Bjørn Lomborg, author of
The Skeptical Environmentalist (the book has its own Wikipedia page!), provided a
very nice op-ed recently in the Washingon Post that debunks the often-heard claim that global warming is associated with increased weather
volatility. In his recounting, higher average temperatures have occurred alongside no clear trend in the variability of temperatures. And in some cases, the outcomes triggered by weather extremes, deaths due to cold snaps or heat waves for example, may have actually been dampened by the increase in average temperatures.
I know part of my own perception of this has stemmed from discussions about hurricane intensity and (average) temperature, such as on
this NOVA page. And
Tom Friedman's use of "global weirding," which sounds like it's referring to variance but might not be after a closer look.