How Fast Is the Probability of Extreme Temperatures Increasing?

So awhile back I hypothesized that the probability of extreme temperatures increases exponentially when global temperatures increase linearly.

Recently the NY Times posted some data that I think lends some qualitative support to this contention. It's in a graphical form, not numerical, so I can't really analyze it statistically -- only by eyeball. They're the changing probability distributions of summer temperatures in the northern hemisphere:

I don't know -- is the forward tail increasing outward (leftward) faster than the leftward movement of the the distribution peaks? It kind of looks like it, to me....