《上海财经大学学报》
2022第24卷第4期

(一) 第一个挑战：“科学”的经济政策为什么没有使人类避免经济危机？

 图 1 美国大缓和期间的宏观数据

 \begin{aligned} (\mathrm{y}-\overline{\mathrm{y}})_{\mathrm{t}}= & \alpha_{0}+\alpha_{1}(\mathrm{y}-\overline{\mathrm{y}})_{\mathrm{t}-1}+\alpha_{2} \mathrm{E}_{\mathrm{t}}(\mathrm{y}-\overline{\mathrm{y}})_{t} \\ &+\alpha_{3}\left(\mathrm{i}-\mathrm{E}_{\mathrm{t}}(\pi)_{\mathrm{t}+1}\right)+{\mathrm{s}_1}\end{aligned} (1)
 $\pi_{\mathrm{t}}=\beta_{1} \pi_{\mathrm{t}-1}+\beta_{2} \mathrm{E}_{\mathrm{t}}(\pi)_{\mathrm{t}+1}+\beta_{3}(\mathrm{y}-\overline{\mathrm{y}})_{\mathrm{t}}+\mathrm{s}_{2}$ (2)
 $\mathrm{i}_{\mathrm{t}}=\mathrm{r}^{*}+{\mathrm{x}_ 1}\left(\pi-\pi^{\mathrm{T}}\right)+{\mathrm{x}_2}(\mathrm{y}-\overline{\mathrm{y}})_{\mathrm{t}}+{\mathrm{s}_3}$ (3)

Mishkin认为，作为科学的货币政策有以下九大共识：（1）通胀膨胀始终且无处不是一种货币现象。货币增长是通货膨胀的最为重要的信息之一，但通货膨胀的最终来源并不一定是扩张性的货币政策。（2）价格稳定具有十分重要的作用和收益。这就是通胀盯住制，认为价格稳定就可以使市场完全发挥作用，使经济持续稳定地处于通胀状态，所以价格稳定成为唯一的政策目标。（3）失业与通货膨胀并不存在上期替代的关系。（4）预测在宏观经济中扮演着十分重要的角色。（5）泰勒规则对于价格稳定十分重要。（6）时间不一致问题与货币政策相关。（7）中央银行独立性将大幅度改善宏观经济绩效，这就要求目标独立、工具独立、机构权限独立。（8）对于名义锚的可信承诺将有助于价格和产出的稳定，这就是我们讲的货币政策规则与通胀目标制。（9）金融摩擦在经济周期中具有较为重要的地位。但实际上，特别是在2003年以前，通用的DSGE模型中没有金融摩擦的因素。

Jackson Hole会议也提出一些观点，基本上大同小异。当2008年经济危机全面爆发之后，新共识提出的结论直接破灭。周期问题和危机问题没有被解决，作为科学的货币经济学没有预测到大危机的到来并采取相应的措施。在此期间，伦敦政经学院的几位教授给英国女王写信道歉；哈佛大学的大学生集体退出曼昆的课程，认为他讲的没有用。大家可以看到，从2003年到2007年，如果按照新共识的标准，美国所有宏观参数都是稳定的，没有任何迹象表明美国会出现金融危机和经济危机。而金融危机的爆发直接击破了美国货币政策能够避免危机的豪言，更为重要是，一些经济参数的变化与新共识得出的结论相互冲突，这就引发了整个宏观经济学界的大讨论

2016年，著名经济学家罗默在《宏观经济学的困境》一文中指出，“在30余年的时间里，宏观经济学已经开始倒退了。目前，对于问题的识别和处理并没有比20世纪70年代早期有所进步，（经济学家们）因其晦涩难懂而逃避这个问题的挑战。宏观经济理论大家们装作不知道‘货币政策收紧可能会导致经济衰退’这样简单的论断而无视不争的事实。他们构建的模型将宏观经济总体变量的波动归因于假想出来的因果力量，而那些因素并不会被人们的行为所影响”。

