The euro's current weakness has one culprit: Greece. At 14 percent of GDP, Greece's latest current-account deficit was the largest of the eurozone countries after Cyprus. Its debt-to-GDP ratio stood at 113 percent by the end of 2009. As this year's deficit is projected to be more than 12 percent of a shrinking GDP, the debt-to-GDP ratio will soar above 125 percent by the end of 2010, the highest in the eurozone.

Investors have reacted by trying to get out of the euro and, in particular, steer clear of Greek government debt. Greece had to offer them increasingly higher interest rates to stay put. In January, the interest premium was 2.73 percentage points relative to German public debt. If this premium prevails, Greece will have to pay 7.4 billion euros more in interest per year on its 271 billion euros debt than it would have to pay at the German rate.

The problem is not only the premium itself, but the imminent risk that Greece will not be able to find the 53 billion euros it needs to service its debt falling due in 2010, let alone the estimated additional 30 billion euros to finance the new debt resulting from its projected budget deficit.