By Chase Purdy
There’s a line that stretches (click here) down North America, singeing into the continent a border that separates an arid west from a humid east. And it’s on the move.
Called “the 100th Meridian,” the line slices through Canada, the Dakotas, Nebraska, Kansas, Oklahoma, Texas, and eastern Mexico. It exists because the Rocky Mountain range blocks moisture that would sweep into the Great Plains from the Pacific Ocean, while storms in the Atlantic Ocean push moisture into the US midwest, bumping against more
moisture that barrels north and slightly east from the Gulf of Mexico during the summer....
...Drawing on climate models, regional vegetation data, US Department of Agriculture data, land model simulations, and weather station data, Seager was able to confirm in a recent study (pdf) that the 100th Meridian is more or less as Powell predicted. Except, as he shows in an accompanying study, by now the line has shifted eastward 140 miles (pdf).
As Seager explains it, meteorological models for a long time have predicted a decline in the precipitation coming up from the US southwest into the midwest. That will be exacerbated by rising temperatures caused by fossil fuel-generated greenhouse gases: as the atmosphere warms it can draw more moisture out of the land. The scientific term for this phenomenon is called evapotranspiration, and over time can cause arid landscapes to expand....
