Developed countries wouldn't encounter famine unless the cooling event was to last longer than a year, due to canned food and grain stockpiles, and in this case losses could not be compensated with imports to the northern hemisphere from the southern hemisphere or vice versa.
Developed countries wouldn't encounter famine unless the cooling event was to last longer than a year, due to larger canned food and grain stockpiles in these countries. However, if the impactor was similar in size to the K/T boundary impactor, agricultural losses might not be compensated with imports to the northern hemisphere from the southern hemisphere or vice versa.