Global warming deniers are sure to come flying from the nearest dark corner to cry "foul!" with some comment like, "every time there's a snowstorm, you say it doesn't disprove global warming, but then every time there's a heatwave, you say it PROVES global warming!"
Let's just head them off at the pass: there is some serious weight behind these claims.
First, it's not just heat. global warming has weighted the dice in favor of extreme rainfall events, too, including the floods that rocked Tennessee and Kentucky this spring. Witness Kevin Trenberth of the National Center for Atmospheric Research speaking recently to Joe Romm of Climate Progress:
There is a systematic influence on all of these weather events
And as Romm pointed out in his epic post yesterday, the ratio of record highs in the U.S. to record lows has been steadily increasing for decades. Even if one ignores the fact that 2010 is on pace to set a new high for the the hottest year on record - that's for the whole planet, much of which is also experiencing record heat - the overarching trend is pretty convincing: