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Lesson M12.L02: The 2008 Global Financial Crisis: Causes and Contagion

Module: Financial Crises; Macroeconomics: What Have We Learnt? Level: intro Duration: 30 minutes Learning Objective: Explain how subprime mortgage securitisation triggered the 2008 GFC and spread globally. Data as of: 2024 Provenance: OpenStax Macro 3e | Khan Academy Macro | MIT OCW 14.02

Explanation

The Global Financial Crisis (GFC) of 2007–2009 was the worst financial crisis since the Great Depression. Its origins lay in the United States housing market and a financial innovation that turned risky mortgages into globally traded securities.

The chain of events:

  1. US housing bubble (2000–2006): US house prices rose dramatically, fuelled by low interest rates, loose lending standards, and the belief that prices would never fall nationally. Lenders issued subprime mortgages — loans to borrowers with poor credit histories — often with "teaser" low initial rates that would later reset higher.

  2. Securitisation: Banks packaged thousands of mortgages into mortgage-backed securities (MBS) — financial products that paid investors from the interest and principal repayments on the underlying mortgages. These were further bundled into collateralised debt obligations (CDOs). Rating agencies rated many of these instruments AAA (lowest risk), based on flawed models that assumed US house prices would never fall nationally.

  3. Global distribution: MBS and CDOs were sold to banks, pension funds, and insurance companies worldwide. The risk was distributed globally — but so was the eventual loss.

  4. The collapse (2006–2008): US house prices began falling — eventually dropping about 30% from peak to trough (2006–2012). Subprime borrowers defaulted in large numbers. MBS and CDO values collapsed. Losses cascaded through the global financial system.

  5. Lehman Brothers (September 2008): The failure of investment bank Lehman Brothers — which held massive MBS positions — triggered a global credit freeze. Banks stopped lending to each other. Global trade finance collapsed. Economies worldwide fell into recession.

Worked Example

How securitisation spread risk — and losses:

Suppose a US bank originates 1,000 subprime mortgages, each A$200,000, with a 10% default rate assumed:

Step 1 — Face value of mortgage pool: 1,000 × \(200,000 = **\)200,000,000** (US$200m)

Step 2 — Expected losses at assumed 10% default, 50% recovery: Defaulting loans = 1,000 × 0.10 = 100 loans Loss per default = $200,000 × (1 − 0.50) = $100,000 Expected loss = 100 × \(100,000 = **\)10m** (5% of pool)

Step 3 — Actual default rate hits 25%, recovery falls to 30%: Defaulting loans = 250 Loss per default = $200,000 × (1 − 0.30) = $140,000 Actual loss = 250 × \(140,000 = **\)35m** (17.5% of pool)

Step 4 — Impact on AAA-rated senior tranche: The CDO was structured so the top "senior" tranche (60% of the pool = $120m) was supposedly safe — losses would be absorbed by junior tranches first. But: Total losses = $35m Junior tranche (40% = $80m) absorbs first $35m → exhausted if losses exceed $80m? No — $35m < $80m, so senior is protected. BUT: if default rate hits 50%: losses = 500 × $140,000 = $70m < $80m — still OK. If recovery falls to 0%: 250 defaults × $200,000 = $50m — still absorbed. Stress scenario (40% default, 0% recovery): 400 × $200,000 = $80m — junior tranche wiped out, senior tranche begins losing. This is exactly what happened — models underestimated correlations between defaults.

Common Misconception

Misconception: "The GFC was caused by greedy individual bankers acting illegally, and fixing banking ethics would prevent future crises."

Correction: While unethical behaviour occurred (predatory lending, misleading ratings), the deeper causes were systemic: flawed risk models that assumed house prices had no national correlation; regulatory gaps that allowed off-balance-sheet vehicles to hide risk; perverse incentive structures where originators of loans bore no risk from defaults ("originate-to-distribute"); and insufficient capital buffers at banks globally. Ethics reform alone would not have prevented the crisis — structural regulatory reforms (higher capital requirements, stress testing, restrictions on proprietary trading) were needed and subsequently implemented under Basel III.

Practice Prompts

  1. Explain in simple terms what "securitisation" means and why it was supposed to make the financial system safer — but actually made it more fragile. → Answer: Securitisation means pooling many loans together and selling shares in the pool's cash flows as tradeable securities (MBS, CDOs). It was supposed to diversify risk: no single investor would be exposed to any one mortgage. In theory, spreading risk across many global investors made the system safer. In practice, it made the system more fragile because: (1) the securities were complex and opaque, so buyers trusted ratings without understanding the underlying risk; (2) risk was hidden in off-balance-sheet vehicles; (3) when house prices fell nationally (not just locally), defaults were correlated — the assumed diversification evaporated — and losses hit all holders simultaneously, spreading the crisis globally rather than containing it.

  2. US house prices fell from a peak index of 200 in 2006 to 140 in 2012. Calculate the percentage decline. If a subprime borrower had bought a house at peak for US$400,000 with a 5% deposit, what was their equity position at the 2012 trough? → Answer: Percentage decline = (200 − 140) / 200 × 100 = 60/200 × 100 = 30% decline Purchase price = $400,000; deposit (equity) = 5% × 400,000 = $20,000; mortgage = $380,000 House value at trough = \(400,000 × (1 − 0.30) = **\)280,000 Equity at trough = $280,000 − \(380,000 = **−\)100,000 (deeply underwater) The borrower owes $100,000 more than the house is worth — strong incentive to default ("jingle mail"). This is why default rates surged so sharply.

  3. Why did the failure of Lehman Brothers in September 2008 turn a US housing crisis into a global economic recession? → Answer: Lehman was a globally interconnected investment bank. Its failure created massive uncertainty about which other institutions held similar toxic assets. Banks stopped lending to each other (interbank lending froze) because no one could assess counterparty risk. This credit freeze cascaded: businesses couldn't get trade finance; supply chains collapsed; exports and imports fell sharply worldwide. In Australia, commodity demand fell as China's export sector was hit, and domestic credit conditions tightened. The crisis spread from US housing to global recession through the interconnected financial system and subsequent collapse in confidence and trade.

Further Resources