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Author Topic: Modelling permafrost carbon feedback  (Read 7041 times)

wili

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Modelling permafrost carbon feedback
« on: May 02, 2013, 08:16:06 PM »
I don't know if this should be here or in the 'Science' thread, but it strikes me that this is a very important recent paper that was discussed on a number of climate science forums, and would be worthwhile discussing here.

http://www.nature.com/ngeo/journal/v5/n10/full/ngeo1573.html

Significant contribution to climate warming from the permafrost carbon feedback


    Andrew H. MacDougall,   
    Christopher A. Avis   
    & Andrew J. Weaver

    Nature Geoscience
    5, 719–721
    (2012)

Abstract:

Permafrost soils contain an estimated 1,700 Pg of carbon, almost twice the present atmospheric carbon pool1. As permafrost soils thaw owing to climate warming, respiration of organic matter within these soils will transfer carbon to the atmosphere, potentially leading to a positive feedback2. Models in which the carbon cycle is uncoupled from the atmosphere, together with one-dimensional models, suggest that permafrost soils could release 7–138 Pg carbon by 2100 (refs 3, 4).

Here, we use a coupled global climate model to quantify the magnitude of the warming generated by the feedback between permafrost carbon release and climate. According to our simulations, permafrost soils will release between 68 and 508 Pg carbon by 2100.

We show that the additional surface warming generated by the feedback between permafrost carbon and climate is independent of the pathway of anthropogenic emissions followed in the twenty-first century.

We estimate that this feedback could result in an additional warming of 0.13–1.69 °C by 2300. We further show that the upper bound for the strength of the feedback is reached under the less intensive emissions pathways. We suggest that permafrost carbon release could lead to significant warming, even under less intensive emissions trajectories.


I would appreciate it if someone with greater skills than I have in that direction could cut and past the figures from the article linked above.

Here is the coverage by Skeptical Science of the piece (from which I stole my subject headline):

http://www.skepticalscience.com/Macdougall.html

It was also covered nicely by Kathy (whose very appropriate imho response was "oh shit!") at Climate Sight:

http://climatesight.org/2012/10/02/permafrost-projections/

The otherwise-staid Tamino used "Oh Shit" as the title for his entry on this same article (and maybe is the one I should have used here):

http://tamino.wordpress.com/2012/10/04/oh-shit/

If people have other links to discussions on the topic, please include them. I will just give a bit of a summarizing quote from Kate here:

As a result of the thawing permafrost, the land switched from a carbon sink (net CO2 absorber) to a carbon source (net CO2 emitter) decades earlier than it would have otherwise – before 2100 for every DEP. The ocean kept absorbing carbon, but in some scenarios the carbon source of the land outweighed the carbon sink of the ocean. That is, even without human emissions, the land was emitting more CO2 than the ocean could soak up.

Concentrations kept climbing indefinitely, even if human emissions suddenly dropped to zero.


This is the part of the paper that made me want to hide under my desk.

This scenario wasn’t too hard to reach, either – if climate sensitivity was greater than 3°C warming per doubling of CO2 (about a 50% chance, as 3°C is the median estimate by scientists today), and people followed DEP 8.5 to at least 2013 before stopping all emissions (a very intense scenario, but I wouldn’t underestimate our ability to dig up fossil fuels and burn them really fast), permafrost thaw ensured that CO2 concentrations kept rising on their own in a self-sustaining loop...
As if that weren’t enough, the paper goes on to list a whole bunch of reasons why their values are likely underestimates...

This paper went in my mental “oh shit” folder, because it made me realize that we are starting to lose control over the climate system.

No matter what path we follow – even if we manage slightly negative emissions, i.e. artificially removing CO2 from the atmosphere – this model suggests we’ve got an extra 0.25°C in the pipeline due to permafrost.


(My emphases.)

(Mods, please move this to science, if that is the appropriate thread.)
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Bruce Steele

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Re: Modelling permafrost carbon feedback
« Reply #1 on: May 03, 2013, 06:17:44 AM »
Wili, Also from  Open Mind  was a link attributed to Caldiera.                                                                https://docs.google.com/viewer?a=v&pid=forums&srcid=MDE0NTY3NTk0NzY2MTMxMzQ4MjEBMTgwMTQzMDc0MzY5MDkyODI5NDgBLTFNOGdQajF4YkVKATQBAXYy


Same article. I was wondering what methane ppb would increase to? 68-508 pg carbon is a large spread but what would the methane range look like? Are we already on schedule with the recent increases?

