Check out this scary animation of NASA data showing changes in extreme temperature deviations. NASA Climate guru James Hansen put these charts together, using temperatures from 1951 to 1980 as a base period for the bell curve.

So, those years are the "average weather events," where the graphs start.

As you can see in the video (and have probably experienced in real life) extreme weather is becoming more frequent since the 1980s. The bell curve of temperature shifts to the right as extreme heat becomes more frequent:

The research was published in the journal Proceedings of the National Academy of Sciences on August 6.

"This summer people are seeing extreme heat and agricultural impacts," Hansen said in a NASA statement. "We're asserting that this is causally connected to global warming, and in this paper we present the scientific evidence for that."

It's more and more likely that our summers will be defined as "hot," "very hot" and "extremely hot" summers.

(Via Brain Pickings' Maria Popova and a Sun Microsystem employee).