Get uncomfortable, this could take a while: James Saft

(James Saft is a Reuters columnist. The opinions expressed are his own)

By James Saft

LONDON (Reuters) - A housing market bubble of historic proportions is unwinding, raising the risk that the current period of poor economic growth in the United States could be measured in years not quarters.

While the first problems emerged in subprime lending, it has become clear that housing is falling across geographies, price categories and borrower types.

And with momentum now behind a fall, the implication is that the process will take a long time and destroy trillions of dollars of capital.

"It is such a big crisis that it is of historic importance," Yale economist Robert Shiller said in an interview at the World Economic Forum in Davos last week.

"It may represent a major turning point and we will see years of falling home prices and associated economic weakness."

Shiller, the originator of the Case-Shiller index of U.S. house prices, said house prices could fall by as much or more than they did in the 1930s, when an extended fall took them down by 25 percent in nominal terms.

They have fallen 6.7 percent in the year to November, according to the Case-Shiller measure.