Background
As recounted by Beniston and Goyette (2007), "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)," and in this regard they remark that "such statements are often supported by climate model results, as for example in the analysis of GCM and/or RCM simulated temperature and precipitation (Mearns et al., 1990, 1995) or in multiple-model simulations over Europe."

What was done
Noting that "coral records closely track tropical Indo-Pacific variability on interannual to decadal timescales (Urban et al., 2000; Cobb et al., 2001; Linsley et al., 2008)," Ault et al. employed 23 coral δ¹⁸O records from the Indian and Pacific Oceans to extend the observational record of decadal climate variability back in time to cover the period from AD 1850-1990.

What was learned
The seven scientists identified "a strong decadal component of climate variability" that "closely matches instrumental results from the 20th century." In addition, they report that the decadal variance they uncovered was much greater between 1850 and 1920 than it was between 1920 and 1990.

What it means
In the words of the researchers who performed the analysis, "we infer that this decadal signal represents a fundamental timescale of ENSO variability," whose enhanced variance in the early half of the record "remains to be explained." We would only add that it also "remains to be explained" why climate models tend to suggest just the opposite of what actually occurs in the real world.

References
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.

Cobb, K.M., Charles, C.D. and Hunter, D.E. 2001. A central tropical Pacific coral demonstrates Pacific, Indian, and Atlantic decadal climate connections. Geophysical Research Letters 28: 2209-2212.

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.

Linsley, B.K., Zhang, P., Kaplan, A., Howe, S.S. and Wellington, G.M. 2008. Interdecadal-decadal climate variability from multicoral oxygen isotope records in the South Pacific Convergence Zone region since 1650 A.D. Paleoceanography 23: 10.1029/2007PA001539.

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.

Shar, 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.

Urban, F.E., Cole, J.E. and Overpeck, J.T. 2000. Influence of mean climate change on climate variability from a 155-year tropical Pacific coral record. Nature 407: 989-993.