“Prove” has different meanings for most people compared to scientists. As you say, it is impossible to prove that something like this, which results from a complex set of conditions and most likely a complex set of causes, results from a single thing. So we speak in probabilities, confidence intervals, and significance. That’s just science speak.
This results from human-made global warming in the same way as a smoker’s lung cancer results from smoking. The conclusion is also the same in both cases: “don’t do it”. Nobody can prove that it will kill, but it drastically increases the odds.
Also, note that this is not at all unexpected. I remember articles in scientific vulgarisation magazines in the 1990s discussion this and the fact that, counter-intuitively, global warming could result in local cooling in Western Europe because of a weakened Gulf Stream. We are still far from that.