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Interviewee: David Battisti, University of Washington
The report shows that by 2100, rising temperatures will have a significant impact upon crop yields, most noticeably in the tropics and sub tropics. David Battisti, professor of atmospheric sciences at the University of Washington says, “You’re talking about very large reductions in yields, on the order of 20, 30, 40 percent.”
Battisti says that in those most affected areas, “The odds are greater than 90 percent that they (temperatures) will exceed anything ever observed.”
He and Rosamond L. Naylor, associate professor of economics at Stanford University, used projections by the Intergovernmental Panel on Climate Change (IPCC) . Those projections earned IPCC a share of the Nobel Prize along with former Vice-President Al Gore.
The researchers used the IPCC computer models to show climate change for the rest of this century and broke the projected temperatures down to averages for each season in various parts of the world. Since average summers can be either hotter or cooler than usual, the seasonal averages form a bell-like curve, with normal years forming the bulk of the center curve and cold and warm years at either end. The researchers took the projected seasonal averages and moved the middle of that curve accordingly. In the tropics, where the averages don’t change much, the researchers found that the low end of the new curve was higher than the high end of the current curve.
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Climates in the higher latitudes also show dramatic change. In their report, published in the journal, “Science,” Battisti and Naylor describe changes in temperatures in France. “The warmest on record to date so far, the odds are 50-50 basically that that’s going to be the (average) temperature in the summer at the end of the century.” That’s significant because the warmest summer on record was in 2003, when anywhere from 30,000 to 50,000 deaths in Europe were blamed on the heat.
Too much of a good thing
While warm weather at the right time can kick start growth, a hotter than average summer for the entire season is not good for plants. In their report the researchers noted that during that same 2003 European heat wave, “Italy experienced a record drop in maize yields of 36% from a year earlier, whereas in France maize and fodder production fell by 30%, fruit harvests declined by 25% and wheat harvests…declined by 21%.” Maize is any of several varieties of corn.
Other studies have looked at the impact of a warmer climate on key crops. One study found that increased average night temperatures will adversely impact rice crops.
However, it is in the developing countries that Battisti sees the greatest urgency for finding a solution. He says that in those areas by the end of the century, “You should expect large reductions in yields.” What’s worse, he points out that these areas “already need food today,” with a billion malnourished people. Battisti says the area’s economy is also a problem, noting, “There’s not many options in this case in terms of changing what you grow or investing in new technologies because these places are relatively poor today.”
The authors say that among the solutions that need to be explored are finding varieties of today’s crops that will withstand future growing conditions.
Of the climate itself, Battisti says, "In a sense you can say that the climate of the end of this century is really out of bounds from any experiences to date."
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