Wednesday, August 26, 2009

Permafrost and Carbon Stores

One of the biggest concerns with regards to the consequences of climate change is mass thawing of Arctic permafrost. Although average global temperatures have increased by 0.6 C in the last 100 years, most of which has occurred in the last decade,1,2 such a statement can be misleading when considering the problem of permafrost thawing. Initially one would be hard pressed to view an increase of 0.6 C as a significant threat to permafrost stability, but unfortunately average temperatures in Arctic regions are increasing at a much more rapid pace than the rest of the world with increases ranging from 3-7 C leading to permafrost active layers having already begun to increase in depth.3,4,5

For reference the active layer of permafrost is defined generally as the seasonally thawing layer overlying permafrost, basically the active layer thaws during the summer and refreezes during the winter. Measuring how the active layer in permafrost increases is important because most of the biochemical and hydrological processes that take place in permafrost regions occur within the active layer. In contrast very little to zero biological or chemical activity occur in non-active layer areas due to the sub-zero temperatures that keep the environment frozen.

Although modeling and empirically measuring permafrost thawing is important there are two significant problems. One of the problems with permafrost study is the continuing loss of palsas, which are telltale signs of permafrost in the discontinuous zone and sometimes regarded as the only real reliable evidence pertaining to permafrost existence in the discontinuous zone.6,7 This reduction makes measuring the influence of climate change on the discontinuous zone, both in extent and rate of disappearance, more difficult. Fortunately carbon stores in the discontinuous zone are less significant when compared against those in the continuous zone. The second problem is the same problem normal climate modeling suffers from, an incomplete understanding of positive and negative feedback loops within the climate itself. Unfortunately recent empirical evidence has demonstrated that current models have underestimated the rate of surface sea ice melt, sea level rise and the neutralization/masking influence of aerosols.8,9 These underestimations combined with only recent realizations that significant ice loss will have an accelerated effect on permafrost melt and there is a high probability that existing models regarding CO2 release from permafrost underestimate the total consequence.

Most of the empirical evidence that tracks permafrost thawing only does so on a regional level. However, because most of the progressive warming in the Arctic appears to be generally uniform, regional analysis can be applied at some level to unanalyzed regions to generate a ballpark understanding of universal thawing. One particular study from Sweden calculates an average permafrost thawing at between 0.7 and 1.3 cm/yr;10 however, unfortunately this rate has a significant standard deviation because in the past decade thawing increased to 2 cm/yr including an 81% loss of total permafrost from discontinuous zone sampling points.10 If one assumes that this rate increases at 5% per year due to continuing global warming (a conservative estimate) by 2030 an additional 0.78 meters permafrost will thaw.

The reason surface permafrost thawing is a concern is because most of the organic carbon from permafrost originated from plant photosynthesis and growth within a dynamic active layer over millions of years there are higher carbon concentrations near the surface of permafrost, thus the first half to full meter of thaw will probably be the most important with regards to the amount of carbon released over a given period of time. Basically the first ‘layer’ of thawing will be akin to destroying a dam as a significant amount of CO2 and methane will be released into the atmosphere, then as more thawing occurs a more constant, but lower amount of CO2 and methane will be continually released.

Mass thawing of permafrost is a significant consequence because over history permafrost has naturally sequestered anywhere from 98 petagrams (108 billion tons) to 1672 petagrams (1842 billion tons)11 of releasable carbon material or 1/6 to 2 times the total amount of carbon currently in the atmosphere locked in approximately 14.7 to 20.4 million square km of permafrost.11,12 The disparity in estimates is so significant because some estimates include cryogenic (freeze-thaw) mixing and sediment deposition at greater depths previously unconsidered.11 The larger estimate of 1672 petagrams was determined after the initial estimate of 98 – 100 petagrams by digging to a greater depth in Arctic permafrost (approximately 3 meters instead of 1 meter).11,13 Also estimations of sequestered carbon could be smaller than reality due to discounting current rates of ebullition of methane from Arctic lakes.2 Note that when discussing the influence that permafrost thawing will have on climate change Arctic centralized permafrost is far and away the most important because although the Southern Hemisphere has permafrost it typically has a much lower stored carbon count.13

