The US dollar ($US) is on a roller coaster. And since S&P downgraded Greece to BBB+, the dollar has been on the rise. One can attribute the recent shift in the $US to many things - improving US economic conditions, return to risk, or relative weakness in other G7 countries, whatever. But what is clear, is that the dollar's gaining some strength, 4.7% since the beginning of December on a trade-weighted basis.
But this is not sustainable. As economic recoveries diverge (i.e., the G7 recovery is expected to be slower than that in key emerging markets), the dollar will likely fall. That's just gravity, and a necessary condition for sorting out global trade flows.
The chart illustrates the effective value of the $US, which is a composite index of the value of the $US against US trading partners (one source for this data is the Bank of England). As recently as November, the $US slid to its lowest value since March 2008. At that time - and really anytime the $US initiates a descent - Washington gets all worked up; but why? One of the necessary conditions for the re-balancing of trade flows between major trading partners is dollar depreciation.
Just look at the contribution to GDP growth from exports in 2006 and 2007, when not coincidentally the dollar was sliding.
http://www.roubini.com/us-monitor/258170/gravity_will_drag_the__u_s_
