Adam Hayes 2015年9月3日
這個月，中國通過貨幣貶值震驚了世界並導致道瓊斯工業平均指數進行了自2010年閃電崩盤以來最劇烈的下跌，在2015年8月24日開盤時下跌了1000點。人民幣對美元下降了超過3.5%。這看起來不多，但是中國政府歷來對美元執行嚴格的匯率控制。中國已經成為世界上第二大經濟體，也是世界貿易的重要組成部分。
諷刺的是，多年來美國政府一直向中國施壓貶值人民幣，聲稱這使人民幣在國際貿易中具有不公平的優勢並人為控制資本和勞動力價格低廉。現在中國政府採取緊急措施貶值他們的貨幣，被指責成為全球市場帶來不確定性。
這個最近的事件並不是什麼新鮮事。自從全球貨幣放棄國際標準並允許他們互相之間自由浮動匯率，發生過許多貨幣貶值事件，不僅僅傷害涉及國家的居民，使全球都跟著波動。如果影響如此普遍，國家為什麼對貨幣貶值呢？
促進出口
在國際市場中，來自一個國家的商品必須和來自全世界的商品競争。美國的汽車市場必須和日本和歐洲的汽車市場競争。如果歐元對美元貶值，歐洲制造商制造的汽車在美國以美元出售，將會比之前便宜的多。另一方面，貨幣價值更高則出口到外國的商品價格更昂貴。
換句話說，出口商在國際市場變得更有競争力。鼓勵出口打擊進口。但是有一些值得註意的地方，因為兩個原因。首先，當全世界都需求出口商的商品時，價格會上升，使貶值影響變得正常。第二點就是其他國家發現這種方式有效，他們就會被激勵對他們的貨幣進行貶值。這將導致貨幣戰争和無節制的通貨膨脹。
縮小貿易赤字
由於出口變便宜進口變昂貴，出口增加，進口減少。這有利於改善國際收支，出口增加，進口減少，縮小貿易赤字。現在持續的赤字並不少見，美國和其他一些國家連續多年貿易失衡。然而經濟理論認為貿易赤字是不可持續的，這將導致危險的債務水平並削弱經濟。國内貨幣貶值可以幫助矯正國際貿易支出並削減赤字。
然而這種原理存在一個缺點。貨幣貶值也會增加外幣計價的債務負擔。這對使像印度和阿根廷這樣擁有巨大金額美元和歐元債務的國家來說是個很大的問題。這些國外債務變得更加難以償還，削減國内貨幣市場信心。
降低主權債務負擔
如果政府有用大量的主權債務他們可能會出台弱勢貨幣政策。如果還款是固定的，貶值將會使還款更加便宜。
比如政府每個月需要對未償還債務支付100萬美元的利息。但是如果這100萬美元國際債務價值降低，這部分債務則更容易償還。在我們的例子中，如果國内貨幣貶值到原來一半的價值，那麼100萬美元的債務就只值50萬美元。
再次，這種策略需要小心使用。因為全球大多數國家都有各種形式的未償還債務，這可能引起貨幣戰争。這種策略在國家持有大量國外債券時也會失效，因為這將使這利息支付更加昂貴。
總結
貨幣貶值可以被國家用來實現經濟政策。擁有比世界其他國家價值更低的貨幣將刺激出口，縮小貿易赤字和減少未償還債務的利息支付。然而，貨幣貶值也有負面影響。他們在全球市場帶來不確定性，可能導致市場下跌和刺激衰退。國家間可能會進入一個以牙還牙的貨幣戰争。這是一個非常危險弊大於利的惡性循環。
3 Reasons Why Countries Devalue Their Currency
By Adam Hayes, CFA | Updated September 03, 2015
This month, China surprised world markets and spurred the most precipitous drop in the Dow Jones Industrial Average – falling more than 1000 points at the open of Monday August, 24 2015 – since the flash crash of 2010, by taking moves to devalue their currency. The Yuan is now down over 3.5% against the U.S. dollar over the past twelve months. This may not seem like a lot, but the Chinese government has traditionally held a strict peg to the dollar. The Chinese economy has become the second largest in the world, and is an integral component of global trade.
