Meetings of G20 finance ministers and EU leaders top and tail this week with Greece’s fate uppermost in policymakers’ minds and global turbulence caused by diverging monetary policies and cheap oil coming a close second. The central bank world has been upended by a steepling fall in oil prices, and the effect that may have on inflation and growth, and the prospect of the European Central Bank creating 1 trillion euros out of thin air. The Swiss National Bank caused currency turmoil by abruptly ending its Swiss franc cap.