What was done
The authors constructed a two-century (1802-2009) instrumental record of annual surface air temperature within the Atlantic-Arctic boundary region, using data obtained from "recently published (Klingbjer and Moberg, 2003; Vinther et al., 2006) and historical sources (Wahlen, 1886)" that yielded "four station-based composite time series" that pertain to Southwestern Greenland, Iceland, Tornedalen (Sweden) and Arkhangel'sk (Russia). This operation added seventy-six years to the previously available record, the credibility of which result, in Wood et al.'s words, "is supported by ice core records, other temperature proxies, and historical evidence."

What was learned
The U.S. and Icelandic researchers report that their newly extended temperature history and their analysis of it reveal "an irregular pattern of decadal-scale temperature fluctuations over the past two centuries," of which the early twentieth-century warming (ETCW) event -- which they say "began about 1920 and persisted until mid-century" -- was by far "the most striking historical example."

What it means
In discussing their findings, Wood et al. write that "as for the future, with no other examples in the record quite like the ETCW, we cannot easily suggest how often -- much less when -- such a comparably large regional climate fluctuation might be expected to appear." Nevertheless, they say that if past is prologue to the future, "it would be reasonable to expect substantial regional climate fluctuations of either sign to appear from time to time," and, therefore, that "singular episodes of regional climate fluctuation should be anticipated in the future," which also implies that any rapid warming that may subsequently occur within the Atlantic-Arctic boundary region need not be due to rising greenhouse gas concentrations, as it could well be caused by the same unknown factor that caused the remarkable ETCW event, which further implies that the Arctic is not the "canary in the coal mine" that climate alarmists always make it out to be.

References
Klingbjer, P. and Moberg, A. 2003. A composite monthly temperature record from Tornedalen in northern Sweden, 1802-2002. International Journal of Climatology 23: 1465-1494.

Vinther, B.M., Anderson, K.K., Jones, P.D., Briffa, K.R. and Cappelen, J. 2006. Extending Greenland temperature records into the late eighteenth century. Journal of Geophysical Research 111: 10.1029/2005JD006810.

Wahlen, E. 1886. Wahre Tagesmittel und Tagliche Variationen der Temperatur an 18 Stationen des Russichen Reiches, Suppl. Rep. Meterol., S. Halbleder, St. Petersburg, Russia, 345 pp.