If we were to get appreciably warmer, wheat cultivation would expand across wide swaths of Canada and Russia, as evidenced by history and a number of studies. The largest study, conducted by the International Institute for Applied Systems Analysis, includes temperature impacts, CO2 fertilization, and adaptation, and projects a 40.7 percent increase in grain production by 2050. Without global warming, production might have been half a percentage point higher.
We still are below levels in our recent (in geologic time) past. The Norse explorers called it "Greenland" because grass grew there, sufficient to raise sheep and cattle. The onset of the "Little Ice Age" put an end to that.