Program on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (REDD). “If carbon payment schemes such as REDD are to succeed in Indonesia, they must be based on accurate assessments of the amount of carbon stored in the country’s forests. These calculations need to be based on local and realistic figures.”
The reported implications for future carbon payment schemes are echoed in the comments of another of the report’s co-authors, Lee White, Gabon’s chief climate change scientist.
“The removal of nearly 5 billion tons of carbon dioxide from the atmosphere by intact tropical forests, based on realistic prices for a ton of carbon, should be valued at around US$21 billion per year,” White asserts. “This is a compelling argument for conserving tropical forests."
Rich polluting countries can assist with conserving forests by, Lewis says, “transferring substantial resources to countries with tropical forests to reduce deforestation rates and promote alternative development pathways.”
Sunderland cautions that any investment in REDD or similar carbon payment schemes must first formalize and enforce land rights for forest dwellers. “It’s absolutely essential that a significant proportion of any payments for environmental services, such as REDD payments, are made to those who rely on forests for their well-being,” he says. “After all, up to a billion of the world’s poorest people rely on forests in one way or another for their livelihoods.”
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