November 17, 2006

Cooling the Debate: A Longer Record of Greenland Air Temperature

Filed under: Arctic, Polar, Temperature History

The reconstruction of Earth’s climate history is important because it contextualizes the recent global climate for which we have direct evidence through instrumental observation. Therefore, reconstructions are an important component of the climate change debate, as they speak to alarmists’ claims that Earth’s climate has warmed to a level that is unprecedented within the last two millennia, and therefore unnatural. The natural proxies used for reconstructing climate (e.g., ice and sediment cores) must be verified through comparison with an overlapping instrumental record, and obviously, the longer the instrumental record, the better.

Contextualizing the recent climate in the high latitudes of the Northern Hemisphere is especially important, as it is across this region that the largest increase in surface air temperature has been both observed during the 20th century and predicted for the 21st century. These ideas highlight the importance of snow cover, its sensitivity to temperature, and its positive feedback to the overlying atmosphere. Higher temperatures in typically snow covered regions may lead to a reduction in snow cover, and in turn, a reduction in the refrigeration of Earth’s atmosphere from beneath, and even greater atmospheric warming. The vision of out-of-control warming in Earth’s frozen regions makes the leap toward a breakdown of the global oceanic circulation system and global sea level rise an easy one.

Until recently, the instrumental air temperature record for Greenland, an epicenter of glacial study and climate reconstruction, was confined to the period 1873 to present. However, recent collaboration between the Danish Meteorological Institute (DMI) and the Climatic Research Unit (CRU) at the University of East Anglia (United Kingdom) has resulted in the compilation of instrumental data for 13 stations along the southern and western coasts of Greenland that date back to 1784. The data represent the addition of 74 complete winters and 52 complete summers to the previous record along roughly the southern two-thirds of the western Greenland coastline.

The extended surface air temperature record was constructed and analyzed by a group of researchers from the University of Copenhagen (Denmark), and the aforementioned CRU (United Kingdom) and DMI (Denmark) (Vinther et al. 2006). In satisfying a major priority of the work, the temperature record clearly verifies ice core records for Greenland. A second priority of contextualizing the recent climate of Greenland has resulted in further complication of the global warming debate. As the popularized side of the debate has led us to expect, the authors found that the coldest year (1863) and the coldest decade (1810s) are early in the record, well before the ballyhooed warming of the 20th century. Problematic from a climate change standpoint is the fact that the two distinct cold periods that made the 1810s the coldest decade followed an 1809 “unidentified” volcanic eruption and the eruption of Tambora in 1815 – unusual geologic events that defined the climate. However, of greater importance is the fact that the researchers found the warmest year on record to be 1941, while the 1930s and 1940s are the warmest decades on record. This represents very bad news for climate change alarmists, since the warmest period was NOT the last quarter of the 20th century. In fact, the last two decades of the 20th century (1981-1990 and 1991-2000) were colder across the study area than any of the previous six decades, dating back to the 1900s and 1910s (Table 1). When examining the instrumental records of the stations it is apparent that no net warming has occurred since the warm period of the 1930s and 1940s (Figure 1).


Table 1. Decadal merged Greenland temperatures. Values in parentheses are based on at least 8 or 9 years/seasons. (Taken from Vinther et al. 2006)


Figure 1. The historical record of seasonal and annual Greenland surface air temperatures after merging data from three stations with long instrumental records. The thick lines represent decadally filtered data, where grey lines indicate filtering based on incomplete data. The thin, horizontal grey lines represent the 20th century average temperatures. Data coverage for each of the three stations is indicated by the horizontal bars at the bottom, for which black bars indicate complete observations and grey bars indicate incomplete observation years. (Taken from Vinther et al. 2006)

In a region of the world where climate models indicate that the greatest impacts of CO2-induced global warming will be most rapid and most evident, this recent extension of instrumental surface air temperature records produces a climate history that seems to suggest otherwise. If global climate models are correct, the increase in CO2 concentration since 1930 should be evidenced rather dramatically in air temperature across a high-latitude region of the Northern Hemisphere such as Greenland. The evidence provided by the instrumental record of air temperature along the western and southern coasts of Greenland produces doubt in the degree to which increased CO2 concentrations impact high latitude climate as represented by the climate models upon which climate change alarmists are hanging their hats.

Reference:

Vinther, B.M., K.K. Andersen, P.D. Jones, K.R. Briffa, and J. Cappelen. 2006. Extending
Greenland temperature records into the late eighteenth century. Journal of Geophysical Research, 111, 10.1029/2005JD006810.




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