Artful Dodger

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Re: Modelling permafrost carbon feedback
« Reply #2 on: May 03, 2013, 07:49:26 AM »
Hi wili

Carbon emissions from permafrost are expected to peak around 2100, then trail off slowly until 2200, by which time they are as bad as they are now.

Here's the Money$hot from a Climate Progress blog post on the topic:



NSIDC bombshell: Thawing permafrost feedback will turn Arctic from carbon sink to source in the 2020s, releasing 100 billion tons of carbon by 2100.

The paper cited is this: (pdf here)

Schaefer, Kevin, et al. "Amount and timing of permafrost carbon release in response to climate warming." Tellus B 63.2 (2011): 165-180.
Cheers!
Lodger

wili

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Re: Modelling permafrost carbon feedback
« Reply #3 on: May 03, 2013, 01:40:54 PM »
Thanks for the added info and links. It is my (feeble) understanding that it is uncertain exactly how much of the carbon released from permafrost will be as methane rather than CO2. The MacDougal study only considers CO2.

"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

Artful Dodger

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Re: Modelling permafrost carbon feedback
« Reply #4 on: May 05, 2013, 12:26:14 PM »
It is my understanding that it is uncertain exactly how much of the carbon released from permafrost will be as methane rather than CO2. The MacDougal study only considers CO2.

Hi wili,

Rather, these studies treat ALL released carbon to be in the form of CO2. So these studies will be right in the long term, but will miss important positive feedbacks over the mid-term (say, 20 year time horizon).

That seems to be the one most important for human society, doesn't it?
Cheers!
Lodger

AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #5 on: June 03, 2014, 03:49:54 AM »
The linked reference provides information on new permafrost behavior that the modelers need to consider:


Martin A. Briggs, Michelle A. Walvoord, Jeffrey M. McKenzie, Clifford I. Voss, Frederick D. Day-Lewis and John W. Lane , (2014), "New permafrost is forming around shrinking Arctic lakes, but will it last?", Geophysical Research Letters, DOI: 10.1002/2014GL059251

http://onlinelibrary.wiley.com/doi/10.1002/2014GL059251/abstract?

Abstract: "Widespread lake shrinkage in cold regions has been linked to climate warming and permafrost thaw. Permafrost aggradation, however, has been observed within the margins of recently receded lakes, in seeming contradiction of climate warming. Here permafrost aggradation dynamics are examined at Twelvemile Lake, a retreating lake in interior Alaska. Observations reveal patches of recently formed permafrost within the dried lake margin, colocated with discrete bands of willow shrub. We test ecological succession, which alters shading, infiltration, and heat transport, as the driver of aggradation using numerical simulation of variably saturated groundwater flow and heat transport with phase change (i.e., freeze-thaw). Simulations support permafrost development under current climatic conditions, but only when net effects of vegetation on soil conditions are incorporated, thus pointing to the role of ecological succession. Furthermore, model results indicate that permafrost aggradation is transitory with further climate warming, as new permafrost thaws within seven decades."
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #6 on: September 30, 2014, 01:07:54 AM »
The linked paper with an open access pdf, indicates that most permafrost degradation estimates have ignored the Tibetan Plateau's permafrost.  Considering this additional carbon source, "…the present study suggested that the permafrost organic carbon pools of Northern Hemisphere should be updated from 1672 to 1739 Pg."

Mu, C., Zhang, T., Peng, X., Cao, B., Zhang, X., Wu, Q., and Cheng, G.: The organic carbon pool of permafrost regions on the Qinghai–Xizang (Tibetan) Plateau, The Cryosphere Discuss., 8, 5015-5033, doi:10.5194/tcd-8-5015-2014, 2014

http://www.the-cryosphere-discuss.net/8/5015/2014/tcd-8-5015-2014.pdf

Abstract: "Presently, Northern Circumpolar Soil Carbon Database was not involved permafrost organic carbon storage on the Qinghai–Xizang (Tibetan) Plateau (QXP). Here we reported a new estimation of soil organic carbon (SOC) pools of the permafrost regions on the QXP at different layers from the top 1 to 25 m depth using a total of 706 soil profiles. The SOC pools were estimated to be 15.29 Pg for the 0–1 m, 4.84 Pg for the 1–2 m, 3.89 Pg for the 2–3 m and 43.19 Pg for the layer of 3–25 m. The percentage (64.3%) of SOC storage in deep layer (3–25 m) on the QXP was larger than that (38.8%) in the northern circumpolar permafrost region. In total, permafrost region on the QXP contains approximately 67.2 Pg SOC, of which approximately 47.08 Pg (70.1%) stores in perennially frozen soils and deposits. The present study suggested that the permafrost organic carbon pools of Northern Hemisphere should be updated from 1672 to 1739 Pg."
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morganism

