Home / News / The Line in America’s Psychogeography Shifts East

The 100th meridian, which divides the arid western United States from the humid eastern U.S., is a well-ingrained element of American lore. American geologist and explorer John Wesley Powell first recognized this north–south dividing line in 1878 and argued that in areas west of the meridian development had to take account of environmental limits. A couple of years ago, Lamont-Doherty Earth Observatory climate scientist (a newly elected AGU Fellow; see page: 56) Richard Seager was handed a small cleaning cloth printed with a population map and saw compelling evidence for Powell’s imaginary line.

“I immediately noticed there were two straight lines, one in the Sahel at the southern edge of the Sahara and also a straight north–south line at the hundredth meridian. This means that once you get to the 100th meridian there is a tremendous drop off in the population density to the west.” said Seager. While Congress ignored Powell’s advice, it was clear to Seager that the environment had in fact greatly influenced how the West was developed.

“once you get to the 100th meridian there is a tremendous drop off in the population density to the west”

Seager and his team were already working on a large NSF-funded research project on climate variability and change across the North American west and its implications for land, water, and ecosystems. Exploring the dividing line and its storied history and social ramifications was an enticing direction to push that work.

Two summer interns and two research papers later, Seager’s inquiry has yielded measurable proof that Powell’s line – the longitudinal boundary cutting northward through the eastern states of Mexico and on to Texas, Oklahoma, Kansas, Nebraska, the Dakotas, and the Canadian province of Manitoba and beyond – not only is a real climate divide but is also reflected in population and agriculture differences on opposite sides, and, as a result of climate change, has shifted and will continue to shift eastward. Since 1979, the year when accurate satellite imagery began to be acquired on a routine basis, that line has migrated about 140 miles east, expanding the arid climate of the western plains to the east.

Seager believes that the implications are large. These changes in humidity, rainfall, and aridity are bound to influence agricultural decisions on how the land is used and what crops are grown, which in turn will create new and different domestic and international crop markets. This shifting line is likely to impact as well the wallets and the dinner plates of families throughout America.

“changes in humidity, rainfall, and aridity are bound to influence agricultural decisions”

“As the line moves eastward as aridity increases, you would expect the corn area to become increasingly restricted into the Midwest, where it’s humid enough for the crop. You would also expect wheat to move eastward, and you would also expect range land to move eastward. But there’s a problem there, because as you move eastward you go to lower altitudes and higher temperatures, which will push beef productivity down. It’s too hot for the animals. So, there will be agricultural consequences of these increases in aridity,” said Seager.

He predicts that as drying progresses, just as farms west of the 100th meridian are typically larger than those to the east, farms to the east of the current divide will have to become larger in order to remain viable. Farmers may need to turn from corn to wheat or some other more suitable crop. Corn is a very high-demand crop in the U.S. for use as animal feed and as a ubiquitous sweetener in American processed foods. Farmers might turn to irrigation of corn, but that process is expensive, and whether they irrigate will depend on groundwater availability and how markets respond.

“Corn is a high-value product. It’s going into processed food because people love sweet things, and it’s going into animal feed because people love their meat. You might see production more restricted and higher prices for corn-based products, which could lead to a change in U.S. food production that would be beneficial to health. More wheat and less corn and meat mean a better diet,” Seager added.

For now, Seager’s papers on the 100th meridian continue to draw the media spotlight. Dozens of publications covered the findings, and even now, months after the studies were released, Seager is receiving invitations to deliver talks outlining his work defining and tracking the aridity divide.

“What’s unique about this story is the way it combines historical perspectives on the development of the West with future projections about climate and impacts to our economy and food,” noted Seager.

“More wheat and less corn and meat mean a better diet”

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