特朗普减税与加大基础设施投资新政的期盼，引发了最近一波美元飙升的行情，但美元的快速升值所导致的美元回流，将无可避免地带来全球信贷紧缩，如果处理不当，对全球经济和美国经济都将是沉重打击。
特朗普赢得美国总统大选之后的三周里，美元兑众多富裕国家货币的汇率经历了最为凌厉的一次上涨，大量持有离岸美元债的新兴国家，如巴西、智利、土耳其，其货币兑美元也大幅下跌。相比而言，人民币兑美元的汇率尽管也下跌，但相比而言幅度并不大（见下图），部分体现自去年八月汇改以来人民币盯住一篮子货币的稳定性。
不过，恰如本篇封面文章所述，美元的快速升值对全球经济与美国经济都不是好事，持续升值所带来的连锁反应，就像开启了潘多拉盒子，也一定会对人民币的汇率乃至中国经济带来负面影响。管理人民币汇率并没有什么好的办法：加速贬值会加剧资本外流、一次性贬值到位则可能影响金融稳定，而更多对资本项下流出的控制则会对经济产生影响。
坚挺的美元
为什么日趋强劲的美元会对世界经济不利？
世界上最重要的货币正在展现实力。特朗普赢得美国总统大选之后的三周里，美元兑众多富裕国家货币的汇率经历了史上其中一次最为凌厉的上涨。目前美元相较2011年的低价位上涨了40%。相对于新兴市场货币，美元也表现强劲。人民币兑美元已跌至2008年以来的最低水平；据说焦虑的中国官员正考虑进一步严格限制本国公司的海外收购，以遏制汇率的下行压力。至于自食苦果的印度，该国的货币兑美元已达历史最低点。其他亚洲货币的跌幅也是自1997-1998年金融危机以来前所未见的。
数年来美元一直在逐渐积聚力量。但最近这次飙升的推动力是美国经济政策组合或许会发生转变的大背景。投资者已下注大笔资金，赌的是特朗普会减税，并且将投入更多公共资金整修美国摇摇欲坠的基础设施。大手笔的财政刺激会让美联储更快加息以抑制通货膨胀。美国十年期国债收益率已从大选当晚的1.7%升至2.3%。更高的收益会吸引更多的资本流入。
世界最大经济体强有力的增长听来似乎颇令人期待。一个被广为援引的先例是里根总统的首个任期：当时预算赤字扩大，利率高企，美元同时也在猛涨。那段时期在国外引发了问题，而这一次可能还会更加复杂。尽管美国经济占世界经济的比重缩小了，但全球金融和信贷市场的规模已呈爆炸式增长。美元已经变得越来越关键——这让强劲的美元对世界、对美国都更加危险。
世界新秩序
美国作为贸易强国的相对影响力已经逐步减弱：以美国为最大出口市场的国家数量从1994年的44个降至二十年后的32个。但美元作为交易和储值货币的霸主地位仍然无可撼动。美元的力量在某些方面显而易见。2014年的一项估算表明，事实上的美元区（包括美国和货币盯住美元的国家）可能要占世界人口的60%及全球GDP的60%。
其他因素就没那么明显了。发生在美国境外的美元融资数额近年来已飙升。随着新兴市场越来越富裕、越来越渴望融资，它们对于美元的需求也在增长。金融危机以来，美国的低利率已经让养老基金转向他处以寻求更高的收益。它们涌向诸如莫桑比克和赞比亚这样不可思议的地方购买以美元计价的债券，也购买新兴市场里较大的公司发行的债券。这些公司都非常乐于以比国内更低的利率贷到美元。根据央行官员交流平台国际清算银行（Bank for International Settlements）的数据，截至去年这类美元债务已达近十万亿，其中的三分之一在新兴市场。
当美元升值时，偿还这些债务的成本也增加了。但是更强劲的美元所带来的痛苦要远远超出其对美元借款人的直接影响。因为便宜的离岸借款在很多情况下已经带来了本地信贷供应的增加。资本流入推高了本地资产价格，进而鼓励更多借款。新兴市场公司借来的美元并不全都用于投资；有些钱最终存入了银行账户（在那里可以被再次借出）或是为其他公司提供融资。
日趋强劲的美元使这一循环发生了逆转。随着美元上涨，借款人需要节约现金来支付不断增长的偿债成本。随着资金流出，资产价格出现下跌。结果是美国以外很多地方的信贷状况与美元的命运绑得更紧。一些货币近来对美元贬值最多的国家正是像巴西、智利、土耳其这样持有大量美元债务的国家，这绝非偶然。
全视之眼
更强劲的美元对于美国自身也有潜在的危险。强势货币会挤压出口、刺激进口，因此贸易赤字将会扩大。在里根时期，飙升的赤字引发了贸易保护主义。而这一次美国已经存在巨额赤字，且该赤字已经被政治化，尤其是被特朗普政治化了。他认为这一赤字证明国际贸易规则受到操控，偏向其他国家。特朗普曾威胁说要对从中国和墨西哥进口的商品征收高额关税来平衡贸易，赤字扩大会让特朗普更有可能将威胁付诸行动。如果特朗普屈从其贸易保护主义者的本能，其后果对所有人来说都会是灾难性的。
自然，这很大程度上取决于美元的走向。许多投资者都很乐观。美元相对于其他货币来说开始变得更贵了。如果新兴市场有麻烦，美联储一贯会选择推迟加息。然而外汇市场往往会很长时间大幅背离基本价值。逃离美元的投资者想要转投何处也未可知。觊觎美元皇冠的两大货币欧元和人民币各自都有根深蒂固的问题。本月将召开下一次议息会议的美联储可能会发现，要在这一升温当中的经济体中避免紧缩比以往更困难。
如果美元持续强劲，来自贸易保护主义者的压力会不会被协调一致的国际行动所平息？一些人开始探讨一个堪比《广场协议》（1985年由美国、日本、英国、法国和西德签订）、旨在再次让美元贬值的新协定，这一想法看上去不合时宜。日本和欧洲正在对抗低通胀，对推高本币毫不热心，更不用提要这么做可能需要执行的紧缩货币政策了。
由于看好更强劲的增长前景，美国的股票市场已恢复元气。它们太目空一切。全球经济仍旧疲软，美元的强劲会让它更加羸弱。
原文：
THE world’s most important currency is flexing its muscles. In the three weeks following Donald Trump’s victory in America’s presidential elections, the dollar had one of its sharpest rises ever against a basket of rich-country peers. It is now 40% above its lows in 2011. It has strengthened relative to emerging-market currencies, too. The yuan has fallen to its lowest level against the dollar since 2008; anxious Chinese officials are said to be pondering tighter restrictions on foreign takeovers by domestic firms to stem the downward pressure. India, which has troubles of its own making (see separate leader), has seen its currency reach an all-time low against the greenback. Other Asian currencies have plunged to depths not seen since the financial crisis of 1997-98.
