Arctic Sea Ice Update

Notwithstanding very abundant sea ice in the eastern Bering Sea this winter, Arctic-wide sea ice is now vying with 2019 for record-low extent at this time of year; it has been running near the bottom of the "pack" (pun intended) since November.  The following chart provides a comparison to 2019 (the previous record low at this date), 2012 (the year of the record low in September), and last year.

Deficits relative to the 1981-2010 normal are widespread across the marginal seas of the Arctic:

It's an interesting question as to whether the developing big El Niño episode will have a positive or negative effect on Arctic sea ice this summer.  Several of the strongest El Niño events of recent decades developed in parallel with substantial year-on-year declines in Arctic sea ice extent, so the risk of another major drawdown would seem to be elevated.  Here's a scatterplot of year-on-year change in September ice extent versus the June-August Niño3.4 SST anomaly; the notable recent years are 2023, 2015, 2002, and 1997 (lower right quadrant).

However, it's equally clear that there is actually not much correlation overall between year-on-year ice change and the phase of ENSO during summer.  In particular, pre-1997 El Niño events didn't have a consistent relationship with ice changes, and many stronger La Nina summers show modest ice declines rather than gains.

For a bigger picture, here's the correlation of June-August detrended SSTs with the year-on-year ice change:

The colors indicate the SST anomalies that would normally be associated with an increase of sea ice.  Clearly, the North Atlantic and North Pacific have more correlation than the tropical Pacific, but this doesn't imply causation; the SST patterns revealed here may simply reflect the impact of circulation patterns that affect sea ice extent.  Nevertheless, it's interesting to observe that a negative PDO pattern (like recent years) tends to favor higher sea ice extent, and that's confirmed in a scatterplot - although the correlation is not statistically significant:

The atmospheric anomalies themselves show a greater connection with sea ice change, of course; but those anomalies are relatively unpredictable at seasonal time scales.  A positive Arctic Oscillation, for example, slows the summer ice melt, whereas a negative AO phase tends to bring a reduction in ice extent.

ENSO does tend to be inversely correlated with the AO phase in summer, so it's more likely than not that we'll have a negative AO pattern this summer, i.e. more high pressure over the Arctic (and favoring warm and dry conditions in much of Alaska).  This points toward greater sea ice loss, as in other recent El Niño summers; but time will tell if this year fits the same pattern.