Saturday, June 5, 2021

Arctic-Wide Temperatures

Several years ago I spent some time looking at Arctic-wide air temperature trends based on measurements at climate observing sites around the basin, and it's probably worth returning to that idea for an update.  See here (and links therein) for previous work.  In my fresh look at this, I found 32 sites - distributed fairly evenly around the Arctic land areas - that have nearly complete data since 1980 and also report reliably on a daily and monthly basis.  Here's a map of the sites:

This set of locations is designed to sample both inland and coastal environments above the Arctic Circle (neglecting interior Greenland); previously I was focused on coastal sites clustered around the central Arctic Ocean.

The chart below presents a multi-decadal view of monthly mean temperatures at these locations; the black line shows the 32-station average of the monthly departure from normal, with "normal" being defined as 1991-2020.  The red and blue lines show the highest and lowest monthly anomalies within the set (with the largest anomalies occurring in winter, when variance is highest).  Click to enlarge:

The overall warming trend amounts to +0.76°C per decade (using linear regression), or a little over +3°C in the 41-year period.  This is much more warming than has occurred across the globe as a whole, illustrating the reality of "Arctic amplification".  I should note, however, that this analysis is based on the unadjusted ("unhomogenized") data from GHCN-M, so it's the "raw" data without corrections for changes in station siting, instrumentation, or observing practices; read more here.

Looking at the last decade or so, it's remarkable to see the jump up that occurred in winter 2015-2016, when the super El NiƱo occurred; temperatures seem to have remained at a higher baseline since then.  Since 2016, it has become fairly uncommon to have any station with a -5°C anomaly (even relative to the warmer 1991-2020 average), whereas most months in the past few years have had at least one site with a +5°C anomaly.

Interestingly, November of last year was the second warmest month in this period of record, with a +3.7°C average anomaly for the 32 sites.  Only January 2016 was warmer, at +4.3°C.  Again, this is relative to the new 1991-2020 baseline.

However, there was quite a drop-off in Arctic-wide temperatures as last winter progressed, and both February and March were colder than the new normal.  Here's a chart of the daily progression (with a few missing days just before the turn of the year).  For a little over two months in late winter, the Arctic was generally colder than normal, but it warmed up considerably in April, reaching 4.7°C above normal by late April.  The year-to-date temperature anomaly so far (January through May) is +0.47°C.

Now that I've identified this more comprehensive set of stations, I'll be able to slice and dice the historical data in various ways, and keep on top of Arctic temperature variations going forward.  If readers have any suggestions for interesting analysis, feel free to leave a comment.

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