Background
The authors write that "increasing weather-related natural disaster losses have been well documented (Rogers et al., 2010; Wirtz, 2010)," and they say that various societal and building code changes are known to influence the time series of these extreme events. Considerable research has thus focused on determining, in their words, "whether an anthropogenic climate change signal is present after these changes have been accounted for by a processes called loss normalization (Pielke Jr. et al., 2008; Crompton and McAneney, 2008; Bouwer, 2010)," but they report that in spite of these efforts, "no insured or economic loss normalization study has yet been able to detect an anthropogenic signal across a range of perils and locations around the world (Bouwer, 2011)."

In an attempt to determine the odds of breaking through this detection barrier, Crompton et al. focused their attention upon US tropical cyclone loss data. Knowing, however, that Chen et al. (2009) and Knutson et al. (2010) had failed to find a clear signal of man's impact on Atlantic hurricanes, they asked a somewhat more tractable question: "if changes in storm characteristics in fact occur as projected, then on what timescale might we expect to detect the effects of those changes in damage data?"

What was done
Employing the ensemble projection of 18 global climate models derived from the World Climate Research Programme's Coupled Model Intercomparison Project 3 (CMIP3, based on the IPCC's A1B emissions scenario), plus individual projections obtained from four of the CMIP3 models -- (1) the Geophysical Fluid Dynamics Laboratory GFDL-CM2.1, (2) the Japanese Meteorological Research Institute MRI-CGCM, (3) the Max Planck Institute MPI-ECHAM5, and (4) the Hadley Centre UK Meteorological Office UKMO-HadCM3 -- the three researchers estimated "the time that it would take for anthropogenic signals to emerge in a time series of normalized US tropical cyclone losses."

What was learned
Crompton et al. determined, as they describe it, that "depending on the global climate model(s) underpinning the projection, emergence timescales range between 120 and 550 years, reflecting a large uncertainty." And they report that "it takes 260 years for an 18-model ensemble-based signal to emerge."

What it means
Based on their results, the US and Australian scientists "urge extreme caution in attributing short term trends (i.e., over many decades and longer) in normalized US tropical cyclone losses to anthropogenic climate change," suggesting that "anthropogenic climate change signals are very unlikely to emerge in US tropical cyclone losses at timescales of less than a century."

References
Bouwer, L.M. 2011. Have disaster losses increased due to anthropogenic climate change? Bulletin of the American Meteorological Society 92: 39-46.

Chen, K., McAneney, J. and Cheung, K. 2009. Quantifying changes of wind speed distributions in the historical record of Atlantic tropical cyclones. Natural Hazards and Earth Systems Science 9: 1749-1757.

Crompton, R.P. and McAneney, K.J. 2008. Normalized Australian insured losses from meteorological hazards: 1967-2006. Environmental Science and Policy 11: 371-378.

Knutson, T.R., McBride, J.L., Chan, J., Emanuel, K., Holland, G., Landsea, C., Held, I., Kossin, J.P., Srivastava, A.K. and Sugi, M. 2010. Tropical cyclones and climate change. Nature Geoscience 3: 157-163.

Pielke Jr., R.A., Gratz, J., Landsea, C.W., Collins, D., Saunders, M.A. and Musulin, R. 2008. Normalized hurricane damage in the United States: 1900-2005. Natural Hazards Review 9: 29-42.

Rogers, B., Mehlhorn, J. and Schwarz, S. 2010. Natural catastrophes and man-made disasters in 2009: Catastrophes claim few victims, insured losses fall. Sigma No. 1/2010. (Available at http://media.swissre.com/documents/sigma1_2010_en.pdf)

Wirtz, A. 2010. Great natural catastrophes -- causes and effects. Natural Catastrophes 2009. Analyses, Assessments, Positions. (Available at http://www.munichre.com/publications/302-06295_en.pdf)