Exactly this. The 'study' hasn't controlled for anything. There precisely no discussion of the weather (the summer months are suspiciously absent from the data set, nor the weather patterns commented on - Sydney, Australia had one of the wettest summers on record over 2011/2012), the economies of the countries involved, let alone a year over year data comparison.

The only thing "gone in 60 seconds", is the credibility of the authors of this study.