Janet Yellen may have to fight in the global currency war, whether she wants to or not.

The dollar is on a tear, rising to the highest level in more than a decade, in part because of the Federal Reserve's plans to raise interest rates this year. Money is flowing to the U.S., where the economy looks pretty good as Europe battles deflation and oil-dependent developing nations sputter as commodities slump.

Gary Cohn, president and chief operating officer of Goldman Sachs Group Inc., sees a big problem in all of this. The dollar's ascent is already eating into American corporate profits, with PepsiCo Inc. predicting the trend will reduce earnings growth by 7 percent this year. Raising rates could send the dollar even higher.