What was done
The authors analyzed several climatic variables over the past century in Iceland, including air pressure, temperature, precipitation and sunshine data, in an effort to determine if there is "possible evidence of recent climatic changes" in that cold island nation.

What was learned
For the period 1923-2002, no trend was found in either annual or monthly sunshine data.  Similar results were reported for annual and monthly pressure data, which exhibited semi-decadal oscillations throughout the 1820-2002 period but no significant upward or downward trend.  Precipitation, on the other hand, appears to have increased slightly, although the authors question the veracity of the trend, citing a number of biases that have potentially corrupted the data base.

With respect to temperature, the authors indicate that, of the handful of locations they examined for this variable, all stations experienced a net warming since the mid-1800s.  The warming, however, was not linear over the entire time period.  Rather, temperatures rose from their coldest levels in the mid-1800s to their warmest levels in the 1930s, whereupon they remained fairly constant for approximately three decades.  Then came a period of rapid cooling, which ultimately gave way to the warming of the 1980s and 90s.  However, it is important to note that the warming of the past two decades has not resulted in temperatures rising above those observed in the 1930s.  In this point the authors are particularly clear, stating emphatically that "the 1990s was definitely not the warmest decade of the 20th century in Iceland, in contrast to the Northern Hemisphere land average."  In fact, a linear trend fit to the post-1930 data would actually indicate an overall temperature decrease since that time.

As for what may be responsible for the various trends evident in the data, Hanna et al. note the likely influence of the sun on temperature and pressure values in consequence of their finding a significant correlation between 11-year running temperature means and sunspot numbers, plus the presence of a 12-year peak in their spectral analysis of the pressure data, which they say is "suggestive of solar activity."

What it means
It is readily apparent from the data presented in this study that Iceland has not experienced any unprecedented warming in the latter part of the 20th century.  This finding must come as more bad news to the world's climate alarmists, whose claim of unprecedented CO2-induced global warmth in the 1990s continues to wilt away, one location at a time.