Will global warming affect corn and soybean yields in Kentucky in 2009? It is impossible to answer this question. As every farmer knows, there is a lot of variation in the weather from one year to the next in Kentucky (see Figure 1). For example, there was more than 15 inches of rain in the wettest summers at Henderson, KY (3 out of 31 years), but only about 5 inches (2 out of 31 years) in the driest years. Maximum temperature was a boiling hot 94 degrees in 1980 but it was almost chilly at less than 84 degrees as recently as 2004. These year-to-year fluctuations are much larger than the small yearly changes predicted by the global warming models. The 31 years of data from Henderson and other locations in western and central Kentucky don’t show any evidence that summers are getting any warmer, wetter or drier.
Yields in 2009 will depend upon the weather this summer. If we have plenty of rain yields will probably be high, if we don’t yields will be low. We don’t need global warming to get this variation. At the time this article when to press (Feb. 12, 2009) the long-range National Weather Service forecast for this summer is not very helpful, giving an equal chance of above- or below-normal precipitation and air temperature for June, July and August in Kentucky. No one knows for sure what the weather will do this summer, but if it turns out to be a bad year we shouldn’t blame it on global warming.