"I think there are very good reasons to believe that the current U.S. heat wave is at least partly caused by global warming," Kevin Trenberth, one of the nation's top global-warming computer modelers, wrote in an e-mail. ... "Heat waves have...increased most places around the world."
"It is true that the current heat wave could have occurred by chance. But I believe that the likelihood of such occurrences increases due to global warming," said [noted atmospheric scientist and climate modeler, Govindasamy] Bala [of Lawrence Livermore National Laboratory]. ...
James O'Brien, Florida's state climatologist...criticized colleagues who he thinks are too quick to link short-term and long-term weather. He recalled that in 1988, "we had a big Midwest heat wave ... which (NASA scientist) Jim Hansen told the U.S. Senate was due to global warming."
Philip Klotzbach, an atmospheric scientist at Colorado State University [wrote in an email]: "Heat waves have happened for many years (i.e., the Dust Bowl in the 1930s), so to say that this one particular event is caused by global warming is really impossible." (SF Chronicle)
So there you have it -- jury's still out. Nifty map, though.