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Re: Modelling permafrost carbon feedback
« Reply #7 on: November 17, 2014, 12:28:28 AM »
Looks like there is no noticeable increase in permafrost release in 2012, from the CARVE project

http://www.jpl.nasa.gov/news/news.php?feature=4376

LRC1962

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Re: Modelling permafrost carbon feedback
« Reply #8 on: February 05, 2015, 05:14:17 PM »
Here is a 3 part interview with Dr Natalia Shakhova.
https://www.youtube.com/watch?v=dQDVr1eMLK8
https://www.youtube.com/watch?v=6BVsS6vo60Y
https://www.youtube.com/watch?v=80ooWqpCdZE
In it she describes what is happening both with the permafrost and the Arctic shelf. Some interesting points. The permafrost in Siberia had already risen from -17C to -7 before the the more resent events had occurred in the Arctic. Note: regardless of it still being below zero that is a lot of heat going into the permafrost before the last major up swing in temps have even started. She believes that there are major deposits of free methane (not hydrates) below the permafrost just waiting for an avenue to get to the atmosphere. Now Dr. Richard Allyn and others have pointed out recently that because of the physics hydrates that belches will not occur and that it will come as a slow release. If Dr Natalia Shakhova is right than major belches could actually occur with potential total release of 50 gts from what I understood and that is not including all the release of the hydrates. Another point is that the permafrost is melting far faster then anyone predicted even 10yrs ago, but when questioned about it would not say because she has no idea other than what they though they knew 10 yrs ago no longer applies.
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #9 on: February 26, 2015, 12:57:25 AM »
The linked paper says that there is so much concern about permafrost degradation that they now have to write papers to advise young scientists to go into this field:

http://www.the-cryosphere-discuss.net/9/1209/2015/tcd-9-1209-2015.html
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LRC1962

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Re: Modelling permafrost carbon feedback
« Reply #10 on: February 26, 2015, 01:14:02 AM »
Unfortunately we seem to have to leave it to the Russians to find things out. Canada would be a great place to do research. Unfortunately all papers and communications by any scientist in Canada have to be cleared by the Can. gov. before release (and they are very much against anything indicating the Arctic is melting) or they will be prosecuted. A true travesty and abuse of power IMHO.
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #11 on: February 28, 2015, 12:41:54 AM »
I have read that permafrost degradation also produces significant amounts of nitrous oxide; so I hope that the recent acceleration of nitrous oxide concentration at Mauna Loa indicated in the attached plot (with data through Feb 21 2015) does not indicate that the degradation of permafrost is moving into its main phase:
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #12 on: February 28, 2015, 01:25:15 AM »
The following two references adds some support for the statement in my last post that degradation of certain types of permafrost can produce high rates of nitrous oxide emissions:

MARUSHCHAK, M. E., PITKÄMÄKI, A., KOPONEN, H., BIASI, C., SEPPÄLÄ, M. and MARTIKAINEN, P. J. (2011), Hot spots for nitrous oxide emissions found in different types of permafrost peatlands. Global Change Biology, 17: 2601–2614. doi: 10.1111/j.1365-2486.2011.02442.x


http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02442.x/abstract


Abstract: "Recent findings on large nitrous oxide (N2O) emissions from permafrost peatlands have shown that tundra soils can support high N2O release, which is on the contrary to what was thought previously. However, field data on this topic have been very limited, and the spatial and temporal extent of the phenomenon has not been known. To address this question, we studied N2O dynamics in two types of subarctic permafrost peatlands, a peat plateau in Russia and three palsa mires in Finland, including also adjacent upland soils. The peatlands studied have surfaces that are uplifted by frost (palsas and peat plateaus) and partly unvegetated as a result of wind erosion and frost action. Unvegetated peat surfaces with high N2O emissions were found from all the studied peatlands. Very high N2O emissions were measured from peat circles at the Russian site (1.40±0.15 g N2O m−2 yr−1). Elevated, sparsely vegetated peat mounds at the same site had significantly lower N2O release. The N2O emissions from bare palsa surfaces in Northern Finland were highly variable but reached high rates, similar to those measured from the peat circles. All the vegetated soils studied had negligible N2O release. At the bare peat surfaces, the large N2O emissions were supported by the absence of plant N uptake, the low C : N ratio of the peat, the relatively high gross N mineralization rate and favourable moisture content, together increasing availability of mineral N for N2O production. We hypothesize that frost heave is crucial for high N2O emissions, since it lifts the peat above the water table, increasing oxygen availability and making it vulnerable to the the physical processes that may remove the vegetation cover. In the future, permafrost thawing may change the distribution of wet and dry surfaces in permafrost peatlands, which will affect N2O emissions."


Bo Elberling, Hanne H. Christiansen & Birger U. Hansen, (2010), "High nitrous oxide production from thawing permafrost", Nature Geoscience 3, 332 - 335
doi:10.1038/ngeo803

http://www.nature.com/ngeo/journal/v3/n5/abs/ngeo803.html

Abstract: "Permafrost soils contain nearly twice as much carbon as the atmosphere. When these soils thaw, large quantities of carbon are lost, mainly in the form of methane and carbon dioxide. In contrast, thawing is thought to have little impact on nitrous oxide emissions, which remain minimal following the summer thaw. Here, we examined the impact of thawing on nitrous oxide production in permafrost cores collected from a heath site and a wetland site in Zackenberg, Greenland. Rates of nitrous oxide production in the heath soil were minimal, regardless of the hydrological conditions. Although rates of nitrous oxide production in the wetland soil were low following thawing, averaging 1.37 μg N h−1 kg−1, they were 18 μg N h−1 kg−1 for permafrost samples following thawing, drainage and rewetting with the original meltwater. We show that 31% of the nitrous oxide produced after thawing and rewetting a 10-cm permafrost core—equivalent to 34 mg N m−2 d−1—was released to the atmosphere; this is equivalent to daily nitrous oxide emissions from tropical forests on a mean annual basis. Measurements of nitrous oxide production in permafrost samples from five additional wetland sites in the high Arctic indicate that the rates of nitrous oxide production observed in the Zackenberg soils may be in the low range."
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #13 on: March 01, 2015, 04:29:42 AM »
Looking at the attached NOAA map of surface temperature anomalies for January 2015 it is not difficult to believe that permafrost degradation is accelerating:
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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RaenorShine

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Re: Modelling permafrost carbon feedback
« Reply #14 on: March 10, 2015, 10:43:07 AM »
Excellent summary of current methane release discussion has been posted by robertscribbler

https://robertscribbler.wordpress.com/2015/03/09/cause-for-appropriate-concern-over-arctic-methane-overburden-plumes-eruptions-and-large-ocean-craters/

Concern Over Catastrophic Methane Release — Overburden, Plumes, Eruptions, and Large Ocean Craters

Depending on who you listen to, it’s the end of the world, or it isn’t. A loud and lively debate that springs up in the media every time a new sign of potential methane instability or apparent increasing emission from methane stores is reported by Arctic observational science.

A really long blog post but well worth reading (and rereading) in full, with primers on the various release mechanisms and future release possibilities.

AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #15 on: March 25, 2015, 09:46:34 PM »
Here is another reference on modeling permafrost degradation (& I do not think that this is the final answer to the question of how much GHG will be emitted with continued global warming):

Chadburn, S. E., Burke, E. J., Essery, R. L. H., Boike, J., Langer, M., Heikenfeld, M., Cox, P. M., and Friedlingstein, P.  (2015), "Impact of model developments on present and future simulations of permafrost in a global land-surface model", The Cryosphere Discuss., 9, 1965-2012, doi:10.5194/tcd-9-1965-2015.

http://www.the-cryosphere-discuss.net/9/1965/2015/tcd-9-1965-2015.html

Abstract: "There is a large amount of organic carbon stored in permafrost in the northern high latitudes, which may become vulnerable to microbial decomposition under future climate warming. In order to estimate this potential carbon-climate feedback it is necessary to correctly simulate the physical dynamics of permafrost within global Earth System Models (ESMs) and to determine the rate at which it will thaw.

