Background
The authors write that "exposure and vulnerability to weather and climate-related natural hazards largely determine the severity of impacts of these extremes," and since planning requires reliable knowledge of the relevant climate phenomena, they state that "a robust characterization in terms of frequency and intensity of current and future extreme precipitation is of great relevance." But they readily admit that "global climate models still cannot adequately capture the frequency, intensity, tendency, and spatial distribution of observed precipitation extremes over large regions in the world," citing Sun et al. (2006), Allan and Soden (2008), O'Gorman and Schneider (2009) and Min et al. (2011).

What was done
Hoping to improve on this sorry situation, Toreti et al. evaluated "simulated daily precipitation extremes in the twentieth century assuming stationary processes," and they provided "for the first time a comprehensive global assessment of seasonal future changes in daily precipitation extremes identifying regions where both consistency (i.e., models agreement) and reliability (i.e., goodness of fit of the applied statistical model) are achieved."

What was learned
The nine researchers report that "for the subtropics and tropics, the lack of reliable and consistent estimations found for both the historical and future simulations might be connected with model deficiencies in the representation of organized convective systems." In addition, they state that "a reliable characterization of daily extreme precipitation cannot be achieved for larger areas of the world, where an estimation of the return levels cannot be obtained." And they add that "a glance at the individual simulations reveals remarkable intermodal differences."

What it means
With all of the trouble researchers are finding with the ability of the world's most cutting-edge climate models to "predict the past," so to speak, it makes little sense to put much faith in what they are predicting for the future.

References
Allan, R.P. and Soden, B.J. 2008. Atmospheric warming and the amplification of precipitation extremes. Science 321: 1481-1484.

Min, S.K., Zhang, X., Zwiers, F.W. and Hegerl, G.C. 2011. Human contribution to more intense precipitation extremes. Nature 470: 378-381.

O'Gorman, P.A. and Schneider, T. 2009. The physical basis for increases in precipitation extremes in simulations of 21st-century climate change. Proceedings of the National Academy of Sciences USA 105: 14,773-14,777.

Sun, Y., Solomon, S., Dai, A. and Portmann, R.W. 2006. How often does it rain? Journal of Climate 19: 916-934.