Sadly these discrepancies are rather meaningless because even if the lowest estimate of 98 petagrams was correct (it is unlikely that it is) it would still result in the release of enough carbon-based material (both methane and CO2) into the atmosphere to facilitate a very high probability of serious and permanent detrimental climate change regardless of what steps humans take in the future. At least that scenario represents the common belief. There are some that acknowledge that there is a little more wiggle room as permafrost thawing may increase the probability of excess small flora growth, mostly shrubs, that could absorb some of the released CO2 from permafrost.14,15 Unfortunately this additional sink capacity is only short-lived and the total time between conversion from sink to source is unknown, although it seems that 5-20 years is a reasonable range.

Therefore, with the stakes so high, the first line of defense would be to reduce the emission of greenhouse gases into the atmosphere to reduce the probability of initializing the catalytic cascade of permafrost thawing. Unfortunately it does not appear, based on all available empirical evidence regarding the speed of climate change, psychological importance attributed to climate change by the mass population and general inaction by the governments of most major emitters, that this necessary reduction in emissions will occur in time to prevent major thawing. Therefore, it is important to develop strategies to reduce the influence of the carbon released from its permafrost cage on overall climate change.

There appear to be three stages of intervention for neutralizing the influence of carbon-based gases from thawing permafrost. The first stage involves refreezing the permafrost by changing the local environment to compensate for the average global temperature increase brought on by excessive greenhouse gases in the atmosphere. The second stage involves trapping the methane and CO2 once it escapes the permafrost, but before it can leave the localized environment of its origin. The third stage involves augmentation of technologies that would accelerate removal of these carbon-based gases from the atmosphere. Clearly the third strategy is simple air capture, but the problem with depending on air capture is that the potential release from permafrost stores would easily eliminate any economic viability (whatever may even exist now) of the air capture strategy due to the shear amount of methane and CO2 available for release. Therefore, the focus should be on the first two stages.

It is difficult to fathom successful execution in either of the first two stages because of the shear depth of action required. Recall that Arctic permafrost covers 14.7 to 20.4 square km of the planet’s surface (depending on the exact definition of permafrost utilized). To propose any type of program to reduce even 20% of the greenhouse gases that would be released from permafrost over the course of thawing seems insane. However, such a program must occur if humans are to maintain a climate that can carry a capacity of billions of humans. Unfortunately focus on the first stage does not appear to be a viable attack strategy because to compensate for the increased average global temperature technology will need to be incorporated to provide cooling. Realistically the immediate concern is that the energy and materials required to pursue such a strategy could be unavailable. Note that in this instance the economics for neutralization at this stage are rather meaningless because averting significant detrimental climate change provides more economic benefit than almost any strategy to reduce the probability of climate change. Instead the shear amount of material required may not physically be available.

For example there are two main strategies that can be implemented to cool the permafrost environment despite higher average global temperatures. The first option would involve developing some form of gargantuan air conditioner that would function over an area of who knows say 1 square mile. Recall the total surface area of permafrost in the Arctic and one quickly realizes that it would be borderline impossible to implement a mechanical-based direct heat exchanger type strategy using air conditioners or any other type of apparatus. The second option is rather exotic involving dispersal of a cooling gas, perhaps something like freon on to the surface of the permafrost to reduce temperatures. This option has a lot of similarity to the sulfur-dioxide atmospheric release geo-engineering option. Unfortunately not only would this strategy suffer from the same problems as the first option in the amount of resources required, but there also would be potential environmental damage due to freon or whatever else particles being transferred out of the permafrost region by wind gusts or consumption by wildlife. Thus, although possible, neither or these strategies appear probable.

