What is going to happen to the world economy this year? Much the most plausible answer is that it is going to grow. As I argued in a column published at this time last year, the most astonishing fact about the world economy is that it has grown in every year since the early 1950s. In 2017 it is virtually certain to grow again, possibly faster than in 2016, as Gavyn Davies has argued persuasively. So what might go wrong? The presumption of economic growth is arguably the most important feature of the modern world. But consistent growth is a relatively recent phenomenon. Global output shrank in a fifth of all years between 1900 and 1947. One of the policy achievements since the second world war has been to make growth more stable. This is partly because the world has avoided blunders on the scale of the two world wars and the Great Depression. It is also, as the American economist Hyman Minsky argued, because of active management of the monetary system, greater willingness to run fiscal deficits during recessions and the increased size of government spending relative to economic output. Behind the tendency towards economic growth lie two powerful forces: innovation at the frontier of the world economy, particularly in the US, and catch-up by laggard economies. The two are linked: the more the frontier economies innovate, the greater the room for catch-up. Take the most potent example of the past 40 years, China. On the (possibly exaggerated) official numbers, gross domestic product per head rose 23-fold between 1978 and 2015. Yet so poor had China been at the beginning of this colossal expansion that its average GDP per head was only a quarter of US levels in 2015. Indeed, it was only half that of Portugal. Catch-up growth remains possible for China. India has still greater room: its GDP per head was about a 10th of US levels in 2015. The overwhelming probability is that the world economy will grow. Moreover, it is highly likely that it will grow by more than 3 per cent (measured at purchasing power parity). It has grown by less than that very rarely since the early 1950s. Indeed, it has grown by less than 2 per cent in only four years since then – 1975, 1981, 1982 and 2009. The first three were the result of oil price shocks, triggered by wars in the Middle East, and Federal Reserve disinflation. The last was the Great Recession after 2008’s financial crisis. This is also consistent with the pattern since 1900. Three sorts of shocks seem to destabilise the world economy: significant wars; inflation shocks; and financial crises. When asking what might create large downside risks for global economic growth, one has to assess tail risks of this nature. Many fall into the category of known unknowns.