Martin Wolf warns that US stock valuations now exceed even the 1929 peak. Irving Fisher's infamous "permanently high plateau" forecast preceded the Great Crash; today's Shiller Cape 41.4 in July 2026 surpasses the 1929 level of 32.6, with only the 1999 dotcom bubble higher at 44.2.

Robert Shiller's cyclically adjusted price/earnings ratio and "excess Cape yield" (now 1.4 per cent vs 4.7% average) signal poor future returns. The "Buffett indicator" tops 200% market-cap-to-GDP, and the US market commands 55 per cent of global equity value.

An AI-driven boom fuels optimism, with hyperscalers and chipmakers dominating. Chris Watling notes AI-linked stocks represent 40 per cent of S&P 500 capitalization. Yet history shows transformative technologies — railways, internet — typically trigger over-investment, destructive competition, and painful consolidation.

Prospective real returns are just 2.4 per cent, less than half the historic 5.6%. Joachim Klement argues earnings themselves are bubbly. Triggers for correction are unknown, but destabilising shocks loom.