Midwest Climate Change Introduces A New Hardiness Map and Challenges For Local Growers

For Kansas City metro area gardeners, the latest USDA plant hardiness map revealed some surprises–many growers have watched their land warm over the last decade, pushing them from zone 6a to 6b. While the hardiness map primarily highlights the extremities of the temperature spectrum, they are a canary for what many already know–the climate is changing, and so are the plants that may thrive here. 

While many may welcome more southerly varietals, the shift has more significant implications. Eugene S. Takle, Ph.D., professor emeritus of agricultural meteorology in the Department of Agronomy at Iowa State University, has been researching the farther-reaching effects of climate change. 

Takle says that while extreme temperatures are one part of agricultural success, humidity levels, freeze-thaw cycles, and wind speeds also have a significant impact. Over the last few months, he and his team of researchers have been digging into comprehensive data that reveals how the warming climate impacts an area that the nation relies upon for consistent food and power. 

Longer Growing Season

Takle says that not only are the lows not as extreme, but the growing season has lengthened by 10 to 14 days over the last 30 years. 

“That extended growing season is extremely consequential to agriculture,” Takle says. “Farmers are adapting and planting longer season hybrids and getting better yields.” 

But it’s not all good news–the warmer, longer growing season has more pest and pathogen issues. Some insects have longer lifecycles or more life cycles because they have longer periods of favorable temperatures and less severe freezing periods. 

More Humid Weather

If you feel like summers are more humid now, you’re not imagining things. Takle says that humidity has increased, and with it, fungus, mold, and more extreme weather like thunderstorms, torrential rains, and tornadoes. 

“It’s to the point where it’s affecting farmers’ ability to get the crops in. Although warmer temperatures should mean a longer growing season, muddy fields mean it’s harder to get the planting done,” Takle says. 

Farmers are buying larger machinery to facilitate faster planting in between consequential rain events as a coping strategy. 

Upper Extremes Are Mellowing

Although the overall temperature is warming, Takle says that Iowa, in particular, has had fewer days of extreme heat in recent years, and remarkably, it’s due to increased humidity over the Gulf of Mexico. 

Takle explains that as the water temperature in the Gulf of Mexico warms, it produces greater atmospheric humidity. That humidity pushes northward, creating higher daily rainfall counts and cloudier weather in the early spring. Those clouds also protect against extreme temperatures, which lowers the number of high-temperature days, offering a small silver lining to global climate change.