Arctic climate change – it’s recent carbon emissions we should fear, not ancient methane ‘time bombs’
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Over thousands of years, carbon has built up in these frozen soils, and they’re now estimated to contain twice the carbon currently in the atmosphere. Some of this carbon is more than 50,000 years old, which means the plants that decomposed to produce that soil grew over 50,000 years ago. These soil deposits are known as “Yedoma”, which are mainly found in the East Siberian Arctic, but also in parts of Alaska and Canada.
As the region warms, the permafrost is thawing, and this frozen carbon is being released to the atmosphere as carbon dioxide and methane. Methane release is particularly worrying, as it’s a highly potent greenhouse gas.
This study suggested to many that ancient methane emissions are not something we should be worried about this century. But in new research, we found that this optimism may be misplaced.
We went to the East Siberian Arctic to compare the age of different forms of carbon found in the ponds, rivers and lakes. These waters thaw during the summer and leak greenhouse gases from the surrounding permafrost. We measured the age of the carbon dioxide, methane and organic matter found in these waters using radiocarbon dating and found that most of the carbon released to the atmosphere was overwhelmingly “young”. Where there was intense permafrost thaw, we found that the oldest methane was 4,800 years old, and the oldest carbon dioxide was 6,000 years old. But over this vast Arctic landscape, the carbon released was mainly from young plant organic matter.
This means that the carbon produced by plants growing during each summer growing season is rapidly released over the next few summers. This rapid turnover releases much more carbon than the thaw of older permafrost, even where severe thaw is occurring.
So what does this mean for future climate change? It means that carbon emissions from a warming Arctic may not be driven by the thawing of an ancient frozen carbon bomb, as it’s often described. Instead, most emissions may be relatively new carbon that is produced by plants that grew fairly recently.
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The East Siberian Arctic is a generally flat and wet landscape, and these are conditions which produce lots of methane,
as there’s less oxygen in soils which might otherwise create carbon dioxide during thaws instead. As a result, potent methane could well dominate the greenhouse gas emissions from the region.https://theconversation.com/arctic-climate-change-its-recent-carbon-emissions-we-should-fear-not-ancient-methane-time-bombs-135270Papers mentioned:
Old carbon reservoirs were not important in the deglacial methane budget (PW)
https://science.sciencemag.org/content/367/6480/907and
East Siberian Arctic inland waters emit mostly contemporary carbon (Open Access)
https://www.nature.com/articles/s41467-020-15511-6