November 6, 2006

The Arctic Precipitation Conundrum

Filed under: Arctic, Polar, Precipitation

The Arctic region has become a bit of an epicenter of the global warming debate. Snow and ice cover are touted as effective monitors of large-scale climate change, the greatest warming in recent decades is said to have occurred over portions of the Arctic, and climate models predict that the region will experience some of the most significant warming in the future. Throw-in the idea that melting snow and ice increases the input of fresh water to the Arctic and northern Atlantic Oceans, which alters the oceanic thermohaline circulation, which changes the global climate further, and you can understand why the global warming crusade gets dreamy-eyed when thinking of the cold northern latitudes. The truth of the matter is that there have been many contradictions to the doomsday scenarios associated with the Arctic region – enough to champion a movie sequel “Day After Tomorrow 2: Hold the Phone!”

In a recent issue of Geophysical Research Letters, a consortium of scientists from the Universities of New Hampshire and Delaware reported on their research that engaged the idea that “both theoretical arguments and models suggest that net high-latitude precipitation increases in proportion to increases in mean hemispheric temperature.” This idea stems from the basic atmospheric principle that warm air stores more water vapor than cold air. Citing the Arctic Climate Impact Assessment (2005), the authors state that in regard to the Arctic, “Warming is predicted to enhance atmospheric moisture storage resulting in increased net precipitation, since precipitation increases will likely exceed evaporative losses.” Whether or not the actual data support these ideas is important, as previous research has documented significant increases in river discharge across Eurasia since the 1930s (Peterson et al. 2002). This takes us back to alteration of the oceanic thermohaline circulation. As the authors state, previous work has determined that “increased precipitation is the most plausible source for the observed discharge trend.”

The group of researchers, led my Michael Rawlins of the Institute for the Study of Earth, Oceans, and Space at the University of New Hampshire, studied precipitation derived from historical station data to better understand the role of precipitation in the discharge increases across Eurasia. Rawlins et al. calculated trends in spatially-averaged values of annual rainfall and the water equivalent of snowfall across the six largest drainage basins in Eurasia that are associated with rivers that deliver water to the Arctic Ocean. Three different data sets were analyzed for the period 1936-1999, the period over which previous research reported increases in discharge, and a period purported by climate change alarmists to be associated with unprecedented global warming.

In contradiction to theory, Rawlins et al. report that annual rainfall across the total area of the six basins that they studied actually decreased consistently and significantly over the period (Figure 1). Again, theory suggests that atmospheric warming, and an increase in water storage, results in a precipitation increase. The record of annual snowfall across northern Eurasia paints a less clear picture, as it increased significantly, but only until the late 1950s, after which a moderately significant decrease occurred, such that there was “no significant change” in snowfall over the entire 64-year period (Figure 1). Rawlins et al. report that the finding that annual total precipitation (rainfall plus snow water equivalent) decreased over the period is “consistent with the reported decline in total precipitation” of Berezovskaya et al. in 2004.

Figure 1. From Rawlins et al. (2006), spatially averaged water equivalent of annual rainfall (top) and snowfall (bottom) across the six Eurasian basins studied. Black, red, and blue lines represent each of the three data sets used.

The findings of the work are significant because they go against the theory, and therefore, model predictions, that “net high-latitude precipitation increases in proportion to increases in mean hemispheric temperature.” If this theory is wrong it represents a significant blow to the established principles of atmospheric physics. Another possibility is that Arctic temperatures during the late 20th century may not have been significantly different than those of the 1930s. This is a possibility that has also been recently suggested by Groisman et al. (2006) in their analysis of an under-utilized Arctic data set. Either possibility, or a combination of the two, presents a conundrum for climate change alarmists: the picture in the Arctic just got cloudier…and the clouds are not bringing the increase in precipitation that they expected.


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

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

Groisman, P.Y., R.W. Knight, V.N. Razuvaev, O.N. Bulygina, and T.R. Karl. 2006. State of the ground: Climatology and changes during the past 69 years over northern Eurasia for a rarely used measure of snow cover and frozen land. Journal of Climate, 19, 4933-4955.

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

Rawlins, M.A., C.J. Willmott, A. Shiklomanov, E. Linder, S. Frolking, R.B. Lammers, and C.J. Vörösmarty. 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.

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