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"150 Years Later, the American Divide Is Shifting"—April 13, 2018
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Many recognize a sharp divide in the U.S. right now, but another divide in America, which was noticed 150 years ago, has recently been studied and has some implications for the future as climate change continues.

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If you were to drive from Denver to Kansas City along Interstate 70, you’d be traveling though semi-arid grassland and you’d see a lot of sky but not many trees. It’s pretty dry. But somewhere around the eastern part of Kansas, what were brown expanses suddenly become more green and lush.

John Wesley Powell noticed, too, although he wasn’t driving on an Interstate. In the 1860s, the famed explorer-scientist led a series of expeditions into the Rocky Mountains and was the first white man to float down the Colorado River. His observations comparing the arid lands in the west to the humid east led him to conclude there was a distinct boundary between the two and it was along the 100th meridian. Powell’s symbolic line runs north to south from Manitoba, Canada, through the Dakotas, Nebraska, Kansas, Oklahoma, and Texas down to Mexico. Surprisingly, no one has actually tested Powell’s description of this aridity divide from a scientific perspective—until now.

Dr. Richard Seager of Columbia University’s Lamont-Doherty Earth Observatory, along with other researchers recently studied the divide. They did a review of literature about Powell’s observation, but he said they weren’t able to find any climate environmental scientists who had looked at this issue about whether he was right.

John Wesley Powell Seager said that Powell noted that the 100th Meridian was a rather sharp divide between the arid West and the more humid East. Powell argued that because that was so, the way that the western expansion had been done into the eastern part of the plains would have to be different when it went west across the 100th meridian where water was far more scarce. Seager and his colleagues his colleagues were curious if the 100th meridian is still a dividing line and what may happen to it in the future. They concluded that Powell was correct and that there is a very real divide in aridity, which you can see in the climate, moisture in the soil, and vegetation.

Their study shows that in winters the western plains are much drier than the east because moisture coming from the Pacific is rung out by the Rocky Mountains, but east of the boundary the plains get moisture from the Gulf of Mexico and the Atlantic. Patterns in the summer continue the moisture divide. The boundary in the U.S. is one of only two straight-line climate divides in the world—the other being in in the Sahara Desert in Africa.

The research also found that this U.S. divide is on the move—because of climate change. It will likely nudge east based on two factors. First, scientists have known for over a decade that winter precipitation in the Southwest has declined due to global warming, but also, Seager says, warming temperatures everywhere, which increase dryness, will pull more moisture out of the surface. These two conditions will cause a shift in the aridity boundary.

Seager said the level of aridity that used to be at the 100th meridian will start moving a few degrees of longitude eastward over the current century. The eastward move of aridity has implications for agriculture, meaning there won’t be as many crops grown west of the divide, but more rangeland for animals. Also, wheat is likely to replace corn as the main crop to the west of the aridity divide.

According to Seager, the real lesson is to pay attention to the one-armed explorer and geographer of the West who observed conditions 150 years ago and based his recommendations on them. Now when we’re dealing with climate change, Seager says, we should be thinking the way Powell did. The decisions we make should be well informed by the science, based upon what the environmental conditions are, and what makes sense about how to make the best use of them in a sustainable way. He noted that Powell’s ideas from 150 years ago are coming back and are more relevant than ever now that we are changing the climate system.

The studies were published in the journal Earth Interactions.




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