The timing of this week's G20 summit could be crucial in an uncertain market. News agencies are quoting World Bank president Robert Zoellick's assessment that the gathering of the most influential nations should send a "strong signal" that Europe will follow through on plans to overcome its sovereign debt crisis. Zoellick was responding to Greece's call for a referendum on a new bailout plan, a development that he says adds to market uncertainty. Fearing a referendum could lead to "a mess", the central banker says it would be very useful if the G20 leaders "can send a strong signal on follow-through after the euro zone announcement so as to sustain and build confidence".