Tuesday, March 5, 2019

Can New Permafrost Models Shed Light On The Pace Of Global Warming?

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Figure 1: Component models - of varying complexity - in the "Permafrost Modeling Toolbox" (from EOS, Vol. 100, p. 33)

No photo description available.

Figure 2:  Computation of projected permafrost melting into the 2090s using  CMIP5  to calculate relative steepening of permafrost active layer thickness (from EOS, Vol. 100, p. 33)

When last in Alaska, in March 2005, my wife and I got to see many sights including massive wilderness regions near Mount McKinley ('Denali") as well as immense glaciers in the southern region just below Anchorage. In the latter case, we were shown just how much glaciers had receded in just the last two decades. 
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On our dog sled trek near Chena Hot Springs, AK.  We had to choose a path where the ice hadn't melted as rapidly as it had in other places.
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Janice on her snowmobile near the Trans--Alaska pipeline.  Melting permafrost had affected its stability - supports as well.

Meanwhile, during a visit to the Ice Art Exhibit in Fairbanks, several ice towers (including one 150' tall) collapsed due to melting permafrost beneath.  When we visited the Geophysical Institute two days later, we were informed by one atmospheric physicist that "this is just the beginning, wait until homes, downtown buildings are affected."

Eight and a half years later the Nov. 26, 2013  issue of the peer-reviewed journal Nature Geoscience, featured a ground breaking paper by Natalie Shakhova and Igor Semiletov of the University of Alaska- Fairbanks' International Arctic Research Center.  In the paper the authors warned that the Arctic Ocean is releasing methane at a rate more than twice what existing scientific models predicted. The two UAF researchers focused on the continental shelf off the northern coast of eastern Russia - the East Siberian Arctic Shelf. Underlying this region is sub -sea permafrost. When the permafrost melts, the methane (CH4 )  is  released.

In an update (2017)  of their earlier permafrost research,

Current rates and mechanisms of subsea permafrost degradation in ...

The authors actually showed the rate and mechanisms of subsea permafrost degradation and that it is a prerequisite to meaningful predictions of near-future methane (CH4 ) release in the Arctic.  

While the gradual warming of permafrost has been well documented in the Arctic, another  (2017) study published in  Nature Geoscience indicated that a brief period of unusual warmth can cause a rapid shift. Focusing on the polygon ice troughs associated with wedges of ice that thrust deeply into the ground, the study found the ice wedges are quickly melting, amplifying the loss of permafrost by altering the storage and movement of water.  The latter, of course, clearly shows the role of hydrology in permafrost dynamics.

It's an interesting kind of  paradox:  Climate change is currently thawing  vast expanses of Arctic permafrost, and the effect is to release methane - an even more potent greenhouse gas than CO2. The released CH4 then goes into the atmosphere to accelerate climate change, further thawing permafrost  and activating more methane release. 

This is all serious research given that permafrost is hundreds of meters deep in many places and has been frozen for millennia.  It covers approximately  24 percent of the Arctic and stores nearly 1,700 gigatons of organic carbon, far greater than the amount of carbon already in the atmosphere.

Ice-wedge degradation has been observed before, but this is the first study to determine that rapid melting of ground ice  (as opposed tp sub-sea permafrost) has become widespread throughout the Arctic. The research team predicts that the melting—already occurring at sub-decadal timescales—will expand and intensify across the region, and this could escalate global warming and create more feedbacks. 

 All of which strongly demonstrates the need for more powerful, and accurate models of permafrost thawing, especially which show the various ways it thaws. 

 Currently, the ways that permafrost thaws is being investigated on multiple fronts given it is is interwoven with hydrological and geomorphological processes and how carbon and toxic heavy metals spread throughout the thawing Arctic.  To be sure, we need more refined models and approaches given there remain are sweeping, yet unanswered, research questions..

For example, the thawing ground below creates unique geomorphic patterns: drooling solifluction lobes that form when wet soil oozes downhill, giraffe skin polygons formed by ice wedges filling the cracks in freeze-shrunken soil, thaw lakes and seasonal wetlands, and melting coastal bluffs.

