Thawing ground inside the Arctic circle could release as much nitrous oxide (N2O) into the atmosphere as tropical rainforests – previously the biggest known natural emitter of the powerful global warming gas.
Research by a team led by Carolina Voigt of the University of Eastern Finland reveals that N2O escape from subarctic peatlands is increasing as global warming prompts the thawing of permafrost.
N2O is recognised as a particularly robust contributor to climate change, because it causes two types of atmospheric damage.
“Nitrous oxide has an atmospheric lifetime of 110 years,” wrote Australian global warming experts Peter Grace and Louise Barton in 2014.
“The process that removes nitrous oxide from the atmosphere also depletes ozone. So nitrous oxide is not only a greenhouse gas, but also an ozone destroyer.”
In the latest research, published in the US journal Proceedings of the National Academy of Sciences, Voigt and her colleagues note that although carbon emission associated with Arctic climate change has been well studied, the potential role of N2O remains poorly understood.
This, they suggest, needs to be urgently addressed.
“Vast stocks of nitrogen (more than 67 billion tons) in the permafrost, accumulated thousands of years ago, could now become available for decomposition, leading to the release of nitrous oxide to the atmosphere,” they write.
“N2O is a strong greenhouse gas, almost 300 times more powerful than CO2 for warming the climate.”
To test the effects of permafrost thaw Voigt and her team established 16 peatland “mecocosms” – medium-sized experimental test plots – each around 80 centimetres long and 10 wide. Some of the plots were bare, while others contained either lichens, vascular plants or both.
The subsurface regions of the test areas were then exposed to different concentrations of water, to simulate various permafrost thaw scenarios.
The researchers found that when the thaw exposes bare land – a common occurrence in the Arctic region – nitrous oxide emissions increased fivefold, matching the levels emitted by rainforest soils.
The presence of vegetation and standing water both decreased emission levels. However, the scientists suggest that climate change-induced permafrost thaw is likely to be a relatively dry process, one that doesn’t favour the retention of moisture or plants.
On present calculations, around one quarter of the Arctic region landmass is bare peat.
The researchers did not attempt to calculate the total amount of N2O likely to be released during a widespread permafrost thaw because, they noted, there was not enough data to allow them to accurately determine the levels of moisture present in all areas.
However, their conclusion – conservative and cautious – will worry climate change researchers and policy-makers alike.
“At a global scale, this [study] puts Arctic N2O emissions from thawing permafrost in the range of emissions from fossil fuel combustion, industrial processes, and biomass burning, the second largest anthropogenic N2O sources after agriculture,” they write.