An adverse supply shock is a negative disturbance that makes firms less willing or less able to produce at any given price. In the short run, it typically raises inflation while lowering output and employment.
Why It Is Different From A Demand Shock
A demand slowdown usually lowers both output and inflation. An adverse supply shock creates a harder policy problem because it pushes output and prices in opposite directions. That is why it is closely associated with stagflation.
Common Sources
Adverse supply shocks often come from:
- energy or food price spikes
- supply-chain disruption
- war or sanctions affecting key inputs
- natural disasters
- sudden tax or regulatory changes that raise production costs
- disease outbreaks that reduce labor availability or productive capacity
The Short-Run Macro Mechanism
In the aggregate-demand and aggregate-supply framework, the short-run aggregate-supply curve shifts left. Real output falls from potential while the price level rises.
A reduced-form way to express the inflation effect is:
[ \pi_t = \pi_t^e + \kappa(y_t - y_t^*) + u_t ]
Here u_t is a cost-push term. When u_t is positive, inflation rises for a given output gap.
Why Policymaking Gets Harder
Central banks face a trade-off after an adverse supply shock:
- tightening policy may slow inflation but deepen the fall in output
- easing policy may support demand but allow inflation to stay higher for longer
Governments can sometimes help through targeted supply measures, temporary relief, or investment in resilience, but they usually cannot remove the shock immediately.
Why Economists Care
Supply shocks explain why inflation can rise even when the economy is weak. They also matter for credibility and expectations. If households and firms start expecting repeated cost shocks to feed into wages and prices, inflation can persist longer than the original shock itself.