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Precipitation (Trends - Arctic) -- Summary
Rawlins et al. (2006) state that "warming is predicted to enhance atmospheric moisture storage resulting in increased net precipitation," citing as the basis for this statement the Arctic Climate Impact Assessment (2005). Likewise, Peterson et al. (2002) have written that "both theoretical arguments and models suggest that net high-latitude precipitation increases in proportion to increases in mean hemispheric temperature," citing the works of Manaabe and Stouffer (1994) and Rahmstorf and Ganopolski (1999). Do real-world data bear them out? In the paragraphs that follow, we evaluate this question in light of the results of three studies that come to bear upon it.

Curtis et al. (1998) examined a number of climatic variables at two first-order Arctic weather stations (Barrow and Barter Island, Alaska) that began in 1949, finding that both the frequency and mean intensity of precipitation at these two locations decreased over the period of record. Contemporaneously, they report that temperatures in the western Arctic increased, but that "the observed mean increase varies strongly from month-to-month making it difficult to explain the annual trend solely on the basis of an anthropogenic effect resulting from the increase in greenhouse gases in the atmosphere." Be that as it may, the four researchers concluded that the theoretical model-based assumption that "increased temperature leads to high precipitation ... is not valid," at least for the part of the western Arctic that was the focus of their analysis.

Lamoureux (2000) analyzed varved lake sediments obtained from Nicolay Lake, Cornwall Island, Nunavut, Canada, which were compared with rainfall events recorded at a nearby weather station over the period 1948-1978 and thereby used to reconstruct a rainfall history for the surrounding region over the 487-year period from 1500 to 1987. The results were suggestive of a small, but statistically insignificant, increase in rainfall over the course of the record. However, heavy rainfall was most frequent during the 17th and 19th centuries, which were the coldest periods of the past 400 years in the Canadian High Arctic, as well as the Arctic as a whole. In addition, Lamoureux found that "more frequent extremes and increased variance in yield occurred during the 17th and 19th centuries, likely due to increased occurrences of cool, wet [our italics] synoptic types during the coldest [our italics] periods of the Little Ice Age [our italics]." Consequently, the results of this study also contradict the story promulgated by climate alarmists relative to the effects of global warming on extreme weather events and weather variability, both of which are typically claimed to increase with an increase in air temperature. Here, however, in a part of the planet predicted to be most impacted by CO2-induced global warming -- the Canadian High Arctic -- a warming of the climate is demonstrated to reduce weather extremes related to precipitation.

Most recently, Rawlins et al. (2006) calculated trends in the spatially-averaged water equivalent of annual rainfall and snowfall across the six largest Eurasian drainage basins that feed major rivers that deliver water to the Arctic Ocean for the period 1936-1999, over which time interval climate alarmists claim the globe's mean temperature rose to a level -- and at a rate -- that was unprecedented over the past two millennia. Their results indicated that annual rainfall across the total area of the six basins decreased consistently and significantly over the 64-year period. Annual snowfall, on the other hand, exhibited "a strongly significant increase," but only "until the late 1950s." Thereafter, it exhibited "a moderately significant decrease," so that "no significant change [was] determined in Eurasian-basin snowfall over the entire 64 year period." The researchers' bottom-line finding, therefore, was that annual total precipitation (including both rainfall and snowfall) decreased over the period of their study; and they note that this finding is "consistent with the reported (Berezovskaya et al., 2004) decline in total precipitation."

In light of the findings reviewed above, either (1) the theoretical arguments and model predictions that suggest that "high-latitude precipitation increases in proportion to increases in mean hemispheric temperature" are not incredibly robust, or (2) late 20th-century temperatures may not have been much warmer than those of the mid-1930s and 40s, or (3) both of the above, any or all of which choices fail to provide support for the standard climate-alarmist scenario of catastrophic CO2-induced global warming and its many conjectured negative planetary impacts.

References
Arctic Climate Impact Assessment. 2005. Arctic Climate Impact Assessment - Special Report. Cambridge University Press, New York, New York, USA.

Berezovskaya, S., Yang, D. and Kane, D.L. 2004. Compatibility analysis of precipitation and runoff trends over the large Siberian watersheds. Geophysical Research Letters 31: 10.1029/20004GL021277.

Curtis, J., Wendler, G., Stone, R. and Dutton, E. 1998. Precipitation decrease in the western Arctic, with special emphasis on Barrow and Barter Island, Alaska. International Journal of Climatology 18: 1687-1707.

Lamoureux, S. 2000. Five centuries of interannual sediment yield and rainfall-induced erosion in the Canadian High Arctic recorded in lacustrine varves. Water Resources Research 36: 309-318.

Manabe, S. and Stouffer, R.J. 1994. Multiple-century response of a coupled ocean-atmosphere model to an increase of atmospheric carbon dioxide. Journal of Climate 7: 5-23.

Peterson, B.J., Holmes, R.M., McClelland, J.W., Vorosmarty, C.J., Lammers, R.B., Shiklomanov, A.I., Shiklomanov, I.A. and Rahmstorf, S. 2002. Increasing river discharge to the Arctic Ocean. Science 298: 2171-2173.

Rahmstorf, S. and Ganopolski, A. 1999. Long-term global warming scenarios computed with an efficient coupled climate model. Climatic Change 43: 353-367.

Rawlins, M.A., Willmott, C.J., Shiklomanov, A., Linder E., Frolking, S., Lammers, R.B. and Vorosmarty, C.J. 2006. Evaluation of trends in derived snowfall and rainfall across Eurasia and linkages with discharge to the Arctic Ocean. Geophysical Research Letters 33: 10.1029/2005GL025231.

Last updated 17 October 2007