WITH another month of jobs data in hand, economics writers can't help but note the remarkably stable pattern in employment growth. Payrolls rose by 155,000 jobs in December of 2012, according to figures released by the Bureau of Labour Statistics on Friday. Average monthly employment growth for all of 2012 was 153,000—the same as in 2011. This coincidence could be down to shortcomings in data gathering; new revisions may well nudge up the rate of employment growth in 2012. We had better hope so.

December marked half a decade since the beginning of the last recession and 42 months since the recovery began in June of 2009. It would be nice if business cycle expansions never had to end. In some places they seem not to (see Australia). Yet new downturns have been an inevitability in modern economies. The chart at right shows the duration of expansions since the Second World War. On average, the economy has grown about 58 months at a time during this period, an age the current American expansion will reach in April of next year. Since the Volcker recession, good times have gone on for longer—95 months on average—though the expansion of the 2000s was just 73 months long, a milestone the current recovery will reach in July of 2015. Perhaps the present recovery will more closely resemble that of the 1990s, which lasted a full decade. But it would probably be unwise to count on that.

That's a disturbing possibility. At the last Federal Reserve meeting Chairman Ben Bernanke announced new thresholds that would be used as guidelines for deciding when to raise the Fed's benchmark interest rate. Based on these guidelines and the Fed's projections for labour market improvement, it reckons that rates may begin to go up around 2015—not, that is, until the economy is firmly within the window in which we would expect a new downturn. That's bad news. It suggests that the economy may be well on its way back toward recession at a time when the Fed's policy rate is at most a percentage point or two above zero. That, in turn, gives the Fed very little room to ease in response to economic weakness before running back into the constraints that have kept it, by its own admission, from addressing unemployment as aggressively as it would have had there been the opportunity to continue cutting rates.

Without an acceleration in the pace of growth, in other words, the American economy may remain stuck in this trap for more than one business cycle. That's rough news for workers. The Fed projects an unemployment rate between 6.0% and 6.6% in 2015, above the Fed's estimate of the economy's "full-employment" unemployment rate. At the pace of job growth in 2011 and 2012, the economy will only regain its pre-recession level of employment, of about 138m jobs, in March of 2015. A new recession may become a risk at a time when the economy has yet to work off the unemployment problem from the last downturn, and in a world in which the Fed is unwilling to respond as aggressively as the case demands because of its concerns regarding the risks of "unconventional" policy.

If that unpleasant outcome is to be avoided, the economy needs faster growth. Faster growth should bring back full employment sooner, reducing the risk that millions of the still-unemployed will drop out of the labour force forever, cutting America's growth potential. Just as important, an economy that's running hotter will generate upward pressure on interest rates sooner, giving the Fed more time to ease rates up in order to give itself a cushion to slash its policy rate into the next economic swoon.

The Fed often behaves as if time is no worry. It is. The longer current conditions persist, the greater the odds that the economy will suffer large and quasi-permanent damage from the 2007-9 recession. And the greater the risk that the Fed goes into the next downturn with its quiver empty of its favourite arrows. That will mean that the next downturn will be deeper than it should be, saddling with country with still larger an unemployment problem. That threat is a pretty good reason to worry less about (if not actively court) more inflation.

And because it's the worry of the day in Washington it's worth pointing out that current, disappointing growth rates make it harder to stabilise growth in the government's debt load, while the Fed's zero interest rate problem means that fiscal policy may have to do more of the job of economic stabilisation next time around. Of course, if America is bound to stay stuck in a low-growth equilibrium for the foreseeable future then, like Japan, it may be able to run up enormous piles of sovereign debt with little impact on interest rates. But elected officials squawking about America's fragile fiscal future ought to be more worried about present growth.