US absorbed CO2 despite drought

The drought of 2012 in the US did not prevent plants and trees from acting as a carbon sink. The warm spring actually enabled them to absorb more carbon, compensating for reductions during the subsequent summer drought.

In 2012, the US was afflicted by the hottest and driest summer since the 1930s, a period that later became known as the Dust Bowl. The spring of 2012 was the warmest on record, followed by drought and hot temperatures in the summer months.

Climate researchers had assumed that the drought of 2012 would have turned the US into a carbon source, as happened in Europe during the soaring summer temperatures of 2003 when plants reduced growth (and therefore CO2 intake during photosynthesis) due to the dry and hot conditions.

But as a team of scientists from the US, Australia, the Netherlands and Switzerland have now shown, the US remained a carbon sink – taking up more carbon from the air than they release – despite the drought.

The reason is that the warm spring caused trees, grasses and crops to start growing earlier in the year, thus absorbing more carbon from the air than during a normal spring, writes the Federal Institute of Technology (ETH) in Zurich. While the ecosystems absorbed less carbon than usual in the subsequent summer drought, the overall carbon balance remained positive.

“The increase in carbon uptake during the warm spring compensated for the reductions in uptake during the drought,” says ETH researcher Sebastian Wolf, who led the study.

The Appalachian forests were a particularly effective carbon sink, absorbing additional carbon during the spring and remaining largely unaffected by the drought in the summer months.

The study, “Warm spring reduced carbon cycle impact of the 2012 US summer drought”, was recently published in the journal PNAS.

 

Image credit: CraneStation, flickr/Creative Commons

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