Effects of Climate Change

The Effects of Climate Change on Corn Yield

"It's like farming in Hell"

Climate change has been a hotly debated topic for years, and regardless of the cause, the world is growing steadily warmer.  The 2012 heat waves experienced this year, with some areas of the Midwestern U.S. reaching triple digit temperatures for record days in a row, has had a crippling effect on corn yields.  “You couldn’t choreograph worse weather conditions for pollination,” Fred Below, a crop biologist at the University of Illinois at Urbana-Champaign, told Bloomberg News recently. “It’s like farming in Hell" (5).  

Increasing Temperatures

The latest forecasts now show that for each one degree increase in global temperature, expected impacts include (3):

• 5% to 15% reductions in the yields of crops as currently grown, 
• 5% to 10% changes in precipitation across many regions,
•  3% to 10% increases in the amount of rain falling during the heaviest precipitation events,
• 5% to 10% changes in stream flow across many river basins,
• 200% to 400% increases in the areas burned by wildfire in parts of the western United States.

Crop yield change (%) against global temperature change per degree Celsius. (3)

Increased annual average temperatures, especially an increase in temperatures during spring and summer months, is especially detrimental to corn production due to the change in soil moisture content, pollen viability, and speed the development of corn.  In areas of most production in the United States, corn grows best in years with cooler than normal temperatures.  Corn grows best within certain "heat units," usually around 10 degrees Celsius, so any temperatures that fall above or below the unit range will prevent the corn from maturing (2).  This further amplifies the effects of climate warming on corn as the optimal thermal range of the plant is already within cooler temperatures than we are currently experiencing.  The plant is not adapted to warmer climates, causing the yield to reduce (3).  Models have also shown that corn yield is reduced in most areas with drier soil conditions, sometimes reducing the yield to only half of the field capacity (14).  

Projected changes in Midwestern states' climates based on emission scenarios.  By the end of the century, Illinois and Michigan could potentially have climates similar to the current climates experienced in Texas.  This will ultimately decrease corn production in those states as it will be too hot for corn to grow (15).

Regions where corn is currently grown will experience dramatic climate changes, primarily increased temperatures and different precipitation patterns.  One effect of climate change is that areas of corn production will have to relocate to northern latitudes where temperatures will be optimal for corn growth.  

Mean annual temperature (degrees C) and average corn yield (billion bushels).  Kernahan original figure.

Corn yield as a function of temperature.  Corn production may increase slightly with increased temperatures, but ultimately will drop significantly when temperatures exceed corn's thermal optimum (8).

Changes in Precipitation Patterns - Droughts During Summer Months

While increased temperatures during growing seasons are a main concern, so are changes in precipitation patterns.  Droughts during summer months are becoming more frequent and more intense, causing a decline in corn and other crop production.  Precipitation events will be more intense during winter months, and fewer during summer months, which will be especially detrimental to crop production (11).  In 2012, crop production decreased by 58% compared to 2011 due to intense droughts throughout the Midwest region in the United States (5).  The plants are not receiving enough water to grow properly, changing the soil moisture content and ability of the plant to absorb water needed for photosynthesis.  These droughts are only going to increase in severity and frequency with climate change and increasing temperatures.  Precipitation during summer months are expected to decline 5-22% depending on location under higher emissions (15).

Projected summer temperatures warmer than warmest on records - indicates dramatic increase in growing season temperatures (7).

Changes in Precipitation Patterns - Flooding During Winter Months

Changes in winter precipitation patterns will also have an effect on corn production.  The soil quality and moisture content will change with intense precipitation events before the growing season, also adding to crop depletion (13).  Flooding due to heavier precipitation patterns before growing season can alter the soil moisture content to an extent that it contributes to a $1.5 billion loss in crop production annually (13).  Based on models, heavy precipitation events will increase by 30% in 2030, and by 65% in 2090, meaning that by 2030 crop production in the United States could be cut in half (13).  

Simulated and reported corn losses due to change in soil moisture content in Iowa (13).

Annual and seasonal precipitation changes for corn-growing states based on lower and higher emission scenarios.  Winter and spring precipitation events are heavier and more frequent, whereas summer precipitation events are fewer (15).

Though heavy precipitation events would not directly kill corn crops as it is not during the growing season, the change in the soil moisture content will make it even harder to grow crops in the summer.  Furthermore, flooding can also cause bacteria to build in the soil, spreading disease or allowing for invasive species to take up residence in the new areas.  This will ultimately have a detrimental effect on corn production during the summer months (16).