The dollar has been gradually gaining strength for years. But the prompt for this latest surge is the prospect of a shift in the economic-policy mix in America. The weight of investors’ money has bet that Mr Trump will cut taxes and spend more public funds on fixing America’s crumbling infrastructure. A big fiscal boost would lead the Federal Reserve to raise interest rates at a faster rate to check inflation. America’s ten-year bond yield has risen to 2.3%, from almost 1.7% on election night. Higher yields are a magnet for capital flows.
Zippier growth in the world’s largest economy sounds like something to welcome. A widely cited precedent is Ronald Reagan’s first term as president, a time of widening budget deficits and high interest rates, during which the dollar surged. That episode caused trouble abroad and this time could be more complicated still. Although America’s economy makes up a smaller share of the world economy, global financial and credit markets have exploded in size. The greenback has become more pivotal. That makes a stronger dollar more dangerous for the world and for America.
Novus ordo seclorum
America’s relative clout as a trading power has been in steady decline: the number of countries for which it is the biggest export market dropped from 44 in 1994 to 32 two decades later. But the dollar’s supremacy as a means of exchange and a store of value remains unchallenged. Some aspects of the greenback’s power are clear to see. By one estimate in 2014 a de facto dollar zone, comprising America and countries whose currencies move in line with the greenback, encompassed perhaps 60% of the world’s population and 60% of its GDP.
Other elements are less visible. The amount of dollar financing that takes place beyond America’s shores has surged in recent years. As emerging markets grow richer and hungrier for finance, so does their demand for dollars. Since the financial crisis, low interest rates in America have led pension funds to look for decent yields elsewhere. They have rushed to buy dollar-denominated bonds issued in unlikely places, such as Mozambique and Zambia, as well as those issued by biggish emerging-market firms. These issuers were all too happy to borrow in dollars at lower rates than prevailed at home. By last year this kind of dollar debt amounted to almost $10trn, a third of it in emerging markets, according to the Bank for International Settlements, a forum for central bankers.
When the dollar rises, so does the cost of servicing those debts. But the pain caused by a stronger greenback stretches well beyond its direct effect on dollar borrowers. That is because cheap offshore borrowing has in many cases caused an increased supply of local credit. Capital inflows push up local asset prices, encouraging further borrowing. Not every dollar borrowed by emerging-market firms has been used to invest; some of the money ended up in bank accounts (where it can be lent out again) or financed other firms.
A strengthening dollar sends this cycle into reverse. As the greenback rises, borrowers husband cash to service the increasing cost of their own debts. As capital flows out, asset prices fall. The upshot is that credit conditions in lots of places outside America are bound ever more tightly to the fortunes of the dollar. It is no coincidence that some of the biggest losers against the dollar recently have been currencies in countries, such as Brazil, Chile and Turkey, with lots of dollar debts.
The eye of providence
There are lurking dangers in a stronger dollar for America, too. The trade deficit will widen as a strong currency squeezes exports and sucks in imports. In the Reagan era a soaring deficit stoked protectionism. This time America starts with a big deficit and one that has already been politicised, not least by Mr Trump, who sees it as evidence that the rules of international commerce are rigged in other countries’ favour. A bigger deficit raises the chances that he act on his threats to impose steep tariffs on imports from China and Mexico in an attempt to bring trade into balance. If Mr Trump succumbs to his protectionist instincts, the consequences would be disastrous for all.
Much naturally depends on where the dollar goes from here. Many investors are sanguine. The greenback is starting to look dear against its peers. The Fed has a record of backing away from rate rises if there is trouble in emerging markets. Yet currencies often move far away from fundamental values for long periods. Nor is it obvious where investors fleeing America’s currency might run to. The euro and the yuan, the two pretenders to the dollar’s crown, have deep-seated problems of their own. The Fed, whose next rate-setting meeting comes this month, may find it harder than before to avoid tightening in an economy that is heating up.
If the dollar stays strong, might protectionist pressure be defused by co-ordinated international action? Nascent talk of a new pact to rival the Plaza Accord, an agreement in 1985 between America, Japan, Britain, France and West Germany to push the dollar down again, looks misplaced. Japan and Europe are battling low inflation and are none too keen on stronger currencies, let alone on the tighter monetary policies that would be needed to secure them.
Stockmarkets in America have rallied on the prospect of stronger growth. They are being too cavalier. The global economy is weak and the dollar’s muscle will enfeeble it further.（完）