Uh-oh, it looks as though the J-curve is back.
That's if the July trade figures from the Australian Bureau of Statistics (ABS) on Thursday are any guide.
The trade account slipped into deficit in July, a $1 billion turnaround from a $243 million surplus in June to a deficit of $765 million.
These seasonally adjusted figures are volatile, often misleadingly so.
In trend terms, as worked out by the bureau, the deficit is expanding by a bit over $80 million a month.
Exports are rising by $134 million a month but imports are heading higher by $216 million a month.
It may be that the J-curve is at work.
It's a concept that was talked about a lot during the mid-1980s, when the monthly trade figures were a much bigger deal than they are now.
Back then, export commodity prices had slid sharply and the newly-floated Australian dollar had fallen in sympathy.
There are obviously strong parallels with the current situation, with commodity prices down 20 per cent or so in foreign currency terms since mid-2011 and the Australian dollar dropping about 15 per cent since the April peak.
A lower exchange rate makes exporters more competitive and should cut demand for imports in favour of local product.
That should eventually help the trade balance, but the shift in production and buying patterns takes time.
And it's certainly a slower process than the price effects.
Import prices - and that includes imports of services like holidays abroad - respond fairly quickly to the lower exchange rate.
But the effect of the lower exchange rate takes longer to offset the falls in export prices.
As a result, the price effects of a lower exchange rate favour a smaller surplus or bigger deficit, by adding more to import prices than export prices, especially in the short term.
The switch in buying and production patterns work in the other direction, helping to move the trade balance back into surplus.
But trade volumes take longer to respond, especially for export industries dominated by large scale raw materials producers.
The switch to local suppliers instead of imports can take a long while too, especially if the local industry has been gutted by a long period of a punishingly high exchange rate and has to start from square one.
All this means the impact of the fall in the Australian dollar can be expected to push the trade balance into the red in the short term - the down leg of the J - and back into the black hopefully with a higher surplus than before - the upward leg of the J.
We may have seen the first part of the downward leg in the July trade figures on Thursday.
And if historical experience is any guide, it could be quite a while before the figures turn around.
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