Here is a thought experiment that illuminates the challenges currently facing macroeconomic policymakers in the US and the rest of the industrial world.

以下是一个阐释美国及其他工业化国家的宏观经济政策制定者目前所面临挑战的思维实验。

Imagine that in a brief period inflation expectations around the industrial world, as inferred from both the markets for indexed bonds or inflation swaps, rose by nearly 50 basis points to a level well above the 2 per cent target with larger increases foreseen at longer horizons.

试想在一段短暂的时期里，从指数挂钩债券市场或通胀掉期市场来推断，工业化国家的通胀预期上升了近50个基点，达到远高于2%目标的水平，同时从较长时期来看预计还会有更大幅度的上升。

Imagine that at the same time survey measures of inflation expectations, such as those calculated by the University of Michigan and New York Federal Reserve in the US, were rising sharply.

试想一下，在同一时间里，通胀预期的调查数据，比如由美国密歇根大学(University of Michigan)和纽约联邦储备银行(New York Fed)得出的结果，也在迅速上升。

Imagine also that commodity prices were soaring and that the dollar experienced a decline seen once every 15 years.

试想大宗商品价格也在飙涨，而美元经历了15年一遇的贬值。

Imagine that the market estimate of future monetary policy in the US was far tighter than the Federal Reserve’s own policy projections.

试想市场所预估的美国未来货币政策比美联储(Fed)本身的政策预期要紧得多。

Imagine that measures of gross domestic product growth were accelerating with increasing signs of a worldwide boom.

试想国内生产总值(GDP)增长数据正在加速上升，同时有越来越多的迹象指向了全球范围内的繁荣。

Imagine too that no serious efforts were under way to reduce deficits.

试想不会有什么严肃的举措即将出台以减低赤字。

Finally, suppose that officials were comfortable with current policy settings based on the argument that Phillips curve models predicted that inflation would revert over time to target due to the supposed relationship between unemployment and price increases.

最后，假设官员们基于菲利普斯曲线(Phillips curve)模型的主张，对当前的政策环境感到满意。该模型预测，由于失业率和价格上涨之间应有的关系，通胀将随着时间推移趋向目标值。

I think it is fair to assert that in this hypothetical circumstance there would be pervasive concern that policy was behind the curve. There would be fears that much was at risk as inflation expectations were becoming unanchored and that a substantial set of policy adjustments were appropriate.

我认为可以合理地断言，人们会在这种假设的情况下普遍担忧政策落后于形势。人们会担心，随着通胀预期变得失去控制，很多事物都处于危险之中，进行一系列重大政策调整恐怕是适当的。

The key point is that allowing not just a temporary increase in inflation but a shift to abovetarget inflation expectations could be very costly.

关键问题在于，如果不仅放任通胀暂时上升，还任由通胀预期转向高于目标的水平，代价可能非常高昂。

At present we are living in a world that is the mirror image of the hypothetical one just described. Market measures of inflation expectations have been collapsing and on the Fed’s preferred inflation measure are now in the range of 1-1.25 per cent over the next decade.

目前我们生活在与刚刚描述的假想完全相反的世界。通胀预期的市场衡量指标一直在下滑，美联储偏好的通胀衡量指标目前所处的范围是，未来10年通胀率为1%到1.25%。

Inflation expectations are even lower in Europe and Japan. Survey measures have shown sharp declines in recent months. Commodity prices are at multi-decade lows and the dollar has only risen as rapidly as in the past 18 months twice during the past 40 years when it has fluctuated widely.

欧洲和日本的通胀预期更低。调查数据表明近来数月出现了大幅下滑。大宗商品价格处于数十年来的低点。美元在过去18个月内的升值速度在其币值大幅起伏的过去40年里只出现过两次。

The Fed’s most recent forecasts call for interest rates to rise almost 2 per cent in the next two years, while the market foresees an increase of only about 0.5 per cent.

美联储的最新预测主张利率会在接下来2年内上升近2%，而市场预测利率仅会上升约0.5%。

Consensus forecasts are for US growth of only about 1.5 per cent for the six months from last October to March. And the Fed is forecasting a return to its 2 per cent inflation target on the basis of models that are not convincing to most outside observers.

对美国从去年10月到今年3月这6个月期间的增长率，共识预测仅为约1.5%。美联储还基于无法让大多数外部观察者信服的模型预测通胀会回归2%的目标。

Despite the apparent symmetry, the current mood is nothing like the one posited in my hypothetical example.

即使现在的情况和我设想的情形明显存在对称性，两种情况下的市场情绪也完全不相像。

While there is certainly substantial anxiety about the macroeconomic environment, as judged from the meeting of the Group of 20 big economies in Shanghai last week, there is no evidence that policymakers are acting strongly to restore their credibility as inflation expectations fall below target.

尽管从近期二十个大型经济体在上海举行的二十国集团(G20)会议来看，现在显然存在对宏观经济环境的严重焦虑情绪，但没有证据表明政策制定者在采取有力行动，在通胀预期下滑至目标水平以下之际重建他们的信誉。

In a world that is one major adverse shock away from a global recession, little if anything directed at spurring demand was agreed. Central bankers communicated a sense that there was relatively little left that they can do to strengthen growth or even to raise inflation. This message was reinforced by the highly negative market reaction to Japan’s move to negative interest rates. No significant announcements regarding non-monetary measures to stimulate growth or a return to target inflation were forthcoming, either.

在这个只要再发生一次重大负面冲击就会进入全球衰退的世界，各方为刺激需求而达成的一致即使存在，也是很少的。央行官员们传递出一种感觉，即在提振增长、或者哪怕只是提高通胀方面，他们能做的相对而言已经所剩无几。市场对日本负利率举措的极为消极的反应加强了这一讯息。也没有谁宣布有什么提振增长或者回归通胀目标的非货币政策的重大举措即将出台。

Perhaps this should not be surprising. In the 1970s it took years for policymakers to recognise how far behind the curve they were on inflation and to make strong policy adjustments.

或许这不应让人感到惊讶。上世纪70年代，政策制定者花了数年时间才认识到他们在通胀方面落后形势有多远，进而采取强有力的政策调整。

Policymakers continued to worry about a supposed lack of demand long after it was an important problem. The first attempts to contain inflation were too timid to be effective and success was achieved only with highly determined policy. A crucial step was the abandonment of the idea that the problem was structural in nature rather than driven by macroeconomic policy.

在所谓的需求不足成为一个重大问题很久以后，政策制定者仍旧担心这个问题。当年遏制通胀的最初尝试过于小心翼翼，无法起到效果，只是后来通过非常坚决的政策才取得了成功。关键的一步是放弃认为问题本质上是结构性的，而非由宏观经济政策造成。

Today’s risks of embedded low inflation tilting towards deflation and of secular stagnation in output growth are at least as serious as the inflation problem of the 1970s. They too will require shifts in policy paradigms if they are to be resolved.

如今，根深蒂固的低通胀正演变为通缩的风险，以及产出增长长期停滞的风险，至少和上世纪70年代的通胀问题一样严重。如果想要应对这些风险，现在也需要转变政策范式。

In all likelihood the important elements will be a combination of fiscal expansion drawing on the opportunity created by super low rates and, in extremis, further experimentation with unconventional monetary policies.

重要的政策要素很有可能将是以下二者的结合：利用超低利率所创造的机会进行财政扩张，和在极端情况下进行进一步非常规货币政策实验。