The world economy will not grow as it did during the boom, so how will it now expand? That is the cardinal problem in macroeconomics. The sources of demand that propelled the world into the boom have become sickly. The households and governments of the big deficit countries, such as the US and UK, are overstretched. They must take a break from their voracious consumption. So, if there is to be a sustainable recovery, who will step up to the cash register?

In Washington this week, a horde of 130 US Congressmen wrote to the Treasury with a demand: that it charge China with being a “currency manipulator” in its currencies report, due out in April, and that the US should retaliate by taxing Chinese imports.

Incendiary language, but a serious issue. The Chinese currency policy is, in effect, a development policy that works by subsidising foreign consumers who buy Chinese goods. The export machine, at its peak in 2008, was running a colossal $426bn current account surplus.

China is sticking with this mercantilist policy. This year, its current account surplus is expected to be $291bn (€213bn, £190bn). While the world rode the crest of a credit boom, it could find willing buyers for Chinese goods. But, after the bust, China is a source of excess supply and its refusal to consume drags on the world economy.

So Chinese people must be allowed to spend away. The adjustment would be a wrench – and not just because exporters would shed jobs. It would require reform of welfare (so that consumers save less for fear of emergencies) and of the financial sector (so that savings earn a better return). This could not be achieved overnight and would have political implications. But it could be done.

Similarly, there is no one instrument that will turn Germany, another saver-nation, into a big-spender. But this aim is worth pursuing. With an expected current account surplus of $187bn this year, the Bundesrepublik should spend more.

If Germany does not, it will force its less competitive eurozone partners to stagnate and deflate. Wolfgang Schäuble, the German finance minister, last week proposed that there should be severe penalties for governments that borrow too much. On its own, this would be a recipe for hyperstagnation: it would force deficit countries to retrench without pressing surplus countries to expand.

So the world faces a choice: either the serial exporters can choose to consume more and rebalance the world economy through growth. Or – as Mr Schäuble would prefer – they can sit on their hands, allow demand to crumble and rebalance the world economy through stagnation. There is only one sane answer.