From Weather to Climate

2010 February 18
by Otto

One of the disconnects I have with the global warming debate is when scientists talk in the most apocalyptic terms about temperatures rising by one or two degrees. It seems hard to imagine that such a small shift could mean so much, especially when the temperature rises and falls so much throughout the day, and when one January day it’s 60F and the next day the temperature plummets to -25F. Wouldn’t two degrees get lost in the shuffle? And are they measuring in the sun or in the shade?

I was researching Bozeman’s temperature data the other day to understand the weather conditions my house’s heat recovery ventilation system will face. On the Western Regional Climate Center’s website I found a table of data of daily highs and lows in Bozeman, averaged over the years 1971-2000. It was fascinating because the averages smoothed out into an almost perfect graph:

Daily Highs/Lows in Bozeman, MT 1971-2000

Daily Highs/Lows in Bozeman, MT 1971-2000

The graph almost doesn’t quite capture just how smoothly the average temperature rises and falls. For the first two weeks of January, for example, the average lows are 12.2, 12.4, 12.6, 12.8, 12.9, 12.9, 13.0, 13.1, 13.2, 13.3, 13.4, 13.6, 13.8, and 13.9. It continues that way, almost exactly 0.1 degree per day, until three days at the end of July, where the highs are 83.3 and the lows are 52.8, and then the temperature begins to slide back down.

I think of Bozeman weather as unpredictable. It can snow in July and it can be shirtsleeves weather in January. Yet when you average together just 30 years of data, weather has already given way to climate, and suddenly it becomes obvious: when it comes to a warming planet, even one degree has nowhere to hide.

See the complete data here:

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