The southerly march of the cold level might be beneficial.
Consider the palm tree, and Green Jays, and fire ants and Africanized bees..... all south loving species. They stop migrating northward somewhere in Texas.
If the cold continues south, perhaps the native Mexican human species will find it too cold north of the river and will quit coming.
Global cooling might save America
OOps..... left out the obvious.
Global Warming causes Mexican migration