I've learned not to comment on the markets, since wild up and down swings are not uncommon. However, today's market drops are predicated on the scariest of all possible economic news -- a downturn in the housing market.

In short, the economy, horrid as it is, has been propped up by consumer spending spurred by mortgage refinancing and a strong real estate market. However, Greenspan cautioned today that the 2003 housing market was shaping up poorly:

A home-mortgage refinancing boom and rising home values have been key pillars supporting consumer spending, the main force keeping the economy going. Greenspan said an expected cooling on the refinancing and home appreciation fronts could turn homeowners into more cautious consumers.

"The frenetic pace of home equity extraction last year is likely to appreciably simmer down in 2003, possibly notably lessening support to household purchases of goods and services," Greenspan said in a speech delivered via a satellite video link to the Independent Community Bankers of America meeting in Orlando, Fla.