In a recent EOS, Karl, Gleason, Menne McMahon, Hein, Brewer, Kunkel, Arndt, Privette, Bates, Groisman and Easterling write on recent US climate change involving high temperatures and droughts. The conclusion is, of course, that thing are changing, especially in the spring and summer with rising maximum (MxT) and minimum (MnT) temperatures.
The warmth of the spring and summer of 2011 and 2012 is unprecedented in the observational record for its overall magnitude, spatial extent, and persistence and is part of a highly significant national trend. In the absence of trends, the standardized temperature anomaly for spring and summer of 2012 was about a one in 1600-year event for MxT and 450-year for for MnT. The extremely high MxT in the drought-stricken area during spring and summer of 2011 and 2012 is in contrast to the weakly increasing trend of MxT in that area. This is attributed to multi-decadal increases in precipitation in that area, in contrast to the past two dry summers.
Nationally, no long-term trends are evident for drought severity. With increasing temperatures expected in the long term [Karl et al., 2009], continued increases in the extreme upper tails of temperature distribution are likely. During times of drought, the feedbacks of higher temperature extremes and dry conditions are likely to amplify both temperature extremes and drought severity in the United States.