As described in the previous essay, 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 measure?
This photo shows the giant buds, just opening, of black oak (Quercus velutina).
When we talk about global warming, we can mean lots of different things. It is better to talk about global climate change or even global climate disruption. For global warming, it would seem to be a simple matter of measuring temperatures and seeing if they increase from year to year. But this, by itself, is unsatisfactory, for reasons such as these:
Where do you measure the temperature? Air temperature may be warmest near the ground, and cooler the further you go up in the atmosphere. Air temperature is what affects budburst, since buds are up in the air. But soil temperature is also important, since warmer soil might mean earlier root activity and earlier rising of the sap. Aerial buds do not just open when it is warm enough but also in response to sap rising in the wood.
Temperature is enormously variable. You cannot simply measure it in one place and use this temperature to represent the air temperature. Meteorologists have little stations to measure air temperature (and lots of other things) in numerous locations, but even this is not enough. Temperatures can vary from one location to another just a few feet away.
When do you measure the temperature? The maximum temperature in the day, or the minimum at night? Also, we suspect that springtime temperatures are what matter the most, but winter temperatures can also be important. Some tree buds must have a certain number of days of winter chilling before they can open in the spring.
Other factors are always important, such as wind speed, soil moisture, and the moisture status inside the twigs.
It is not just the temperature that matters to humans, but how it makes us feel. Weather predictions indicate not only the actual temperature but the way it feels to the body. The same is true of trees. We are interested not so much in the actual temperature of the air as in how the temperature affects biological activities such as the opening of the buds.
The climate could be getting warmer even if the temperatures do not increase. Springtime could just come earlier and autumn later, without a change in the average temperature.
If all of this makes it seem hopeless to study global warming, I am happy to report that organisms themselves can transduce all the environmental variables, over time, into biologically meaningful measurements. In the case of trees, all of the variations in temperature, moisture, and wind can be summarized by budburst date, something that the plants, not we, control. Budburst date is the one variable I measured. I used weather data as background, but not for analysis.
By opening their buds earlier and earlier each year, the trees are telling us that it is getting warmer. See the next essay for other scientifically important concepts in the study of global warming.


