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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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Fig. 1 Planet Earth (NASA)

Every educated person on the planet has heard about the threats to human existence imposed by Global Warming. Yet, few of us are knowledgeable enough to explain the basic mechanisms that determine our climate, especially when talking to those among whom are doubting members of the choir. Understanding the essential elements of Global Warming requires effort and an intellectual expenditure, but you can converse intelligently on the subject, while stopping short of explaining the situation on the basis of a thermodynamic theory of equilibrium. Besides, the earth’s climate has never truly been in any form of equilibrium–some positive or negative driving force or energy imbalance has always been trying to change our climate, though, until now, such changes have taken place over millenia, not over the two hundred plus years of the industrial revolution.  Our climate has always been changing, even though the time constants for change are way beyond a human lifetime, and lie properly scaled and recorded within the geological and paleoclimatological record, which gives up its secrets slowly. But once properly deciphered that record reveals a surprisingly coherent history for those willing to put the effort into interpreting the scrolls, or to be more accurate, deciphering the core drillings of oceans and glaciers. Of course, we don’t yet have a complete story. There are large gaps in our knowledge, but we know enough already to be mesmerized by our planetary history and the forces that have shaped our climate. And we should know enough to be alarmed and very wary about our future.

It is now clear that never before in our climate history have we witnessed the kind of experiment now underway–the forcing of our planet to go through something it has never experienced before–a sharp, man-made increase in atmospheric carbon dioxide that is now taking place and pushing us towards a climatological precipice that we might not be able to escape. But if we act quickly, this experiment is still under our control, depending on whether we can muster the political will to curb our use of fossil fuels and restore energy balance to keep the planet as it was, with atmospheric carbon dioxide at 350 parts per million (ppm) or less ; it is now at 387 ppm and rising at a rate of about 2 ppm per year. The alternative is that we run the risk of higher levels of carbon dioxide that will trigger the melting of Greenland and the polar ice caps and eventually raise our sea level by 270 feet! We are probably not at risk for a sea level increase of that magnitude during this century, but we do run the risk of having this kind of sea level rise take place, and once it starts, there will be nothing we can do to stop it. Not only will this massive ice melting proceed out of our control, it will cool the local regions where the melting takes place, impact our weather systems and change the driving forces for oceanic currents. The emergency we must address now has been created by the fact that the carbon dioxide we have put into the atmosphere has a very long half-life and its actions on our planet will be with us for a  very long time. Couple this reality to the fact that we are already seeing weather patterns that reflect Global Warming and you inescapably conclude that our short-term climate does not look good–it will inescapably be more violent. But, we can still do something for the long-term, by acting soon and now is not too early. There is little doubt that if we continue to burn fossil fuels through a business-as-usual mode, our planet will be markedly different and our planetary future will be seriously in doubt. In many ways, that’s the shock–not only that the climate is never in equilibrium, but that it is also super-sensitive to the very fuels we have chosen as our cheapest form of energy. For too long we have assumed constancy in our climate lives: that luxury has now gone, at least the assumption part of it.

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From National Geographic

Week before last, temperatures in International Falls Minnesota reached 46 degrees below zero and that was the air temperature, without the windchill.  An Arctic blast of cold air broke free from its northern moorings and spread rapidly into Minnesota and nearby states. At those temperatures, breathing through your nose is a challenge, as ice crystals form within the nasal cavity and you quickly find it best to breathe through a scarf or some other device, like a face mask that quickly gets warmed by your breath. But in time, even these filters develop ice crystals and breathing through them can become more labored. Most Minnesotans know what to do under these conditions–they go outside only when they have to and spend more time indoors. Air hockey anyone?

All humans share a short nasal cavity; sufficient time has not elapsed to see if evolutionary adaptations might arise in Minnesotans, such as a longer nasal cavity that would serve to mitigate nasal ice crystal formation.  In response to this dry arctic air that crept into Minnesota week before last, I found myself shuttered inside, thinking about polar bears and the special adaptive features they have developed to make it through winters that actually don’t get a lot colder than what we observed recently in Minnesota (January temperatures in the Arctic get to about 58 degrees below zero, so we truly got a blast of real Arctic air), though they stay that way much longer. Polar bears are insulated by about 4 inches of blubber, lying immediately underneath their skin. They also have a larger head and a longer nasal cavity when compared to Brown bears. The longer nasal cavity is probably better at warming the cold air when breathing through the nostrils and polar bears have an olfactory apparatus that can detect minute odor levels miles away.  You have heard of the infrared cameras that one uses to gauge heat loss and identify areas in your home that are losing heat through poor insulation. Well, the polar bear is so well insulated that they are virtually invisible to an infrared camera. They are one of the most efficient animals for heat retention we know of.

