So, can we say anything about how the recent move in the euro fits into this story? One way, I’d suggest, is to ask how much of the move can be explained by changes in the real interest differential with the United States. US real 10-year rates are about the same as they were in the spring of 2014; German real rates at similar maturities (which I use as the comparable safe asset) have fallen from about 0 to minus 0.9. If people expected the euro/dollar rate to return to long-term normal a decade from now, this would imply a 9 percent decline right now.
What we actually see is almost three times that move, suggesting that the main driver here is the perception of permanent, or at any rate very long term European weakness. And that’s a situation in which Europe’s weakness will be largely shared with the rest of the world — Europe will have its fall cushioned by trade surpluses, but the rest of us will be dragged down by the counterpart deficits.
Now, this is not how most analysts approach the problem. They make a forecast for the exchange rate, then run this through some set of trade elasticities to get the effects on trade and hence on GDP. Such estimates currently indicate that the dollar will be a moderate-sized drag on US recovery, but no more. What the economic logic says, however, is that if that’s really true, the dollar will just keep heading higher until the drag gets less moderate.