Jim Hansen takes analysis of summer extremes & greenhouse heating back through 30’s. Rebuts critics and says his conclusions, even with different baselines, hold up. Click for his update. He says this figure illustrates key points, as follows: 
"United States summer temperature anomalies (Fig. 5) are particularly instructive. Despite the small area of the contiguous 48 states (covering only about 1.5% of the world’s area), the effect of global warming during the past three decades is readily apparent. Only two of the past 15 summers have been cooler than either the 1931-1980 or 1951-1980 average. There is even a hint of the increased variability that the "bell curve" reveals more convincingly.
"Fig. 5 is an alternative view of the concept that is being illustrated with the ‘loaded dice’. In either case, it is important that the public understand that the anomalous warmth of 2012, even though its extremity is caused by global warming, should not be assumed to represent a new norm. Climate will continue to be variable and there is still a significant chance of a season being cooler than the long-term average.

'Fig. 5 also reveals that the 1930s heat was exceptional. It was not until 2012 that the 1936 extreme temperature was exceeded by a significant amount.”

Jim Hansen takes analysis of summer extremes & greenhouse heating back through 30’s. Rebuts critics and says his conclusions, even with different baselines, hold up. Click for his update. He says this figure illustrates key points, as follows: 

"United States summer temperature anomalies (Fig. 5) are particularly instructive. Despite the small area of the contiguous 48 states (covering only about 1.5% of the world’s area), the effect of global warming during the past three decades is readily apparent. Only two of the past 15 summers have been cooler than either the 1931-1980 or 1951-1980 average. There is even a hint of the increased variability that the "bell curve" reveals more convincingly.

"Fig. 5 is an alternative view of the concept that is being illustrated with the ‘loaded dice’. In either case, it is important that the public understand that the anomalous warmth of 2012, even though its extremity is caused by global warming, should not be assumed to represent a new norm. Climate will continue to be variable and there is still a significant chance of a season being cooler than the long-term average.

'Fig. 5 also reveals that the 1930s heat was exceptional. It was not until 2012 that the 1936 extreme temperature was exceeded by a significant amount.”