Grudd, H., Briffa, K.R., Karlen, W., Bartholin, T.S., Jones, P.D. and Kromer, B. 2002. A 7400-year tree-ring chronology in northern Swedish Lapland: natural climatic variability expressed on annual to millennial timescales. The Holocene 12: 657-665.
What was done
Tree-ring widths from 880 living, dead, and subfossil northern Swedish pines (Pinus sylvestris L.) were assembled by the authors into a continuous and precisely dated chronology covering the period 5407 BC to AD 1997. The strong association between these data and summer (June-August) mean temperatures of the last 129 years of this period then enabled them to produce a 7400-year history of summer mean temperature for northern Swedish Lapland.
What was learned
The most dependable portion of the record, based upon the number of trees that were sampled, consists of the last two millennia, which the authors say "display features of century-timescale climatic variation known from other proxy and historical sources, including a warm 'Roman' period in the first centuries AD and a generally cold 'Dark Ages' climate from about AD 500 to about AD 900." They also note that "the warm period around AD 1000 may correspond to a so-called 'Mediaeval Warm Period', known from a variety of historical sources and other proxy records." Lastly, they say "the climatic deterioration in the twelfth century can be regarded as the starting point of a prolonged cold period that continued to the first decade of the twentieth century," which "Little Ice Age," in their words, is also "known from instrumental, historical and proxy records."
Going back further in time, the tree-ring record displays several more of these relatively warmer and colder periods. And in a telling commentary on current climate-alarmist claims, they report that "the relatively warm conditions of the late twentieth century do not exceed those reconstructed for several earlier time intervals." In fact, the warmth of many of the earlier warm intervals significantly exceeds the warmth of the late 20th century.
What it means
The data reported in this study clearly indicate the recurring nature of relatively colder and warmer periods, such as the Little Ice Age and Medieval Warm Period, in northern Swedish Lapland. They also clearly indicate that the late 20th century warmth of this region was in no way unprecedented. In fact, when viewed within the context of the entire record, it looks absolutely normal.
Reviewed 1 October 2003