如何爲世界經濟注入活力 這是個難題

Why are real interest rates so low? And will they stay this low for long? If they do – as it seems they might – the implications will be profound: good for debtors, bad for creditors and, above all, worrying for the vigour of global demand.

爲何眼下實際利率這麼低？這一局面還將延續很久嗎？如果確實如此（目前看來有這樣的趨勢），那麼影響將十分深遠：債務人受益，債權人受損，並且最重要的是，不利於全球需求的活躍。

The International Monetary Fund’s latest World Economic Outlook includes a fascinating chapter on global real interest rates. Here are its most significant findings.

在國際貨幣基金組織(IMF)最近公佈的《世界經濟展望》(World Economic Outlook)報告中，有一章關於全球實際利率的分析令人關注。以下就是那一章的最重大發現。

First, globalisation has integrated finance. There used to be wide variation in real interest rates between different countries. That is no longer the case, since interest rates everywhere now respond to common influences.

首先，全球化促使金融一體化。以前，不同國家的實際利率存在很大差距。現在已不是這樣，因爲如今各地的利率都對共同的影響因素做出反應。

Second, real interest rates – which are adjusted for inflation – have declined a long way since the 1980s. Ten-year rates are close to zero while short-term rates are negative. But the expected real return on equity (estimated from the dividend yield plus the expected growth of dividends) has not fallen by as much (see charts).

其次，自上世紀80年代以來，經通脹調整後的實際利率已下降了很多。10年利率接近於零，短期利率則爲負值。但預期實際股本回報率（通過股息率和預期股息增長率估算得出）的下降幅度不如實際利率（見圖表）。

How is one to understand these developments? The real return on financial assets depends on various factors: how much people want to save and invest; what kind of assets savers prefer to hold; and changes in monetary policy. These are not independent of one another. Above all, central banks charged with hitting an inflation target must respond to shifts in demand by changing their monetary policies.

應如何理解這些變化呢？金融資產的實際回報取決於多個不同因素：人們想要儲蓄多少、投資多少？儲蓄者更願意持有何種資產？以及貨幣政策發生了何種變化？這幾個因素並非相互孤立。最重要的是，各國央行肩負着達到某一通脹目標的使命，它們必須通過改變貨幣政策來回應需求變化。

The IMF reckons that, in the 1980s and early 1990s, changes in monetary policy were the most powerful influence on real interest rates. In the late 1990s, fiscal tightening became the main force driving down real rates. Another important factor was the falling price of investment goods relative to consumption goods. Falling relative prices of information technology mean this is still true.

IMF認爲，上世紀80年代到90年代初，貨幣政策的改變是對實際利率影響最大的因素。上世紀90年代末，財政緊縮成爲壓低實際利率的主要因素。另一個重要因素，是投資品價格相對消費品價格不斷降低。信息技術價格相對下降意味着，眼下情況仍然如此。

Since the late 1990s, however, much has changed. In emerging economies the savings rate has gone up, largely because incomes were rising. Investors began to favour assets deemed safe. Most importantly, recent financial crises have caused investment to collapse and private savings to jump in the affected economies.

但自從上世紀90年代末以來，情況發生了很大變化。在新興經濟體，儲蓄率上升，主要是因爲收入在增加。投資者開始青睞所謂安全資產。最重要的是，近來的金融危機導致在受到衝擊的經濟體中，投資顯著減少、私人儲蓄大幅增加。

The IMF argues that declining inflation risk has not contributed to the fall in long-term rates, since the “term spread” – the gap between short and longer-term rates – has not fallen. More important has been the effect of changes in national savings and investment. At the global level, savings must equal investment. So changes in the observed global savings rate will tell us nothing about whether there has been a growing “savings glut” – by which I mean an excess of desired savings over desired investment. Only a shift in the price – the real rate of interest – reveals that.

IMF提出，通脹風險降低沒有起到助力長期利率降低的作用，因爲“期限利差”——指短期利率與長期利率之間的差值——並未下降。更重要的是國民儲蓄與投資變化的影響。在全球範圍來看，儲蓄必然等於投資。所以，我們觀察到的全球儲蓄率，根本無法告訴我們“儲蓄過剩”是否一直在升高。此處“儲蓄過剩”是指超出意願投資額的那部分意願儲蓄。唯有價格——實際利率——的變化能揭示這一點。

Strikingly, the 10-year real rate of interest was 4 per cent in the mid-1990s, 2 per cent in the 2000s, before the crisis, and close to zero thereafter. At least two factors lay behind this precipitous fall. Investment fell a long way in high-income economies but soared in emerging ones, especially China; yet the savings rates of emerging economies rose even more than their investment rates. Consequently, these economies became big net exporters of capital.

引人注意的是，上世紀90年代中，10年期實際利率爲4%，到本世紀頭十年（危機之前）降至2%，再後來降至接近零。10年期實際利率陡然下跌背後至少有兩個因素在起作用。高收入經濟體投資一路下滑，但新興經濟體——尤其是中國——投資卻大舉升高；不過，新興經濟體儲蓄率增幅甚至比投資率增幅還要高。結果，這些經濟體成了資本淨出口大國。

Emerging countries also largely nationalised this capital outflow. Their governments then tended to buy “safe” assets, especially to put in the foreign exchange reserves. This helps explain the portfolio move towards highly rated bonds.

