“接棒”耶倫，鮑威爾接過了什么樣的經(jīng)濟命題？

Janet Yellen has completed her term as chair of the US Federal Reserve with unemployment much lower than it was when she began, inflation low and closer to target than when she began, and with the financial system better capitalised and more liquid than the one she inherited. What more can anyone ask from a Fed chair?

珍妮特•耶倫(Janet Yellen)已經(jīng)完成了她作為美聯(lián)儲(Fed)主席的任期，此時的失業(yè)率比她就任時低得多、通脹保持較低水平且更接近目標、金融體系的資本狀況更好且流動性更充足。人們還能對美聯(lián)儲主席有更多的要求嗎?

Ms Yellen’s success is a tribute to her judgment and thoughtfulness. Importantly, though, like Alan Greenspan in the 1990s, she recognised quickly a major structural change in the economy and adjusted policy away from where traditional models would guide it. In Mr Greenspan’s case the structural change was the acceleration of productivity growth. In Ms Yellen’s, it was the decline in the neutral rate of interest — the rate of interest at which saving and investment would balance without either a major acceleration or deceleration in growth.

耶倫的成功充分體現(xiàn)了她的判斷力和縝密思維。但很重要的是，正如上世紀90年代的艾倫•格林斯潘(Alan Greenspan)一樣，她很快意識到了經(jīng)濟的重大結(jié)構(gòu)性變化并相應(yīng)調(diào)整了政策，而不再遵循傳統(tǒng)模型。格林斯潘察覺到的結(jié)構(gòu)性變化是生產(chǎn)率增長加速，而耶倫發(fā)現(xiàn)的是“中性利率”(neutral rate of interest)下降。所謂中性利率，是指儲蓄和投資達到平衡而且經(jīng)濟增長既沒有大幅加速也沒有大幅減速的利率水平。

The fashionable view at the Fed and elsewhere when Ms Yellen took office in 2014 was that growth was slow despite very low interest rates because of “headwinds” — transitory factors associated with the financial crisis that would soon recede. When the headwinds receded, it would be possible for the economy to enjoy sustained growth with the “normal” 4 per cent federal funds rate. On this view, the near zero rate policy in place was highly expansionary and risked dangerous inflation.

2014年，當耶倫就任美聯(lián)儲主席時，不管是在美聯(lián)儲內(nèi)部還是其他地方，普遍觀點是，盡管利率非常低，但經(jīng)濟增長緩慢，這是因為存在一些“逆風”——與金融危機有關(guān)的將很快消退的暫時性因素。當逆風退去，經(jīng)濟有可能在4%的“正常”聯(lián)邦基金利率的情況下實現(xiàn)持續(xù)增長。按照這種觀點，利率接近于零的政策是高度擴張性的，可能帶來危險的通貨膨脹。

By 2014, after five years of financial repair, the headwinds theory was losing credibility. Estimates of the neutral rate were starting to come in suggesting that it had been trending down for a long time. More straightforwardly, despite near zero rates and the completion of financial repair as measured by credit spreads in 2009, growth remained very slow. That is why I sought to resurrect the secular stagnation theory — the idea that the economy, except at moments of financial excess, was likely to suffer from an excess of saving over investment and be prone to sluggishness and insufficient inflation.

2014年，在金融體系經(jīng)歷了五年的修復(fù)期后，上述逆風理論失去了可信性。對中性利率的估計開始表明它很長時間以來處于下行趨勢。更簡單地說，盡管利率維持在接近于零的水平且根據(jù)2009年的信用息差衡量已經(jīng)完成了金融修復(fù)過程，但經(jīng)濟增長仍然非常緩慢。于是我重新提出了“長期經(jīng)濟停滯理論”：除了金融領(lǐng)域存在過度行為的時候以外，經(jīng)濟很可能受到儲蓄大于投資的打擊，容易出現(xiàn)增長停滯和通脹低迷的情況。

Without endorsing the idea of secular stagnation, Ms Yellen led the Fed gradually but firmly to the recognition that the neutral rate had declined significantly, and to the corollary conclusion that policy was not as expansionary as was generally supposed. Her instincts were corroborated, and even proved to have been if anything too cautious as growth and inflation generally fell short of the Fed’s expectations during her tenure — even as interest rates were kept lower than expected and federal deficits increased more than expected.

