Climate change already affecting crops

Peter Goldmark in the Guelph Mercury via Newsday: An article in the new issue of Science magazine will sound an alarm bell around the world — if we're alert enough to hear it. It's by David Lobell, an assistant professor of environmental science at Stanford University, and two co-researchers, and it presents strong evidence that global warming has already negatively affected yields for wheat and corn over the last three decades.

The world's ability to produce enough food is central to our prospects for economic stability, peace and some modicum of fairness. Many factors affect crop yields, among them quality of seed stock, efficient use of fertilizer and pesticides, and frequency of storms and other natural disturbances. The significance of this article is that looking across a period long enough to produce meaningful statistics, the authors maintain that the yield for wheat and corn has dropped below what statistical models suggest it would have been had there not been a measurable increase in temperature over that period.

Yes, there's that dreaded word “model” creeping in here. “Model” conjures up pictures of computers performing incomprehensible calculations that no layperson can understand. But Lobell and his team employed widely used statistical techniques to hold constant the other forces that affect crop yield, and then used historical records to construct a 30-year path with no temperature increase. They compared that with actual crop yields and found that the real-world results were indeed lower — about 3.8 per cent lower for corn and 5.5 per cent for wheat. If this trend is confirmed and continues, that means one of the most feared potential effects of global warming has started to make itself felt: the food squeeze.

The theory of global warming predicts that the greatest temperature rises should occur at higher latitudes, both north and south. That's precisely the pattern shown in the crop yield losses: The country suffering the greatest loss was Russia, which grows its wheat at higher latitudes than most other countries. France, which is fairly far north, also showed significant loss. The United States, which grows its corn and wheat at latitudes farther south, showed almost no change at all.

The absolute amounts of grain tonnage lost are still relatively small, and their effect in annual harvest figures is completely masked by year-to-year variations due to drought, flooding, storms and other natural variations. But over decade-long periods, the trend is visible….

A Boise Valley wheat field around 1920