新興國家也將大部分資本輸出國有化了。於是，它們的政府傾向於購買“安全”資產，尤其是作爲外匯儲備。這有助於解釋投資組合爲何向高評級債券傾斜。

The story, in brief, is that shifts in the balance between desired real savings and investment generated a large fall in real interest rates. These were accompanied by changes in portfolio preferences towards safe assets and the collapse in the pre-2000 equity bubble. The shift in the distribution of income towards capital and highly paid employees in high-income countries also weakened demand. The central banks then responded with aggressive monetary policies. These supported explosions of credit generally linked to house-price surges. Both imploded in the crisis. As Lawrence Summers has argued, the high-income economies seem to be worryingly unable to generate good growth in demand without extreme credit instability.

簡言之，情況是意願實際儲蓄與意願實際投資之間的差額發生變化，導致實際利率大幅下降。另外兩個因素是，投資組合偏好發生變化、向安全資產傾斜，以及2000年前股票泡沫的破滅。在高收入國家，收入分配向資本方和高薪員工傾斜，也弱化了需求。於是各中央銀行推出了激進的貨幣政策。這推動了信貸大膨脹，信貸大膨脹通常看來與房價猛漲脫不開干係。信貸和房價在危機中都崩潰了。正如勞倫斯•薩默斯(Lawrence Summers)所指出那樣，令人擔憂的是，高收入經濟體似乎無法在不製造極端信貸動盪的前提下，推動需求強勁增長。

This is not a short-term story. The label “secular stagnation” looks apposite. The IMF agrees that real interest rates could remain low for a prolonged time. If governments persist with planned tightening of fiscal policies, this seems certain. If investment rates fell sharply in China, global real rates might need to fall still further. That is difficult while inflation is so low.

這種情況並不是短期內的。“長期增長停滯”(secular stagnation)看上去是個貼切的論斷。IMF贊同實際利率可能在長期內維持低位的觀點。如果各國政府堅持按計劃實行緊縮的財政政策，則看來註定會出現這種局面。如果中國投資率大幅下降，那麼全球實際利率可能需要進一步下降。在通脹如此低的情況下，這很難辦到。

What might reverse this? The obvious possibility is a jump in investment in high-income countries driven by the relatively high expected returns on equity. The obstacles here are threefold. One is that chief executives are not rewarded for investing for the long term; another is that investment goods are becoming cheaper all the time; and another is that, when the future is uncertain and the economy sluggish, companies rationally prefer to wait before they invest.

靠什麼才能扭轉這一局面？一個顯而易見的可能藥方，是相對較高的預期股本收益率驅動高收入國家的投資猛增。這裏有三重障礙。一是首席執行官沒有動力爲長期而投資；另一個是投資品的價格一直在降低；最後一個是，當未來不確定、經濟又低迷時，企業出於理性考慮，願意觀望而不願投資。

Another possibility is a big fall in savings in emerging economies. But this seems unlikely, at least without a collapse in oil prices.** That leaves the option of sustained fiscal deficits in high-income countries, ideally to be invested in infrastructure. Housing-related credit booms are a far worse option. Redistribution towards the spenders seems quite inconceivable.

第二個可能藥方，是新興經濟體儲蓄率大幅下降。但這似乎不可能實現，至少油價不暴跌的話就不太可能實現。那就只剩下一個選擇，即高收入國家維持財政赤字，最好投資於基礎設施。與房地產相聯繫的信貸繁榮則是一個糟糕得多的選擇。通過再分配向花錢者傾斜看上去不可思議。

If real interest rates do indeed remain low for a long time, creditors are going to find life difficult. But managing the post-crisis public finances should be far easier than the hysterics assume. A really big question in such a world is whether conventional inflation targets might be too low, because they do not give enough room for real interest rates to fall as far below zero as necessary.

如果實際利率確實長期維持在低水平，那麼債權人未來會覺得日子不好過。但管理後危機時代的公共財政，應當會比歇斯底里者認爲的容易得多。如此世界一個真正的大問題，是常規的通脹目標定得可能太低了，因爲沒有給實際利率在必要時降至負值留下足夠大的空間。

The immediate question, however is: how do we generate the demand that is needed to mop up potential global supply? Failure to answer that need in a sensible way was a leading cause of the crisis. Continued failure will blight the recovery or, worse, cause another bout of financial and economic upheaval. Do not imagine these challenges will soon vanish. They look like a semi-permanent condition.

不過，當前的緊迫問題是，我們應如何產生支撐潛在全球供應所離不開的需求？不能以合理方式滿足這一要求是過去引發危機的一個主要因素。這一要求繼續得不到滿足將阻礙復甦，更嚴重者，將引發又一輪金融與經濟動盪。不要臆想這些挑戰不久後就會消失，它們看來就像一種半永久性的病症。