Therefore, with thawing all but guaranteed on some level and any form of air capture extraordinarily unlikely to neutralize the carbon-based gases released from the thawing, it appears that the only available option is try to reduce the amount of gas released into the atmosphere by absorbing the gas prior to its escape from the local region of ejection. Basically a large swatch of permafrost needs to interact with a molecule or structure that can absorb or render the methane and CO2 released from the permafrost inert. There are a limited number, but multiple options that fit these criteria, but the most efficient means to accomplish this goal may be to revisit bio-char.

A vast majority of the publicity surrounding bio-char involves its use as a supplementary tool to reduce the amount of atmospheric CO2 through disallowing the respiration or decomposition-based release of CO2 previous absorbed by plant life. However, bio-char has other notable qualities aside from sequestering absorbed CO2: enhancement of crop yield, enrichment of soil and even the possibility to absorb nitrogen oxides and methane.16,17,18 Although there is not a significant amount of research regarding bio-char/charcoal and its interaction with methane, initial studies have concluded that charcoal (basically what bio-char is) completely suppresses methane emissions from both soybeans and B. humidicola at 20 g/kg of soil.19 Unfortunately there is a significant caveat to this analysis, the lingering question of whether or not plants produce a significant amount of methane in that bio-char actually acts as a genuine absorption medium. This lack of available information pertaining to the maximum absorption capacity of methane in bio-char raises the question of whether or not bio-char deployment in permafrost environments will make any significant difference in methane neutralization.

For the moment assume that bio-char does indeed absorb significant quantities of methane, thus making it a viable candidate for limiting permafrost carbon based release. The big advantage that bio-char has over other absorption technologies is that the energy and technological requirements to generate large quantities are significantly lower. Also bio-char can be produced at a large scale relatively quickly once the necessary infrastructure is established. Another advantage to using bio-char is even if its ability to absorb methane proves to be insignificant, its ability to enhance soil quality and increase crop yields would more than likely have some positive influence on the already reported increased shrub and other flora growth in thawed permafrost regions increasing their ability to act as a carbon sink.

So how much bio-char would be required to accomplish 100% Arctic permafrost coverage? First it is assumed that the pyrolysis process utilized to synthesize the bio-char is either 80% or 100% efficient and slow pyrolysis is used to maximize bio-char production from the pyrolysis process. An important lingering issue is what plants should be cultivated for use as feedstock in the pyrolysis process? Although it would be useful to convert large amounts of forest residue to bio-char because it is already available, such a strategy may produce erosion and growth problems; therefore it may be wiser to develop specific soil plots to grow feedstock for bio-char production. Bio-char synthesis through pyrolysis is known to be dependent on the lignin content of the particular feedstock.20 Therefore, it would be wise to grow high lignin content feedstock to maximize bio-char synthesis rates. However, it must be pointed out that the feedstock grown for bio-char production will consume land that would more than likely be otherwise utilized for the growth of food stocks. So if not enough land is available for both food production and bio-char production, additional bio-char feedstock plots will have to be transferred to non-ideal soil to compensate for the reduction in available high quality soil. To that end if an appropriate amount of land is available then a mixture of legumes (to maintain soil quality), grain husks and kernels would be appropriate; if land availability is deemed to be a limiting factor then a crop like switchgrass and grain husks would be useful as the feedstock.

Empirical evidence has identified an average bulk density for bio-char generated from various sources ranging from 0.30 to 0.43 g/cm3.21 From this range assume a bulk density of 0.35 g/cm3 as there is evidence to suggest that higher pyrolysis temperatures generate higher density bio-char, but also result in less total bio-char.21 Bio-char thickness will average 10 cm and will have a 42% synthesis rate from pyrolysis. Fortunately this analysis only has the simple goal of generating a realistic estimate of the required bio-char to cover Arctic permafrost, thus the assumption that the area of permafrost is in the shape of a square can be made (yes this assumption is irrational for an exact figure, but such an assumption will result in a meaningful ballpark figure). Using the above information and assumptions an 80% conversion efficiency would require 6.43125 x 10^17 to 8.925 x 10^17 grams of bio-char whereas a 100% conversion efficiency would require 5.145 x 10^17 to 7.14 x 10^17 grams. Both examples would require over 1 x 10^18 grams of feedstock.

