Arctic Temperature Trends
By Paul Homewood
A few days ago, I compared temperature trends in the Arctic and Antarctic, which suggested that :-
1) Since 1980, temperatures had fallen in the Antarctic by 0.87C, nearly as much as the rise of 1.01C in the Arctic (to August 2012).
2) Arctic temperatures fell sharply between 1938 and 1980 by 0.75C, leaving only a modest increase of 0.26C for the whole period 1938-2012.
I now want to concentrate on two further issues in the Arctic thrown up by that analysis.
Long Term Arctic Trends
It is well known that the period around 1940 marked a warm spell in the Arctic, but GISS records date back to 1880, so what do these show?
I have plotted the full GISS record, and also the UAH one since 1980. Because GISS and UAH use different periods to calculate their anomalies from (GISS is 1951-80, UAH is 1981-2010), the two datasets can only be directly compared by re-centering one set. Therefore I have done this with the UAH set, by realigning the 1980 figure with the GISS one, as follows:-
GISS 1980 : +36
UAH 1980 : –22
UAH 1980 Re-centered : –22 + 58 adj = +36
All UAH anomalies from 1980 – 2011 are therefore INCREASED by +58.
The data shows a steady rise in temperature up to 1943, which was followed by a decline which lasted till 1979. The upward trend since has tended to follow the earlier rate of rise.
Between 1880 and 1943, the rate of rise was 0.31C per decade. Since 1980, the rise has been 0.27C per decade based on UAH figures, although the GISS rise is greater.
Regardless of the exact numbers, it is clear that the warming of the Arctic is not a recent, post 1980 phenomenon. It is actually something that has been going on since the end of the LIA.
Professor Jorgen Steffensen believes that, in Greenland at least, the period around 1875 was the coldest point since the end of the ice age. Should we really be surprised that temperatures have recovered somewhat since?
Divergence between GISS and UAH
The GISS dataset shows a much bigger rise in temperature since 1980, than does UAH. This can be seen clearly below.
Remember that the UAH figures are re-centred, so that both GISS and UAH sets start with the same anomaly in 1980. Since then, GISS show an increase of 1.60C, but according to UAH the rise is only 0.86C. Although there were some discrepancies in the early part of the record, with UAH showing lower anomalies, the two datasets had converged again by the early 2000’s. Indeed, in 2004 UAH actually showed a warmer result. Since then, however GISS has been showing a much greater rate of warming.
A similar comparison between the two satellite datasets, UAH and RSS, shows that RSS produce even less of a warming trend than UAH do.
The increase between 1980 and 2011 is illustrated below for the three systems.
|Arctic Temperature Anomaly (ReCentered)||RSS||UAH||GISS|
So GISS show more than a degree of warming more than RSS.
The fact that GISS is wildly out of line with both satellite sets suggests that the problem lies with the former rather than the latter. This may be connected to the fact that we have very little surface station coverage in the Arctic, as can be seen in the GISS map below.
But if the satellites are correct, and in particular RSS, the amount of warming in recent years is not exceptional and is just part of a much longer trend.
Links to datasets