Bull markets, it is said, climb a wall of worry. When the last worrier turns into a fully invested optimist, the market has nowhere to go but down. That might be what has just happened: so much optimism was already in the prices of financial assets — in the US, above all — that once worry returned they had nowhere to go but down. How far might unfolding events exacerbate the worries? A long way, is the answer.

As the annual meetings of the IMF and World Bank last week made clear, reasons for concern abound. Above all, a struggle between old and new superpowers has arrived. This may change everything.

The good news is that the IMF’s World Economic Outlook continues to forecast strong economic growth, with global output growing 3.7 per cent this year and next (at purchasing power parity), as in 2017. The bad news is that this is a reduction of 0.2 percentage points in 2018 and 2019 from its April forecast. Above all, “the balance of risks?.?.?.?has shifted to the downside in a context of elevated policy uncertainty”.