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A 1500-Year Temperature Proxy from Southwestern Greenland
Reference
Millet, L., Massa, C., Bichet, V., Frossard, V., Belle, S. and Gauthier, E. 2014. Anthropogenic versus climatic control in a high-resolution 1500-year chironomid stratigraphy from a southwestern Greenland lake. Quaternary Research 81: 193-202.

What was done
Noting that "chironomid assemblages are widely considered to be a valuable climate proxy in the sediment record," Millet et al. (2014) set out to reconstruct a 1500-year history of past temperatures in the Norse Eastern Settlement area of Greenland in an attempt to "provide new insights into the relationship between the Norse society and local climate change." To accomplish this objective, they analyzed chironomid assemblages from sediment cores obtained from Lake Igaliku (61°00'N, 45°26'W, 15 m asl), a small lake located in southern part of Greenland. A relationship between the chironomid assemblage data and mean summer (JJA) temperature recorded at the Ivittuut weather station (AD 1873-1960) and at the Narsarsuaq weather station allowed the scientists to ultimately reconstruct a proxy for summer temperatures in this region.

What was learned
According to the authors, "several climatically different periods [were] identified throughout the record," including "a phase of likely warmer climate until ca. 680 AD," followed by slightly cooler conditions. A "short-lived warm event" ensued between ca. AD 1000 and 1060, whereupon the climate shifted "toward colder conditions, as "a strong cooling trend" occurred around the end of the 13th century up until the early 20th century. Buried within this long term cooling trend were two periods of relatively warmer temperatures, from AD 1460-1640 and AD 1780-1840. The record ends with "a strong warming" from 1920 through the end of the record.

What it means
The Lake Igaliku temperature proxy reveals the presence of the millennial-scale climate oscillation seen in many other records around the world, which produced the well-known Roman Warm Period, Dark Ages Cold Period, Medieval Warm Period, Little Ice Age, and Current Warm Period. But that is not all the proxy record reveals. Quoting Millet et al., "the AD 1280-1920 time window" associated with the colder conditions of the Little Ice Age "is characterized by high climate variability," which higher variability, they add, is also seen in reconstructions from the nearby Igaliku Fjord, where other researchers have shown "the Medieval Warm Period was [also] followed by a cooling that corresponded to the Little Ice Age and was [also] marked by a more unstable climate." This latter finding pertaining to climate variability is significant, because it provides empirical data that suggest that warmer climates tend to be more stable and less variable than colder ones, which data-driven deduction is just the opposite of what some climate alarmists contend will occur in consequence of CO2-induced global warming.

Reviewed 27 August 2014