The combination of 1.) extra ocean to atmosphere heat transfer enabled by record low sea ice and 2.) pulses of warm air from the south has produced stunning large temperature departures from normal.
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 polward 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 here.
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.