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解读美联储的长期低利率之谜

2013-04-05 18:57

决策者和投资者仍担心现今全球超低利率带来的风险,学术经济学家继续争论低利率的根本原因。现在,每个人都接受了美联储主席伯南克(Ben Bernanke)在2005年的声明中指出的“全球储蓄过剩”是问题的根源。但经济学家在为什么过剩,会持续多久,最根本的是,它是否一件好事方面存在分歧。

伯南克的演讲强调了几个因素——全球储蓄需求下降,而供应增加。无论哪种方式,利率将下降,以便世界债券市场出清。他指出了90年代末的亚洲金融危机是如何造成该地区贪婪的投资需求崩溃,同时,亚洲各国政府囤积流动性资产以对抗另一个危机。伯南克还指出,德国和日本的老龄人口退休储蓄的增加,以及石油出口国的储蓄,由于这些国家人口快速增长和对石油长期收益的担忧。

货币政策,顺便说一句,在伯南克的诊断中并不显著。同大多数经济学家一样,他认为,如果决策者试图将利率维持在极低的水平太久,最终需求将飙升,通货膨胀跳升。所以,如果通胀水平较低且稳定,央行不应因低长期利率受到指责。

事实上,我强烈怀疑,如果就全球长期维持低利率的原因对投资者进行调查,货币政策将会出现在列表的顶部,不会缺席。事实上,很多持有这种观点的投资者在将所有责任归咎于货币政策前应该三思。不过,虽然央行设置短期利率,他们对长期实际利率(经通胀调整后的利率)几乎没有影响,除了通过投资组合管理政策(例如“量化宽松”)进行温和影响。

自2005年以来,发生了很多变化。我们经历了金融危机,伯南克列举的一些因素已经大幅逆转。例如,亚洲投资再度复苏,以中国为首。然而全球利率现在比那时更低。为什么?

有几个相互竞争的理论,它们中的大多数很精妙,但是没有一个完全令人满意。一种观点认为,长期增长的风险已经上升,这推升了相对安全的资产的溢价和普遍提高了预防性储蓄。(当然,没有人会认为任何政府债券是完全安全的,尤其在通货膨胀和金融压抑的影响下。)当然,2008年的金融危机唤醒了“大缓和”的观点支持者,他们认为长期波动率已经下降。许多研究表明,确定长期增长趋势预期比以往变得更加困难。例如,对技术进步是加速或减速的争论。地缘政治势力的改变也增加了不确定性。

另一类学术理论追随伯南克(甚至更早的杜利(Michael Dooley)、福克兹兰道(David Folkerts-Landau)、加伯(Peter Garber),将低长期利率归咎于新兴经济体日益增长的重要性,重点在私人储蓄而不是公共储蓄。因为新兴经济体相对与资产市场而言较弱,他们的公民在发达国家的政府债券中寻求避风港。一个相关的理论是,新兴经济体的公民很难在国内快速增长但波动的环境中分散大量的风险,由于社会安全网疲软,他们觉得特别容易受到损害,所以他们大量储蓄。

这些解释都有一定道理,但应该认识到的是央行和主权财富基金,而不是私人公民,是大量储蓄盈余的直接责任人。认为政府与私人公民有相同的意图有点吃力。

此外,细细品味,新兴市场的解释尽管方便,但不如它看起来那么引人注目。新兴经济体的增长速度远超过发达国家,新古典增长模型表明,这应推动全球利率上升,而不是下降。

同样的,新兴市场国家整合进全球经济时带来了大量的劳动力。根据标准贸易理论,全球劳动力过剩应该意味着资本回报比率增加,推动利率上升,而不是下降。

当然,任何的解释必须包括全球信贷收缩,尤其是中小企业信贷。更严格的监管标准关闭了一个重要的全球投资需求来源,给利率下行压力。

我最好的猜测是,当全球不确定性褪色,全球经济增长回升,全球利率也将开始上升。但预测这一过渡的时机是很困难的。令人不解的全球储蓄过剩也许延续很多年。

the long mystery of low interest rates

2013-04-05 18:57

As policymakers and investors continue to fret over the risks posed by today’s ultra-low global interest rates, academic economists continue to debate the underlying causes. By now, everyone accepts some version of US Federal Reserve Chairman Ben Bernanke’s statement in 2005 that a “global savings glut” is at the root of the problem. But economists disagree on why we have the glut, how long it will last, and, most fundamentally, on whether it is a good thing.

