Kuuvik River Expedition Science -- Permafrost Melt

“Warming already under way thaws permafrost, soil that had been continuously frozen for thousands of years.  Thawed permafrost releases methane and carbon dioxide.  Those gases reach the atmosphere and help trap heat on Earth in the greenhouse effect.  The trapped heat thaws more permafrost, and so on.”
                                                                                                     - The Montreal Gazette, 7 September 2006

Permafrost melt is an ongoing phenomenon that is resulting in the escalation of global climate change.  Permafrost -- frozen ground with a temperature that continuously remains below zero degrees Celsius -- currently overlays about 24% of the exposed Northern Hemisphere land surface.  During the previous 20-30 years permafrost temperatures have increased almost everywhere that permafrost is found, with temperatures of the uppermost layer of Arctic permafrost soil increasing by up to 3°C since the 1980s.  Such warming is causing some permafrost terrain to melt, which is a concern because the melting of permafrost releases greenhouse gases into the air which, in turn, can instigate further permafrost melt and further climate warming -- thus perpetuating a vicious cycle.

Permafrost bound organic matter, ancient vegetation that was frozen amid ice up to millions of years ago, represents one of the largest organic carbon reservoirs in the Earth System.  This carbon "sink" is estimated to hold about 960 gigatonnes of carbon (1 Gt = 1 billion tonnes) in the upper part of the permafrost (1-25 metres below the surface).  The size of this permafrost carbon sink was vastly underestimated until only a few years ago, which indicates that there is still much to learn about permafrost.  Moreover, the current estimate of 950Gt for the size of the permafrost carbon sink does not include the carbon stored by deeper permafrost, which can extend below 25 metres to at least 1400 metres in some locations.  Nonetheless, 950 gigatonnes is a major C-sink.  That quantity, in comparison, exceeds the 750Gt of organic carbon that is now in our atmosphere, and it also more than doubles the total amount of 350 GtC that is stored in the vegetation of all the world’s forests.

The permafrost carbon sink is for the most part ‘inactive’ at present – in other words, the C-sink has so far vented only a small portion of its fossilized carbon into the sky in the form of greenhouse gas emissions.  At present, most all Northern Hemisphere permafrost terrain functions as an impervious biogeochemical barrier -- preventing moisture and gaseous exchange between soils and the atmosphere because of its “frozen lid”.  Yet that frozen lid is now starting to thaw.  Longer summers and higher temperatures are melting the frost off whole areas of surface vegetation, changing the insulating properties of the ground cover, and enabling long dormant soils to ‘breathe’ again via gas exchange with the atmosphere.  Organic material in thawing permafrost decomposes rapidly.  The warmer the soil gets the quicker the rate at which micro-organisms can decay the previously frozen ancient vegetation.  Notably, the microbial decomposition of formerly permafrosted terrain is now happening at some places on Earth.  This means that oxidized carbon is being vented to the sky in the form of carbon dioxide -- and methane, a more potent form of greenhouse gas, is being vented up too.

Whether or not former permafrost areas emit organic carbon to the sky in the form of carbon dioxide or methane depends upon the landscape surface characteristics of the formerly permafrosted areas in question.  If the former permafrost areas are dried by warming temperatures and thawing occurs in the presence of oxygen then the formerly permafrosted areas emit carbon dioxide skyward.  If the former permafrost areas are water-saturated and thawing occurs amid anaerobic conditions then former permafrost areas emit methane.  The venting of methane to the atmosphere has especially significant implications for accelerating climate change because the global warming potential of methane is 25 times more powerful than carbon dioxide, which means that over the course of one hundred years the emission of 1 kilogram of methane into the sky exerts a radiative forcing effect on our planet Earth's energy balance that is equivalent to the emission of 25 kilograms of carbon dioxide.

The trends for methane emissions from “not-so-perma” permafrost terrain in the Northern Hemisphere are ominous.  In Siberia, a region with colossal stores of partially decomposed organic matter sealed below frozen substrate, methane flux to the atmosphere was recently documented to be occurring five times faster than estimated before.  Accordingly, Russian and American scientists have calculated that methane emissions for the region have increased at least 58% since 1974.  Moreover, radiocarbon dating of methane emitted from the Siberian research sites indicates that at least 40% of the methane emitted at those locations is from vegetatation that lived and froze 35,260–42,900 years ago; thus vegetation frozen since the Pleistocene epoch is now decomposing and emitting methane.

During the Pleistocene epoch most of the northern Siberian plains were unglaciated and accumulated vast volumes of organic carbon in sediments.  Hence in just one part of Siberia, for instance, an area known as the Yedoma Ice Complex, the Siberian landscape is currently storing about 500Gt of near-surface carbon.  This high-latitude carbon sink is vulnerable and could greatly intensify global warming via greenhouse gas emissions if northeast Siberia continues to warm in the future, as computer climate models suggest it will.  Not counting future greenhouse gas emissions from everywhere else in the world, the Yedoma Ice Complex alone has the potential to release an amount of methane that is about ten times the amount now in Earth’s atmosphere.  According to the Earth System scientists who have verified the accelerating Siberian emissions “the large pool of still-frozen Pleistocene-age C in Siberia is a methane time bomb” -- a time bomb ticking to emit about 100 times the amount of carbon that humans currently pollute each year via burning fossil fuels.

Permafrost is a temperature sensitive indicator of millennial climatic variability -- that fact is increasingly obvious to more and more people.  With Arctic temperatures now warming and snow and ice decreasing, permafrost is melting.  Which raises the logical question: how much permafrost will melt worldwide, and how soon will it happen?  An American climate model run answered this question in 2005, and calculated that up to 90% of all Northern Hemisphere permafrost will melt before the year 2100.  The very serious implications of this model result, incidentally, would only be further accentuated if such a climate model were to factor-in the since discovered accelerating methane flux emanating from the Yedoma Ice Complex.   Simple lesson then -- we humans, via our naive meddling with the chemistry of the atmosphere that keeps us alive, have sparked unusual biogeochemical fluxes in our Earth System that are serious and seemingly irreversible.