耶倫不認同長期停滯理論，在她領(lǐng)導(dǎo)下，美聯(lián)儲逐步地得出一個堅定的看法，認為中性利率已經(jīng)大幅下降，并推斷政策的擴張性不像人們普遍認為的那樣強烈。她的直覺得到了證實，甚至可能顯得有點過于謹慎，因為在她的任期內(nèi)，經(jīng)濟增長和通脹水平大體上沒有達到美聯(lián)儲的預(yù)期——即使是在利率低于預(yù)期而聯(lián)邦赤字增長超出預(yù)期的情況下。

It is fortunate for the American economy that Ms Yellen recognised changes in its structure and deviated from models and policy rules derived from historical experience. Had she followed such models we quite likely would be in recession right now. Yet it must be acknowledged that growth in recent years associated with low interest rates would not have been as great as it was without the stock market increasing at a manifestly abnormal rate and without increases in borrowing that far outstripped growth in incomes.

對于美國經(jīng)濟來說幸運的是，耶倫看出了經(jīng)濟結(jié)構(gòu)變化，沒有遵循基于歷史經(jīng)驗的模型和政策規(guī)則。如果她遵循此類模型，我們現(xiàn)在很可能已經(jīng)處于衰退之中。但必須承認的是，如果股市沒有以明顯反常的速度上漲，如果借貸增長沒有遠超收入增長，近年來低利率環(huán)境下的經(jīng)濟增長也不會如此強勁。

Thus the first challenge facing the estimable Jay Powell as Fed chairman is working out how to achieve growth that is both adequate and financially sustainable. Even with very low interest rates, the normal level of private saving consistently and substantially exceeds the normal level of private investment in the US. And the differential is magnified by inflows of foreign capital. This creates a deflationary tendency that can be offset only by budget deficits or financial conditions that artificially depress saving and increase investment.

因此，令人尊敬的杰伊•鮑威爾(Jay Powell)出任美聯(lián)儲主席面臨的第一個挑戰(zhàn)就是，搞清楚要如何實現(xiàn)足夠強勁且在財政上可持續(xù)的經(jīng)濟增長。即使利率維持在非常低的水平，美國私人儲蓄的正常水平仍然持續(xù)、大幅地超過私人投資的正常水平。而外國資本流入會放大這種差距。這會造成通貨緊縮的趨勢——只能通過預(yù)算赤字或者人為抑制儲蓄、促進投資的金融狀況來抵消。

Asset values and levels of borrowing cannot indefinitely grow faster than gross domestic product, even though their ability to do so for a time has contributed to economic success over the past few years. If the Fed raises rates sufficiently to assure financial stability, there is the risk that the economy will slow too much. If it focuses on maintaining the growth necessary to meet its inflation target, there is the risk of further increases in leverage and asset prices setting the stage for trouble down the road .

資產(chǎn)價值和借貸水平的上升不可能無限期地超過國內(nèi)生產(chǎn)總值(GDP)增速，盡管它們在一段時間內(nèi)保持這種狀況的能力促成了過去幾年的經(jīng)濟成功。如果美聯(lián)儲以足夠大的力度加息以確保金融穩(wěn)定，經(jīng)濟增長有可能放緩太多。如果美聯(lián)儲著重于維持實現(xiàn)通脹目標所需的經(jīng)濟增長，就有可能造成杠桿率和資產(chǎn)價格進一步上升，給未來埋下隱患。

There is a very difficult balance to be struck. Except in the aftermath of recessions it has been a long time since the US economy grew well with a stable financial foundation. History will judge how stable the financial conditions of recent years have been. Prior to that we were in recovery from the 2008-09 recession. That in turn was preceded by a period of financial excess in housing and other markets. Prior to that came the 2001 recession and recovery, which in turn was preceded by the internet and stock market bubbles of the late 1990s.

這是一個非常難以實現(xiàn)的平衡。除了歷次衰退過后那段時期，美國經(jīng)濟在金融基礎(chǔ)穩(wěn)定的情況下實現(xiàn)良好增長已經(jīng)是很久以前的事情了。歷史將對近年來金融狀況的穩(wěn)定程度做出評判。在那之前，我們處于從2008-09年的衰退中復(fù)蘇的時期。再往前溯是住房及其他市場存在金融過度行為的時期。再往前是2001年的衰退和復(fù)蘇，更早則是上世紀90年代末的互聯(lián)網(wǎng)和股市泡沫。

So it has been a generation since the US economy enjoyed stable, financially sustainable growth from a position of strength. Good luck Mr Chairman.

因此，算起來，美國經(jīng)濟獲得那種穩(wěn)定、在財政上可持續(xù)的強有力增長距今已經(jīng)過去了一代人的時間了。祝新主席好運。

The writer is Charles W Eliot university professor at Harvard and a former US Treasury Secretary

本文作者為哈佛大學(xué)(Harvard)查爾斯•W•艾略特大學(xué)教授，曾任美國財政部長