Friday, October 23, 2015

Warming Permafrost

A pair of articles related to North Slope environmental conditions caught my eye recently, one concerning warming permafrost and the other regarding Dalton Highway construction in response to flooding last spring.  I'll say a few words about the former today and look at the latter in a subsequent post.

In the first article, Vladimir Romanovsky of UAF is quoted as expressing astonishment at rapid rates of warming in permafrost near the Arctic coast, particularly in the last decade.  I'm not familiar with the literature of permafrost studies, so I haven't found published results illustrating the recent trends, but I did find some informative figures at the permafrost database site.  Looking at the "west dock" measurement location at Prudhoe Bay, the following figure shows a striking trend of long-term warming through 2010, and if the professor was accurately quoted, then I'm sure the trend has continued or even accelerated in the past 5 years.
The following chart only extends through 2007, but it shows a similar pattern of significant warming.


A third chart from the database site focuses on temperatures close to the surface, and in this case there is no obvious trend.


I verified the lack of a warming trend in the near-surface temperatures by downloading the daily measurements at 0.85m depth - see below.  The summer peak in temperature at this particular location showed only a very small increase over the decade ending in 2012 (the most recent available).


If we look at air temperature measured near Prudhoe Bay (see below), we see that 2014 and 2015 year-to-date have brought some of the warmest conditions on record, and this may have produced the acceleration in sub-surface warming that the professor seems to be alluding to.  Note that the 1998 spike in temperatures appears to have been responsible for the rapid warming observed between 1998 and 1999 in the first chart above, so it's quite possible that a similar thing has happened again lately.  I'll see if I can obtain some more recent borehole data to document the latest changes.


A note on the chart above: I've combined the climate data from the old Prudhoe Bay observing site (through May 1999) with data from the Deadhorse airport just a few miles to the south (since June 1999).  Deadhorse is a bit colder, being located farther from the moderating influence of the ocean, so the warming trend would actually be a bit steeper if we had observations from the same location over the entire history.  Nevertheless, the temperature drop from 1998 to 1999 was definitely real, as a very similar drop was also observed at Barrow.

8 comments:

  1. Can you coorelate this to snow depth (or snowfall if the data doesn't exist)? I'm wondering if the warmer temperatures and decline in fall sea ice is leading to more snowfall and therefore more insulating snow cover deeper into winter. Although I'm aware that the north coast is quite windy, and snowfall may not matter.

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    1. Mike, your idea seems plausible although as you note the winds prevent widespread deep snow cover (and also wreak havoc with snowfall measurements). The Prudhoe Bay SNOTEL site has only reported snow depth since 2011, but I'll take a look at the precipitation data (since 2004).

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    2. I briefly looked into the data from Prudhoe Bay and the much longer-term record from Barrow. At the former, the 2003-2014 average October-November precipitation was 1.0", which is more than I expected, but as I mentioned snow depth wasn't reported until 2011. In the past 4 years, the November 30 snow depth has been 7", 6", 7", and 0" (with precip of 0.8, 1.4, 0.9, and 0.9").

      At Barrow there have been snow depth measurements for many years. I'm not sure how these correspond to reality under windy conditions, but there has been a small increase in snow depth since 2000; for example, the December mean snow depth was 7.8" from 1930-1999, and 9.0" from 2000-2014.

      The Barrow CRN (2002-present) and the new Deadhorse CRN will eventually provide a nice record of precipitation changes, but snow depth is always going to be a difficult parameter on the North Slope.

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  2. Without dipping much into the controversial stream of climate warming I've wondered what conditions are required for the initial formation, subsequent maintenance, and then thawing of permafrost?

    It would seem that from what we now know a look backwards in time to reconstruct the scenarios I mention would be informative.

    Maybe it's already been done. Saying things are changing to me implies a variety of trends in temperature over time.

    Gary

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    1. Here's a start to my question above. There's likely better and others.

      Lunardini, Virgil J. (April 1995). "Permafrost Formation Time" (PDF). CRREL Report 95-8. Hanover NH: US Army Corps of Engineers Cold Regions Research and Engineering Laboratory.

      Gary

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    2. Gary, interesting question and a useful link, thanks. Even in 1995, the author surmised that "the present climate of Prudhoe
      Bay is probably considerably warmer than it has been on average over the past glacial cycles." The permafrost may have been warming for centuries, with modern changes perhaps more rapid than in times past.

      But it seems our estimates of permafrost processes and timescales are necessarily based on models with attendant assumptions, because "ground truth" observations (pardon the pun) have only been made very recently.

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