What was done
The authors note that the mean temperature of the globe has risen by about 0.6°C over the past century and look for possible impacts of this phenomenon on extreme weather events, which if found, they state, "would add to the body of evidence that there is a discernable human affect on the climate."

What was learned
Few changes of significance were observed.  As might be expected, "in some areas of the world increases in extreme events are apparent, while in others there appears to be a decline," so that the overall global response is pretty much of a wash.  However, "the number of intense and landfalling Atlantic hurricanes has declined."

What it means
Since there has been no net change in worldwide extreme weather, application of the criterion proposed by the authors suggests that there is no "discernable human affect on the climate."  We might quibble with them, however, in regard to Atlantic hurricanes.