Drought, extreme rainfall and flooding, hurricanes/wind damage, severe freezes, and heat stress cause significant damage to farming operations, says David F. Zierden, Florida State Center for Ocean Atmospheric Prediction Studies climatologist. Zierden discussed climate trends and variability concerning the 2020 peanut crop, during a recent online USA Peanut Congress.
"One of the prevailing trends we've seen across the globe is the increase of carbon dioxide concentration in our atmosphere since around 1954," Zierden said. "We see an exponential increase in CO2 concentrations. We're now up over 415 parts per million carbon dioxide concentration. This is what industrialization and the burning of fossil fuels have done to change our atmosphere over time."
A graph with global average temperatures since 1880 shows a very steady increase in global average temperature since about 1900, at the dawn of the industrial age.
"What is even more alarming is each of the last five years has been the five warmest on record since this data was compiled," he said. "In 2019, the global average temperature was the second warmest on record, only behind 2016. Now, 2020 is on pace to break the 2016 record."
As greenhouse gases are added to the atmosphere, the global climate has responded by getting warmer.
"Looking at Florida temperatures, 57 out of the last 60 months have been warmer than average, including the last 22 months in a row," Zierden said. "This also includes seven months of record warm temperatures, and overnight temperatures are the most affected."
A graph showing the statewide average temperatures depicts a shift of nearly 2 degrees Fahrenheit in Florida's average temperatures over the last five years.
"This isn't just confined to Florida," he said. "If we look at the five-year average temperatures for the United States, it shows across the entire Southeast the last five years have been by far the warmest period on record since 1895."
Nighttime temperatures are affected more than the daytime highs.
"In 2017, peanut yields across north Florida were drastically reduced in some fields up to 30% to 40% less than expected, and we had plenty of rainfall that year," Zierden said. "Scientists and Extension experts were struggling to find out why there were such decreased yields. There was an increase in the overnight temperatures across north Florida in June, July, and August, so I believe it affected the physiology of the peanut plants for the soil temperatures to remain elevated overnight. I'm sure this is not the whole story, but it could be part of the story."
Another effect from increasing temperatures across the Southeast is winter temperatures have not been as cold in the past eight to 10 years.
"Warmer winters mean fewer days of freezing temperatures and fewer severe freezes, so pest and disease are surviving and overwintering better than they have before," he said.
Trends in rainfall
Also, we see a year to year variability in rainfall. It is harder to discern any long-term trends.
"2019 was certainly a wet year, especially the upper Midwest," Zierden said. "The United States had its wettest year on record. It was an exceptional year but not necessarily part of a long-term trend. What can we say about trends in precipitation?"
Data show year-to-year rainfall variability with some years more or less rain, but no noticeable changes in the amount of precipitation over time. However, the amount of heavy precipitation events, or excessive rainfall at one time, across the Southeast has increased.
"How do growers and producers cope with this increased frequency of extreme rainfall events? Some farmers I know have planted a high residue cover crop for the last 10 years during the winter," he said. "When it comes springtime, they terminate the cover crop, and then do strip or conservation tilling right into the heavy batch of mulch. The benefits are overwhelming, but the mulch helps during heavy rain events. It also helps keep soil temperatures down, organic matter in the soil, as well as a myriad of benefits in addition to making it more climate-resilient."
2020 peanut crop
Current sea surface temperatures of the last week confirm the likelihood of an active hurricane season, Zierden said.
"Coldwater has broken through to the surface in the Pacific Ocean as illustrated by the NOAA model, which predicts La Niña conditions," he said. "La Niña, which is a colder ocean-atmosphere, has not much influence in summer months but would lead to dryness in the fall and winter. What does this mean for us? This is the official seasonal forecast from NOAA's Climate Prediction Center. Because of the prevailing trends, most of the United States is forecasted for an increased chance of above-normal temperatures, based on the overall trend of rising temperatures across the U.S."
There is a 60% chance of it being a more active hurricane season this year, a 30% chance of near normal, and only a 10% chance of a less active season than usual.
"The precipitation forecast for the next three months favors above-normal precipitation for most of the southeastern United States," he said. "This could be good news for the growing season to help water the growing peanut crop."