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上周，當中國央行觸發自上世紀90年代以來最大的兩個人民幣單日最大跌幅時，很多人都敏銳地宣告匯率戰爭重新開始。自2008年金融危機以來，匯率戰爭已經成為全球經濟的特征之一。
但是，如果北京此舉引發美國以及其他國家政府的“匯率戰士”可以預見的政治回應的話，這便忽視了一個如今在很多貿易經濟學家看來日益得到充分證明的事實：作為貿易武器的匯率跟過去不一樣了。
在一項對包括中國在內的46個國家所做的新研究中，世界銀行(World Bank)的經濟學家得出，作為推動出口的工具，如今貨幣貶值的效果僅為上世紀90年代中期時的一半。
此外，世界銀行的經濟學家發現，國家融入全球經濟的程度越深——上世紀90年代以來中國令人矚目地實現了這種融入——匯率變化對出口可能帶來的影響就越小。
該研究的作者之一米歇爾脠咜(Michele Ruta)稱，對于壓低本幣匯率以尋求在國際貿易中獲得競爭優勢的國家而言，“關于貶值能帶來多少影響，預期與實際情況存在差異”。他稱，如今現實情況是，多年的數據表明，貶值的影響很可能比過去低得多。
造成這種情況的原因有很多。但是，魯塔及其同事稱，最大的原因是，過去20年全球供應鏈得到發展以及如今很多產品都是由很多產自不同國家的部件組裝而成的。
其結果是，對于包括中國在內的許多經濟體而言，計算貶值影響的方法變得復雜得多了。
匯率走低仍然會降低很多商品的出口價格、從而提升它們在海外的競爭力，與此同時增加進口的成本。對于一些簡單的產品，比如一瓶由瑪格麗特河(Margaret river)產區的葡萄釀造而成的澳大利亞西拉(Shiraz)葡萄酒，這一論斷仍然成立、并且仍是重要的。澳元走低將降低這瓶葡萄酒的出口價格，提高它對海外消費者的吸引力，同時提高澳大利亞從法國或智利的競爭對手進口葡萄酒的價格。
但是對于更加復雜的產品，比如很多在中國組裝的電子產品，匯率走低的實際影響計算起來要困難得多。以智能手機為例，屏幕可能是從日本進口的，主芯片可能是從韓國進口的，其他部件在東南亞、歐洲和美國采購。所以，盡管人民幣貶值理論上降低制成品銷往海外的價格，但它也提高了進口部件的成本。（中國進出口網）
When China’s central bank last week triggered the two biggest single-day falls in the renminbisince the 1990s, plenty of people were keen to proclaim a resumption of the currency warsthat have been a feature of the global economy since the 2008 financial crisis.
But if Beijing’s move prompted a predictable political response from currency warriors inWashington and other capitals, it ignored what many trade economists see as an increasinglywell-documented fact: currencies are not the trade weapon they once were.
In a new study of 46 countries including China, economists at the World Bank found thatcurrency devaluations were these days only half as effective a tool for boosting exports asthey were in the mid-1990s.
Moreover, the World Bank economists found the further countries became integrated into theglobal economy — as China has done in spectacular style since the 1990s — the less theeffect was likely to be of any currency changes on their exports.
For countries that weaken their currencies to seek competitive advantage in global tradethere is a “distinction between the perception of the impact of a depreciation and the actualimpact a depreciation can have”, says Michele Ruta, one of the study’s authors. The realitytoday, he says, is that years of data show the impact is likely to be much less than it used tobe.
There are a number of reasons for that. But the biggest, say Mr Ruta and his colleagues, is thedevelopment of global supply chains in the past two decades and the reality that manyproducts today are agglomerations of parts made in many different countries.
The result is a much more complex calculus for many economies, including China.
Weaker currencies still lower the cost and therefore raise the international competitiveness ofmany goods exports while increasing the cost of imports. For something as simple as a bottleof Australian Shiraz from grapes grown on Margaret river vines, that reality still holds andmatters. A weak Australian dollar will lower the cost of an exported bottle and make it moreattractive to offshore consumers. It will also increase the price of imports into Australia ofFrench or Chilean rivals.
But for more complex products, like many of the electronic items assembled in China, the realimpact is far more difficult to calculate.