Additional new processes within JULES, the land surface scheme of the UK ESM (UKESM), include a representation of organic soils, moss and bedrock, and a modification to the snow scheme. The impact of a higher vertical soil resolution and deeper soil column is also considered.

Evaluation against a large group of sites shows the annual cycle of soil temperatures is approximately 25 % too large in the standard JULES version, but this error is corrected by the model improvements, in particular by deeper soil, organic soils, moss and the modified snow scheme. Comparing with active layer monitoring sites shows that the active layer is on average just over 1 m too deep in the standard model version, and this bias is reduced by 70 cm in the improved version. Increasing the soil vertical resolution allows the full range of active layer depths to be simulated, where by contrast with a poorly resolved soil, at least 50% of the permafrost area has a maximum thaw depth at the centre of the bottom soil layer. Thus all the model modifications are seen to improve the permafrost simulations.

Historical permafrost area corresponds fairly well to observations in all simulations, covering an area between 14–19 million km2. Simulations under two future climate scenarios show a reduced sensitivity of permafrost degradation to temperature, with the near-surface permafrost lost per degree of warming reduced from 1.5 million km2 °C−1 in the standard version of JULES to between 1.1 and 1.2 million km2 °C−1 in the new model version. However, the near-surface permafrost area is still projected to approximately half by the end of the 21st century under the RCP8.5 scenario."
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #16 on: April 02, 2016, 03:53:34 PM »
The linked (open access) reference demonstrates that increases in GMST will dominate future increases in Arctic soil heat content and that changes in snow extent will play a secondary role.  Thus with Arctic Amplification we can expect the permafrost to thaw as GMST increases:

Shi, X., Troy, T. J., and Lettenmaier, D. P.: Effects of pan-Arctic snow cover and air temperature changes on soil heat content, The Cryosphere Discuss., doi:10.5194/tc-2016-70, in review, 2016.


http://www.the-cryosphere-discuss.net/tc-2016-70/

Abstract. Soil heat content (SHC) provides an estimate of the integrated effect of changes in the land surface energy balance. It considers the specific heat capacity, soil temperature, and phase changes of soil moisture as a function of depth. In contrast, soil temperature provides a much more limited view of land surface energy flux changes. This is particularly important at high latitudes, which have and are undergoing surface energy flux changes as a result of changes in seasonal variations of snow cover extent (SCE) and hence surface albedo changes, among other factors. Using the Variable Infiltration Capacity (VIC) land surface model forced with gridded climate observations, we simulate spatial and temporal variations of SCE and SHC over the pan-Arctic land region for the last half-century. On the basis of the SCE trends derived from NOAA satellite observations in 5° latitude bands from April through June for the period 1972–2006, we define a snow covered sensitivity zone (SCSZ), a snow covered non-sensitivity zone (SCNZ), and a non-snow covered zone (NSCZ) for North America and Eurasia. We then explore long-term trends in SHC, SCE, and surface air temperature (SAT) and their corresponding correlations in NSCZ, SCSZ and SCNZ for both North America and Eurasia. We find that snow cover downtrends have a significant impact on SHC changes in SCSZ for North America and Eurasia from April through June. SHC changes in the SCSZ over North America are dominated by downtrends in SCE rather than increasing SAT. Over Eurasia, increasing SAT more strongly affects SHC than in North America. Overall, increasing SAT during late spring and early summer is the dominant factor that has resulted in SHC changes over the pan-Arctic domain, whereas reduced SCE plays a secondary role that is only important in the SCSZ.
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #17 on: April 06, 2016, 11:47:46 PM »
It maybe that the linked (open source) reference indicates that the increase of Arctic biogenic volatile emissions with warming might serve as a negative feedback:

Magnus Kramshøj, Ida Vedel-Petersen, Michelle Schollert, Åsmund Rinnan, Josephine Nymand, Helge Ro-Poulsen & Riikka Rinnan (2016) "Large increases in Arctic biogenic volatile emissions are a direct effect of warming", Nature Geoscience, doi:10.1038/ngeo2692