Permafrost thaw contributes to the global hydrological and carbon cycles, but it also has a significant impact on roads, housing, and coastal infrastructure. This impact is predicted to create a multibillion-dollar infrastructure maintenance problem for Alaska over the span of the 21st century
To fix ideas first with basics, permafrost refers to ground that stays at or below 0°C for 2 or more years—can be found under 24% of the Northern Hemisphere’s land surface [Zhang et al., 1999]. The frozen subsurface profoundly influences the hydrological cycle of the Arctic region.

To address the issue of more refined models, climate scientists at the University of Colorado- Boulder   have developed online, easily accessible permafrost process models for use by scientists and educators.  This has been through the Community Surface Dynamics Modeling System (CSDMS) or the Permafrost Modeling Toolbox. (See Fig. 1)

The UC climate scientsts' "toolbox"  includes three permafrost models of increasing complexity, all driven by local climate forcing, to meet a variety of needs:

  • An empirical model, the Air Frost Number model [Nelson and Outcalt, 1987] predicts the likelihood of permafrost occurring at a given location.
  • An analytical-empirical model, the Kudryavtsev model [Anisimov et al., 1997] provides an exact solution to thermodynamic equations accounting for snow, vegetation, and soil to calculate active layer thickness, the average annual thaw depth.
  • A numerical heat flow model, the Geophysical Institute Permafrost Lab (GIPL) model [Jafarov et al., 2012] includes the latent heat effects in the active layer zone. This model divides a vertical profile into multiple layers of soil and substrate with different thermal properties, and it calculates temperature profiles with depth.

The first two models are developed as “components” that can be coupled to other CSDMS models. The GIPL model functions as a stand-alone code, and it will be fully embedded into the CSDMS model coupling framework at a later date. All three models are inherently one-dimensional; that is, they calculate the thermal state over time for a single vertical column, but they do not calculate heat exchange among columns. However, each model can run regional simulations or even be implemented for the entire Arctic region.
The current project pairs these models with preassembled data sets of input parameters. Casual model users can then quickly run experiments for selected time series and given regions. Data sets include long-term climatological and permafrost observations in coastal and interior Alaska (Barrow and Fairbanks, respectively), as measured at Circumpolar Active Layer Monitoring Network (CALM) and U.S. Geological Survey stations

Access to data and models together allows users to compare model output with in situ observations directly. Additionally, a regional climatological data set comprising observed monthly temperature and precipitation data for the 20th century is available to drive the models for Alaska. 

To explore future trends in permafrost, another data set comprises parameters of the Coupled Model Intercomparison Project Phase 5 (CMIP5) modeled climate data until 2100, specifically applied to the known permafrost zone.  (See Fig. 2)

Applications of the permafrost toolbox include calculating permafrost for real-world sites in the Arctic region, looking at warming trends over the past century, making maps of future permafrost, and comparing models with different complexities.

Figure 2 shows one such example: Calculations of the current and future active layer thickness over the entire Arctic region demonstrate a considerable deepening of this critical seasonal layer. This experiment is relatively straightforward to perform using the Web-based modeling tool.

Can such tools help us learn enough about  the physical processes of permafrost dynamics. Four hands-on modeling labs are already available for new users. This material is accessible for teaching use, and the online labs include instructions for classroom use and undergraduate lesson plans.  

Nevertheless, we need advances on multiple research fronts, in particular reconciling the different existing permafrost thawing models, i.e. between the UC-Boulder thawing model and the UAF model of Shakhova and Semiletov.  Special attention needs to be paid to the projections of permafrost thawing (Fig. 2) and the degree to which these vary model to model.  If in fact similar rapid permafrost melting is found to be consistent between differing models, we need to be much more concerned about accelerated global warming - and its consequences.

 In the meantime, the UC breakthrough (published in Eos, op. cit.) is a good, solid start.

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