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But contrary to popular perceptions, Watson's data suggest that a hotter climate doesn't necessarily mean a return to the parched summers of his childhood. The warming of the Nineties has been concentrated in late winter, specifically in a gradual rise of the nightly low temperature. According to Watson's analysis, since 1971 average February temperatures have risen 3.5 degrees from historic norms dating back to 1820. Meanwhile, the daily maximum temperatures from July through December have not risen appreciably.
This, Watson explains, means that climate change could actually have some positive effects for Minnesotans. Though the bock-beer warmup's most pronounced effects occur in February, it lingers into May, possibly benefitting farmers by adding two weeks to the growing season.
"You can't say this whole thing is bad," Watson concludes with the kind of ambivalence that comes naturally to a weatherman, but doesn't do much for politicians or news types. "We can't even be sure that the global warming hasn't counteracted global cooling. And it would be much worse for us if it got colder. I think what the greenhouse effect really does is just increase uncertainty--and people don't like uncertainty."
Lee Frelich has heard Watson make his argument, and while he respects the meteorology behind it, he's not sure he agrees with the conclusion. For more than a decade, the University of Minnesota forest ecologist has been reconstructing the weather history of the Great Lakes through land surveys performed for the federal government between 1850 and 1900.
Because the surveyors were required to note evidence of forest fires and blowdowns, Frelich and his colleagues were able to cobble together evidence of major storms in the last century. Some areas affected were as large as 20,000 acres. But that, Frelich points out, is beans compared to more recent events. Both the so-called Flambeau Blowdown--which occurred in northern Wisconsin in 1977--and this summer's BWCA storm flattened forests on more than half a million acres. "I think we've seen a genuine increase in the frequency of severe storms," Frelich offers, "and I think that it is caused by global warming."
Those storms, in turn, could alter the landscape in much of the state, Frelich continues. "I don't think any trees are going to pack their bags and leave because it gets up to 80 degrees in northern Minnesota in the summer instead of 75. But if this leads to more big storms, that will change the forest quite rapidly." Especially, Frelich adds, if the state becomes drier--a development that, he says, could disrupt the natural succession in forest types.
A couple of years ago, Margaret Davis, a renowned paleo-ecologist at the U, told state legislators that Minnesota may wind up looking "like northern Nebraska"--a largely treeless tract of grassland--by the end of the next century. The conclusion was based on some 40 years of research in which Davis has documented the changing ecology of the upper Midwest by examining pollen sediments in lakes and bogs; among other things, she found that between 8,000 and 5,000 years ago, a dramatic decline in rainfall allowed the prairie to replace forests in much of western Minnesota.
Some of the early global-warming models anticipated a drier climate for much of Minnesota in the next century. More recent studies have suggested there might be more rain, at least in parts of the state. Either way, says Davis, the warming may cause the region's climate swings to become more pronounced, increasing the likelihood of both excessively wet and very dry weather. "I think the aspect of climate change that would cause us the most problems would be an increase in variability," she says. "If there's an increase in drought variability, that would be very bad news for this area."
One thing most researchers agree on is that, as the old saw goes, when it rains, it pours. Warm years often follow warm years. Cool years follow cool years. Scientists have learned that major changes in climate can sometimes occur over relatively short periods of time--and that once in place, a pattern can stay put for centuries. In the mid-1700s, the peak of a 500-year-long "Little Ice Age" brought 40-below temperatures to places like Paris and London. Paintings from the period depict ice skaters on the Thames.
But within any large weather regime there are smaller ones, periods of warming and cooling called Bruckner cycles that can last anywhere from 8 to 35 years. They, too, are part of nature's pattern, Watson says, visible to anyone who cares to look closely. Since 1989, for instance, the Twin Cities have experienced regular January rains. "You get a preponderance of the same kinds of weather, so you see that the weather from one year to the next is not totally random," he explains. "Cycles tend to perpetuate themselves." In Watson's estimation, we are in the midst of a cycle he calls "the little steam age."
Because it sits at the center of the North American land mass, Minnesota has always had an especially turbulent and variable climate. Many researchers argue that that makes the state more vulnerable to climate change. But, Watson argues, it is also worth remembering that violent weather was always a part of this landscape--people just didn't pay as much attention. That's why he doesn't entirely trust the conclusions Frelich and others draw from historic evidence: "It's anecdotal. In the olden days, because the land was empty, you didn't have people observing tornadoes. Nowadays, with the built-up country and urban sprawl and radar and satellite, tornadoes don't get missed, so the data is being gathered by two different methods."