I conducted a sixteen-year study of budburst dates in Oklahoma deciduous trees, and I found that winter buds opened in spring earlier and earlier each year, consistent with global warming. The results were highly significant. I did not, however, have time to publish this study in a scientific journal before I retired. I decided instead to publish it on my website. Here is the link to the article, with illustrations. Please note that the mailing address on the cover page is now obsolete; you may contact me through the website email link (stanriceauthor@gmail.com).
I here address an interesting point about this research, aside from its unsurprising conclusion. And that point is, what do we do with the data?
(This is a photo of the just-opening buds of black hickory. Oaks have lots of bud scales, but hickory just has two big scales for each bud.)
My statistical analyses indicated quite clearly that all but one of the 22 tree species had earlier budburst over the course of 16 years—an average of about one day earlier each year. But this is an average. Budburst came later in silver maples—but this is because they died in the summer droughts. Pecan trees opened their buds about one day earlier each ten years, whereas sweetgums opened their buds about three and a half days earlier each year. This means the makeup of our forests might change with global warming, since not all tree species will react to it the same way.
Also, it is completely incorrect to assume that global warming means that each year is warmer than the previous year. One year can differ strikingly from the next. What we are looking for is an overall trend. This is obvious from the data presented in my graphs in the paper.
Science must also avoid what is called extrapolation. We cannot simply take this one-day-per-year rate and extend it into the past or the future. Particularly, the future. If, for example, sweetgums opened their buds three and a half days earlier each year (with the average date in my study being February 24 in 2009), this would mean that in 2029 they would open in the middle of winter, about December 19, and back in 1999 they would have opened at the end of March. I was on site in 1999, though I’d not yet begun my measurements. But I know they opened before the end of March. And they cannot open their buds in December unless winter completely vanishes. This is unlikely to happen. At least, not soon.
What this means is that one-day-per-year earlier budburst is what I observed in the study period, but there were earlier times, and may be later times, when this rate did not occur. Extrapolation is invalid, as Mark Twain explained. If the Mississippi River gets 10 miles shorter each year, then at some point, Twain quipped, St. Louis and New Orleans would be next to each other and need a joint board of aldermen. If it gets 10 miles longer each year, then in a few years it would stick out over the Gulf of Mexico (Gulf of America?) like a fishing rod.
Scientists should not extrapolate beyond their data. We can interpolate, within the range of data, but not extrapolate outside of it. All I can say is, this is what happened during my sixteen-year study period. As you can see from the figures in the paper, budburst dates sometimes came earlier (especially 2017) and sometimes later (for example, 2018). It changes every year, but these changes are against a background of earlier budburst, as indicated by the statistical analyses.
Yes, sixteen years in which at least twice a week, during February and March, I walked past each tree and looked for budburst. It sounds like a lot of boring work. But it was not, for me: I came to know each of these trees as an individual, and I looked forward every year to its emergence from dormancy.
As indicated in these four essays, the science of global warming is not just something to argue about—and we are all tired of arguing—but an invitation to the adventure of scientific discovery. We can, by using science, listen to what the trees have been telling us all along.
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