Boreal Forests' Uptake Of Carbon From Atmosphere Slowing Down
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In northern Eurasia, the annual net sink rate increased from the 1960s to the 2000s, but since then, the rate at which carbon is sequestered by the region has leveled and even showed signs of weakening, said Michael Rawlins, an assistant professor in the University of Massachusetts’ Department of Geosciences. In a study published in Biogeosciences, Rawlins and his team compared estimates of the rate of carbon sequestration occurring in this region from nine models, and they all suggested a weakening carbon sink. In time, the emissions are projected to overtake the ability of forests to contain them and, as he put it, “it is thought that the region will switch from a net carbon sink to a net carbon source sometime this century.”
The carbon cycle represents a movement of carbon between different systems—forests, soil, ocean systems and the atmosphere. This entails both an uptake and a release of carbon by these systems. Sinks are those zones that take in more carbon than they emit, effectively storing the carbon and preventing it from contributing to global warming.
The burning of fossil fuels essentially reintroduces ancient carbon that is stored in the depths of the earth back into the carbon cycle. Although the oceans are currently the greatest carbon sink, terrestrial carbon sinks also play a significant role in keeping the carbon out of the atmosphere. “Land areas that sequester carbon help to offset the anthropogenic emissions of carbon dioxide,” Rawlins explained.
Race between sinks and sources
Northern Eurasia plays an important part in the global carbon cycle because of its large areas of forest and huge soil carbon reservoirs, he added. The net land carbon sink for northern Eurasia amounts to approximately 0.48 petagram of carbon per year, about 6.5 percent of global carbon emissions, according to Rawlins. “The region’s land carbon sink contributes to the sequestration of a significant percentage of the global emissions,” he said. “I am surprised that the sinks keep taking in more carbon as the emissions keep increasing,” said Richard Houghton, a senior scientist at the Woods Hole Research Center. “You would expect that eventually they would stop taking it up.” That process may already be underway, and northern Eurasia may not be the only region where this slowing down of carbon uptake has been observed.
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http://www.scientificamerican.com/article/northern-forests-falter-in-combating-climate-change/
