Milk comes from contented cows, and the decline in milk production due to climate change varies across the country, since there are humidity and temperature swings between night and day vary as well. The humidity and hot nights make the Southeast the most unfriendly place for dairy cows. The Economist quotes economist Yoram Bauman as saying, "Cows are happy in parts of Northern California and not in Florida."
Researchers have developed software that will advise dairy farmers across the country on how their milk production will do, through 2080. The Economist quotes researcher Guillaume Mauger as saying, "Using US Department of Agriculture statistics, if you look at milk production in the Southeast versus the Northwest, it’s very different. It’s reasonable to assume that some of that is due to the inhospitable environment for cows in the Southeast.
"Perhaps most significantly, those regions that are currently experiencing the greatest losses are also the most susceptible: they are projected to be impacted the most by climate change." Soon milk–like oranges–will only be produced in certain parts of the country, meaning that it will have to be shipped long distances and the price will rise.
Or maybe farmers will move their cows instead. The Economist quotes Yoram Bauman as saying, "You can pick up dairy cows and truck them elsewhere."