NANJING, JIANGSU, CHINA — In view of expectations that global food production will have to meet a 60% increase in demand by the middle of the 21st century, a group of scientists designed a study to examine changes in crop yields likely to take place as a result of increases in temperatures that may take place as a result of climate change.
Results of the scientists’ efforts, “Similar estimates of temperature impacts on global wheat yield by three independent methods” published on-line Sept. 12 in Nature Climate Change, indicated that three independent methods of inquiry used in the study came up with similar estimates of the effects of warming temperatures on global yields of wheat.
The three methodologies used in the study included grid-based simulations, point-based simulations compared for 97 countries and statistical regressions. What these differing ways of collecting data show, study authors said, is that “average reductions in global wheat yields with 1 degree Centigrade global temperature increase estimated from grid-based simulations, point-based simulations, and statistical regression at global level were all between 4.1% and 6.4%. The average estimated temperature impact from all three methods (and four studies) was a 5.7% reduction in global yield per degree of global temperature increase.”
In addition, past studies using similar methods reported an average of 5.9% wheat yield decrease with 1 degree Centigrade warming.
Study authors said more detailed examinations were made for the top five wheat-producing countries, the United States, China, India, Russia and France, “resulting in similar values for temperature impacts on country wheat yields.”
For the United States, scientists examined a recent study using data from wheat variety trials from 1985 to 2013 in Kansas that reported a 7.3% decrease in wheat yield (corrected for global temperature change) with 1 degree Centigrade global temperature increase.
“This result is similar to the other estimated temperature impacts on wheat yields for the U.S.,” the study said.
“With the different temperature impact methods used, despite some variation, there is a general similarity in the magnitude of negative effects of increasing temperature on wheat yields for major wheat-producing countries,” the study said, noting that the five largest wheat-producing countries represent more than 50% of total global wheat production.
Study authors noted that higher yield reductions were observed in locations with higher baseline temperatures, even if the temperature change remained no more than 1 degree centigrade, than locations with lower baseline temperatures.
“For example, at Aswan in Egypt, point-based and grid-based simulations showed about 11% and 20% decline in yield with 1 degree Centigrade temperature increase, while for Krasnodar in Russia, point-based and grid-based simulations estimated about 4% and 7% yield decline with 1 degree Centigrade global increase,” study authors said.
Effects of temperature on wheat yields were consistent with reports of impacts on other crops, such as maize, soybeans and cotton.
“An increase in extreme temperature events with increasing mean temperatures is likely to further contribute to yield decline in wheat,” the study said.
The different means of studying the effects of rising global temperatures and crop yields were discussed in detail in the published report.
“The first study divided the globe into geographical grid cells defined by latitude and longitude and used climate and crop management data integrated over each grid as input for seven crop models,” said the study authors, adding that this grid-based system was used to estimate yield changes for other crops, such as rice, corn, wheat and soybeans.
Also used were data from 30 different field sites deemed to be representative of two-thirds of worldwide wheat-producing areas. In this point-based approach estimates from sentinel sites were scaled up and extrapolated to cover geographical areas with similar conditions, study authors added.
Statistical regressions, utilized in the research done to assess impacts of higher temperatures on global wheat yields, also have been used to quantify impacts of rising temperatures on wheat, corn, barley, soybean sorghum and rice yields.
The article said, “statistical models do not directly consider processes inherent to crop growth. However, statistical models may include indirect effects of climatic variability, such as those related to pests and diseases, which are not well captured by simulation models.”
Evidence has indicated that the use of several modes of investigation in an ensemble approach is more consistently accurate when comparing measurements taken from different parts of the world, which the study authors said increases confidence in the measurements offered in their research.
But they cautioned against applying global yield impacts from rising temperatures to local and regional scales. They also said results may be altered by farmers’ own adaptation to climate changes through changing planting dates or cultivars.
In conclusion, the scientists emphasized the importance of assessing climate change impacts on crop production in order to meet global food security challenges ahead. This inquiry needs “an integrated use of climate, crop and economic models,” they added.
“The consistent negative impact from increasing temperatures confirmed by three independent methods” requires further investment in climate change adaptation strategies to combat adverse effects on global wheat production, including genetic improvements and management adjustments, the study authors said.
But they also suggested these negative impacts on wheat yields “might be compensated by increasing atmospheric C02 concentrations under full irrigation and fertilization.”
