If US central bank chief Janet Yellen happens to look over her shoulder at the next gathering of international financiers and see

her peers from Australia, Canada, Japan, and the euro zone huddled together in intense talks she'll know immediately that there's only one possible subject of conversation: what to do about the falling US dollar.

Central bankers around the world are at their wits' end, trying to work out how to respond to the drop in the US dollar, which shows little sign of abating. They're worried that as their currencies strengthen against the US dollar, their country's goods will become much more expensive in global markets, which will crimp demand, while imported goods will become cheaper. Falling exports will dampen growth, while cheaper imports will put further downward pressure on feeble inflation.

And greenback has had a highly unusual trajectory this year. It began the year at a 14-year high, prompting Donald Trump - who was then US President-elect - to complain that that it was "too strong".

He repeated the charge three months later. "I think our dollar is getting too strong, and partially that's my fault because people have confidence in me", he told Wall Street Journal in April. But, he added, the strength of the currency "will hurt ultimately". the US economy.