The S&P 500 has surged 12% YTD, driven by AI megacaps. Economist David Rosenberg, known for predicting the 2008 crash, warns of a “gigantic price bubble” with negative returns ahead due to extreme valuations. The S&P 500’s Shiller CAPE near 37.5 signals a historically fragile setup.

Concentration risk in the S&P 500 is at a record high, with the top 10 names driving the index. Nvidia trades at 51 times earnings, with stocks over 3% weight accounting for 30-35%. Tight leadership means index returns rely heavily on mega-caps, posing risk if they falter.

Major banks have varying forecasts for the S&P 500: Deutsche Bank at 7,000 (+6.3%), Goldman Sachs at 6,600 (+0.2%), JPMorgan at 6,500 (-1.3%), Barclays at 6,450 (-2.0%), and Bank of America at 6,300 (-4.3%). The market outlook remains cautious amidst concerns of a potential bubble burst.

Read more at Yahoo Finance: Veteran economist drops surprise verdict on the S&P 500