The 100th Meridian, Where the Great Plains Begin, May Be Shifting

Warming Climate May Be Moving Western Aridity Eastward

by |April 11, 2018

In 1878, American geologist and explorer John Wesley Powell drew an invisible line in the dirt—a long line. It was the 100th meridian west, the longitude he identified as the boundary between the humid eastern United States and the arid Western plains. Running south to north, the meridian cuts through eastern Mexico, Texas, Oklahoma, Kansas, Nebraska, the Dakotas, and the Canadian province of Manitoba on its way to the pole.

Powell, best known for exploring the Grand Canyon and other Western places, was wary of settlement in that often harsh region, and tried convincing Congress to lay out water and land-management districts crossing state lines to deal with environmental constraints. Western politicians hated the idea, fearing it might limit development and their own power, and it never went anywhere. It was not the first time politicians would ignore the advice of scientists.

Now, 140 years later, in two just-published papers, scientists examine how the 100th meridian has played out in history, and what the future may hold. They confirm that the divide has turned out to be real, as reflected by population and agriculture on opposite sides. They say also that the line appears to be slowly moving eastward, due to climate change, and that it will probably continue shifting in coming decades, expanding the arid climate of the western plains into what we think of as the Midwest. The implications for farming and other pursuits could be huge.

The 100th meridian west (solid line) has long been considered the divide between the relatively moist eastern United States, and the more arid West. Climate change may already have started shifting the divide eastward (dotted line).

One can literally step over the meridian line, but the boundary it represents is more gradual. In 1890, Powell wrote, “Passing from east to west across this belt a wonderful transformation is observed. On the east a luxuriant growth of grass is seen, and the gaudy flowers of the order Compositae make the prairie landscape beautiful. Passing westward, species after species of luxuriant grass and brilliant flowering plants disappear; the ground gradually becomes naked, with bunch grasses here and there; now and then a thorny cactus is seen, and the yucca plant thrusts out its sharp bayonets.” Today, his description would only partly apply; the “luxuriant grass” of the eastern prairie was long ago plowed under for corn and other crops, leaving only scraps of original landscape. The scrubby growth of the far west remains more intact.

“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 both papers.  “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 environment affects human decisions. They appear in the current edition of the journal Earth Interactions.

While the climate divide is not a literal line, it is about the closest thing around–arid on one side, relatively wet on the other. Powell noted correctly 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’s team identifies two other factors. In winter, Atlantic storms bring plenty of moisture into the eastern plains and Southeast, but the storms don’t make it far enough to moisten the western plains. In summer, moisture from the Gulf of Mexico moves northward, but that also curves eastward, again providing the East with rain, while the West gets cheated. Seager says there is only one other such major straight-line climate divide on the global map: the one separating the Sahara Desert from the rest of Africa, also due to cutoffs of prevailing oceanic winds.

In the United States, the effects show up in obvious ways. To the west, population density drops sharply. There are fewer homes, commercial facilities and roads. Farms are fewer, but bigger, reflecting the economics of less water and lower productivity. To the east, 70 percent of the crop is moisture-loving corn; to the west, aridity-resistant wheat is dominant.

With the camera looking west, horses graze about 300 miles east of the 100th meridian. This area could become dryer if current projections of climate play out. (Kevin Krajick/Lamont-Doherty Earth Observatory)

Now, warming climate appears to be pushing the divide east. In the northern plains, rainfall has not changed much, but temperatures are going up, increasing evaporation from the soil. Further south, shifts in wind patterns are causing less rain to fall. Either way, this is pushing aridity eastward. As a result, data collected since about 1980 suggests that the statistical divide between humid and arid has now shifted closer to the 98th meridian, some 140 miles east. (In Texas, this would move it roughly from Abilene to Fort Worth.) Seager says year-to-year weather variations may blur the data, and so far the changes are still too small and gradual to yet affect land use over wide areas. But he is confident that aridity will perceptibly move eastward during the 21st century, and eventually effect large-scale changes.

Seager predicts that farms further and further east will have to consolidate and become larger in order to remain viable. And unless farmers turn to irrigation or otherwise adapt, they will have to switch from corn to wheat or some other more suitable crop. Large expanses of cropland may fail altogether, and have to be converted to western-style grazing range. Water supplies could also become a problem for urban areas.

