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Extreme Precipitation Trends of North America
Kunkel, K.E.  2003.  North American trends in extreme precipitation.  Natural Hazards 29: 291-305.

What was done
The author notes that "several studies have argued that increasing greenhouse gas concentrations will result in an increase of heavy precipitation (Cubasch et al., 2001; Yonetani and Gordon, 2001; Kharin and Zwiers, 2000; Zwiers and Kharin, 1998; Trenberth, 1998)."  Hence, he analyzed pertinent precipitation data from Canada and the United States, looking for trends in extreme events over the course of the past century.

What was learned
Kunkel reports "there has been no discernible trend in the frequency of the most extreme events in Canada."  In the United States, on the other hand, he finds "there has been a sizable increase in their frequency since the 1920s/1930s."  Going back a little further in time, however, the data indicate that "frequencies [of extreme precipitation events in the Unites States] in the late 1800s/early 1900s were about as high as in the 1980s/1990s."

What it means
In the words of the author, "the present study, extending to 1895, is important because it shows that frequencies of extreme events were about as high around the turn of the 20th century as they were at the end of the 20th century," noting further that "this early episode of high frequencies occurred at a time when anthropogenic forcing of the climate system was very small."  This observation suggests, as he remarks, "that natural variability in the frequency of precipitation extremes is quite large on decadal time scales and cannot be discounted as the cause or one of the causes of the recent increases."  What is more, the lack of any net change in extreme precipitation frequency over a 100-year period of what climate alarmists call "unprecedented global warming" is pretty strong evidence that state-of-the-art climate models are widely missing the mark when they indicate that greenhouse gas-induced warming "will result in an increase of heavy precipitation."

Cubasch, U., Meehl, G.A., Boer, G.J., Stouffer, R.J., Dix, M., Noda, A., Senior, C.A., Raper, S. and Yap, K.S.  2001.  Projections of future climate change.  In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Dai, X., Maskell, K. and Johnson, C.A. (Eds.), Climate Change 2001: The Scientific Basis. Contributions of Working Group 1 to the Third Assessment Report of the Intergovernmental Panel on Climate Change.  Cambridge University Press, Cambridge, UK.

Kharin, V.V. and Zwiers, F.W.  2000.  Changes in the extremes in an ensemble of transient climate simulations with a coupled atmosphere-ocean GCM.  Journal of Climate 13: 3670-3688.

Trenberth, K.E.  1998.  Atmospheric moisture residence times and cycling: Implications for rainfall rates with climate change.  Climatic Change 39: 667-694.

Yonetani, T. and Gordon, H.B.  2001.  Simulated changes in the frequency of extremes and regional features of seasonal/annual temperature and precipitation when atmospheric CO2 is doubled.  Journal of Climate 14: 1765-1779.

Zwiers, F.W. and Kharin, V.V.  1998.  Changes in the extremes of climate simulated by CCC GCM2 under CO2-doubling.  Journal of Climate 11: 2200-2222.

Reviewed 18 June 2003