What is an "average" summer?

July 19, 2011

Sunday the Atlanta Journal-Constitution (AJC) had an article claiming that this summer is no hotter than usual. For each date, they gave this year's high, the record high, and the average high. I'll explain below why these figures don't show this is an "average" summer. However, the easy thing to note is that the list started June 21 (1st day of summer). Of course, the really notable thing about this year is how early the heat started - back in May. We certainly were close to or exceeding highs for those days on several (?many) dates. It looks to me like a misuse of statistics for the purpose of climate change denialism. Wouldn't be a surprise, because the AJC is owned by a Republican.

And I notice they chose to print these figures during a brief cooler spell (starting July 15), and before the temperatures are predicted to get hotter again in a day or two.

Considering the temperatures in the list they published, of with June 21 thru July 16, the question is, was this stretch of dates unusually hot. The claim is that the figures show it wasn't. This might be true, but it is not proved by these statistics.

Comparing the high for this year, with the record highs for the same date, none of these dates had a high that reached the record high for that date.
If you are like me, and have a habit of looking at the weather history when you look at the weather report in the paper or on-line, you will know that the record highs come from many different years. From our own experience with the weather, we know that in some cases, they were part of a short hot spell within a less extreme season.

Comparing this years highs with average highs for this date, we find there were 21 days that exceeded the average (sometimes by only one degree), 3 days less than the average, and one day the same as the average for the same day. If this were really an "average" period, we would expect to see about the same number of days below the average as above it.

I'm going to do some calculations when I'm at home or at least somewhere where I can plug in and not use up my batter, and update this with what I find, looking at the differences between this year's highs and the average highs.

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