The 100th Meridian is an invisible line reaching from the North Pole down through Canada, the U.S., Mexico, and on to the South Pole. The line was first identified in 1878 by the American geologist and explorer John Wesley Powell. At that time, it was at 100 degrees west longitude, also known as the 100th meridian.
“Powell talked eloquently about the 100th meridian, and this concept of a boundary line has stayed with us down to the current day,” said Richard Seager, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory, and lead author of two studies about the shifting climate boundary.
“We wanted to ask whether there really is such a divide and whether it’s influenced human settlement.” He calls the studies an example of “psychogeography”-the examination of how the environment affects human decisions.
In the United States, the 100th Meridian slices through the Dakotas, Nebraska, Kansas, Oklahoma, Texas, and exists because of the Rocky Mountain Range. The “Rockies” block the moisture from the Pacific Ocean from sweeping into the Great Plains, while storms forming in the Atlantic Ocean push moisture into the U.S. Midwest.
Powell’s warnings went unheeded
Powell was the first European to explore the Colorado River and the Grand Canyon as well as other regions of the West. And even then, he realized the environmental constraints that would eventually be needed because of the harshness of the geological terrain and the effects of the mountains on climate.
Powell later served as the second director of the U.S. Geological Survey from 1881 to 1894. During his tenure, he touched off controversy by advocating strict conservation of water resources in the developing states and territories of the arid West.
“There is not enough water to irrigate all the lands,” he remarked at a Los Angeles Congress of farmers and developers in October 1893. “I tell you, gentlemen, you are piling up a heritage of conflict and litigation over water rights, for there is not enough water to supply the land.”
Modern-day evaluation of the 100th Meridian
Seager and his team revisited the 100th Meridian region as part of their ongoing work to better understand how geography can be impacted by climate change, and by extension, how people living in the region are experiencing that change.
The team’s work is detailed in two studies, one that examines how it has played out in history so far, and what the future may hold. One very obvious finding is that the 100th Meridian is very real – as reflected by population and agriculture on opposite sides of the imaginary line, according to Science Daily.
Using climate models, regional vegetation data, US Department of Agriculture data, land model simulations, and weather station data, Seager’s team was able to confirm the 100th Meridian is more or less as Powell predicted. Except, by now the line has shifted eastward 140 miles.
Meteorological models have predicted a decline in the amount of precipitation coming from the southwest into the Midwest. This is exacerbated by rising greenhouse gases that warm the atmosphere. The warm atmosphere, in turn, draws more moisture from the land. The term for this is called “evapotranspiration,” and over time can cause arid landscapes to expand.
Seager points out that Powell was correct in his observations that the western plains are dry in part because they lie in the rain shadow of the Rocky Mountains, which rake off almost all the moisture blowing in from the Pacific Ocean.
Seager also notes that this visual dividing line is only seen in one other part of the world -The line separating the Sahara Desert from the rest of Africa – also due to cutoffs of prevailing oceanic winds.
How the effect shows up in the U.S.
You can actually see the meridian concept and its effect on the land. To the west of the line, populations drop off and there are fewer roads, homes and commercial facilities. There are few small farms. But the ones you find are larger and primarily depend on arid-resistant crops like wheat. In the more humid east, populations and infrastructure abound. Farms are generally smaller and apt to grow more moisture-loving crops, like corn.
But the researchers say that because of anthropogenic climate change, the boundary between the dry West and the wetter East has moved two degrees further east, to the 98th Meridian. As an example, in Texas, the boundary has moved approximately from Abilene to Fort Worth.
And as that boundary continues to move eastward, it will have an impact on agriculture and the economy of the United States. “Large expanses of cropland may fail altogether and have to be converted to western-style grazing range. Water supplies could become a problem for urban areas,” according to Columbia University’s Earth Institute,
Farmers and state and local governments should be planning for the changes to come, rather than waiting until it is too late. Whether we will be able to stop the eastward march of the boundary is really up to us. “The only way that would happen is if we start getting very serious about reducing greenhouse-gas emissions,” Seager says.
The two studies were published in the Journal of the American Meteorological Society, Earth Interactions.
Whither the 100th Meridian? The Once and Future Physical and Human Geography of America’s Arid–Humid Divide. Part I: The Story So Far.
Whither the 100th Meridian? The Once and Future Physical and Human Geography of America’s Arid–Humid Divide. Part II: The Meridian Moves East.
