What will replace the dollar as global currency?

``Go back to 2001, and the proportion of central bank reserves held in dollars was 71%. It only goes down a bit every year. But over time, that starts to add up. Once the dollar drops below 50% of central bank holdings, we can officially declare that its days as the reserve currency are done. It looks like that will happen some time between 2015 and 2020 -- but it could well be sooner. ''