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Wednesday, 18 January 2017

A New Study Suggests that Carbon-hungry Plants Help Keep Atmospheric CO2 Levels in Check

(SNAPPA Science) Carbon-hungry plants may have halted the growing build-up of greenhouse gas in the atmosphere, scientists claim.
A new study suggests that while human activity continues to pour out increasing amounts of carbon dioxide (CO2), raising the risk of catastrophic global warming, mother nature has come to the planet’s rescue.
Rising CO2 is said to have stimulated the growth of more photosynthesising plants, which in turn have captured more of the greenhouse gas from the atmosphere and kept its levels in check.
Between 2002 and 2014, rising levels of atmospheric CO2 have held steady at about 1.9 parts per million (ppm) per year. Even though the gas was still accumulating, there was no acceleration in the build-up.
Photosynthesising plants absorb carbon, which they use to produce sugar and starch using energy from sunlight. The more carbon there is in the atmosphere, the more plant growth is stimulated. For this reason, large forested areas of the Earth, such as the Amazon basin, are important “carbon sinks”.
Study author Dr Trevor Keenan, from the US Department of Energy’s Berkeley National Laboratory, said: “This highlights the need to identify and protect ecosystems where the carbon sink is growing rapidly.”
During the latter half of the 20th century, the growth rate of atmospheric CO2 climbed steadily from 0.75 ppm/year in 1959 to 1.86 ppm/year in 2002. But an analysis of the latest data last year by Keenan’s team found that since 2002, the growth rate had remained flat.
The “pause” in CO2 build-up was surprising because it had occurred at a time when human activity was pumping record amounts of carbon into the atmosphere. The scientists suspected the carbon must be disappearing into a “sink”. Besides vegetation, other carbon sinks include the oceans and peaty soil.
Computer simulations combined with satellite observations of vegetation and ground and atmospheric measurements of CO2 pointed strongly to plants. The models suggested that rising CO2 levels caused land-based ecosystems to double their carbon uptake between the 1950s and 2000s, the researchers reported in the journal Nature Communications. This had risen from between one and two petagrams (trillion kilograms) of carbon per year to two to four pentagrams.
In comparison, human activity was emitting between nine and 10 petagrams of carbon per year. Thanks to the plants, the amount of human-generated carbon remaining in the atmosphere had actually fallen by 20%. But CO2 take-up by vegetation should not be seen as a solution to global warming, the scientists warned.
Keenan said: “Unfortunately, this increase is nowhere near enough to stop climate change.
“We’ve shown the increase in terrestrial carbon uptake is happening, and with a plausible explanation why. But we don’t know exactly where the carbon sink is increasing the most, how long this increase will last, or what it means for the future of Earth’s climate.”

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(Schalk van Zuydam/AP)
British climate scientist Professor Chris Rapley, from University College London, said: “This study points out that over the last decade the atmospheric CO2 content and global temperature continued to rise, but the rate of temperature rise slackened; as a result, plants appear to have absorbed CO2 more readily. The authors make it clear that this effect is almost certainly temporary.
“What this research does not show is that humanity can relax when it comes to the dangers to agriculture posed by climate change. The ‘greening’ effect of CO2 will ultimately be overwhelmed by the plants’ own respiration and decay, which will cause even more CO2 to be released.”
Professor Corinne Le Quere, director of the Tyndall Centre at the University of East Anglia, said: “This study highlights just how sensitive the natural environment is to a changing climate and how important it is to protect natural vegetation so it continues to absorb part of our carbon emissions.”