低增長是後危機時代的現實 Slow growth is a fact of life in the post crisis world

Once the acute phases of the financial and euro crises were over, it was clear that it would take time for advanced economies to recover. The history of past financial crises gave a clear warning that recovery would typically be long and painful.

在金融危機和歐元危機過了嚴重的階段後，發達經濟體顯然需要時間來實現復甦。以往金融危機的歷史提供了明確的警示：復甦進程通常漫長而痛苦。

Today, the scars are largely healed but growth is still slow. Before the crisis, any economist would have predicted that an economy with interest rates close to zero and no other major brakes on demand would see high growth rates and quickly overheat. Yet this is not what we have seen. The reason, I believe, must be found in mediocre medium term prospects, which in turn affect current demand and growth.

如今，危機造成的創傷已基本痊癒，但經濟增長依然緩慢。在危機爆發前，任何一位經濟學家都會這樣預測：在利率接近零又不存在其他重大需求抑制因素的背景下，經濟無疑將快速增長，並且很快就會過熱。然而我們看到的卻不是這樣。我認爲原因一定出在不太好的中期前景，後者反過來影響了當前的需求和增長。

Estimates of long term potential growth in advanced countries have come down by 0.5 to 1 per cent since 2007. Some of the decline is due to ageing, some to lower productivity growth. The effect of an ageing population was largely predictable, and indeed largely predicted. (Whether it was taken into account by firms thinking about their investment plans is unclear.)

自2007年以來，對發達國家長期潛在經濟增長率的預估下調了0.5-1%。一部分原因是人口老齡化，還有一部分原因是生產率增速下降。人口老齡化的影響大體上是可預見的，而且基本上也被預測到了。（不清楚企業在制定投資計劃時是否會考慮人口老齡化因素。)

Productivity growth has been much lower since 2007, More so in Europe where the rate has declined by over 1 per cent in major countries, than in the US, where it has only declined by 0.5 per cent. This decline reflects in part cyclical factors and the effect of lower capital accumulation. But there is more to it: for the US at least, the evidence points to a slowdown in underlying productivity, starting before the crisis and reflecting the end of a period of successful implementations of IT innovations. The safe assumption is that the high pre-crisis productivity growth rate was unusual, and we should expect lower underlying productivity growth in future.

生產率增速自2007年以來下降了很多，而且在歐洲下降得比在美國厲害——歐洲主要國家的生產率增速下滑超過了1%，而美國只下降了0.5%。生產率增速下降在一定程度上反映了週期性因素以及資本積累減少的影響。但還有更多原因：至少就美國而言，證據表明潛在生產率出現了放緩，從金融危機爆發前就開始了，反映了一段IT創新得到成功應用的時期的結束。可以斷定，金融危機前處於高水平的生產率增速並不尋常，我們應該預計未來潛在生產率增速會降低。

Low potential growth is bad news for the medium term. But it may explain what is happening today. A main finding of a paper that Eugenio Cerutti, Lawrence Summers and I wrote in 2015 was that, over the past 40 years, recessions in advanced countries have been associated surprisingly often with lower growth following the recession.

潛在經濟增長率較低對中期來說是壞消息。但它或許可以解釋當前的情形。我與歐金尼奧•切魯蒂(Eugenio Cerutti)、勞倫斯•薩默斯(Lawrence Summers)2015年合寫的一篇論文的一個主要結論是，在過去40年中，發達國家的經濟衰退出奇頻繁地與衰退結束後增速較低有關。

One interpretation is the presence of hysteresis, namely that the recession affects potential growth. Another is that the causality runs in reverse: bad news about future potential growth leads to a recession. So, for example, when companies realise that sales prospects are worse than they thought, they cut down on investment. And consumers, realising that their income prospects have worsened, cut on consumption.

一種解釋是存在滯後現象，即經濟衰退影響潛在增速。另一種解釋是二者的因果關係正好倒過來：關於未來潛在增速的壞消息導致了經濟衰退。比如說，當企業意識到銷售前景比他們認爲的更糟糕時，他們會減少投資。而意識到自己收入前景惡化的消費者會減少消費。

Monetary policy can limit the drop, but not eliminate it. In a 2013 paper I co-wrote, we showed formally that this interpretation fits postwar US data well. I believe that it also explains what we observe today. The result in this case is not a recession, but a weak recovery.

貨幣政策可以限制這種下滑，但無法消除。在我2013年與人合寫的一篇論文中，我們嚴謹地提出，這種解釋與美國戰後的數據相當契合。我相信它也可以解釋我們今日所看到的情況。只不過在這裏結果並非衰退，而是疲弱復甦。

This weak recovery in advanced countries also goes a long way in explaining the slowdown in emerging markets. While domestic factors play a role, and the evolution of China is largely sui generis, lower exports, less demand for commodities, and a resulting drop in commodity prices, have led to lower output.

發達國家的疲弱復甦對於解釋新興市場增長放緩也大有幫助。雖然有國內因素的作用，而且中國的情況很大程度上具有獨特性，但出口下滑、大宗商品需求減少以及由此帶來的大宗商品價格下跌，已經導致產出下滑。

If this new narrative is right, the baseline forecast is for a slow but continued recovery, as the adjustment to the reality of lower potential growth plays out in advanced economies, and the adjustment to the commodity bust works itself out in emerging market and developing economies. It suggests that some of the scary talk, and some of the exotic policy measures being discussed, from helicopter money to large negative nominal rates, are not the order of the day. They should be kept in reserve in case bad things happen, but the expectation should be that they will not be needed.

如果這種新的分析正確的話，基準預測就是經濟將會緩慢而持續地復甦，發達經濟體將逐漸適應潛在增長率下降的現實，新興市場和發展中國家將逐漸適應大宗商品泡沫破裂。這表明，一些引發恐慌的言論及部分正在討論的非常規政策措施——從“直升機撒錢”到較大負值的名義利率——並不是當下最重要的事。這些政策應該留待形勢嚴峻的時候使用，但我們最好期待不需要使用到這些措施。

The focus should be increasingly on medium term growth, and the redefinition of normal fiscal and monetary policies in an environment of lower growth and lower interest rates.

我們應該更多地着眼於中期增長，以及在低增長、低利率的環境下如何重新定義正常的財政和貨幣政策。