Leopold Center for Sustainable Agriculture

How climate change already affects farming

Back to Leopold Letter Spring 2011

 Iowa farmers already are dealing with the effects of climate change, and they’ll need to do even more in the future to adapt to more extreme weather events.

That was the take-home message from Gene Takle, one of the nation’s leading climate scientists and director of Iowa State University’s Climate Science Program team. Takle spoke February 6 at the annual Shivvers Lecture coordinated by the Leopold Center. A modest but engaged audience gathered in Ames for his presentation, “Will Climate Change Impact the Sustainability of Iowa Farms?”

“Sustaining agricultural production without depleting our natural resources will be increasingly difficult in the future given changes in our climate,” Takle said. “Farmers already are adapting to climate change. The question is whether they’ll be able to continue to adapt as more changes occur.”

Takle was a member of the Iowa Climate Change Impacts Committee that recently submitted its report to the Iowa Legislature. The group found that Iowa farmers have been adapting to climate change in these ways:

  • Longer growing season: Plant earlier, longer season hybrids and harvest later.
  • Wetter springs: Larger machinery enables planting in small weather windows.
  • More summer precipitation: Higher planting densities for higher yields.
  • Wetter springs and summers: More subsurface drainage tile is being installed; even sloped surfaces are being tiled to take care of excess water.
  • Fewer extreme heat events: Higher planting densities with fewer pollination failures.
  • Higher humidity: More spraying for pathogens, which are favored by moist conditions; more problems with fall crop dry-down; wide bean heads for faster harvest due to shorter harvest period during daylight hours.
  • Drier autumns: Delay harvest to take advantage of natural dry-down conditions.

The report indicated that more intense rain events have led to soil erosion and affected water quality through loss of nitrate fertilizer, sediment and runoff from manure application. Waterlogged soil in spring leads to shallow root systems that are prone to disease, nutrient deficiencies and drought later in the season.

He explained that natural processes and cycles affect these changes in climate, such as variations in the Earth’s orbit, fluctuations in solar energy and gases released by volcanic eruptions. However, climate models show that natural processes cannot account for abrupt warming trends observed since 1965. Only when the influences of greenhouse gases and sulfate aerosols are included can the trends be explained.

Among the many examples from the lecture is the fact that global temperatures in 2010 and 2005 are tied as the warmest years on record since 1880. Eighteen different climate models predict a global temperature increase of 1.5 to 6.5° F within the next 100 years.

When looking at precipitation, fewer records are available and precipitation is difficult to simulate. However, 2010 stands out because it had the highest global total precipitation in 111 years of recorded data.

One of the expected results of climate change is that extreme weather events will become more common. Heat waves will be longer and more severe, droughts will be more frequent and severe, there will likely be an increase in severe thunderstorms (and perhaps in tornadoes), and the winter storm tracks are shifting so that the strongest storms are likely to become stronger and more frequent.

In the United States, climate models indicate that the West will become dryer while the Southeast will become wetter. “Iowa sits pretty close to the gradient between these regions, which suggests we’ll have a lot of year-to-year variability in precipitation,” Takle said.

To illustrate his points, Takle discussed Iowa’s experience with flooding in 1993, 2008 and 2010 and reviewed weather records in Des Moines and Cedar Rapids. Iowa has experienced more frost-free days and fewer days that are very cold (-10° F) or very hot (over 100° F).

Because solar energy is expended to evaporate moisture from wet soils, less energy is available to heat air. In Iowa, that effect has kept summer temperatures from exceeding 100° F in recent years, Takle explained. “Our higher than normal precipitation is masking a warming that has been going on in Iowa,” he said.

The Shivvers lecture has been presented at ISU since 1969 in memory of John Shivvers, who farmed near Knoxville. The lectures focus on ways that agriculture can sustain rather than destroy natural resources.

Back to Leopold Letter Spring 2011