How climate change is affecting agriculture with Dr. Jennifer Wells

Impacts of Climate Change
Now that agricultural companies, including Truterra, have entered the carbon credit marketplace, farmers have found themselves in the spotlight of carbon sequestration and climate change. The topic of climate change is often controversial, so instead of debating the legitimacy of climate change, let’s proceed with some facts regarding weather patterns from the EPA.¹

• US and global temperatures are increasing - Average temperatures have risen across the contiguous 48 states since 1901, with a higher increase over the past 30 years. Eight of the United States top 10 warmest years on record have occurred since 1998. Global temperatures have followed the same trend and all of the global top 10 warmest years on record have occurred since 2005.
• Seasonal temperatures - As the earth warms overall, average temperatures increase throughout the year, but the increases may be larger in certain seasons than in others. Since 1896, average winter temperatures across the contiguous 48 states have increased by nearly 3°F. Spring temperatures have increased by about 2°F, while summer and fall temperatures have increased by 1.4°F.
• High and low temperatures - Since the 1970s, unusually hot summer days have become more common in the past 20 in the United States when compared to the years before. Unusually hot summer nights have become more common at an even faster rate. The United States has experienced many winters with unusually low temperatures, unusually cold winter temperatures have become less common—particularly very cold nights (lows). Record-setting daily high temperatures have become more common than record lows. 
• Heat waves - A series of unusually hot days is referred to as a heat wave. Heat waves are occurring more than they used to in major cities across the United States. Heat waves are occurring three times more often than they did in the 1960s—about six per year as compared to two per year. Also, in recent years, the average heat wave in major U.S. urban areas has been about four days long. This is about a day longer than the average heat wave in the 1960s.
• Heavy precipitation - In recent years, a higher percentage of precipitation in the United States has come from intense single-day events. The number of extreme single-day precipitation events remained fairly steady between 1910 and the 1980s but has risen substantially since then. Nationwide, nine of the top 10 years for extreme one-day precipitation events have occurred since 1996.
• Tropical cyclone activity- Tropical storm activity in the Atlantic Ocean, the Caribbean, and the Gulf of Mexico has increased during the past 20 years. Storm intensity, duration, and frequency is closely related to variations in sea surface temperature, and the tropical Atlantic soil surface temp has risen significantly during that time.
• River flooding - Increases and decreases in the frequency and magnitude of river flood events vary by region. Floods have generally become larger across parts of the Northeast and Midwest and smaller in the West, southern Appalachia, and northern Michigan. Large floods have become more frequent across the Northeast, Pacific Northwest, and parts of the northern Great Plains, and less frequent in the Southwest and the Rockies.

 
How does this affect agriculture?
US agriculture exists in a complex space of trying to grow more yield with less land and inputs, all while trying to navigate ecosystem services and climate change. The increase in atmospheric carbon, rising temperatures, changes in precipitation patterns and dioxide will affect agricultural productivity in both positive and negative ways.
 
Increased CO₂ in the atmosphere – Since CO₂ stimulates photosynthesis and plant growth, increased CO₂ levels can have a positive effect on yield. In fact, yields of wheat, rice, and soybeans under field conditions increased approximately 12% to 15% under 550 ppm compared with 370 ppm CO₂ concentrations.² Increased CO₂ concentrations have also shown to reduce the effects of environmental stress in plants. Some scientists think the increase in CO₂ levels in the past several years has contributed greatly to increase in yields, which have been largely credited to genetic gain. However, while the interaction between increasing CO₂ levels and crop yield is positive, it also has the same effect on weeds. The increase in growth of weeds can change the weed/crop competition dynamic. Faster growing weeds are often harder to kill, which can cause significant yield loss. In addition, a change in weed growth and infestation can contribute greatly to an increase in insects and other pathogens which would result in additional yield loss.²
 
Air temperatures – As the air temperatures continue to increase gradually over time, more frequent extreme high and low temperatures and extended heat waves, agricultural yields will inevitably be negatively impacted.  Each plant species (and hybrids and varieties within species) has an upper and lower boundary for growth and reproduction. As temperatures continue to increase over time, the temperatures could shift to where the current species grown is no longer a viable option for profitability in certain areas. The increasing extreme high temperatures, both day and night, can also be detrimental to plant growth. Extreme high temperatures or heat waves during the pollination period can cause significant yield loss and possible crop failure. High nighttime temperatures during grain, fiber or fruit production can also lower yield and overall quality. And finally, higher temperatures can cause faster growth and development, which result in smaller plants and lower yields.
 
Water – Climate change affects water thru heavy precipitation events, increased hurricane activity and flooding. All of these have a negative effect on yield, and often cause a total crop failure. While yield loss is evident with drought, excess precipitation can be just as damaging. A heavy precipitation event can cause flooding, erosion, and decreased soil quality, all of which can lead to yield loss or crop failure. If the heavy rainfall event is soon after planting, it could also cause a grower to replant the field, which can be very costly. Examples of increased hurricane and flooding activity have recently made the news with Hurricane Ida’s devastation in Louisiana which caused flooding in other states as well. One of the hardest hit areas was middle Tennessee, which was just one week out from a devastating flood which left at least 22 dead and thousands of acres underwater.³
 
Conclusion – Climate change affects agriculture directly through the immediate effects of temperature, precipitation, and CO₂. It can also cause indirect detrimental effect through crop species shift, increased weeds, insects, and disease. While the goal is to minimize climate change through programs like the Science Based Target Initiative and ecosystem services, it is likely that climate change will continue. Farmers will need to be nimble and adapt to changing environments, and like everything else, those that stay educated and up to date on the changing science will fare the best.


Sources

¹Climate Change Indicators: Weather and Climate | US EPA
²CC and Agriculture Report (02-04-2013)b.pdf (usda.gov)
³22 dead, many missing after 17 inches of rain in Tennessee (apnews.com)