Initially the bio-char demands seem to sink the idea. However, there are two important considerations that would decrease the requisite demand. First, the above mass demands are to cover all of the permafrost (more or less due to the square assumption) in the Arctic; however, to avert climate change due to the release of carbon stores from permafrost not all of this carbon needs to be neutralized. Unfortunately there is no good way of estimating what percentage of coverage is required largely because there is no evidence to assume whether or not carbon stores are divided equally within permafrost. Second, the required bio-char thickness for aiding flora growth and methane absorption may not have to be as large as 10 centimeters, although not a lot of relief should be expected from this consideration.

Overall it is imperative that action is taken against the potential climate altering release of CO2 and methane from permafrost, for it is highly likely that thawing will be significant enough that these reserves will play a role in the prospect of continuing climate change. It is unclear whether or not bio-char can be a temporary or even permanent solution to the permafrost release concern due to the shear amount that appears to be required. However, there is enough evidence to suggest that bio-char, where it is successfully deployed, would have a positive effect in helping limit the total release of CO2 and methane from permafrost stores, thus affording society more time to reduce existing and future emissions reducing the probability of further permafrost thawing. If the world is going to undertake an extensive bio-char production program, which most environmentalists believe it should, then it may be more beneficial to deposit the bio-char in the Arctic than in a neighboring field.

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2. Walter, Katey, Smith, Laurence, Chapin III, Stuart. “Methane Bubbling from northern lakes: present and future contributions to the global methane budget.” Phil. Trans. R. Soc. A. 2007. 365: 1657-1676.

3. “Annual Arctic Report Card Shows Stronger Effects of Warming.” October 16, 2008.

4. Lachenbruch, A.H., and Marshall, B. V. “Changing climate: geothermal evidence from permafrost in the Alaskan Arctic.” Science. 1986. 234:689–696.

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6. Lyon, S.W., et, Al. “Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis.” Hydrol. Earth Syst. Sci. 2009. 13: 595–604.

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10. Akerman, H. J., and Johansson, M. “Thawing permafrost and thicker active layers in sub-arctic Sweden.” Permafrost Periglac. 2008. 19(3): 279–292.

12. Schuur, Edward, et, Al. “Vulnerability of Permafrost Carbon to Climate Change: Implications for the Global Carbon Cycle.” BioScience. 2008. 58 (8): 701-714.

13. Slanina, Sjaak. "Permafrost in the Arctic." Encyclopedia of Earth. October 11, 2007. International Arctic Science Committee.

14. Wagner, D., and Liebner, S. “Global Warming and Carbon Dynamics in Permafrost Soils: Methane Production and Oxidation.” Permafrost Soils. Soil Biology. 2009. 16: 219-236.

15. Schuur, Edward, et, Al. “The effect of permafrost thaw on old carbon release and net carbon exchange from tundra.” Nature. May 2009. 459: 556-559.

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17. Glaser, B. Lehmann, J, Zech, W. “Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal - a review.” Biology and Fertility of Soils. 2008. 35: 4.

18. Lehmann, J., and Rondon, M. “Bio-char soil management on highly-weathered soils in the humid tropics.” Biological Approaches to Sustainable Soil Systems. 2005. Boca
Raton, CRC Press, in press.

19. Rondon, M.A., Ramirez, J. A., Lehmann, J. “Greenhouse Gas Emissions Decrease with Charcoal Additions to Tropical Soils.”

20. Amonette, Jim. “An Introduction to Biochar: Concept, Processes, Properties, and Applications.” Harvesting Clean Energy 9 Special Workshop. Billings, MT Jan 25, 2009.
21. Lehmann, Johannes, and Joseph, Stephen. Biochar for Environmental Management: Science and Technology. ISBN-10: 184407658X. Earthscan Publications Ltd. Mar. 2009. pp. 28-29.

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