September 30, 2014

Medina
Mostly cloudy
59°F

Polar positives: Dead bugs and refreshed lakes

From a field station in northern Wisconsin, where the previous night’s low was a numbing 29 degrees below zero, climate scientist John Lenters studied computer images of ice floes on Lake Superior with delight.

It may be hard to think of this week’s deep freeze as anything but miserable, but to scientists like Lenters there are silver linings: The extreme cold may help raise low water in the Great Lakes, protect shorelines and wetlands from erosion, kill insect pests and slow the migration of invasive species.

“All around, it’s a positive thing,” Lenters, a specialist in the climate of lakes and watersheds, said Wednesday.

Ice cover on the Great Lakes has been shrinking for decades, but this year more than 60 percent of the surface is expected to freeze over at some point — an occurrence that could help the lakes rebound from a prolonged slump in water levels.

Even agriculture can benefit. Although cold weather is generally no friend to crops, some of southern Florida’s citrus fruits can use a perfectly timed cooldown, which they were getting as midweek temperatures hovered around freezing.

“A good cold snap lowers the acidity in oranges and increases sugar content, sweetens the fruit,” said Frankie Hall, policy director for the Florida Farm Bureau Federation. “It’s almost been a blessing.”

Scientists noted that subzero temperatures and pounding snowfalls like those that gripped much of the nation for several days are not unheard-of in the Midwest and Northeast and used to happen more frequently.

For all the misery it inflicted, the polar vortex that created the painfully frigid conditions apparently broke no all-time records in any major U.S. cities, according to Jeff Masters, meteorology director of Weather Underground.

“I’m just happy to see that we have a normal winter for once,” said Lenters, who works for Limnotech, an environmental consulting firm in Ann Arbor.

As the climate has warmed, the absence of bitter cold has actually been damaging.

The emerald ash borer, an insect native to Asia, arrived in the U.S. around 2002 and has killed about 50 million ash trees in the Upper Midwest. But some locales this winter may have gotten cold enough to kill at least some larvae, said Robert Venette, a U.S. Forest Service research biologist in St. Paul, Minn.

A reading of minus 20 will usually produce a 50 percent mortality rate, and “the numbers go up quickly as it gets colder than that,” Venette said.

While the freeze won’t wipe out the ash borer, it will give communities a chance to develop plans for limiting the bug’s spread, he said.

Other pests that originated in warmer places could be affected as well, including the gypsy moth, the hemlock woolly adelgid and the European beetle that carries Dutch elm disease, said Lee Frelich, director of the University of Minnesota Center for Forest Ecology. Native insects have evolved to cope with deep freezes.