This post is a guest contribution by Rebecca Wilder*, author of the of the News N Economics blog.

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.

rw2412a

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.

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The chart illustrates export growth and the contribution to GDP growth, as released by the Bureau of Economic Analysis. Note: an easy way to get this data is to simply download the excel file in the right sidebar of the release page.

A weak dollar can drive economic growth – especially as trade resumes, and emerging markets see a much quicker rebound than that expected for the G7. According to the Financial Times, its already happening – Asia ex-Japan is moving Japan’s export market:

Japanese exports continued to increase in November because of robust demand from Asia, easing concerns about the strength of the country’s economic recovery.

Real exports were up by 0.6 per cent on October, according to Bank of Japan data. This was the eighth consecutive monthly rise, although the pace of increase was the slowest since exports began to recover in April.

A weaker dollar is a big part of the story for a re-balancing of trade flows. And its not just a US and China problem. According to the IMF, the 2007 US current account deficit was $731 billion, while the value of China’s surplus was just half that, $372 billion. It’s much of Asia and the Middle East that are likewise driving imbalances (of course, the US is not an innocent bystander here). The dollar will see weakness again on a trade-weighted basis; that’s gravity.

* Rebecca Wilder is an economist in the financial industry. She was previously an assistant professor and holds a doctorate in economics.

Source: Rebecca Wilder, News N Economics, December 23, 2009.