Monday, July 20, 2009

Nate Silver's Weather Whoopsie

Nate Silver runs the web site, which provides incredibly interesting and valuable coverage of politics, especially election politics. His statistical models predicting the presidential and senatorial elections were incredibly accurate. Since the election, he has been using statistics to look at policy issues as well as political horse races. It's one of the handful of blogs that I read everyday.

In that vein, he posted a piece Saturday challenging climate change skeptics to a bet. He argues that while it seems like it is a little cooler this summer than normal, it actually is not. He used the example of the Minneapolis-based Powerline blog--which had recently posted an article comparing this summer to a "year without a summer" as the basis for his challenge:
Indeed, it's been pretty cool in Minneapolis for the past couple of days; the temperature hasn't hit 70 since midday Thursday. But has it been an unusually cool summer? No, not really. Since summer began on June 21st, high temperatures there have been above average 15 times and below average 13 times. The average high temperature there since summer began this year has been 82.4 degrees. The average historic high temperature over the same period is ... 82.4 degrees. It's been a completely typical summer in Minneapolis, although with one rather hot period in late June and one rather cool one now. (Note: actual high temperatures can be found here and historical averages can be found here.)
After setting up the premise, he issued the challenge:
  • 1. For each day that the high temperature in your hometown is at least 1 degree Fahrenheit above average, as listed by Weather Underground, you owe me $25. For each day that it is at least 1 degree Fahrenheit below average, I owe you $25.
Sounds like a cool idea. Since next to no one reads my blog I'm not eligible for the bet, but I figured I could at least play along for pretend money. Mind you, I am not a all a climate change skeptic--I'm sure that the earth is gradually warming and it would behoove us to do something about it--but it still seemed like a fun game. But then, I clicked on the two links Nate provided in his post and realized that there was a problem.

When you click the Weather Underground site for the actual high temperatures, it defaults to the University of Minnesota weather station. When you click on the Weather Channel site for the historical averages, it shows the averages for the Minneapolis-St. Paul International Airport. In short, he's using different stations for actuals and averages.

That really makes a difference. The average high temperature of 82.4 degrees Nate records for this summer at the University of Minnesota (June 21 through July 18) is significantly higher that the average temperature at the airport, which is just 80.3 degrees during that time. Further using the airport data for June and July, one finds that the temperature has been below average 18 times at the airport, and above average only 8 (with two days right on the number).

On 16 of the 18 times that the temperature was below average, it was below by two or more degrees, which would mean Nate would owe me $400 for those days (had he made the offer in June). On seven of the eight warm days, the temperature was more two or more degrees above normal, so I would owe Nate back $175. As of Saturday night, I would be up $225 for the summer.

(Another little nitpick on the criteria, Nate is using the astronomical Summer, which begins on the Summer Solstice, but the Meteorological summer begins on June 1. If I were to use that criteria, I'd be up $350 since the first half of June was also quite cold in Minneapolis.)

Of course, I'm not going to take the bet. For one, I don't live in Minneapolis. Secondly, my blog isn't large enough to count. Finally, even if one and two were in my favor, chances are that I'd lose out over the next two months because these things tend to even out and a long cool stretch is already behind us.

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