Published on Nov 29, 2020
The globe’s seven warmest years have all occurred since 2012, and Arctic Temperature Amplification has warmed the north at least 3 times faster than the global average. So WHY is Arctic sea ice still hanging on, and why hasn’t it set any new record September minimum since 2012? Since 2000, new record minimums were set in 2003, 2005, 2007, and then 2012; but nothing since then. Clearly, there simply must be some negative feedbacks going on, but what are they, and what mechanisms are in play? I have suggested that the wavy jet streams have brought ridges (warm, humid air) from lower latitudes as far north as the North Pole, even during the completely dark four month winter periods; meanwhile jet stream troughs have carried cool dry polar air as far as the equator, and that the jets have even crossed the equator to join with Southern Hemisphere jet streams. Both these ridges and troughs result in transferring heat from the pole to the equator. I have also made the argument that there is Atlantification (and Pacificication) of the Arctic Oceans, namely marine heat waves in the northern Atlantic and Pacific result in warmer waters entering the Arctic below the surface; since density of sea water depends on both temperature and salinity, warmer but saltier water is more dense than colder fresher surface water and can shoal and melt sea ice from below, and also delay it refreshing in the fall after the minimum extent has been reached.
In the new peer reviewed scientific paper on this topic by Jennifer Francis and Abington Wu, they argue that since 2012 the ice melt rates have been extremely high in the Spring and early Summer from high Sea Level Pressure (SLP), leaving both Arctic scientists and the public with bated breath, thinking that a new record breaking melt year and minimum September sea ice extent was sure to occur. Then, during each August/September an abrupt atmospheric shift has occurred, bringing low SLP, extreme cloudiness, and unfavourable winds for ice reduction, dashing all hopes of a new record minimum or even a Blue Ocean Event (BOE) with near 100% ice loss.
Francis and Wu argue that the mechanism for this late melt season slowdown is associated with jet stream splitting from diminished spring snow cover on northern hemisphere continents, which acts as a negative feedback that stalls late summer Arctic sea ice loss. I chat about the data and analysis that is behind their ideas.
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