An escalation in geopolitical conflicts is the biggest risk to the global economy, according to central bank reserve managers, who are generally positive about the world’s economic outlook, according to an annual survey released on Thursday. The UBS Asset Management survey of 40 leading central banks that manage more than $15 trillion, about half of the world’s foreign exchange (FX) reserves, found two thirds expected the global economy to return to moderate growth and inflation in the next five years.