Warren Buffett's historic $127 billion warning to Wall Street happens to align with another stock market alarm. Specifically, the S&P 500 currently trades at a historically expensive valuation. The index achieved a cyclically adjusted price-to-earnings ratio (CAPE) of 37.9 in December 2024, which is a substantial premium to 20-year average of 27.

Nvidia Corp., the poster child of the AI frenzy, sank 17 per cent and headed toward the biggest market-cap loss for a single stock in market history. The AI leader wiped of $500 billion of its market value and shed 21 per cent off its stock price in two days.

Global investors are worried the emergence of a low-cost Chinese AI model will threaten the dominance of AI leaders.