Wednesday, July 19, 2023

Temperature Comparison at Utqiaġvik

Way back in 2014, I posted some analysis of temperature differences between the airport and CRN sites in Alaska's northernmost town, Utqiaġvik (formerly Barrow).  With more than 20 years of climate data now in the books from the CRN site, I thought it would be interesting to revisit this - and in particular, to take another look at the apparent warming trend in the town's temperature relative to the outlying CRN site.

Here are the previous posts:

The locations of the two thermometers are indicated here:


First, let's confirm the close correspondence between the instruments at the two sites on a monthly mean basis:

No concerns there.  As noted and discussed in the previous posts, daily maximum temperatures tend to be most different between the two sites in summer, and for daily minimum temperatures the greatest differences are found in winter.  In both cases, the airport is usually warmer than the CRN site.  Systematic differences are least in autumn, when there's relatively little land-sea contrast in temperature.


The following charts provide another perspective on the overall relationship between temperature and temperature difference.

Now for the trend over time - see below.  Interestingly, there does seem to be a small but statistically significant increase in the temperature difference between the two sites, with the airport ASOS becoming progressively warmer than the CRN site.

How does the trend vary over the course of the year?

Interestingly, the trend in temperature difference is not confined to one season, but appears throughout the year, although with some variability.  This seems to suggest it is indeed a systematic trend at the local level rather than a trend caused by changing weather patterns at a certain time of year.

The largest trend has occurred for minimum temperatures in summer, and the charts below provide another perspective.  For the minimum temperatures (blue lines), there's a slight but perceptible tendency for relatively cooler CRN temperatures in recent years.  The maximum temperatures are less affected, except in June.

What do we make of this?  Occam's Razor suggests that the growth of the town is producing a gradually increased urban heat island effect.  In my 2014 post, I speculated that urban warming was unlikely to be the cause, because the Utqiaġvik population had decreased in the 2010 census; but the 2020 census reversed that trend, taking the population to an all-time high of about 4900.  This is a modest but perhaps significant increase of 8% in 20 years.

How significant is the divergence in temperatures compared to the overall long-term warming trend?  Well, two decades is not a long time in climate terms, but based on this limited history, the linear trends in annual mean temperature differ by about 15%.

This difference isn't remotely enough to alter the picture of rapid Arctic warming, but nevertheless it does illustrate the value of having a long-term climate monitoring program that's designed to avoid problems of instrument and site changes.  In other words, I'm a big fan of the CRN program.

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