The subprime mortgage financial crisis of 2007 was a sharp rise in home foreclosures which started in the United States during the fall of 2006 and became a global financial crisis within a year.
The crisis began with the bursting of the housing bubble in the U.S. and high default rates on "subprime", adjustable rate, "Alt-A", and other mortgage loans made to higher-risk borrowers with lower income or lesser credit history than "prime" borrowers. The share of subprime mortgages to total originations increased from 9% in 1996, to 20% in 2006. Further, loan incentives including "interest only" repayment terms and low initial teaser rates (which later reset to higher, floating rates) encouraged borrowers to assume mortgages believing they would be able to refinance at more favorable terms later. While U.S. housing prices continued to increase during the 1996-2006 period, refinancing was available. However, once housing prices started to drop moderately in 2006-2007 in many parts of the U.S., refinancing became more difficult. Defaults and foreclosure activity increased dramatically. By October 2007, 16% of subprime loans with adjustable rate mortgages (ARM) were 90-days delinquent or in foreclosure proceedings, roughly triple the rate of 2005. By January of 2008, this number increased to 21%. As of December 22, 2007, a leading business periodical estimated subprime defaults would reach a level between U.S. $200-300 billion.
The mortgage lenders that retained credit risk (the risk of payment default) were the first to be affected, as borrowers became unable or unwilling to make payments. Major banks and other financial institutions have reported losses of approximately U.S. $100 billion as of January 16, 2008, as cited below. Due to a form of financial engineering called securitization, many mortgage lenders had passed the rights to the mortgage payments and related credit/default risk to third-party investors via mortgage-backed securities (MBS). Individual and institutional investors holding MBS faced significant losses, as the value of the underlying mortgage assets and payment streams declined and became difficult to predict.
In addition, certain legal entities designed to isolate this risk from the originating lenders, called collateralized debt obligations (CDO) and structured investment vehicles (SIV), held substantial amounts of MBS. As the value of payments into these entities declined, their value also declined, forcing the sale of MBS at fire sale prices in some instances.
The widespread dispersion of credit risk and the unclear impact on large banks, MBS, CDO, and SIV caused banks to reduce their loans to each other or make them at higher interest rates. Similarly, the ability of corporations to obtain funds through the issuance of commercial paper was impacted. The liquidity concerns drove central banks around the world to take action to provide funds to member banks to encourage the lending of funds to worthy borrowers and to re-invigorate the commercial paper markets.
The combination of impacts due to credit risk and liquidity risk caused several major corporations and hedge funds to shut down or file for bankruptcy. Stock market declines among both depository and non-depository financial corporations were dramatic. Many hedge funds and other institutional investors holding MBS also incurred significant losses.
With interest rates on a large number of subprime mortgages due to adjust upward during the 2008 period, U.S. legislators and the U.S. Treasury Department are taking action. A systematic program to limit or defer interest rate adjustments was implemented to limit the impact. In addition, lenders and borrowers facing defaults have been encouraged to cooperate to enable borrowers to stay in their homes. Restrictions on lending practices are under consideration. Many lenders have stopped subprime lending or dramatically curtailed it.