Given the enormity of the recent mortgage-refinancing boom, which may exceed $2 trillion this year, and the fact that the market for mortgage-backed securities is the largest ($5 trillion) segment of the $20 trillion bond market, additional forced selling could easily occur and put upward pressure on rates (as interest rates rise, households refinance fewer mortgages, resulting in a lengthening of their average age. This effectively results in a rise in the average length of the maturities of portfolios that hold mortgage-backed securities, pressuring portfolio managers to make adjustments by selling Treasuries to shorten the risk-profile of these portfolios. Portfolios that fail to make these adjustments expose themselves to an increasing degree of price sensitivity to changes in market interest rates).