Climate Change Projected To Have Significant Effect on Agriculture
If climate change occurs as projected, it could have a significant effect on agricultural producers, said Jerry Hatfield, director of the USDA-ARS National Soil Tilth Lab in Ames, Iowa. Hatfield spoke at the 2008 K-State Research and Extension Annual Conference in Manhattan, Kansas.
The biggest effect that climate change will have is the increased variability and uncertainty of weather events, especially precipitation, Hatfield said. This will make it difficult for producers to adapt to climate change.
“The increase in precipitation variability within the seasons is among the most important factors about climate change for agricultural producers,” he said.
In the big picture, climate change will result in the movement of entire agricultural growing zones. Wheat, corn, and soybean production, for example, will move northward. This has already happened in the Indian sub-continent, he said. As another example, corn and soybean production has expanded recently in South Dakota.
The effect of warmer temperatures on crop production is complex, Hatfield explained. “The warmer it is, the faster plants grow during the vegetative and reproductive stages. But this does not mean they will be more productive. The critical factor is how warmer temperatures will affect pollination,” he said.
Every crop has an ideal temperature range for pollination. And every crop also has a critical temperature above which pollination failure occurs. For corn, the “failure temperature” is 95 degrees Fahrenheit (F). For soybeans, it is 102 degrees F.
“As the climate gets warmer, there is a greater chance that temperatures will be too high during the critical reproductive periods of crops. This means a greater chance of crop failures,” Hatfield said. The reproductive period also tends to get shortened at higher temperatures.
One of the projections about climate change during the next 100 years is that nighttime temperatures will increase even more than daytime temperatures. These higher nighttime temperatures will also adversely affect crops, he added. When temperatures are too warm at night, respiration continues at a higher rate and less energy is available for grain development.
Overall in the U.S., higher temperatures during this century are projected to decrease corn yield by about 4 percent; wheat yields by 6.7 percent; sorghum yields by 9.9 percent; cotton yields by 5.7 percent, and rice yields by 12.0 percent. Soybean yields in the Midwest are projected to increase by 2.5 percent (the pollination failure temperature for soybeans is high enough that it won’t be reached more often than normal in the more northern latitudes), but soybean yields in the South are projected to decrease by 3.5 percent.
The development of forages will be hastened by warmer temperatures, and the growing season will be lengthened, he added. This will have a negative impact on forage quality and protein content.
Fruit and nut crops will begin flowering earlier in the growing season, making them more susceptible to late spring freeze injury.
Overall, increasing temperatures will expose all plants to more extreme conditions and will potentially limit the reproductive periods of plants growing at their current locations. Increasing temperature will require a change in planting dates or tolerant varieties to avoid exposure to high temperatures, he said.
Climate change will also mean higher CO2 levels and more variable precipitation patterns, Hatfield noted. Precipitation events are projected to be less frequent, but more intense. The patterns of precipitation distribution will be changing.
The effect of higher CO2 levels is complicated, he said. If all other factors remain the same, higher CO2 levels would have a positive impact on crop yields, Hatfield said. But along with higher CO2 levels come higher temperatures and more variable precipitation patterns.
Because of higher temperatures and more variable precipitation, soil water availability will be reduced, and the negative impact of this on crop yields will more than offset the positive effect of higher CO2 levels, he explained.
In addition, the impacts of drought in the future will probably be increased due to climate change. More areas subject to prolonged drought are projected worldwide during this century.
“Water availability and higher temperatures during pollination are projected to be among the primary limitations to plant growth and crop yields in the future,” he said.
It will be even more important in the future that soils have high organic matter levels, which will provide more resiliency for coping with climate variability and periods of moisture deficits, he concluded. Reducing evaporation rates from the soil will also be important.
“Producers should increase the water-holding capacity of their soils to the extent possible,” he said. “Increasing water supply to the crop throughout the growing season will be critical to long-term efficient production.”
Ironically, weeds may thrive under the projected climate change conditions. Higher CO2 levels and higher temperatures will increase the growth of many weeds, Hatfield said.
Climate change will also affect livestock production, Hatfield said. All animals, including humans, have an optimum range of temperatures at which they are most comfortable. With cattle, when temperatures are too warm, their appetite is reduced and their rate of weight gain is reduced. Milk production and conception rates can also be reduced.
Hatfield’s entire presentation at the 2008 K-State Research and Extension Annual Conference can be found at:
-- Steve Watson, CASMGS Communications