What was done
The instrumental or thermometer temperature record typically extends back in time no more than a century for most locations on earth, and few are the stations with temperature records extending over two hundred years.  In the present study, however, Butler et al. standardized three temperature series from Armagh Observatory in Northern Ireland to obtain a nearly continuous record of temperature at this location since 1796.

What was learned
In this longest temperature series for all of Ireland, the authors detected significant year-to-year fluctuations and decadal-scale variability.  On a shorter time scale, wavelet analysis revealed a 7.8-yr cycle that was particularly strong in the winter and spring, which they believe is related to the North Atlantic Oscillation.  On longer time scales, multi-decadal oscillations are noted in the many-year warm and cold periods scattered throughout the record, including a relatively cool interval prior to 1820 followed by a warmer period that peaked about 1830 and lasted until nearly 1870.  Thereafter, a second cool interval ensued, followed by another warm peak between 1940 and 1960, while yet another cool period held sway from 1960 to 1980.  The record then ends with a final warm period over its last decade; but this period is not in any way extraordinary, as the authors say that "in spite of the current warmer conditions, annual mean temperatures still remain within the range seen in the previous two centuries."

What it means
In contrast to the highly publicized climate-alarmist claim that the past two decades have experienced unprecedented warmth due to CO2-induced global warming, the Armagh record indicates that "we are not yet beyond the range of normal variability," to quote its developers.  What is more, Butler et al. note that late 20th-century warmth is typically compared to temperatures characteristic of the beginning of the 20th century, when conditions were noticeably cooler, which comparison, in their words, "exaggerate[s] the subsequent warming in the 20th century."  Their proposed solution is to extend the baseline for comparison further back in time.  We agree, for the crux of the climate change debate rests on obtaining a much longer perspective from which to view the late 20th century, in order to appreciate the degree of natural climatic variability inherent in earth's climate system; and whenever this is done, it is typically concluded that there is nothing unusual or unprecedented about the world's current level of warmth.