Here in southern Michigan we have had winter weather more typical of Dallas during a warm spell that got above 60F and near Memphis with warm spells in the 40s.
It wouldn't take much of a shift of the climatic patterns to bring the cotton belt (Cfa) to where the corn belt is (Dfa). Of course, should the summers go dry things could be more like the Sacramento Valley (Csa).
Discussions of climate are fluid. Despite being at the same latitude as Roseburg, Oregon and Rome, Italy (both with hot-summer Mediterranean climates), Detroit and Chicago both get real winters. Maybe that is because Greenland is still glaciated, and the effective north climatic pole is decidedly closer. Freak weather can offer even the mirror image of 1816 (the "Year without a Summer") as a "Year without a winter" (like 2012). In case anyone gets nostalgic for the winter of 2012, such was not good for crops. Ground water ran short that year, with southern Michigan looking much like the Central Valley of California that year.
But if the Greenland Ice Sheet gets close to vanishing, then weather patterns will shift permanently. Corn, potato, and wheat crops that people need in large volumes will shrink in yield -- and people will be under more insecurity of food supply.
When supplies of such staples as corn, wheat, and potatoes are plentiful... thank some Midwestern blizzards for protecting the groundwater from evaporation.
The greatest evil is not now done in those sordid "dens of crime" (or) even in concentration camps and labour camps. In those we see its final result. But it is conceived and ordered... in clean, carpeted, warmed and well-lighted offices, by (those) who do not need to raise their voices. Hence, naturally enough, my symbol for Hell is something like the bureaucracy of a police state or the office of a thoroughly nasty business concern."
― C.S. Lewis, The Screwtape Letters