Aggregate Supply

Why SRAS Slopes Upward

Look at the upward-sloping curve on the graph. That's your Short-Run Aggregate Supply (SRAS). Drag the price level slider up and notice what happens to output — it rises. The reason is deceptively simple: wages haven't caught up yet.

Imagine the overall price level jumps 10%. Employers are still paying last quarter's wages because contracts lock those numbers in. Revenue per unit climbed, but labor costs didn't budge. Margins widen. Firms ramp up production. Scale that across every factory, office, and restaurant in the economy and you get that upward slope you see on screen.

Two models explain the mechanism.

The sticky-wage model says nominal wages are frozen by contracts. When the price level rises and wages lag behind, hiring gets cheaper in real terms. Workers don't immediately push for raises — their contracts hold, or they simply haven't registered the broader price increase yet. So firms expand output.

The misperceptions model tells a completely different story. A wheat farmer sees wheat prices climb and thinks, "Demand for my wheat just jumped." She plants more. But actually all prices rose together. She expanded based on a misread signal — confusing a general price increase with a rise in the relative price of her product.

Both models land in the same place: higher price levels produce higher output in the short run because input costs, especially wages, are stuck.

What Shifts SRAS

The curve you're looking at shifts left or right when production costs change economy-wide — independent of the price level itself.

Input prices drive most shifts. Toggle the oil price control on the graph and watch SRAS slide left as costs spike. An oil price increase in the style of 1973 raises costs for transportation, manufacturing, agriculture, and chemicals simultaneously. Firms need a higher price level to justify the same output. Falling commodity prices push the curve the other direction.

Productivity improvements shift SRAS right. Workers producing more output per hour — through better tech, better training, smarter management — lower the cost per unit. Every price level now supports more output.

Supply shocks hit suddenly. A hurricane wrecking Gulf Coast refineries. A pandemic shuttering factories. A war cutting off Ukrainian grain exports in 2022. All of these yank SRAS left. A positive shock like the fracking revolution after 2008 pushes it right.

Government regulations and production taxes matter too. A new EPA compliance rule that raises costs for manufacturers shifts SRAS left. A targeted manufacturing subsidy shifts it right.

One distinction the AP Macroeconomics exam hammers repeatedly: demand-side factors (consumer confidence, government spending, money supply) shift AD. Supply-side factors (input costs, productivity, supply shocks) shift SRAS. Mixing these up on a free-response question costs you the entire explanation point.

LRAS and Potential Output

Now look at the vertical line on the graph. That's your Long-Run Aggregate Supply (LRAS).

Given enough time, every sticky price unsticks. Contracts get renegotiated. Workers demand raises that match actual inflation. Firms reprice their goods. The stickiness that gave SRAS its upward slope vanishes completely. Once everything adjusts, the economy's output depends only on real productive capacity — how many workers exist, how much capital they operate, and what technology is available. The price level becomes irrelevant to output. Vertical line.

That line sits at potential GDP, sometimes called full-employment output. The maximum sustainable production level with all resources deployed at normal rates. "Full employment" trips people up. It does not mean zero unemployment. It means unemployment sits at the natural rate — which includes frictional unemployment (people between jobs) and structural unemployment (skills mismatch) but excludes cyclical unemployment.

LRAS shifts only when productive capacity itself changes. Labor force growth from immigration. Capital accumulation from business investment. Technological breakthroughs. Institutional improvements in education or property rights. Notice on the graph that dragging the price level slider does absolutely nothing to LRAS. It stays put.

The Self-Correction Mechanism

Drag actual GDP on the graph to the left of the LRAS line. See that gap? That's a recessionary gap — actual output below potential, unemployment above the natural rate.

The self-correction story goes like this. With high unemployment, workers compete for scarce jobs. Nominal wages fall over time, or at minimum grow slower than they otherwise would. Falling wages reduce production costs. Lower costs shift SRAS right. Watch the curve slide rightward on the graph until output returns to potential GDP at a lower price level.

An inflationary gap self-corrects in reverse. Drag actual GDP to the right of LRAS. Labor is scarce. Workers demand raises. Costs climb. SRAS shifts left. Output cools back to the vertical line.

The real fight in macroeconomics is about speed.

Classical economists say adjustment happens fast enough that government intervention mostly creates noise. Keynesians counter that wages are brutally sticky downward — workers and unions resist pay cuts with everything they've got. In a severe recession, self-correction could drag on for years while millions sit unemployed. The Great Depression took over a decade. The 2001 recession self-corrected in about eighteen months. Severity determines whether patience qualifies as a serious policy stance.

Supply Shocks in History

The 1973 OPEC oil embargo remains the textbook negative supply shock. Prices quadrupled almost overnight. Then in 1979, the Iranian Revolution disrupted supply again and prices doubled. Oil feeds into nearly every production process, so SRAS shifted sharply left both times.

The result was stagflation — rising prices and falling output simultaneously. Before the 1970s, most economists believed inflation and recession couldn't coexist. The Phillips Curve said they moved in opposite directions. Stagflation broke that framework and forced a wholesale rethinking of macroeconomic theory.

COVID-19 produced a very different shock in 2020-2021. Factories shut down across Asia. Shipping containers piled up at wrong ports. The global semiconductor shortage halted auto production at Ford, GM, and Toyota for months. Workers left the labor force entirely. SRAS shifted left dramatically. Meanwhile, the $1,200 and $1,400 stimulus checks plus expanded unemployment benefits shifted AD right. Reduced supply colliding with boosted demand — that collision produced the sharp inflation spike running above 8% by mid-2022.

The policy lesson from both episodes: demand shocks and supply shocks require different responses. A demand-driven recession can be addressed by stimulating spending through fiscal or monetary policy. A supply-driven shock is far harder. Stimulating demand when supply is constrained just piles more inflation onto an already stressed economy.

Worked Example: SRAS Shift and New Equilibrium

Look at the starting position on the graph: long-run equilibrium with a price level of 110 and real GDP of $5 trillion, sitting right on the LRAS line. Potential GDP equals actual GDP. Now hit the oil shock button.

The shock raises production costs economy-wide, dragging SRAS to the left. Watch where the new intersection lands. The short-run equilibrium settles at a price level of 120 and real GDP of $4.6 trillion.

Identify the gap.
Potential GDP = $5T. Actual GDP = $4.6T. Actual falls short of potential. That's a recessionary gap of $400 billion.

What happened on the graph.
Three things occurred at once: the price level jumped from 110 to 120, output fell from $5T to $4.6T, and a deadweight loss region appeared between the old and new equilibrium points. Rising prices with falling output. That's the definition of stagflation.

Self-correction process.
With GDP below potential, unemployment exceeds the natural rate. Over time — toggle the "self-correct" animation — excess unemployment pushes wages down. Falling wages reduce costs. SRAS gradually drifts back rightward. The economy slides along the AD curve toward $5T, and the price level eases down from 120.

The painful reality with a negative supply shock: self-correction means enduring both elevated prices and elevated unemployment during the entire adjustment period. Stimulating AD would close the output gap but worsen inflation. Tightening monetary policy to fight inflation would deepen the recession. Neither tool fixes both problems simultaneously, which is exactly why the 2022 Fed faced such brutal tradeoffs.