Polar bears are the largest land-dwelling carnivores, with males reaching up to 1500 pounds; the largest polar bear on record weighed 2210 pounds. Yet, while they are the dominant predator of the Arctic circle, they are slated for extinction perhaps within the next 50 years. A guaranteed disappearance of a predator at the top of the food chain should bother the Hell of out of all of us, because we are predators at the top the biggest and widest food chain in the world. So if polar bears can disappear with the speed of essentially dimming a switch, why can’t this happen to us just as easily? Well of course, for one thing there are more of us–humans number more than 6 billion and by the middle of this century we are scheduled to reach 9 billion, while polar bears, restricted to the Arctic circle region, number about 20,000 to 25,000; their numbers are already declining while human numbers continue to grow. Then too, we occupy a different niche than polar bears and occupy more temperate zones and insure ourselves an adequate supply of food through agriculture and animal cultivation; most of us don’t have to hunt to eat. In contrast, the polar bears have an established a food chain niche that is critically dependent on the retention of sea ice for foraging. This projected elimination of the species is not because of threats from hunting or factors other than the expected conditions that will be brought about by global climate change and the early seasonal loss of sea ice that polar bears depend on for hunting their primary prey–seals. Persistent sea ice is essential for polar bears to hunt. Normally, the sea ice doesn’t break up until September, at which time polar bears are forced by circumstances to move off the sea ice onto land. In the fall, a pregnant female creates a hibernation den within the snow and enters into a state of semi-hibernation during which time, her cubs are born (2-4) and they feed exclusively on mother’s milk for three to four and a half months.

When a mother polar bear comes out of her winter hibernation, with cubs in tow, she will have lost several hundred of pounds of weight, as she had fattened up before hibernation in order to nurse her cubs that are born during the hibernation period. After the birth of the cubs, but still during the hibernation period, mother’s milk is the exclusive source of nourishment used to feed the cubs. So when she emerges with her cubs in the spring, they are old enough to have some mobility and her first need is to get food to nourish herself and keep producing mile to feed her cubs. It’s as if the termination of the hibernation period brings on a food crisis. Normally, when polar bears emerge from hibernation,  the arctic sea ice is still intact, which is far more conducive for catching seals, the main diet of polar bears.  Even when the sea ice begins to break up in the summer, large chunks of ice allow polar bears to hunt on the ice when seals break through their holes to breathe. But if the sea ice becomes too thin and breaks up into smaller chunks or disappears altogether, seals are no longer constrained to breathe through the ice and polar bears can no longer hunt efficiently.  There are reports of polar bears mating with grizzlies, the result of which is to produce hybrids that are less efficient as swimmers and at greater risk when marginal sea ice conditions appear.  So, the earlier that the sea ice melts or breaks up, the greater is the risk for polar bears. Reports of polar bear drownings have already appeared, presumably as a result of too much ice melting and making swimming distances between ice flows too great.

The story behind the threat of polar bear extinction began  in 2007 and was provided by a report from the U.S. Geological Survey (USGS), indicating that within 50 years, the shrinking sea ice will leave only a small remnant of polar bear populations on the islands of the Canadian Arctic; those along the Alaskan and Russian coasts, which are the populations most often studied, will all be gone. These reports were provided to Congress; a year later, the polar bear was listed as a threatened species under the Endangered Species Act by the United States Department of the Interior.

The report of 2007 made the news in the Anchorage Daily News (article written by  Tom Kizzia, September 8, 2007) and, until recently, nothing had changed to alter these grim projections, based on scientific expectations derived from climate change modeling studies, using what is known as a general circulation model (GCM). Those studies indicated that sufficient carbon dioxide had already accumulated such that a “tipping point” had been reached and nothing could be done to reverse the fate of sea ice in the Arctic as it was shrinking at a much faster rate than earlier models had predicted. In a relatively short time, it was predicted that sea ice would disappear and get broken up earlier and earlier in the year, putting more pressure on polar bears. In these studies, the tipping point concept was based on the idea that ice normally provides a reflection of sunlight and thus returns energy from the surface of the earth, preventing some solar radiation from warming the oceans and land surfaces. But as ice surfaces diminish in area, earth and water surfaces get more sunlight exposure. This phenomenon is referred to as the “albedo” effect; it constitutes a positive feedback from melting ice–the more ice that melts, the more sunlight hits the earth and water surfaces and in turn melts more ice. The ice melt of 2007 was especially worrisome. Thus, USGA report of 2007 suggested that this positive feedback system, had already reached a point that future sea ice would melt, perhaps very rapidly, and eliminate most of the polar bear population within 50 years. According to that report a tipping point had already been reached so that no matter what future reductions in carbon emissions might be achieved, the polar bears were doomed.

The 2007 USGA report was not seriously challenged until a recent article appeared in Nature in December 2010 (volume 468, p. 955-958). This report re-examined the idea of a tipping point for sea ice and the future of polar bears. However, in these new modeling studies, the issue was examined based on the assumption that some reduction in greenhouse gases would take place in the future. Using a similar model to that used to project a poor outcome for polar bears, the paper by Amstrup et al accepted different levels of reductions in green house gases as a basis for generating different models that simulated whether or not a normal  sea ice pattern could be retained under these conditions of reduced carbon dioxide emissions. Five different models of reduced carbon emissions were used, including one proposal to keep the carbon dioxide levels the same as those of the year 2000 (Y2K model); other models used different scenarios for reducing the level of carbon emissions. First, this study confirmed the 2007 USGA results, strongly supporting the idea that if nothing is done, most polar bears are either doomed or will have to dramatically change their hunting habits (and are probably poorly equipped to do so).  However, with reductions in atmospheric carbon dioxide, the Amstrup modeling studies showed that the sea ice could be retained sufficiently to give safe harbor for polar bears. They did not find a “tipping point” that doomed the polar bears and for that reason alone, the study was very encouraging and carried an obviously reduced doomsday prediction. The December 2010 study is exemplary for several reasons. In addition to giving new hope to the polar bears if humans begin to reduce carbon emissions, the Amstrup paper also demonstrates the power of the internet. In a high impact journal such as Nature, papers are given a relatively small amount of space for a single paper–typically three pages or less for an article. But, because information can be stored on the internet, referred to and linked/downloaded while reading the on-line paper, the so called supplemental material can increase the length of the paper by several fold. The polar bear paper referred to was less than three double-sided printed pages in the magazine, but the supplemental material, which contained additional information on the models used, including more color figures and references, was 26 double-sided pages. A second mode of expansion can be seen in the reference section, where if you click on the section, it expands so that each reference has a “show content” link that takes you to an expanded explanation of the reference that has been quoted, what the reference says and why it may or may not be a source of valid observations and conclusions. In short, the Nature paper just described shows why there are no short papers anymore, particularly on a complex subject and within a high impact journal. Now we have three different levels of readership. First, there’s the casual reader, trying to get the general concept of the article, then there’s the serious reader who evaluates the main figures and can talk somewhat intelligently about the article and then there are the global climate change people and serious polar bear biologists who scour through the main article, all the figures, the material in the supplemental section and the expansion of the references, a sort of “why did I use this reference” section. The take home message of all this complexity is that first and foremost, the best and worst case for the future of our polar bears are both based on models–that is all we have to go on. But, increasingly, the models are fed by better and better data and such models are trying to reach down and resolve time limits not achieved in previous work. Instead of centuries long outcomes, models are getting down to half-century and even decades of time. We will see some of these changes within a single human lifetime. But, a single year of weather means nothing–the variables making up our annual weather patterns are too great to project our future from the weather that unfolds in a single season, tempting though it may be to project them forward in time. I seriously doubt that humans have the capacity to remember and log the long-term weather patterns, such that we can become reliable reporters of weather patterns that change over decades: most of us can’t really remember with certainty the weather events of last year. We remember really tough winters and hot summers and there is a sense that we are moving towards warmer conditions, but these transitions are not smooth hyperbolic curves we ride on and that’s why, as much as we like to talk about the weather, we rely on measurements to reveal the true weather trends. Those measurements show, that as the carbon dioxide emissions have increased, the air temperatures are rising, our oceans are warming and expanding, the ice masses are receding and species are threatened. Globally, 25% of mammalian species are threatened with extinction. Habitat loss is the main reason and for the polar bears, the threat of loss of sea ice is also a case of habitat loss, even though it is first and foremost attributed to global climate change and humanoid activity.

RFM

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