(二) 第二个挑战：长期停滞的出现是否意味着经济学和经济政策的深度失败？

 图 2 美国实际GDP和潜在GDP

 图 3 全球GDP平均增速与中美实际利率

 图 4 中美TFP增长率

Summers于2015年提出“零利率下限论”，认为经济长期停滞的根源在于实际利率与均衡利率不匹配。后危机时代经济复苏乏力主要源于经济体内部有效需求不足，进而引致均衡实际利率长期下行，甚至低于零，而名义利率因为“零利率下限”约束，致使扩张性货币政策操作空间有限，现实利率无法逼近均衡利率，总需求受到持续抑制。

2017年Summers又进行了全面解释：一是人口和技术进步增速放缓；二是资本品价格下降；三是收入分配恶化；四是金融危机后导致投资风险偏好和期限溢价变化；五是安全资产的需求上升；六是反通胀因素。其中最典型的解释是，均衡利率、自然利率已经低于零，而我们的利率无法调节到零以下，因此出现长期停滞。当然解决长期停滞最为直接的政策方案就落脚到如何使名义利率或者实际利率能够调整到与均衡利率相匹配，也就是为负。这类政策怎么实施呢？理论上的探索很多，后来使用的超常货币政策也是这类政策的创新之一。

 图 5 2011年以来实际无风险利率水平

 图 6 全球GDP加权的无风险利率（1314-2018）

 图 7 美国菲利普斯曲线

 图 8 欧洲菲利普斯曲线

 图 9 各国10年期国债利率

(三) 第三个挑战：大流行引发的宏观经济学无力，疫情经济学是否引发经济学的革命？

(四) 第四个挑战：新技术、新模式、新经济对于微观基础冲击带来的新挑战

① 本文根据长安讲坛的讲话整理而成，感谢“经济50人论坛”秘书处提供的各种帮助。

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㉟ 海因茨·D.库尔茨、尼里·萨尔瓦多里，李酣：《寻找更好的宏观经济学：回归古典经济学和凯恩斯主义》，《江海学刊》 2020年第4期。

Challenges and Changes Facing Macroeconomics in the Great Era
Liu Yuanchun
President’s Office, Shanghai University of Finance and Economics, Shanghai 200433, China
Abstract: This paper summarizes the five changes of the Great Era in the past 20 years: The first is , the global depression caused by the American financial crisis in 2008. The second is that , since 2010, the world has fallen into “secular stagnation”. The third is that , the pandemic and stagnation caused by the COVID-19 epidemic in 2020. The fourth is that, the digital economy era opened after the wave of informatization. Thw fifth is that , the world began to enter a century of unprecedented changes. The above five aspects show that the world economy has undergone structural upheaval under the superposition of various forces. This upheaval is very different from the generally assumed general market economic environment, which has led to great changes in macroeconomics, thus posing the following four challenges to macroeconomics: First, why did the “scientific” economic policy not prevent mankind from economic crisis? Second, does the emergence of “secular stagnation” mean the deep failure of economics and economic policy? Third, the Great Pandemic causes the weakness of macroeconomics, so will epidemic economics trigger a revolution in economics? Fourth, new technology, new model and new economy bring new challenges to the impact of micro foundation. The four challenges correspond to the four typical facts respectively. They appear at the same time, which have not been completely encountered in other times. The superposition of shocks deserves our attention. We are in a super Great Era. Compared with the traditional system, the new operating system shows a strong fracture. This paper deeply analyzes the practical and theoretical innovations made by the macroeconomic community in response to these challenges, and points out that the reflections on financial failure and macro philosophy brought about by the financial crisis, the reflections on low interest rates and economic stagnation brought about by long-term stagnation, the reflections on various economic indicators and economic logic under extreme conditions brought about by the epidemic and the war, and the reflections on micro assumptions of macroeconomics and changes in economic transmission mechanism brought about by digital technology revolution, have constituted the four main lines of the future development of macroeconomics. No matter whether these theoretical developments are marginal adjustment or revolutionary reconstruction, we need to embrace them with an open attitude.
Key words: macroeconomics    economic logic    micro assumptions    economic transmission mechanism