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Earth Sense: Check of history shows big variations in temperatures
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It’s difficult to see the presence or absence of climatic change from looking at temperature records alone, as a quick analysis of data has shown that I did with Johnny Vardeman last week. Vardeman writes a history-focused column for The Times, and obtained Gainesville temperature data from 1919. Brenau University’s weather station had a complete 2016 set, supplying close to 9,000 temperature measurements.

We compared average monthly temperatures and annual averages. Almost every month, the weather was warmer in 2016 than in 1919. July, for example, had a 1919 average of 77.4 degrees. In 2016, it was 82.6. October averaged 67.1 F recently, vs. 60.1 a century ago. But such numbers can show great variation internally. There can be more changes within a year than there is between several years.

This is where statistical analysis serves as a tool. A procedure called Fisher’s F-test revealed that the differences between 1919 and 2016 were not significant. This came with a confidence level showing that we can be 88 percent certain of the result. Even the fact that the overall average for 1919 was 59.3 degrees, and 2016 reached 63.9 F, doesn’t point to a statistically significant change.

What can’t be seen in a study using a small collection of data like this is the variation that occurs within a month, and even within single days. Farmers, for example, aren’t interested in average weather. They want to know: Are the dates of the last frost changing? If so, young plants can get killed if they’re put out too early. Are record high temperatures just a short spike, which most plants can tolerate, or are they lasting for long periods of time?

We also don’t know, of course, whether 2016 was a typical year, and more hotter-than-average months are in our future. Also, 1919 could have been unusual for the early 20th century.

Climatic change won’t show much in the temperature averages, unless millions of measurements are compared. Many people don’t see much meaning in a shift of 2 degrees up or down. In Gainesville, a daytime high of 87 instead of 85 doesn’t make much difference. But the atmosphere is bouncing around constantly. Any extra heat can change the path and severity of storm systems.

On the coast in particular, such shifts mean trouble for barrier islands, given their elevation of 10 feet or less above sea level.