Monday, May 23, 2016

The Great Melt Is Underway

Anyone who has read the news won't be surprised to learn that it has been an exceptionally hot northern hemisphere cold season (November to April, hereafter just cold season) globally, especially in the Arctic.  Let's have a quick look at the numbers.  Because I'm being lazy, I'm going to mix two global temperature data sets, one produced by the NASA Goddard Institute for Space Studies (NASA-GISS) and the other produced by the National Centers for Environmental Information (NCEI).  Neither of their web sites produced everything I want, but I can get it if I mix and match.

Let's begin with the global temperature anomalies for November to April, which show the past cold season really was quite remarkable, running more than 1ºC (2ºF) above the 20th century average.  The tremendous surge during this period is largely a result of long-term global warming combined with El Nino.

Source: NCEI
The plot below shows the distribution of temperature anomalies for this period (relative now to the 1951–1980 average), illustrating the large positive anomalies in the tropics and most of the northern hemisphere, especially the arctic.  In contrast, the higher latitudes of the southern hemisphere were closer to the 1951-1980 average or in some cases below it.  

Another way to look at this is to average the temperature anomalies around a latitude circle (called a "zonal average) and then plot them from the south to north pole (left to right below).  This shows the near-average temperatures in the high latitudes of the southern hemisphere and the extreme warmth in the high latitudes of the northern hemisphere.

The tendency for the Arctic to warm faster than the global average temperature and exhibit larger positive temperature anomlies is called Arctic amplification.  It is driven by several factors, but feedbacks related to the decline in Arctic sea ice is dominant.

And, speaking of sea ice, the Arctic sea-ice extent is currently running well below prior seasons in the satellite record. Perhaps a record minimum will be reached in September.

Source: NSIDC
Although we may see a temporary decline in global temperature anomalies from their El Nino fueled highs this past cold season, the global warming train has left the station and is accelerating.  The great melt is underway.  


  1. Based on information and belief, why is the Arctic outpacing the Antarctic by such a large margin? That's quite a spread...

    1. There are a variety of factors at play here, including the fact that the Arctic is predominantly covered by sea ice whereas Antarctica is predominantly covered by land ice, differing characteristics of the Arctic and Southern Oceans, regional climate factors, etc. Such an asymmetry has, however, long been anticipated. Perhaps the subject of a future post.

  2. The 2016 sea ice trend is disturbing on many levels...but for the Western US especially so. There has been a lot of research lately on the connection of low late Summer/Fall Arctic Sea Ice and the higher amplitude "RRR" (Ridiculously Resilient Ridge across the Eastern Pacific during the ensuing fall and early winter months. This was especially noticeable from 2012 onward.

  3. And then you have folks like Trump that claims that climate change is due to a Chinese conspiracy to take away jobs from Americans.