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2692.html

Abstract: "Biogenic volatile organic compounds are reactive gases that can contribute to atmospheric aerosol formation. Their emission from vegetation is dependent on temperature and light availability. Increasing temperature, changing cloud cover and shifting composition of vegetation communities can be expected to affect emissions in the Arctic, where the ongoing climate changes are particularly severe. Here we present biogenic volatile organic compound emission data from Arctic tundra exposed to six years of experimental warming or reduced sunlight treatment in a randomized block design. By separately assessing the emission response of the whole ecosystem, plant shoots and soil in four measurements covering the growing season, we have identified that warming increased the emissions directly rather than via a change in the plant biomass and species composition. Warming caused a 260% increase in total emission rate for the ecosystem and a 90% increase in emission rates for plants, while having no effect on soil emissions. Compared to the control, reduced sunlight decreased emissions by 69% for the ecosystem, 61–65% for plants and 78% for soil. The detected strong emission response is considerably higher than observed at more southern latitudes, emphasizing the high temperature sensitivity of ecosystem processes in the changing Arctic."


Edit: Now that I think about it, depending on the timing of any additional cloud formation initiated by the BVOCs, these findings might indicate a positive feedback mechanism (or not).
« Last Edit: April 07, 2016, 10:07:39 AM by AbruptSLR »
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #18 on: April 14, 2016, 04:56:38 PM »
The linked (open access) reference uses models and indicates that carbon emissions from the permafrost will be worse than previously projected:

Mikel González-Eguino & Marc B. Neumann (2016), "Significant implications of permafrost thawing for climate change control", Climatic Change, pp 1-8, DOI: 10.1007/s10584-016-1666-5


http://rd.springer.com/article/10.1007%2Fs10584-016-1666-5


Abstract: "Large amounts of carbon are stored as permafrost within the Arctic and sub-Arctic regions. As permafrost thaws due to climate warming, carbon dioxide and methane are released. Recent studies indicate that the pool of carbon susceptible to future thaw is higher than was previously thought and that more carbon could be released by 2100, even under low emission pathways. We use an integrated model of the climate and the economy to study how including these new estimates influence the control of climate change to levels that will likely keep the temperature increase below 2 °C (radiative forcing of 2.6 Wm−2). According to our simulations, the fossil fuel and industrial CO2 emissions need to peak 5–10 years earlier and the carbon budget needs to be reduced by 6–17 % to offset this additional source of warming. The required increase in carbon price implies a 6–21 % higher mitigation cost to society compared to a situation where emissions from permafrost are not considered. Including other positive climate feedbacks, currently not accounted for in integrated assessment models, could further increase these numbers."
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AbruptSLR

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Re: Modelling permafrost carbon feedback
« Reply #19 on: April 14, 2016, 05:10:29 PM »
The linked (open access) reference indicates that carbon emissions from northern hemispheric permafrost thawing will be significant (3 to 54% of anthropogenic emissions).  See the attached image of the projected annual carbon emissions from northern permafrost until 2300 showing a peak rate of emissions between 2050 and 2100 (depending on the RCP scenario assumed):

MacDougall, A. H. and Knutti, R.: Projecting the release of carbon from permafrost soils using a perturbed parameter ensemble modelling approach, Biogeosciences, 13, 2123-2136, doi:10.5194/bg-13-2123-2016, 2016

http://www.biogeosciences.net/13/2123/2016/

Abstract. The soils of the northern hemispheric permafrost region are estimated to contain 1100 to 1500 Pg of carbon. A substantial fraction of this carbon has been frozen and therefore protected from microbial decay for millennia. As anthropogenic climate warming progresses much of this permafrost is expected to thaw. Here we conduct perturbed model experiments on a climate model of intermediate complexity, with an improved permafrost carbon module, to estimate with formal uncertainty bounds the release of carbon from permafrost soils by the year 2100 and 2300 CE. We estimate that by year 2100 the permafrost region may release between 56 (13 to 118) Pg C under Representative Concentration Pathway (RCP) 2.6 and 102 (27 to 199) Pg C under RCP 8.5, with substantially more to be released under each scenario by the year 2300. Our analysis suggests that the two parameters that contribute most to the uncertainty in the release of carbon from permafrost soils are the size of the non-passive fraction of the permafrost carbon pool and the equilibrium climate sensitivity. A subset of 25 model variants are integrated 8000 years into the future under continued RCP forcing. Under the moderate RCP 4.5 forcing a remnant near-surface permafrost region persists in the high Arctic, eventually developing a new permafrost carbon pool. Overall our simulations suggest that the permafrost carbon cycle feedback to climate change will make a significant contribution to climate change over the next centuries and millennia, releasing a quantity of carbon 3 to 54 % of the cumulative anthropogenic total.
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