The yen's surge to 15-month highs against the dollar Thursday reveals deep problems in global markets, according to Steven Englander, global head of currency and G-10 strategy at Citigroup.
"It's rallying because it's a safe haven currency and the world's falling apart," Englander told CNBC's "Worldwide Exchange." "It's not rallying because there are negative interest rates."
The Bank of Japan and other central banks are working to ease investor doubt that monetary easing is still a reliable backstop.
"The perception is that they're ineffective," Englander said. "I think central banks are going to need more time to actually come up with tools to address the problems that markets are concerned about now."
With Federal Reserve Chair Janet Yellen testifying on Capitol Hill this week, Englander said investors were looking for two things: confidence the U.S. is stable in terms of growth, and reassurance there's "something on the table" besides negative rates or more quantitative easing.