Carbon Sequestration in Permafrost (right) by "Cryoturbination" from Charles Tarnocai
Permafrost (permanently frozen ground) has not been on the radar screen very often in the national conversation about global climate change (GCC). When I started reading about the science underlying GCC a few years ago, I came across brief, scattered descriptions about permafrost; my tendency then was to skip over the pages describing the problem, which wasn’t difficult, as there were few in number and fewer still were the number of scientists who considered the issue to be an emergency situation or a major component of GCC. Indeed, until recently, it was widely assumed that the warming of the permafrost would stimulate new plant growth, such that the net impact would be a sink for carbon, not a source and hence, a protective mechanism for absorbing the carbon hiccups of GCC. The 2007 report from the Intergovernmental Panel on Climate Change (IPCC; Fourth Report: working group I: The Physical Science Basis, p 340) stated “The maximum extent of seasonally frozen ground has decreased by about 7% in the NH from 1901 to 2002, with a decrease in spring of up to 15%. Its maximum depth has decreased about 0.3 m in Eurasia since the mid-20th century. In addition, maximum seasonal thaw depth over permafrost has increased about 0.2 m in the Russian Arctic from 1956 to 1990. Onset dates of thaw in spring and freeze in autumn advanced five to seven days in Eurasia from 1988 to 2002, leading to an earlier growing season but no change in duration:” there was little hint from the report that permafrost was a serious, hidden threat anymore than that attributed to greenhouse gas emissions in general. Thus, until very recently, any special reference to permafrost as a problem seemed to be traveling under the radar screen. Observers and scientists alike have all been rightly focused on the more significant issue of coal-burning power plants, the number one polluter and green house gas emitter and the single biggest danger to our planetary future. But in the last few years, reports started to appear which suggested that permafrost could no longer be ignored in calculations and models about climate change, because more extensive measurements suggested that it is potentially a major source of greenhouse gases, including carbon dioxide and methane and that permafrost may be a storage source for huge quantities of carbon, in the form of plant material that got buried long ago in the layers of permafrost–a source that is now in the process of being “liberated” through exposure to planetary warming. One of the revelations that changed our views on this topic came from recent studies that measured permafrost carbon content at soil depths deeper than 100 cm, revealing that for some permafrost regions, up to 2/3 of the carbon deposits in the soil were deeper than the 100 cm limit used in many previous studies. More measurements and additional studies of this problem are acutely needed to evaluate the significance of this newly revealed, potentially dangerous source of carbon. It could form another positive feedback mechanism for GCC, at a time when we have a hard time dealing with coal-burning power plants.
Recently, Justin Gillis wrote an article in the New York timeswhich provided an excellent, fairly detailed front page story on permafrost, together with information about ongoing studies in Alaska, Canada and other parts of the Northern Hemisphere. These studies are alarming because they indicate that the Northern Hemisphere could become a source of carbon rather than a sink (indeed, it may be there already, though we don’t know this with certainty), created by warming conditions which stimulate bacterial breakdown of dormant sources of carbon.
Permafrost of Circumpolar Region (from Charles Tarnocai)
When oxygen is plentiful, as in the bacterial breakdown of plant material in air, the stored permafrost vegetation is generally broken down into carbon dioxide, but when the region is oxygen-poor, usually when it is submerged in water, bacteria can generate methane gas from this carbon source, which forms bubbles in lakes and ponds as it rises to the surface and ultimately into the atmosphere. Methane gas has been reported in locations in Alaska: once in the atmosphere, it is 33 times more potent than carbon dioxide as a greenhouse gas when measured over a 100 year period. It is far better to burn it off into carbon dioxide than let it reach the atmosphere as methane, even though its half life in the atmosphere is less than that of carbon dioxide. Recent estimates of the amount of carbon that currently exists in the permafrost is about twice the amount that’s in the atmosphere already and could eventually constitute up to 35 percent of today’s annual human emissions. The danger of this source, is that once the process of degradation begins, though it may take 100 years or more to biodegrade its way through the available sources of carbon, it will be impossible to stop. Now is the time to alertly invest in research to evaluate with more certainty the true impact of this new addition to the GCC orchestra. Is it a single instrument or a new section of the band!
The first question of interest of course is what is permafrost? A dictionary definition is that of a subsurface material that remains below zero degrees Centigrade (32 degrees Fahrenheit) for a least two consecutive years. More practically, it’s the area in the Northern Hemisphere that is largely frozen, but some regions of the permafrost have a surface layer which has seasonal plant growth. The permafrost areas, like the rest of the planet, are beginning to warm and there is new cause for concern about the consequences. The earth is heating up more rapidly in the Northern Hemisphere than any other region of the planet. As the reflective glaciers (albedo effect) retreat, the area exposes itself as a less reflective environment, in the form of water and land, and more of the sun ‘s energy is absorbed and accelerates the warming trend; this constitutes a positive feedback system which further accelerates the loss of snow and ice in the region–>more heat–>less ice–>more heat absorbed–>more melting of ice–>where will it all end? Thus, GCC is already generating one positive feedback system in the form of the albedo effect, especially evident in the Northern Hemisphere. Though permafrost also exists within the Antarctic region, it has been less well studied. As glaciers and ice pack formation retreat, more permafrost gets exposed, but the warming of the exposed permafrost appears to be adding another source of carbon that we should seriously worry about. This issue has become of interest lately because studies have shown that permafrost is a rich source of sequestered carbon that has been trapped in the soil for hundreds to thousands of years.
It is counter-intuitive to imagine that permafrost might be a type of soil that holds rich deposits of carbon. One’s first impression is that soils exposed to frozen conditions will be poor in nutritional value and contain less vegetation than that of more temperate soils. But extensive measurements from many different regions of the permafrost indicate that overall, the permafrost can contain higher levels of carbon than more temperate soils and that deep down in the soil, rich carbon deposits can exist. The first figure illustrates how the permafrost becomes increasingly carbonized by a process referred to as “crytoturbination,” (right figure) as if a giant Hobart machine circulated plant deposits (and a few dead animals) from near the surface deeper into the soil, such that very deep layers contain high levels of carbon when compared to soils from more temperate regions (left figure). This process of permafrost carbonation has been going on for thousands of years but it is still surprising that they contain such high levels and deep layers of carbon deposits. The second figure shows, in a color-coded map, the areas of permafrost that presently exist in the Northern Circumpolar regions, based on carbon soil content derived from borehole analysis. If the permafrost source of carbon dioxide/methane gains momentum, it will become another positive feedback mechanism with sufficient potential power to make a big contribution to global warming. Whereas climatologists and plant biologists once considered the exposure of the permafrost to have a positive influence through carbon sequestration, with the new higher estimates of the permafrost carbon content, the process may well have started and whatever benefit we might have derived may be turning into an additional problem for the future of the planet. When you look at it in the following way, you can appreciate the problem: for hundreds of millions of years, the earth accumulated carbon in the form of coal, oil and natural gas. Through man’s ingenious nature, a portion of this carbon has been put into the atmosphere as carbon dioxide and other greenhouse gases, but on a time scale of a few centuries. Since we now understand that the planet is in a delicate balance of carbon dioxide and other greenhouse gases, with the Earth’s ice and snow content, shouldn’t it alarm all of us when we imagine that our actions cannot do anything other than change our planetary weather? What new philosophical form of inquiry is required for man to properly gaze into the future that he has created for himself? Scientific inquiry so far doesn’t seem to work.
RFM
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