Extreme cold helps keep Mother Nature in balance
TRAVERSE CITY, Mich. — 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: Heavy ice cover may help raise low water in the Great Lakes and protect shorelines and wetlands from erosion. The extreme cold could also kill some insect pests and slow the migration of invasive species.
“All around, it’s a positive thing,” said Lenters, a specialist in the climate of lakes and watersheds.
Ice cover on the Great Lakes has been shrinking for decades, but this year more than 60 percent of the surface is expected to be frozen 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 cool-down — 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. Scientists noted that subzero temperatures and pounding snowfalls like those that gripped much of the nation are not unheard of in the Midwest and Northeast and used to happen more frequently. The extremes help keep nature in balance.
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 of their 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.
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.
Extreme cold also reins in invasive nuisance plants such as kudzu, which has ravaged the Southeast but has yet to find its way north, said Luke Nave, a University of Michigan assistant research scientist.