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A change in the air

(What's going on with Minnesota's weather?)

By Rick Moore

From M, summer 2005

Major rainfalls seem to be on the upswing, and there's been a spate of flooding in many parts of Minnesota. Summer's heat waves tend to be bringing with them a woolen blanket of humidity. And what about these wimpy winters? Heck, it hardly ever seems to get below zero anymore.

Those of us who have lived in Minnesota for most of our lives know something's going on with the weather. According to two University climatologists, there are indeed some emerging patterns.

Mark Seeley, University professor of climatology and meteorology and Minnesota Public Radio regular, says that four trends we are experiencing in Minnesota right now "that are statistically significant": warmer winters, higher minimum daily temperatures, higher dew points, and increased precipitation.

These aren't the only four trends, Seeley notes, but they "are the four we spend the most time by far talking about, and those are the four that have the most serious implications for us."

Seeley says the change in the weather is most likely due to a combination of three factors--natural variability, changes in land use and landscape, and "anthropogenic emissions," i.e., human-made greenhouse gases.

Over about the last eight years, the average temperature during the snow season (November through March) is 2-4 degrees warmer than normal, Seeley says, and if you count all Decembers, Januarys, and Februarys in that time, 65-70 percent of all days have had above-normal temps. The upward trend in minimum daily temperatures is also more pronounced in the winter months, says Seeley, and the average minimum temperature in February has climbed by nearly 4 degrees.

For Minnesotans who have refined the ability to cope with the cold, the higher dew points in the summer are something of a wildcard. (The dew point represents moisture in the air, and as the numbers climb above 60, things start getting uncomfortable.) In the last two decades, the Twin Cities has set a new dew point record of 81, and the new state record is 84, says Seeley.

"That level of dew point is what you'd get in the Persian Gulf; in Bombay, India; in the Philippines," says Seeley. "It's not what you'd get at 45 degrees latitude in the central United States in North America.... For us Minnesotans to have to adjust to a 115-degree heat index (temperature plus moisture), that's a big stressor."

According to Don Baker, a retired University climatology professor who was recently given a lifetime achievement award by the University, the increase in wetness is part of a longer trend that began in the '70s. Precipitation levels are up substantially since then in many parts of the state, and at the Waseca Agricultural Experiment Station annual precipitation is up by about six inches, he says.

Along with these trends come some unexpected advantages, as well as some distinct pitfalls. The outdoor construction season in the Twin Cities has been prolonged by the warmer winters, golf courses have opened spontaneously during snow-free stretches, and "I guess you'd have to put [warmer temps] in the asset column for the residential and commercial heating costs," says Seeley.

Summer heat waves are not so kind, he says. More people are falling ill to heat stress, livestock losses (especially poultry) are compounded, and with higher minimum temperatures plants have to consume more energy, making them more susceptible to certain diseases and insects. Baker is especially worried about what might happen if we return to early-20th-century precipitation levels. "We're building a civilization on certainly more moisture than we had in the 1930s, and we're consuming it right up to the hilt," he says. "What's going to happen if [we revert] to the previous amount of precipitation?"

Seeley says the change in the weather is most likely due to a combination of three factors--natural variability, changes in land use and landscape, and "anthropogenic emissions," i.e., human-made greenhouse gases. "Most scientists will acknowledge that all three of these probably come into play," he says. But to what extent each is responsible, "We don't have the knowledge base to give a quantified answer, and the public gets frustrated with that."

Will these trends reverse themselves anytime soon, or are they here to stay? "The history lesson from climatology is they will not go on unabated forever," says Seeley. "We can say that they'll be with us for a while, but we don't know how long."