The Van Trump Report

What Warming Nighttime Temps Could Mean for Agriculture

Understand this is NOT a Climate Change debate! The big questions in climate change debates are how, why, and when? Are we looking at too short of a data set? Are we simply in some type of different rotational cycle that has caused the change? The list of questions associated with climate change debates can go on and on. But today I want to talk about something more specific… Nighttime temps! 

We have all heard the research stories and data being presented by climate scientists regarding the phenomenon of rising average temperatures across the globe but most of that work to this point has focused on daytime temps, something Daniel Cox believes gives us an incomplete picture. Cox, an ecologist at the University of Exeter, recently published a paper on his findings that nighttime temperatures are actually increasing at a faster rate compared to daytime temps in most land areas across the Earth.

As Cox explains, our changing climate has “already messed things up” but says “the 24-hour asymmetry is adding an extra dimension of complexity.” Without understanding these effects, Cox says scientists can’t hope to fully grasp how the natural world will respond. For example, experiments with grasshoppers and spiders have shown that the time of the day at which heating occurs can tip the ecological balance. In a 2017 study, researchers found increased daytime warming led spiders to seek cover earlier in the day, enabling grasshoppers to graze on plants for longer periods uninterrupted. Conversely, the spiders hunted the grasshoppers more fiercely when nighttime temperatures warmed, possibly reducing the insect’s numbers. Cox says these kinds of effects can ripple across a larger ecosystem, with potential impacts for plant communities, wildlife, and agriculture.

Cox and his research team studied climate records spanning 1983 to 2017 covering virtually the entire planet. In some spots, the days warmed considerably while nighttime temperatures barely budged. There were even times of considerable cooling for some environments. However, across more than half the planet, the average annual temperature rise at night was a quarter of a degree Celsius more than that of the days. In fact, here in the US, night-time temperatures have increased at twice the rate of daytime temperatures. Given that different animals and plants carry out different activities and processes depending on the time of day, unequal temperature rises may have a skewed impact, the researchers say.

Cox also included leaf area index in the study, which measured plant canopy coverage used to estimate the productivity of flora. Not surprisingly, temperature extremes in either direction negatively impacted leaf area. As most farmers know, warm nights can negatively weigh on crop yields, especially corn. The most common explanation is increased expenditure of energy due to a higher rate of cellular respiration, aka “corn sweat”, at night. This means more energy expended during the day, making less available for kernel development.

High nighttime temperatures can also result in faster heat unit (GDD) accumulation that can lead to earlier corn maturation, whereas cool night temperatures result in slower GDD accumulation that can lengthen grain filling and promote greater dry matter accumulation and grain yields. Meanwhile, warmer nighttime temps that accompany cloudier days also means plants have a harder time resupplying their energy as photosynthesis requires sunlight.

Understanding the full implications of daily fluctuating temperatures and cloud formation is going to take a lot more research. Clouds can be surprisingly complex phenomena, influenced by a host of other factors. But as this study and others show, climate change isn’t simply a matter of things warming up. Impacts vary widely around the world and temperatures are changing at different rates between seasons or times of day. Wind, rainfall, and snow patterns are also changing. It’s a very complex issue with a lot of possible outcomes that could have a real impact on how and what farmers are producing in the future. (Sources: Popular Science, World Economic Forum, Science Alert, The Guardian)

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