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Global warming

Little changes mean a lot

There is evidence to show that slight temperature changes may have an exponential effect on cloud-forming gasses released by permafrost vegetation

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Discussions about the role permafrost plays in a warming climate typically focus on whether accelerated plant growth could actually slow global warming by removing carbon from the atmosphere.

While this theory is gradually looking more unlikely, new research into plant growth in the Arctic suggests that a second, less-closely studied phenomenon may also be playing a similar role by influencing cloud formation.

It has long been understood that, in addition to oxygen, plants release a type of gas known as biogenic volatile organic compounds. The substances these gasses contain are used by plants to attract beneficial insects and keep harmful ones away. Once in the atmosphere, they can also lead to the formation of clouds, which keep temperatures down by shielding the Earth from the sun’s energy.

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What has not been fully understood is how BVOCs themselves are affected by global warming, and whether they can stimulate enough clouds to mitigate some of the expected increase in temperatures in the Arctic.

Now, scientists from from the Center for Permafrost, at Københavns Universitet (the University of Copenhagen), have presented evidence that this may, in fact, be the case.

In a recent paper*, published by Nature Geoscience, the scientists write that emissions of BVOCs increase exponentially with warming temperatures, meaning they are far more sensitive to climate changes than previously thought.

To determine how plant BVOC emissions react to climate changes, the scientists have, since 2007, been conducting field experiments in Greenland in which they isolate plants in topless greenhouses.

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These greenhouses simulate the effects of a two-degree increase in air temperature. In some cases, the plants released four times more BOVCs than under normal conditions. It is this increased release that the scientists say could lead to the formation of more potentially cloud-forming particles in the atmosphere.

To then test how clouds would affect BVOC emissions, the scientists covered the tops of the greenhouses with a semi-transparent fabric. The result was a 70% reduction in BVOCs.

This, according to Riikke Rinnan, one of the scientists involved in the research, means that BVOC production is 20 times more sensitive to temperature increases than greenhouse-gas release and other biological processes in permafrost areas.

The increased emissions, according to the researchers, have two opposite effects. Firstly, they allow methane, a powerful greenhouse gas, to remain in the atmosphere longer, prolonging its warming effects on the climate.

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Secondly, and likely more importantly, they stimulate cloud production. Though not significant to cancel out temperature increases, additional clouds could help prevent temperature increases from being as pronounced as predicted.

One source of uncertainty is how BVOC production will respond to temperature increases higher than those measured in the experiments.

Ms Rinnan notes that temperatures in the Arctic are predicted to rise even further than those the scientists simulated. Given plants’ sensitivity to change when producing BVOCs, and the substances’ extreme effect on the atmosphere, the effects of the additional temperature rise could be significant.

*Kramshøj, Martin, et al, Large increases in Arctic biogenic volatile emissions are a direct effect of warming, Nature Geoscience, April 4, 2016

Photo: A Dialla