AD/AS Equilibrium and Macroeconomic Shocks

The AD/AS model is the central analytical framework for macroeconomics at A-Level. It brings together aggregate demand and aggregate supply to determine the equilibrium price level and level of real output in the economy. This lesson examines how equilibrium is established, how demand-side and supply-side shocks disrupt it, and how the economy adjusts — with detailed reference to real-world examples including the 2008 financial crisis, the COVID-19 pandemic, and the energy price shock of 2022.

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Establishing Macroeconomic Equilibrium

Macroeconomic equilibrium occurs where the AD curve intersects the AS curve. At this point:

• The quantity of goods and services demanded equals the quantity supplied
• There is no tendency for the price level or real output to change (in the absence of external shocks)
• The price level and level of real GDP are simultaneously determined

Equilibrium in the Classical Model

In the classical model:

• Short-run equilibrium occurs where AD intersects SRAS
• Long-run equilibrium occurs where AD intersects SRAS intersects LRAS (all three curves meet)
• If the economy is not at long-run equilibrium, wages and prices adjust until it returns to LRAS

Condition	Adjustment
AD increases (rightward shift)	Short-run: output rises above Yn, price level rises. Long-run: wages rise (workers demand higher pay to match inflation), SRAS shifts left, output returns to Yn at a higher price level.
AD decreases (leftward shift)	Short-run: output falls below Yn, price level falls. Long-run: wages fall (unemployment puts downward pressure on wages), SRAS shifts right, output returns to Yn at a lower price level.

Equilibrium in the Keynesian Model

In the Keynesian model, the economy can settle in equilibrium at any point along the Keynesian AS curve:

• On the horizontal section: equilibrium with high unemployment and stable prices
• On the upward-sloping section: equilibrium with moderate unemployment and some inflation
• On the vertical section: equilibrium at full employment with demand-pull inflation

The critical Keynesian insight is that equilibrium does not necessarily mean full employment. The economy can be in equilibrium with substantial unemployment if AD is insufficient.

Exam Tip: When drawing AD/AS diagrams, always label both axes (price level on the vertical axis, real GDP on the horizontal axis), label all curves, and clearly mark the equilibrium price level and output. Examiners award marks for accurate, well-labelled diagrams.

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Demand-Side Shocks

A demand-side shock is a sudden, unexpected change in aggregate demand:

Positive Demand-Side Shocks (AD Shifts Right)

Shock	Mechanism	Effect
Tax cuts	Higher disposable income → increased consumption	Output rises; price level may rise depending on spare capacity
Interest rate cuts	Lower borrowing costs → higher C and I	Output rises; if sustained, may fuel asset price bubbles
Rise in consumer/business confidence	Higher spending and investment	AD increases — confidence is self-reinforcing
Exchange rate depreciation	Exports become cheaper; imports dearer → net trade improves	AD rises; may also shift SRAS left if imported inputs become more expensive
Quantitative easing	Central bank purchases assets → lowers long-term rates → boosts spending	AD increases — though the transmission mechanism is uncertain

Negative Demand-Side Shocks (AD Shifts Left)

Shock	Mechanism	Effect
Financial crisis	Credit crunch → banks stop lending → consumption and investment collapse	Sharp fall in output, rise in unemployment, possible deflation
Fiscal austerity	Cuts to G and rises in T	AD falls — magnified by the multiplier
Global recession	Fall in overseas demand → exports decline	AD shifts left — particularly damaging for export-dependent economies
Confidence collapse	Fear of unemployment → precautionary saving → spending falls	Self-reinforcing downward spiral — Keynes's "paradox of thrift"
Interest rate rises	Higher borrowing costs → lower C and I	AD contracts — the Bank of England uses this to control inflation

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Supply-Side Shocks

A supply-side shock is a sudden, unexpected change in the costs of production or productive capacity:

Adverse Supply-Side Shocks (SRAS Shifts Left)

Shock	Example	Effect
Oil price rise	1973 OPEC embargo; 2022 Russia-Ukraine war	Costs rise across the economy → SRAS shifts left → stagflation (higher prices and lower output simultaneously)
Pandemic	COVID-19 (2020)	Labour supply falls, supply chains disrupted → SRAS shifts left
Natural disaster	Fukushima earthquake (2011), flooding	Productive capacity destroyed → SRAS and potentially LRAS shift left
Trade disruption	Brexit customs checks (2021 onwards)	Increased costs of importing/exporting → SRAS shifts left
Wage-push	Rapid wage increases exceeding productivity growth	Unit labour costs rise → SRAS shifts left

Beneficial Supply-Side Shocks (SRAS Shifts Right)

Shock	Example	Effect
Technological breakthrough	Internet revolution (1990s), AI applications (2020s)	Costs fall, productivity rises → SRAS shifts right → lower prices and higher output
Fall in commodity prices	Oil price collapse (2014–15)	Input costs fall across the economy → SRAS shifts right
Immigration	EU enlargement (2004) — inflow of workers to the UK	Labour supply increases → wages held down → SRAS shifts right
Deregulation	Removing red tape reduces compliance costs	SRAS shifts right — though effects may be gradual

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Stagflation: The Worst of Both Worlds

Stagflation — the simultaneous occurrence of stagnation (falling output) and inflation (rising prices) — occurs when an adverse supply-side shock shifts SRAS to the left: