In a comment on the post below, a bunny who wishes to remain Unknown points to a Jennifer Francis's work on how global climate has been changed by climate change and specifically ice melt in the Arctic
which is summarized as
If the theory is correct, that Arctic amplification reduced ice pack alters the jet stream patterns, leading to prolonged weather patterns, then we have entered a new meteorological system. Then shifted probability curves (based on the old meteorology) don't really make sense. The new meteorology we have created could have a very different probability curve for prolonged heat waves (as well as droughts, cold spells, extreme and prolonged flooding events, major snowstorms) in the NH than the prior meteorology.but in passing makes an important point that Eli has repeated several times, most often over at Open Mind. One can too easily fall into the trap of only looking at the statistical properties of some occurrence, it is even more important to understand the physical origins, as a matter of fact the later in IEHO is more important, sometimes you have to wait a bit on the statistics, but the physics (and chemistry) is basic.
Another approach to studying these events tries to identify whether the meteorology of the earth has changed. Prolonged weather patterns produces a heat wave, instead of a hot week. And prolonged weather patterns depend on the positioning of the jet stream. The direct cause of all three events in your post was a stalled jet stream (a blocking pattern in the jet stream).