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Food is on many people's minds—especially around the holidays. But what if global warming were threatening our food supply? As this ScienCentral News video reports, temperature may have a much larger impact on crop yields than previously thought.
Crop Forecast
As many of us sit down to holiday feasts, we also remember that many others go hungry. Now scientists at the Carnegie Institution of Washington say that global warming may have more effect on our nation's— and possibly the world's— production of food crops than previously thought.
"This study shows that increasing temperatures cause a decrease in yield," says Greg Asner, a faculty member in the department of global ecology at the Carnegie Institution of Washington. "We can expect from these results that with the prospect of global warming, the United States and other regions of the world would see decreasing yields as well."
Asner and David Lobell, a research fellow at the Institution and a doctoral student at Stanford University, compared data about crop yields and weather in the United States between 1982 and 1998. The study, the first of its kind, used crop data from the U.S. Department of Agriculture's National Agricultural Statistics Service and weather data reported by the NOAA-CIRES Climate Diagnostics Center. As Lobell and Asner reported in the journal Science, just a 2 °F increase in temperature decreased the amount of corn or soybeans produced by as much as 17 percent, while areas that cooled had increases in yields.
In the top map, areas that cooled between 1982 and 1998 are shown in blue and areas that warmed are in red. In the bottom map, areas with large increases in corn production are shown in red and areas with decreases are shown in black. Generally, crop yields increased in areas where cooling occurred, while in areas that warmed, crop yields increased only slightly or decreased.
"It was quite obvious once we looked at the data," Lobell says. "Believe it or not, nobody had ever looked at these two datasets together, but there are very clear patterns that we see where there are parts of the country that had been cooling and parts of the country that had been warming over the last 20 years and there are very distinct differences in the yield trends in these different regions."
With more warming in the forecast, could losses in crop production ultimately overwhelm gains? "Crop yields are increasing pretty much across the board," Lobell says. "The question is how much are they increasing due to technology advances and how much are they increasing due to fortuitous climate, for example."
Farmers do have options for managing their crops that could counteract the effect of temperature increases. "In terms of managing the effects of global warming, farmers have a limited set of tools at their disposal," explains Asner. "They range from changes in planting dates and crop management and rotation to management of water and nutrients as well. The limitations of management, we still don't know. It's so speculative." Lobell adds that "changing the type of crop that you plant" is another option. But, he adds, "The degree to which these are able to offset the reductions due to climate change is really not well known right now."
The researchers say more studies like this one could eventually lead to much more information about crop yields not only in the United States, but on a global scale as well. "We benefit from the fact that the United States has a very good reporting system for crop yields at the county level," Asner explains. "The rest of the world does not have this kind of information, so we have been using the information put together in this study to help us to develop satellite methods for estimating crop yields worldwide. It's really our only opportunity to do so geographically because many countries do not have the reporting of their crop yields that the United States has."
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