Scott Chan/Shutterstock The '100th meridian west' is an invisible line of longitude that roughly bisects the United States' in half, separating the humid eastern states from the arid western states. Since the 1980s, this climate boundary has been shifting further from the geographical line of longitude, as dry conditions creep into states that have historically been on the more fertile eastern side. While the shift hasn't significantly impacted farming in central US yet, scientists believe it will only be a matter of time before flourishing plains become deserts. One of the fundamental climate constants that has helped define and divide the United States for centuries is shifting in response to global warming, according to new research. The 100th meridian west — the invisible line of longitude that roughly bisects the continental US in half — was historically seen as a boundary separating the humid eastern states from their arid western counterparts.See the rest of the story at Business InsiderNOW WATCH: This incredible animation shows how humans evolved from early lifeSee Also:What Earth Day means when humans possess planet-shaping powersOwning a supercar isn't as cool as you think — here's why8 common words you probably didn't know came from TV showsSEE ALSO: Disturbing before-and-after images show what major US cities could look like in the year 2100