I don't think this is right. You can calculate the probability due to pure chance of having a certain number of extreme events in a year, given their variance s

I don't think this is right. You can calculate the probability due to pure chance of having a certain number of extreme events in a year, given their variance since records began. If we suppose the probability is 10%, then seeing the same or worse year on year would get us to 0.0001% after just 5 years. I don't know the numbers are or if they're even this drastic, but at some point they will be and we'll be able to say with confidence that climate change is the cause.