There have been two Arctic heatwave episodes in 2016: 1.) centered 14-15 November and 2.) 24-25 December. Two more days of data and shortening the time interval to 1 day reveal that the recent heatwave is warmer than that in mid-November. See below…
average (near-surface air) temperature departures from normal, averaged around the world, across east-west belts (2.5 degrees latitude or ~250 km in width north-south) separately for land and ocean areas.
The patterns in the two time periods are similar across the globe. Averaging across latitude is problematic because at the North Pole, the area is much much smaller compared to the equator. Yet, we don’t see large variations at the South Pole as the North Pole. We see a huge Arctic Ocean warm anomaly and a smaller but distinct cold anomaly over land between roughly 50 and 70 deg. N latitude.
Besides being alarmed we’re in uncharted climate territory driven by abrupt human-driven climate change, the concern I have is how the record low Arctic sea ice may be promoting cold-air outbreaks and storminess across the mid-latitudes this cold season.
The image underscores the distinction between ocean and land and thus points to there being something to the pattern: “Warm Arctic, Cold Continents”. What are the impacts? Why should we care? For one, the patterns indicate a system changing state. For two: That change probably affects the frequency and persistence of weather, a hallmark of climate change; changing extremes… more hots and ironically sometimes sharper colds.
Planetary ‘Heat Engine’
Useful to bear in mind that the *normal* excess heating of our planet in the tropics drives all weather and the hydrological system, including polwe-ward oceanic heat transport. Anthropogenic climate heating increases this poleward heat transport, so no surprise the Arctic is heating.
Warm Arctic Cold Continents
Chris Mooney at Washington Post wrote an excellent review, interviewing leading scientists on the issue. Judah Cohen and others published findings that the Warm Arctic Cold Continents pattern is promoted by negative Arctic Oscillation index (AO has been negative in recent weeks) and above average snow cover (recent snow cover is not far under normal for N America and appears above average for Eurasia). Above average Eurasian snow cover favors negative AO (see Cohen et al. 2013). Sea ice decline is shown to moisten Arctic lower atmosphere and promote snow which may reinforce the sea ice decline / cold Eurasia through cold core high pressure over Siberia. James Overland (NOAA, PMEL) found (2009) the normal zonal flow dividing into two, promoting cold air outbreaks to lower latitudes, e.g. what some have called the ‘Siberian Express’ or what can also be a Canadian continental cold air outbreak. see http://www.polarresearch.net/index.php/polar/article/view/15787
By the way
A damping feedback is that thin ice grows fast, provided air temps are sub-freezing, which just isn’t the case around Svalbard where warm air is transported into the Arctic through the main atmospheric and oceanic conduit, the North Atlantic.
Master’s student Karina Hansen appeared at the door to my office at GEUS: “something looks strange” at Spalte Glacier connected to the 79 Glacier far northeastern Greenland.
In Danish, Spalte means “split” or “crevassed”.
The ~9 km wide Spalte Glacier is a tributary of the 79 Glacier which today has the Arctic’s largest ice shelf. The ice shelf forms the end of the North East Greenland Ice Stream, the only Greenland ice stream clearly reaching the highest elevations.
2016 aerial of ‘the new rift’ from Nat J. Wilson
7 Sept Sentinel 2 image from Jens Jacobsen of DMI’s Greenland Ice Service
We observed that between 14 Aug., 2015 and 3 September 2016, a marine-terminating tributary of the 79 fjord glacier, the Spalte Glacier flowing into Dijmphna Sound has detached and area (more than 95 km2) roughly the area of Manhattan Is.
The detachment of the ice shelf fragment appears to be nearly 100% complete.
The floating ice shelf fragment appears to have split into more than one piece already. But the main fragment have not floated away yet. I expect that will happen this year or next.
The fracturing and detachment is partly due to glacier dynamics (flow, stress, strain, pre-existing fractures).
Whether the ice shelf detaching is the consequence of the record warm ‘summer’ (June through August) observed at the DMI Danmarkshavn meteorological station (332 km to the south) is an obvious question.
Using Danish Meteorological Institute air temperature data c/o John Cappelen, the absolute summer temperature at Danmarkshavn was +4.9 C, producing a +2.3 C anomaly from the 1981-2010 “normal” period having temperature +2.6 C.
At Station Nord (220 km to the north) July temperatures were +1.9 C above the 1981-2010 period. Absolute July temperature at Station Nord was +5.9 C, producing a +1.9 C anomaly from the 1981-2010 ‘normal’ period having temperature +4.0 C). The Station Nord summer average temperature was +3.1. Normal is +2.3. So the Station Nord summer temperature anomaly was +0.8 C.
With a few exceptions, marine terminating outlets of the Greenland ice sheet have been retreating in recent decades. Box and Hansen (2015) surveyed 45 of the widest Greenland glaciers, which between 1999 and 2015 collectively lost an area of 1799 square km.
A Clear Statistical Pattern
Summer air temperature records at all 11 Danish Meteorological Institute stations around Greenland are correlated with glacier front area change… in warm summers, more ice area is lost. At 4 of the 11 sites, the confidence in that correlation is above 95%. At 7 of the 11 sites, the confidence in that correlation is above 80% (Box and Hansen, 2015). The physical mechanisms at work are probably hydrofracture in which the weight of water, being more than ice, adds force that can disaggregate ice (e.g. Weertman, 1973; Van der Veen, 1998) and forced convection driving more heat exchange between the (overall warming) ocean and the ice underbelly.
USGS Landsat 8 image sequences below prepared by Karina Hansen and myself.
In August 2010, the longest ice shelf connected to the Greenland ice sheet at Petermann Glacier (also then the Arctic’s largest ice shelf) calved 245 km2. Petermann ice shelf disintegration continued with a 140 km2 calving in 2012 (Jensen et al. 2015). The largest and most consistent (year to year) changes in Greenland glacier area are concentrated in the north of the island (Howat and Eddy, 2011; Box and Decker, 2011). The largest Greenland and Arctic ice shelf is now at the front of the North East Greenland Ice Stream.
Box, J.E. and D.T. Decker, 2011: Greenland marine-terminating glacier area changes: 2000–2010, Annals of Glaciology, 52(59) 91-98.
Box, J.E. and K. Hansen, 2015. Survey of Greenland glacier area changes, PROMICE newsletter 8, december 2015, http://promice.org/Newsletter_08.pdf
Jensen, T., J.E. Box, and C.S. Hvidberg, 2016. A sensitivity study of annual area change for Greenland ice sheet marine terminating outlet glaciers: 1999–2013. Journal of Glaciology, 2016 doi:10.1017/ jog.2016.12
Howat, I.M. and A. Eddy. 2011. Multidecadal retreat of Greenland’s marine-terminating glaciers. J. Glaciol., 57(203), 389–396.
Van der Veen, C. J., 1998: Fracture mechanics approach to penetration of surface crevasses on glaciers. Cold Reg. Sci. Technol., 27, 31–47.
Weertman, J., 1973: Can a water-filled crevasse reach the bottom surface of a glacier? IAHS Publ., 95, 139–145.