My first thought was local weather -- the exclusion zone is a pretty big place. The two pages of their paper I have access to, however, suggests they were quite

My first thought was local weather -- the exclusion zone is a pretty big place. The two pages of their paper I have access to, however, suggests they were quite conscious of that. If they accounted for it properly, the methodology is probably valid. I'd very much like to see the raw data, of course.