Persistent surplus requires some mechanism to remove the excess supplies from the market. Government purchases surpluses create by farm price supports. Impact on taxpayers government expenditures on surplus price floor times surplus government expenditures on storing the surplus. Demand shifts to the right. At the original equilibrium price a shortage develops.
Prices rise in response to the shortage.
Market effects of the change equilibrium price rises. The above are reversed for a decrease in demand. At the original equilibrium price a shortage develops. Prices rise in response to the shortage. Market effects of the change equilibrium price rises.