Even though the odds of a major production slowdown in wheat and corn amid global warming aren't very high, Stanford University and the National Center for Atmospheric Research scientists say the risk is about 20 times more significant than it would be without global warming.
This higher risk may require planning by organizations that are affected by international food availability and price, they say.
"I'm often asked whether climate change will threaten food supply, as if it's a simple yes or no answer," Stanford professor David Lobell said. "The truth is that over a 10- or 20-year period, it depends largely on how fast the Earth warms, and we can't predict the pace of warming very precisely. So the best we can do is try to determine the odds."
Effects of global climate
Lobell and Claudia Tebaldi, NCAR researcher, used computer models of global climate, as well as data about weather and crops, to calculate the chances that climatic trends would have a negative effect of 10% on yields in the next 20 years. According to the research, this would have a major impact on food supply.
Yields would continue to increase, but the slowdown would effectively cut the projected rate of increase by about half at the same time that demand is projected to grow sharply.
The researchers also found that the likelihood of natural climate shifts causing such a slowdown over the next 20 years is only 1 in 200. But when human-induced global warming is factored in, the odds jumped to 1 in 10 for corn and 1 in 20 for wheat.
'Be aware of the risk'
Global yields of crops such as corn and wheat have typically increased by about 1% to 2% per year in recent decades, and the U.N. Food and Agriculture Organization projects that global production of major crops will increase by 13% per decade through 2030—likely the fastest rate of increase during the coming century.
Global demand for crops, however, is also expected to rise rapidly during the next two decades because of population growth, greater per-capita food consumption, and increasing use of biofuels.
Lobell and Tebaldi set out to estimate the odds that climate change could interfere with the ability of crop producers to keep up with demand. Whereas other climate research had looked at the crop impacts that were most likely, Lobell and Tebaldi decided to focus on the less likely but potentially more dangerous scenario that climate change would reduce yield growth by 10% or more.
The researchers used simulations available from an NCAR-based climate model, as well as several other models, to provide trends in temperature and precipitation over the next two decades for crop-intensive regions under a scenario of increasing carbon dioxide. They also used the same model simulations without human-caused increases in carbon dioxide to assess the same trends in a natural climate.
In addition, they ran statistical analyses to estimate the impacts of changes in temperature and precipitation on wheat and corn yields in various regions of the globe and during specific times of the year that coincide with the most important times of the growing seasons for those two crops.
The authors quantified the extent to which warming temperatures would correlate with reduced yields. For example, an increase of 1.8 degrees Fahrenheit would slow corn yields by 7% and wheat yields by 6%.
Depending on the crop-growing region, the odds of such a temperature increase in the next 20 years were about 30% to 40% in simulations that included increases in carbon dioxide. In contrast, such temperature increases had a much lower chance of occurring in stimulations that included only natural variability, not human-induced climate change.
Although society could offset the climate impacts by planting wheat and corn in cooler regions, such planting shifts to date have not occurred quickly enough to offset warmer temperatures, the study warned. The authors also found little evidence that other adaptation strategies, such as changes in crop varieties or growing practices would totally offset the impact of warming temperatures.
"Although further study may prove otherwise, we do not anticipate adaptation being fast enough to significantly alter the near-term risks estimated in this paper," they wrote.
"We can't predict whether a major slowdown in crop growth will actually happen, and the odds are still fairly low," said Tebaldi. "But climate change has increased the odds to the point that organizations concerned with food security or global stability need to be aware of this risk."
The study was funded by the National Science Foundation and the U.S. Department of Energy.