A topic in the Open Knowledge Graph — a free, open map of 15,290 topics and the order to learn them in.
A negative supply shock (oil spike, disaster, productivity decline) reduces aggregate supply, shifting AS curve left. Output falls and price level rises simultaneously—stagflation. Central bank faces a dilemma: tighten to reduce inflation (worsening recession) or accommodate (risking accelerating inflation).
Use 1973-74 oil shock case study: OPEC raised prices, raising production costs globally. AS curve shifts left, pushing up prices and reducing output. Compare policy responses and consequences.
To understand supply shocks, start from the AS-AD model you already know. The aggregate demand curve slopes downward (higher price levels reduce real purchasing power), and the short-run aggregate supply (SRAS) curve slopes upward (higher prices draw out more production). Their intersection determines equilibrium output and the price level. A negative supply shock — an abrupt increase in production costs — shifts the entire SRAS curve to the left. Think of the 1973 OPEC oil embargo: petroleum was an input to nearly every industry, so when its price quadrupled, the cost of producing any given level of output rose sharply. The whole supply schedule shifted inward.
The key consequence is that a leftward AS shift produces a move to a *new* intersection that is simultaneously higher on the price axis and lower on the output axis. This is stagflation: stagnation (falling output, rising unemployment) combined with inflation (rising prices). This combination was deeply puzzling to economists trained on the Phillips curve, which implied that inflation and unemployment move in opposite directions. Supply shocks break that relationship by shifting the economy in a direction the Phillips curve framework doesn't anticipate.
This creates a genuine policy dilemma for the central bank. Tightening monetary policy (raising interest rates, reducing money supply) shifts aggregate demand left, which would counteract the inflation — but it also further reduces output and pushes unemployment higher. Accommodative policy (lowering rates, expanding money supply) shifts aggregate demand right, supporting output — but validates the higher price level and risks entrenching inflationary expectations. There is no policy response that cleanly restores both the original output level and the original price level simultaneously, which is why supply shocks force painful choices.
The severity of outcomes also depends on wage-price dynamics. If workers expect prices to keep rising, they demand nominal wage increases. If those are granted, firms face even higher costs, shifting AS left again — a wage-price spiral. This is why inflation expectations matter so much: a central bank that credibly commits to fighting inflation may be able to prevent the secondary wage-price feedback, even if the initial shock still causes a recession. The 1970s stagflation worsened because expectations became unanchored; the early 1980s recovery required a severe recession to re-anchor them. Understanding supply shocks therefore requires integrating the AS-AD framework with the expectations dynamics you'll encounter in the New Keynesian Phillips curve.