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Global Warming and Climate Variability
Reference
Beniston, M. and Goyette, S. 2007. Changes in variability and persistence of climate in Switzerland: Exploring 20th century observations and 21st century simulations. Global and Planetary Change 57: 1-15.

Background
The authors write that "it has been assumed in numerous investigations related to climatic change that a warmer climate may also be a more variable climate (e.g., Katz and Brown, 1992; IPCC, 2001; Schar et al., 2004)," noting that "such statements are often supported by climate models results, as for example in the analysis of GCM and/or RCM simulated temperature and precipitation (Mearns et al., 1995; Mearns et al., 1990)." Hence, they say "it is of interest to investigate whether, based on long time-series of observational data, this hypothesis is indeed verified in a climate that has experienced a warming of 2C or more."

What was done
Noting that 20th-century warming in the alpine area of Europe "is 2-3 times greater than the global average (Jungo and Beniston, 2001) and provides an observational framework that allows to address the issue of links between mean temperature and its variance," the researchers focused on one Swiss site representative of low elevation (Basel, 369 m above sea level) and another Swiss site representative of high elevation (Saentis, 2500 m above sea level), both of which sites, in their words, "have proven their quality in a number of previous studies (Jungo and Beniston, 2001; Beniston and Jungo, 2002; Benisteon and Stephenson, 2004; Beniston and Diaz, 2004)," where they say it was determined that conclusions based on data from these sites "also apply to most of the other Swiss sites."

What was learned
Beniston and Goyette report that based upon observational data since 1900 at both the low and high elevation sites, "the inter-annual and decadal variability of both maximum and minimum daily temperatures has in fact decreased [authors' italics] over the course of the 20th century despite the strong warming that has been observed in the intervening period [our italics]."

What it means
The Swiss researchers say their observations show that "contrary to what is commonly hypothesized, climate variability does not necessarily increase as climate warms." In fact, they emphasize that "the variance of temperature has actually decreased [our italics] in Switzerland since the 1960s and 1970s at a time when mean temperatures have risen considerably [our italics]." What is more, they state that their findings "are consistent with the temperature analysis carried out by Michaels et al. (1998)," noting that the latter investigators' results "also do not support the hypothesis that temperatures have become more variable as global temperatures have increased over the 20th century."

References
IPCC. 2001. Climate Change 2001. The Scientific Basis. Cambridge University Press, Cambridge, UK.

Katz, R.W. and Brown, B.G. 1992. Extreme events in a changing climate: variability is more important than averages. Climatic Change 21: 289-302.

Mearns, L.O., Schneider, S.H., Thompson, S.L. and McDaniel, L.R. 1990. Analysis of climate variability in general circulation models: comparison with observations and change in variability in 2 x CO2 experiments. Journal of Geophysical Research 95: 20,469-20,490.

Mearns, L.O., Giorgi, F., McDaniel, L. and Shields, C. 1995. Analysis of variability and diurnal range of daily temperature in a nested regional climate model: comparison with observations and doubled CO2 results. Climate Dynamics 11: 193-209.

Michaels, P.J., Balling Jr., R.C., Vose, R.S. and Knappenberger, P.C. 1998. Analysis of trends in the variability of daily and monthly historical temperature measurements. Climate Research 10: 27-33.

Schar, C., Vidale, P.L., Luthi, D., Frei, C., Haberli, C., Liniger, M. and Appenzeller, C. 2004. The role of increasing temperature variability in European summer heat waves. Nature 427: 332-336.

Reviewed 22 August 2007