Missing carbon sink discovered?

Missing Carbon SinkFalmouth, Mass. – The global carbon budget describes the releases of carbon from fossil fuel combustion and deforestation and the uptake of that released carbon by atmosphere, land, and oceans.The carbon budget is important for predicting future rates of climatic change because a major driver of change is the accumulation of carbon dioxide in the atmosphere. And the more carbon that land and oceans take up, the less that remains in the atmosphere. The uptake of carbon by land and the processes responsible are not well understood and have been called the “missing carbon sink”. A new report, co-authored by Woods Hole Research Center scientist Dr. Richard A. Houghton and published by the American Geophysical Union, suggests that some of the uptake of carbon on land might be in massive alkaline aquifers below the earth’s deserts, driven by irrigation.

“The new findings are important,” says Dr. Houghton, “because they suggest that at least some of the drivers of the land carbon sink are different from what we’ve assumed, and that predictions of the rate of climate change may thus need to be revised.”

The team of scientists examined the flow of water through a Chinese desert and found that carbon from the atmosphere was absorbed by crops, released into the soil and washed, with irrigation, into groundwater isolated from the atmosphere – a process that was accelerated when farming and irrigation began in the region 2,000 years ago. The study estimates that agriculture could be responsible for sequestering up to 14 times more carbon than previously thought, depositing it in these underground desert aquifers. Together, these underground pools underlie an area the size of North America and may account for at least a portion of the “missing carbon sink.”

“The carbon is stored in these geological structures covered by thick layers of sand, and it may never return to the atmosphere,” said Yan Li, a desert biogeochemist with the Chinese Academy of Sciences in Urumqi, Xinjiang, and lead author of the study. “It is basically a one-way trip.”

Understanding the processes responsible for carbon sinks could improve models used to predict future climate change and determine the limit to fossil fuel use that is consistent with avoiding major changes in the Earth’s temperature.

Link to abstract »

WHRC is an independent research institute where scientists investigate the causes and effects of climate change to identify and implement opportunities for conservation, restoration and economic development around the globe.