It seems as though the issue of trying to attribute an anthropogenic influence to an extreme weather event is controversial on a number of levels. It sometimes seems to divide even those who largely agree, and almost always produces a push-back from those who appear to want to dismiss the risks associated with climate change. Some of this push-back is justified, but some is no better than those who make overly strong claims about an association between climate change and an extreme weather event. Not being able to make some kind of formal attribution does not mean that there is no link between climate change and these extreme events.
My own view is that asking whether or not climate change caused a particular extreme event is silly; we can’t answer that question. What we can do, though, is consider how anthropogenically-driven climate change has influenced the likelihood of certain events. Naively one might argue that in a warmer world we would expect, for example, an increase in the frequency and intensity of heatwaves and extreme precipitation events. This may be reasonable globally, but as this paper by Friederike Otto and colleagues points out, regionally it depends on both thermodynamic changes (more energy) and changes in atmospheric circulation.
To try and understand how climate change is likely to influence extreme events – regionally at least – one therefore needs to consider both warming (thermodynamics) and how it influences the movement of atmospheric patterns (circulation). Circulation changes could reduce the likelihood of some events in some regions, while enhancing it in others. The key point, though, is that this is not an attempt to determine if climate change is causing these extreme events; it is simply trying to establish how climate change influences the overall risk of these extreme event.
I may not have explained this properly, but fortunately the author is on hand to do a better job than I can.