DOES SIZE REALLY MATTER?
In April the Intergovernmental Panel on Climate Change (IPCC), an international panel of leading scientists, released its fourth and, to date, most comprehensive report on climate research. It relied on projections from a suite of 21 global climate models to make worldwide projections about temperature, precipitation and other aspects of the climate.
For much of the last 20 years, the IPCC has been projecting increases in temperature by the year 2100 that have ranged from 2 to 11.5 degrees. While the uncertainty of this projection has diminished over that period, with a majority of scientists now agreeing that human actions are contributing to — even hastening — the change, scientists have not been able to narrow the range of the temperature forecast.
A tilt by just two degrees either way, though, could have huge implications for water resources, agriculture and air quality. Small differences in temperature during the Midwest summer growing season could spur early – or late – corn pollination. Or if temperatures shift a few degrees too high in July or August, corn kernels at the tips of the cobs can be destroyed.
The range for precipitation forecasts is even greater, with some already dry areas tagged for a decrease by 10 to 20 percent, and higher latitudes expected to see an increase of at least 10 percent.
And both factors are complicated by trying to pinpoint regional manifestations, which makes it hard to say with any certainty what the future frequency of heavy rainstorms or heat waves in various parts of the country would be.
“The global models give a very broad-brush depiction of climate change, and they certainly are useful for getting people to think about possibilities that might occur,” said William Gutowski, a professor at Iowa State University and a lead author of a recent report on modeling released by the U.S. Climate Change Science Program, which coordinates climate research in the U.S. “But what they do not do very well is simulate certain types of extremes.”
By extremes, Gutowski means the kind of flooding that overwhelmed Iowa in June, or the hurricanes that pummel the southern United States every summer and fall. To get at this, it would take models with a far finer resolution.
Most global models have a “resolution” of 300 kilometers, meaning they essentially lay a three-dimensional lattice over the earth, with the resulting cubes measuring 300 kilometers on each side. And at every corner of these cubes, the model can run a series of calculations, or guesses, that approximate climate conditions.
But between these points where the calculations are made, lie plenty of unaccounted for space. “In the whole of Illinois we have only two or three points to work with [in a global model],” said Liang, of the Illinois State Water Survey. And it’s in this empty space between the points that cloud squalls or lakes may hide.
In a regional model, on the other hand, there would be thousands of points for Illinois.
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