What was done
The authors "present a new gridded (0.5° x 0.5° resolution) reconstruction of monthly (back to 1659) and seasonal (from 1500 to 1658) temperature fields for European land areas (25°W to 40°E and 35°N to 70°N)," based on "a large number of homogenized and quality-checked instrumental data series, a number of reconstructed sea-ice and temperature indices derived from documentary records for earlier centuries, and a few seasonally resolved proxy temperature reconstructions from Greenland ice cores and tree rings from Scandinavia and Siberia."

What was learned
The primary finding of the study is actually rather mundane: "late 20th- and early 21st-century European climate [was] very likely warmer than that of any time during the past 500 years," while "the 19th century was the coldest of the last half-millennium."

What it means
Luterbacher et al. state that "detailed insight into high-resolution temporal and spatial patterns of climate change during previous centuries is essential for assessing the degree to which late 20th-century changes may be unusual in the light of preindustrial natural climate variability," and in this claim they are correct.  Unfortunately, their record is way too short to enlighten us much in this regard, as the most impressive and recurrent feature of Holocene climate is the approximate 1500-year cycle that has been documented in dozens of detailed studies [see Climate Oscillations (Millennial Variability) in our Subject Index].  All the study of Luterbacher et al. shows of this likely solar-induced phenomenon [see our Editorial of 28 Nov 2001] is the most recent of its negative phases - the Little Ice Age - and the transition to the start of the current warm phase - the Modern Warm Period - which has only just begun.  To achieve a full and correct understanding of preindustrial climate variability, one must have access to at least one full cycle of the predominant oscillation and preferably two or three of them (the more the better, obviously).  And when such data are in hand, it is abundantly clear there is nothing unusual about either the degree, rate, or timing of the warming of the past century.