AMERICA is used to making the economic weather. It has the world's largest economy, its most influential central bank and it issues the main global reserve currency. In recent months, however, some rich-world economies (notably Germany's) have basked in the sunshine even as the clouds gathered over America.

On August 27th America's second-quarter GDP growth was revised down to an annualised 1.6%. That looked moribund compared with the 9% rate confirmed in Germany a few days earlier. America's jobless rate was 9.5% in July (figures for August were released on September 3rd, after The Economist went to press). But in Germany the unemployment rate is lower even than before the downturn. Other rich countries, including Britain and Australia, have enjoyed sprightlier recent GDP growth and lower unemployment than America.

This unusual divergence within the rich world has fostered many competing theories to explain it, including differences in fiscal policies, exchange rates and debt levels. Most of these do not quite fit the facts. On one account Germany and, to a lesser extent, Britain have been rewarded for taking a firm grip on their public finances. In this view, the promise to tackle budget deficits has had a liberating effect on private spending by reducing uncertainty. In America, by contrast, anxiety about public debt is making businesses and consumers tighten their purse strings.

The theory is a little too neat. Although credible plans to curb deficits are helpful to medium-term growth, they are unlikely to explain sudden spurts. Britain's budget plans were announced towards the end of the quarter, on June 22nd. Germany's were set out two weeks earlier. They could scarcely explain why GDP growth was strong. Indeed for most of the second quarter, fiscal uncertainty hung over both countries: in Britain because of a close election, in Germany because of commitments to help Greece and other countries. And the immediate impact of austerity is to dampen growth: witness the slump in Greece.

Perhaps the explanation is found in currency movements. One effect of the euro-area crisis was to push the euro down against the dollar in the early months of this year—helping German firms but harming American exporters. Much of Germany's second-quarter GDP growth came from trade, even as a wider trade gap sapped America's economy. A weak pound could also explain Britain's renewed economic strength, much as a surge in the yen has increased worries about Japan. On August 30th Japan's central bank said it would offer banks ¥10 trillion ($118 billion) of six-month secured loans at its benchmark interest rate of 0.1%, on top of the ¥20 trillion of three-month loans it had already pledged. It hopes that this flood of money will push down borrowing costs, cap the yen's rise and help exporters.

The currency theory also has holes in it. The yen's surge is too recent to explain why Japan's GDP barely rose in the second quarter. Net trade added almost nothing to Britain's GDP growth in the last quarter. Indeed America's export growth has been much stronger (a sudden surge in imports was behind the second-quarter trade gap). And demand for the sort of exports Germany has done well with, mostly luxury cars and specialist capital goods, tends to be insensitive to shifts in the exchange rate.

Britain is an awkward challenger to another theory: that a debt hangover is holding back consumers in countries that had housing booms. Consumer spending in Britain (and in America) rose at about the same rate as in thriftier Germany during the second quarter.

Britain stands out in another respect, too: its unemployment rate has risen by far less than in other places that had also racked up big mortgage debts. Divergent trends in unemployment may be better explained by the sort of recession each country had than by variations in jobs-market flexibility, says Kevin Daly at Goldman Sachs. In America, Ireland and Spain, the collapse of labour-intensive construction swelled the dole queues. Britain also had a housing boom but its tight planning laws kept its construction industry small, so fewer jobs were lost when the bust came. The downturns in Japan and Germany, deeper than America's (see chart), were mainly caused by the collapse in world trade. That hurt capital-intensive export industries—which were also more likely to rebound quickly—so fewer jobs disappeared.

Some think America's slowness to create new jobs is leading to undue pessimism about the rest of the world's prospects. “If US growth is not enough to give us a big payrolls figure, it's deemed a disaster,” says Marco Annunziata at UniCredit. But fast-growing emerging markets, such as China, have kept the world economy ticking over. Germany has done well because its exporters have made headway there. China's vibrancy also explains why Australia's GDP rose at its fastest rate for three years in the second quarter.

The best explanation for the uneven pattern of rich-world activity is also the most prosaic: America's recovery is more advanced and its firms have rebuilt their stocks sooner. Europe's business cycle tends to lag America's by a quarter or two. Recent indicators point to greater convergence. The index of American manufacturing published by the Institute of Supply Management unexpectedly picked up from 55.5 to 56.3 in August. The corresponding indices for the euro area and Britain fell back, to 55.1 and 54.3 respectively. America's economy may have some unique troubles, but its fortunes are still strongly tied to the rest of the rich world.