Monday, June 24, 2019

Utqiaġvik Temperature Records

Exceptional warmth occurred last week over much of northern Alaska, and a significant new record high temperature was set at Utqiaġvik (formerly Barrow), where the 73°F on Thursday was the highest on record for the month of June; the previous record was 72°F in 1996.  June therefore joins May, October, and January as having set or tied calendar-month high temperature records in the last few years.

There are some interesting aspects to the distribution of Utqiaġvik's calendar-month records over the decades, but first I'll state the obvious: average temperatures have increased very dramatically in the 100+ years of climate observations, and daily record high temperatures have been broken or tied with high frequency in recent years.  The second chart below shows a running 10-year total number of high temperature records, both for daily maximum temperature and for high daily minimum temperature.  Very nearly half of all of the calendar-day high temperature records have been set or tied since 1990.  Note that I'm only using the Weather Bureau/NWS era of 1930-present for the analysis of records.

The distribution of daily low temperature records is even more striking, because the frequency has dropped to just about zero in recent years.  In fact, the last time a calendar-day record was broken (not tied) for daily minimum temperature was in February 2009, and if we allow data from the 1920s, we have to go back to 2006 to find a new low temperature record.

In light of this, the much smaller sample of calendar-month records is interesting; see the chart below.  The red columns show the number of calendar-month high temperature records for non-overlapping decades since 1930; these are the monthly records (set or tied) for daily maximum temperature, of which four have been reached in the past few years.  The blue columns show the high records for daily minimum temperature, and a few of these have also been broken or tied in recent years (January, July, and November).

The obviously interesting aspect of this is how many of Utqiaġvik's calendar-month records were set in the 1930s and are still standing; in fact the largest number of warm records (daily max and daily min) from a single decade is from the 1930s.  This is really quite surprising, given the ramp-up in mean temperatures and daily warm records.  Of course the calendar-month records represent a very small and rather arbitrary sample of the most extreme events, and a more rigorous statistical analysis would be needed to make a definitive statement; but this does seem to suggest that the very extreme warm tails of the temperature distribution have not shifted as much as the less extreme parts of the distribution.  In other words, it appears that the modern warmer climate is not producing very-rare warm extremes of the same amplitude (relative to the mean) as the climate of the 1930s.  I've noted before on this blog that the 1930s was a time of wild extremes in Alaska climate, and this is another piece of evidence in that direction.

Here's the distribution of calendar-month cold records in Utqiaġvik.  The 1970s really stand out, and this is fairly consistent with the mean temperature and the daily records from that decade, although the monthly records suggest that extreme anomalies on the cold side were particularly concentrated in that decade, just as warm extremes were concentrated in the 1930s.

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