100th Meridian, Which Divides the Arid West From the More Humid East, May Be Shifting Because of Climate Change

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By: Pam Wright
Published: April 12, 2018

The 100th meridian, which bisects the Great Plains and separates the arid western states from the moister eastern states, may be shifting as a result of climate change, new studies say. 

The imaginary line, metaphorically "drawn in the dirt" by American geologist and explorer John Wesley Powell in 1878, transects Texas, Oklahoma, Kansas, Nebraska and the Dakotas in the United States, and continues up into Canada's Manitoba.

Powell used the line to try to convince Congress to plan water and land-management districts that crossed state lines based on environmental constraints. His suggestions were met with backlash because legislators feared interstate districts would limit growth. Considering the water issues facing western states today, perhaps legislators should have taken Powell's theories under consideration. 

A team of researchers from the Lamont–Doherty Earth Observatory of Columbia University decided to take a new look at Powell's divide. In one study published in 2017 in the journal of the American Meteorological Society, the team confirmed that Powell was correct in his assumptions based on population and agriculture trends that have developed on opposite sides of the divide. 

In a second study published in March in the AMS journal, the researchers concluded that the line appears to be moving east, which could have big impacts on farming and other pursuits. 

"Adjustment to changing environmental conditions would cause farm size and rangeland area to increase across the plains and percent of cropland under corn to decrease in the northern Plains as the century advances," the study says. 

Richard Seager, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory and lead author of the two papers, calls this type of study “psychogeography” because it studies how the environment affects human decisions.

“Powell talked eloquently about the 100th meridian, and this concept of a boundary line has stayed with us down to the current day,” said Seager.  “We wanted to ask whether there really is such a divide and whether it’s influenced human settlement.” 

The researchers noted that the divide described by Powell played out in how the land was settled and cultivated, including the sharp decline in population west of the line. The once "luxuriant grasslands" described by Powell for the eastern half of the nation has been replaced by cornfields, but the theory was correct, the researchers pointed out.

(MORE: Florida's Urban Areas Are Having Shorter Wet Seasons, New Study Finds)

The divide also determines what crops have been cultivated, with moisture-loving corn grown in the eastern states and wheat in the West. 

The scientists concluded that a change in weather patterns in response to climate change indicates the imaginary line has shifted east about 140 miles towards the 98th meridian since 1980. In Texas, that means the divide has shifted from Abilene towards Fort Worth, according to the study.

Rainfall has not changed much in the northern Plains as a result of climate change, but rising temperatures have increased evaporation from the soil. Meanwhile, in the southern Plains, wind patterns are causing a drop in rainfall. 

The researchers say it is likely that Powell's divide will continue to shift east as the warming planet adapts and weather patterns continue to change. 

Their hope is that the results of the study will contribute to policy decisions that will aid with the "adaptation to changing conditions and avoid the negative effects of surprises followed by crises and social and economic disruption."

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