The ironic thing is that for many years, the United States government had been pressuring the Chinese to devalue the Yuan, arguing that it gave them an unfair advantage in international trade and kept their prices for capital and labor artificially low. Now that the Chinese are enacting emergency measures to devalue their currency, they are being blamed for bringing global uncertainty in markets. (For more, see: The Chinese Devaluation of the Yuan.)
This most recent event is nothing new. Ever since world currencies abandoned the gold standard and allowed their exchange rates to float freely against each other, there have been many currency devaluation events that have hurt not only the citizens of the country involved, but have also rippled across the globe. If the fallout can be so widespread, why do countries devalue their currency?
To Boost Exports
On a world market, goods from one country must compete with those from all other countries. Car makers in America must compete with car makers in Europe and Japan. If the value of the euro decreases against the dollar, the price of the cars sold by European manufacturers in America, in dollars, will be effectively less expensive than they were before. On the other hand, a more valuable currency make exports relatively more expensive for purchase in foreign markets.
In other words, exporters become more competitive in a global market. Exports are encouraged while imports are discouraged. There should be some caution, however, for two reasons. First, as the demand for a country's exported goods increases worldwide, the price will begin to rise, normalizing the initial effect of the devaluation. The second is that as other countries see this effect at work, they will be incentivized to devalue their own currencies in kind in a so-called "race to the bottom." This can lead to tit for tat currency wars and lead to unchecked inflation.
To Shrink Trade Deficits
Exports will increase and imports will decrease due to exports becoming cheaper and imports more expensive. This favors an improved balance of payments as exports increase and imports decrease, shrinking trade deficits. Persistent deficits are not uncommon today, with the United States and many other nations running persistent imbalances year after year. Economic theory, however, states that ongoing deficits are unsustainable in the long run and can lead to dangerous levels of debt which can cripple an economy. Devaluing the home currency can help correct balance of payments and reduce these deficits.
There is a potential downside to this rationale, however. Devaluation also increases the debt burden of foreign-denominated loans when priced in the home currency. This is a big problem for a developing country like India or Argentina which hold lots of dollar- and euro-denominated debt. These foreign debts become more difficult to service, reducing confidence among the people in their domestic currency.
To Reduce Sovereign Debt Burdens
A government may be incentivized to encourage a weak currency policy if it has a lot of government issued sovereign debt to service on a regular basis. If debt payments are fixed, a weaker currency makes these payments effectively less expensive over time.
Take for example a government who has to pay $1 million each month in interest payments on its outstanding debts. But if that same $1 million of notional payments becomes less valuable, it will be easier to cover that interest. In our example, if the domestic currency is devalued to half of its initial value, the $1 million debt payment will only be worth $500,000 now.
Again, this tactic should be used with caution. As most countries around the globe have some debt outstanding in one form or another, a race to the bottom currency war could be initiated. This tactic will also fail if the country in question holds a large amount of foreign bonds since it will make those interest payments relatively more costly. (See also: Why Your Pension Plan Has Sovereign Debt in it.)
The Bottom Line
Currency devaluations can be used by countries to achieve economic policy. Having a weaker currency relative to the rest of the world can help boost exports, shrink trade deficits and reduce the cost of interest payments on its outstanding government debts. There are, however, some negative effects of devaluations. They create uncertainty in global markets that can cause asset markets to fall or spur recessions. Countries might be tempted to enter a tit for tat currency war, devaluing their own currency back and forth in a race to the bottom. This can be a very dangerous and vicious cycle leading to much more harm than good.
本文翻譯由兄弟財經提供
文章來源：http://www.investopedia.com/articles/investing/090215/3-reasons-why-countries-devalue-their-currency.asp