In the past, climate scientists were reluctant to say that any one weather event was caused by global warming. However, that question has been rephrased into," How much more probable is the occurrence of an extreme weather event because of global warming?" That is a question that can be answered by a straightforward statistical analysis, as Dr. Hansen does in the article. Extreme temperature events are 30 times as likely than in 1950's - and 10 times as likely as in 1980's.
John Christy"s comment that "Hansen shouldn't have compared recent years to the 1950s-1980s time period because he said that was a quiet time for extremes.", rather ignores the fact that Dr. Hansen's paper also included a comparison to the 1980 to 2010 , as you can see from the graph on the right.
And Roger Pielke Jr.'s comment, "Just because people understand a fact that doesn't mean people will act on it" is rather meaningless at it is unlikely that someone would act on the fact they don't understand. And both Dr. Pielke and Dr. Christie have done their best to see that people do not understand the facts.