Bernanke’s original speech emphasized several factors – some that decreased the demand for global savings, and some that increased supply. Either way, interest rates would have to fall in order for world bond markets to clear. He pointed to how the Asian financial crisis in the late 1990’s caused the region’s voracious investment demand to collapse, while simultaneously inducing Asian governments to stockpile liquid assets as a hedge against another crisis. Bernanke also pointed to increased retirement saving by aging populations in Germany and Japan, as well as to saving by oil-exporting countries, with their rapidly growing populations and concerns about oil revenues in the long term.

Monetary policy, incidentally, did not feature prominently in Bernanke’s diagnosis. Like most economists, he believes that if policymakers try to keep interest rates at artificially low levels for too long, eventually demand will soar and inflation will jump. So, if inflation is low and stable, central banks cannot be blamed for low long-term rates.

In fact, I strongly suspect that if one polled investors, monetary policy would be at the top of the list, not absent from it, as an explanation of low global long-term interest rates. The fact that so many investors hold this view ought to make one think twice before absolving monetary policy of all responsibility. Nevertheless, I share Bernanke’s instinct that, while central banks do set very short-term interest rates, they have virtually no influence over long-term real (inflation-adjusted) rates, other than a modest effect through portfolio management policies (for example, “quantitative easing”).

A lot has changed since 2005. We had the financial crisis, and some of the factors cited by Bernanke have substantially reversed. For example, Asian investment is booming again, led by China. And yet global interest rates are even lower now than they were then. Why?

There are several competing theories, most of them quite elegant, but none of them entirely satisfactory. One view holds that long-term growth risks have been on the rise, raising the premium on assets that are perceived to be relatively safe, and raising precautionary saving in general. (Of course, no one should think that any government bonds are completely safe, particularly from inflation and financial repression.) Certainly, the 2008 financial crisis should have been a wakeup call to proponents of the “Great Moderation” view that long-term volatility has fallen. Many studies suggest that it is becoming more difficult than ever to anchor expectations about long-term growth trends. Witness, for example, the active debate about whether technological progress is accelerating or decelerating. Shifting geopolitical power also breeds uncertainty.

Another class of academic theories follows Bernanke (and, even earlier, Michael Dooley, David Folkerts-Landau, and Peter Garber) in attributing low long-term interest rates to the growing importance of emerging economies, but with the major emphasis on private savings rather than public savings. Because emerging economies have relatively weak asset markets, their citizens seek safe haven in advanced-country government bonds. A related theory is that emerging economies’ citizens find it difficult to diversify the huge risk inherent in their fast-growing but volatile environments, and feel particularly vulnerable as a result of weak social safety nets. So they save massively.

These explanations have some merit, but one should recognize that central banks and sovereign wealth funds, not private citizens, are the players most directly responsible for the big savings surpluses. It is a strain to think that governments have the same motivations as private citizens.

Besides, on closer inspection, the emerging-market explanation, though convenient, is not quite as compelling as it might seem. Emerging economies are growing much faster than the advanced countries, which neoclassical growth models suggest should push global interest rates up, not down.

Similarly, the integration of emerging-market countries into the global economy has brought with it a flood of labor. According to standard trade theory, a global labor glut ought to imply an increased rate of return on capital, which again pushes interest rates up, not down.

Surely, any explanation must include the global constriction of credit, especially for small and medium-size businesses. Tighter regulation of lending standards has shut out an important source of global investment demand, putting downward pressure on interest rates.

My best guess is that when global uncertainty fades and global growth picks up, global interest rates will start to rise, too. But predicting the timing of this transition is difficult. The puzzle of the global savings glut may live on for several years to come.

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