Carbon release intensified by warmer and wetter climates

A new ETH study confirms that changing climate conditions could reduce carbon absorption. In warmer and wetter areas, carbon stored in the soil is released back into the atmosphere more quickly.

Plants and soil currently consume about a third of anthropogenic carbon emitted to the atmosphere, which makes them a key mitigator of global climate change. Soil plays a prominent role here because it stores a large portion of the organic carbon, delaying the latter’s return to the atmosphere when plants die.

An international team of researchers led by Timothy Eglinton, Professor of Biogeoscience at ETH Zurich, has now confirmed that in a warmer climate, terrestrial ecosystems may release more organic carbon than they do today, thus losing the mitigating effect they have on climate change. Their comprehensive study was recently published in the journal PNAS.

The scientists demonstrated that organic carbon is released from the soils more quickly in warmer areas than in colder ones, leading them to conclude that further warming of the climate may be detrimental to the soil’s capacity to sequester carbon.

Comparing carbon sources

Over a period of several years, the researchers collected sediment samples from the mouths of 36 rivers around the world. Some of the samples were sediment particles that the team filtered directly from the river water, others were material deposits from the riverbanks. On the basis of these samples, the researchers were able to determine the age of the organic carbon that the rivers were exporting to the sea.

Essentially, the idea is that the older the organic carbon in the rivers, the longer it must take in the given catchment for the stored organic carbon to be released and exported after the plants have died. Comparing the age of the organic carbon from the various catchments enables the researchers to determine the key factors that influence the carbon budget and, in turn, how the storage capacity of the soil may change in future.

Their evaluation of the data showed a clear correlation between the average age of plant-​derived carbon in the samples and the climate in the catchment area. In warmer and wetter areas, organic carbon remains in the soil for less time than it does in colder, drier watersheds.

Land use less significant

“Our results confirm that climate has a strong influence on soil behaviour,” Eglinton says. The influence of land use, on the other hand, appears to be less significant, despite changes in recent decades to how many watersheds are managed. “At the moment, modern agriculture appears only to have a secondary impact,” he explains.

Photo credit: Marina & Enrique, flickr/Creative Commons

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