LESSON 2b: CLIMATE EFFECTS ON CROPS

GLOBAL TEMPERATURE CYCLE

The most important factor affecting crop weather seems to be global temperature change or is associated with episodes of global warming and global cooling. Figure 2.16 shows the global temperatures as best we know them. From 1880 to 1940, most people would say, was a global warming trend. From 1940 through about 1972, the warming trend stopped and was perhaps a period of global cooling. After 1972 the global warming trend resumed. You can form your own opinion on that as you look at the data, but warming, cooling, and warming again would be the assessment that I would make, and most people who look at these trends would come to a similar conclusion. This will be discussed in more detail later in the course.

Fig. 2.16 Global average temperature trend (1880-1990).

The global temperature change is the most important weather influence of variability for the simple reason that the El Niño effect during the time of global cooling was not detectable in the Midwest. We could not detect the effects of the El Niño or the effects of the post-El Niño, sometimes called La Niña or anti-El Niño, between 1940 and 1972. The effects of the El Niño-La Niña seemed confined to Peru and Australia, but during the time of global warming, the effect can be measured in the Midwest. In other words, we have greater variability of weather during times of global warming than during times of global cooling.