Arctic warming update

by William Yeatman on January 14, 2005

in Science

Once again claims are flying thick and fast regarding dramatic, in fact, unprecedented Arctic warming.

Once again, we look at the available data, now updated to the end of 2004.

Once again, we find the claims to be dead flat wrong. Click on the following thumbnails to view the full size images in a new browser window. (26365 bytes) We begin, as is our want, with the bare annual mean temperature track for the region 64N-90N. We use this particular dataset since the Arctic Circle describes a line of latitude near but south of the north pole marking the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice – roughly the parallel of latitude approximately 6633′ north and we are thus confident of having captured the boundary between the North Temperate and North Frigid zones.

Rather obviously it indicates a sustained warming, followed by a cooling and recovery. (33746 bytes) Of course, some people want (and others need) rather more aggressive highlighting of apparent trends and so we present the same data with shading and trend lines added. This next graphic shows the very same data with split trends and shading to highlight the warming trend 1880 through 1938 (the warmest year in the series). Had the pre-1938 trend continued there would certainly be some Arctic warming to talk about. Just as well we are not staunch advocates of post hoc, ergo propter hoc or we’d be claiming that increasing the rate of atmospheric CO2 increment stops Arctic warming. (32211 bytes) We would be remiss if we did not point out the most significant warming in the series. (36673 bytes) And now, trends 1918-1938 and 1966-2003 compared (yes, we know data is available in the series to include 2004 but the region’s annual mean temperature fell two-thirds of one degree C from the partial series maximum value of 2003). (30718 bytes) Finally, let’s look at the low-high trend values for the warming periods before and after the cooling demonstrated 1938 – 1966.

In other words, we’ll consider three decades of cooling an anomaly in the series and take a longer perspective – how has the Arctic recovery from the Little Ice Age varied over roughly one hundred and twenty years?

The answer is, it hasn’t. The post-LIA recovery seems to be trundling along the same as before, despite an Earth-insignificant setback of a few decades in between. The last 3-4 decades are not the fastest warming period of the series nor the slowest, rather, with the longer-term perspective they appear very ordinary.

So, according to data from the Global Historical Climatology Network (GHCN), from this file hosted by NASA’s Goddard Institute for Space Studies (GISS), there has been no net Arctic warming since 1938, the Arctic did warm quite abruptly over the two decades prior to that, has subsequently cooled and (nearly) recovered to what it was before being so rudely interrupted.

Beyond all doubt atmospheric carbon dioxide content has increased over the period, mainly from about the time the Arctic shifted to cooling mode for a spell. That trace gas increase has had no apparent effect on the Arctic’s post-LIA warming.

Since the rate of warming is unchanged and the net Arctic temperature has not increased in almost 7 decades it is very difficult to see what all the hysteria is about.

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