A geoscientist is astounded by Earth's huge frozen carbon deposits.

I believe that the vulnerability of soil carbon to warming is one of the largest sources of uncertainty in the projection of future climate change. If, in a warmer world, bacteria decompose organic soil matter faster, releasing carbon dioxide, this will set up a positive feedback loop, speeding up global warming.

I was stunned to learn, from an article by Charles Tarnocai of Agriculture and Agri-Food Canada in Ottawa and his colleagues, that the global mass of soil carbon needs to be revised upwards by a frightening amount: from the 2,500 billion tonnes of carbon previously accounted for to more than 4,000 billion tonnes (C. Tarnocai et al. Glob. Biogeochem. Cycles doi:10.1029/2008GB003327; 2009). This is a result of the previously overlooked presence of vast amounts of peat, Siberian yedoma deposits (organic-rich permafrost) and other frozen carbon stores at high latitudes.

These massive stores deserve special attention because the boreal and arctic regions that house many of them are expected to warm more rapidly than average in the coming decades. Even a small leakage from these stores could cause an explosion in the growth rate of atmospheric CO2 as well as methane, a potent greenhouse gas emitted by flooded thawed soils.

So what do these findings mean for the role of high latitudes in the Earth system? We need more extensive field observations to monitor the stability of frozen carbon, and studies to measure the decomposition rates of such stores. And we should incorporate these processes into climate models such as those used by the United Nations Intergovernmental Panel on Climate Change. If I had to pick just one new PhD subject right now, exploring this terra incognita of frozen carbon and its impact on climate change would be the one.

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