The Weather Corner: On the polar vortex, climate change, and agriculture

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Blizzard in the city. Image credit: Pixabay

Anyone else have to turn on the heater this past month?

As we write this, a split polar vortex is bearing down on the Northern Hemisphere, bringing frigid temperatures and extreme precipitation along with it. Behind the catchy name is a serious weather phenomenon that will affect everyday life in much of the world for weeks and even months to come. You might remember the polar vortex making an appearance in the news in 2019, when Chicago briefly became colder than the North Pole, or the cold snap in East Asia in 2016, when at least 85 people in Taiwan died from hypothermia and cardiac arrest.

So what exactly is a polar vortex? Technically, it’s a unique type of low-pressure system: it’s the large area of frigid air, spinning at a high atmospheric altitude, above the North Pole. The spinning winds form a jet stream. When strong and intact, the jet stream bottles in the cold air above the Arctic, and North America has a generally mild winter.

A polar vortex actually forms every year — the result of polar night, the all-winter dark spell in the Far North. Without sunlight, the air drops to 195 degrees Kelvin (78.15 degrees Celsius, or -108.67 degrees Fahrenheit) and the winds pick up. It vanishes once spring returns, only to re-form around September or October.

However, sometimes, in the dead of winter, warmer air infiltrates and weakens the vortex. It pushes the jet stream further to the south. This brings the frigid air, plus stormy weather and increased snow chances, further south, too.

Image credit: Business Insider

It can be unstable and difficult to forecast. Meteorologists have said that there will likely be old, wonky weather from two weeks to a month or more after the split in the Mid-Atlantic and Northeast as well as Northern Europe and East Asia.

According to the New York Times:

The United States has already seen heavy snowfall in the Sierra Nevada and in the Great Plains in the last week. Earlier this month, Madrid was buried under a paralyzing foot and a half of snow, and parts of Siberia suffered an unusually lengthy cold spell with temperatures of 40 degrees below zero Fahrenheit — and one area recorded a temperature of nearly 73 below. (Last summer, some of the same areas experienced record heat.)

If you think you’ve heard about the polar vortex more frequently in recent years, that’s because you have. While the phenomenon is well-documented, scientists say that its behavior has become more extreme as a result of climate change. Global temperatures are rising, but the Arctic is warming more than twice as quickly than the global surface average. It’s a negative feedback loop: high temperatures have melted a great deal of Arctic sea ice, changing the icy surface that reflects light to a dark surface that absorbs it and warms.

This effect weakens and destabilizes the polar jet stream more often, causing it to dip and carry polar air farther south in never-before-seen ways.

It’s also expected to be an unusually long disturbance this year because of a “sudden stratospheric warming.” AKA, climate change.

So what does all this mean for agriculture?

In North America, the cold temperatures, storms, and increased snow cover have the potential to delay and/or kill crops like winter wheat, and perennial crops like alfalfa and fruit trees and bushes. (The U.S.D.A. estimates that extreme weather, which is exacerbated by climate change, is responsible for about 90% of crop losses.)

The 2019 polar vortex provided suboptimal planting conditions in the Midwest agriculture belt in the spring. Alfalfa and winter wheat crops were severely impacted by winter “heaving,” a soil condition that occurs with swings between freezing and thawing temperatures. The cold also risked damage to peach trees: When temperatures dip near 10 degrees below zero, the cold reaches a critical level for peach trees.

Image credit: Morning Ag Clips

Animal agriculture was also affected that winter. Cargill’s grain facilities in Iowa, Illinois, Indiana, Minnesota, Missouri, and Wisconsin closed for a period. Meat giant Tyson Foods closed six plants in the Upper Midwest over concerns for worker and animal safety.

However, some good news: As for pests, the cold will likely help with suppression as it can freeze more out. The 2019 polar vortex event in the Midwest helped prevent the spread of potential pest insect species that cannot survive winters, like the potato leafhopper and black cutworm.

In addition, if the extreme cold brings about a frost that’s deep enough, it can benefit farmers — the freeze-and-thaw cycle can unexpectedly help soften the soil and ultimately reduce compaction for certain types of crops.

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