THE desire to rescue a damaged reputation is a powerful motivator. That is one conclusion to draw from a new 48-page paper written for the Brookings Institution by Alan Greenspan, the 83-year-old former chairman of America's Federal Reserve. A man once hailed as the world's outstanding central banker is now routinely blamed for the asset bubble and subsequent collapse. This is Mr Greenspan's attempt to set the record straight.

The crisis, he argues, stemmed from a “classic euphoric bubble” whose roots lay in the sharp global decline in nominal and real long-term interest rates in the early part of the 2000s, which fuelled an unsustainable boom in house prices. Thanks to this euphoria, banks misread the risks embedded in complex new financial instruments. Mr Greenspan reckons the best remedy is to improve the system's capacity to absorb losses by raising banks' capital and liquidity ratios and increasing collateral requirements for traded financial products.

So far, so uncontroversial. Mr Greenspan's analysis of the fragilities within finance, and his specific proposals, echo today's policy consensus. The one area where he differs from the reform consensus is over the wisdom of a “systemic regulator”. Today's policymakers see such a regulator, which would monitor the health of the financial system and sniff out incipient problems, as an important improvement. Mr Greenspan says it is impossible to anticipate crises and regards such a regulator as “ill-advised”.

But the biggest gap between Mr Greenspan and conventional wisdom lies in the role of monetary policy in causing the crisis. In Mr Greenspan's telling, central banks were innocent and impotent bystanders in a global macroeconomic shift. Thanks to the end of the cold war and reform in China, he argues, hundreds of millions of workers were absorbed into the global economy. As GDP growth in emerging economies soared, their consumption could not keep up with rapidly rising income, and saving rose. The rise in desired global saving relative to desired investment caused a global decline in long-term rates, which became delinked from the short-term rates that central bankers control.

This explanation is broadly similar to the idea of a “global saving glut” which Ben Bernanke, the Fed's current chairman, has long espoused. The similarities between the two men's defence of their monetary records do not end there. The most combative section in Mr Greenspan's paper—arguing that monetary policy in the early 2000s was not a cause of the housing bubble—is strikingly similar to a speech given by Mr Bernanke at the American Economics Association's annual meeting in January.

Both men make three broad points. First, they deny that monetary policy in the early 2000s was excessively loose by traditional central-bank rules of thumb. That is a criticism frequently made by John Taylor of Stanford University, author of the Taylor rule on how interest rates should change in response to movements in inflation and GDP. Mr Bernanke points out that based on contemporary forecasts for its preferred inflation measure, the Fed actually followed the Taylor rule reasonably closely.

Second, both men say there is no evidence that low short-term rates drove house prices upward. Mr Greenspan argues that the statistical relationship between house prices and long-term rates is much stronger than with the Fed's policy rates, and that during the early 2000s the traditionally high correlation between policy rates and long-term rates fell apart. Mr Bernanke points to structural models which show that only a modest part of the house-price boom can be pinned on monetary policy.

Both are equally sceptical that the increase in adjustable-rate mortgages made short-term rates a more potent driver of house prices. Mr Greenspan says that the pace of adjustable-rate mortgage originations peaked two years before house prices, suggesting they were not driving the bubble. Mr Bernanke argues that the monthly payments on adjustable-rate mortgages were, on average, only 16% lower than those for fixed-rate mortgages—too small a gap to suggest that short-term rates propelled the boom.

Third, Messrs Bernanke and Greenspan point to the global nature of the house-price boom as proof that monetary policy was not to blame. Both cite new research from economists at the Fed showing that the looseness of monetary policy in different countries was not correlated with changes in house prices.

Protesting too much

There is something odd about central bankers denying any responsibility at all for long-term rates, which are, in principle, based partly on an assessment of a stream of short-term rates. Nor is it clear that low short-term rates were as irrelevant as Messrs Bernanke and Greenspan suggest. Jeremy Stein of Harvard University, a discussant of Mr Greenspan's Brookings paper, points out that low policy rates may have mattered a great deal for income-constrained borrowers. He points out that adjustable-rate mortgages were used much more in expensive cities, a trend that became more pronounced as the fund rates fell.

By looking only at the effect of monetary policy on house prices, Messrs Bernanke and Greenspan also take too narrow a view of the potential effect of low policy rates. Several economists have argued convincingly, for instance, that low policy rates fuelled broader leverage growth in securitised markets.

Monetary policy may be a blunt tool to deal with asset bubbles. But that does not mean it is irrelevant. Interestingly, one American central banker has a more nuanced view, arguing that “in the current episode, higher short-term interest rates probably would have restrained the demand for housing by raising mortgage interest rates…In addition, tighter monetary policy may be associated with reduced leverage and slower credit growth.” That was Janet Yellen, president of the San Francisco Fed, who is likely to be Mr Bernanke's new vice-chairman. With luck, she will prompt her boss to have a rethink.