Some historians say it could be argued that the meridian influenced even wider historical trends–everything from the end of slavery (plantations could not expand past the line, weakening the South) to the development of modern firearms (settlers’ single-shot muskets couldn’t compete with native peoples’ rapid-fire arrow attacks, until the settlers became the first, best customers for new Colt repeating revolvers and rifles). The meridian itself is still registered in popular imagination: among them, historical roadside signs, books such Wallace Stegner’s “Beyond the Hundredth Meridian”, and the Canadian rock hit “At the Hundredth Meridian.” “It’s a reminder that climate really matters, then as it does today,” said Seager.

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10 thoughts on “The 100th Meridian, Where the Great Plains Begin, May Be Shifting

  1. Numeosium says:

    Sooo…an imaginary line invented by Man is moving due to the weather. How does that work, exactly?

    Clearly, the ‘bad weather is caused by humans’ Global Alarmist crowd doesn’t think much of the intelligence of the rest of us.

    As for the shifting that the plains may be doing, so what? The Sahara has been moving throughout its history.

    Impact farming? Really? I doubt the situation will change THAT drastically or rapidly. By the time it actually would make any REAL difference to farms, the farmers will have had plenty of time to adjust. On top of that, no farmer alive today will have to worry about it which is what makes this such a silly story to begin with. Not a lot they could do in the first place. We can also be 100% confident that people driving cars & flying planes has nothing whatsoever to do with it.

  2. P Feilen says:

    To promote future study have you any info as to where, lets call it the arid line, manifested it self in say 1828, 1778, 1728 and so on. Charts need to be drawn up on the speed of progression so a logical causation can be named. Also unless it’s an optical oddity it appears the arid line is slightly narrower at the north. Can/do we attribute this and possibly the whole theory/compulsion to climate diversion to say, ummm, a slight axial shift in earth due to a percieved magnetic pole flip that quite possibly is in the early stages of occuring and not to other issues that political forces wish to be the source.

  3. Wendy Krueger says:

    Smaller farms came with the land grants in the 1830’s, and therefore stay to this day. The land grabs of the westward expansion allowed sections to be held, not acres. The larger farms came with the government grants originally- not the lack of water.

  4. dishpit says:

    “no farmer alive today will have to worry about it which is what makes this such a silly story to begin with”

    Yeah, heaven forbid a farmer alive today might worry about what their grandchildren will have to deal with!

  5. Mike says:

    Is there a map that continues on to Canada? Us up here would be very interested to know how we will be drying out.

  6. Lew Olson says:

    So how does this claim corroborate an earlier document at– that show precipitation increases likely for the area and recent temperature and rainfall changes for Northwestern corn belt. I suspect the argument will be that the evapotranspiration in summer will be much higher, but recent weather changes since 1970s in this area have been to the contrary (fewer high summer day temps, mostly higher night time lows). From the mid-50 through the mid70s, Northwest Iowa and Eastern South Dakota, SW Minnesota would see significant crop reduction due to weather about once every 5 years. Many parts of Northwest Iowa haven’t had significant crop yield reduction because of weather since late 70s. If anything the corn growing region has significantly moved west in the last 4-decades. Modern technology? CO2 plant water eficiency?

  7. Mike, As the story states, the line runs up through Manitoba. From there, into the Northwest Territories and Nunavut. Manitoba and other southerly provinces of course have the same Great Plains as the US. You guys even have the best song about it: “The 100th Meridian” by the great Ontario band The Tragically Hip.

  8. Janet rogers says:

    Great article and an astute summary of a changing climate dynamic ! If only our nation had paid more attention to Powell’s observations and instituted federal programs to conserve water! Maybe the tragedy of the dust bowl would have been lessened !!!! YES – climate matters tremendously in how and whether life can adapt, including us. WE better wise up to the reality of climate changes.

  9. Steven Read says:

    I am not sure where new boundary is but the 100th meridian is an absolute based on the angular distance from the prime meridian. The science of climate change is under attack by those who have a vested interest in preserving the status quo that got us where we are. What is more correct to say is the boundary is is moving east of the historical value which was the 100th meridian.

  10. Ginny Liddicoat says:

    Since the 100th meridian is a man-invented line, like state borders, it does not move because of climate change.

    The southward expansion of the Sahara is more likely to be due to grazing practices of domesticated animals. The Gobi, on the other hand, is due to the rain shadow caused by the recent uplift of the Himalayas between the 4th and 14th centuries. At the time of Gengkis Khan, the Gobi was a grassland/great plain/veldt but was already drying. Typically, a negative change in resources leads to empire building.

    It makes sense that warmer temperatures would contribute to more rapid evaporation thus encouraging the aridity moving eastward. I suggest that the continuing uplift of the Pacific coastal ranges may also be playing a part.

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