但是过度消费模式的对立面——过度依赖投资，虽然能够增加总需求但同样是存在局限性的。当个人或者是社会投资的收益下降过多，即使高涨的投资率在短时期内能够刺激维持总需求上涨，但是经济可持续长还是没有保证。改变这种经济增长模式是当前中国面临的重大挑战之一。
同时，在机遇与分配上不断扩大的潮剧，也在威胁着经济增长模式的稳定性。许多国家的人们都可以接受一定程度内由市场导致的收入差距，毕竟天赋以及个人特长有所不同，但是这个差距也是在一定限度之内的。一旦这个限度被打破，最典型的结果就是不平等情绪，接下来便是抗议，最后只好通过政治手段来解决，虽然这种方式有时候会适得其反，甚至是有碍经济发展的。
也许长期可持续发展的最大问题就是自然资源的充裕与否：随着发展中国家40亿人口都在朝着发达国家的收入水平和消费模式靠拢，在未来的二三十年中，产出要比现在增加3倍，才能满足这些增长需求。要想承担得起这样的增长速度，就要求调整现有的经济发展战略。
一些调整会自行发生，比如随着油价以及物价的上涨，人们会有意识节约或者是寻求其他可代替资源。但是其他无法用价格计算的外部环境因素比如全球气候变暖，水资源短缺都要求我们要高度重视，而不是应付或者是得过且过的心态和方法。
所有这些有自限性的增长模式都存在着共同点。首先，从一种或者是几种维度上讲，经济发展的基础，有形或者是无形资产，或者是自然资源都在走下坡路。而我也将社会凝聚力作为经济发展的基础之一：不断扩大的差距正在蚕食着它。
在这个问题上，衡量标准事关重大。说隐形资产不断流失很容易，因为这些东西往往是不规律的或者是不能够直接测量的。因此引起人们对社会稳定性的关注，扩大衡量范围至经济，社会以及环境等领域是十分必要的。
第二，不知名的经济发展模式往往造成很糟糕的结果。预想高出了实际，如果想重新调整系统，保证能够维持经济增长，这是很困难的事情。毕竟，需要弥补以往的投资不足，同时还要承担未来的投资，这样一来就等于有双重的重担压在了肩上。如果不能解决分配公平问题，那么就会出现僵局，瘫痪或者是长时间的经济增长停滞。
最后，这些增长模式之中都夹杂着财政压力。同众所周知的理论相反，从某种程度上讲，在合理的时间里，从凯恩斯需求理论过渡到一个能够自我维持的增长模式与重建财政平衡是不冲突的。相反，无论是单行或者是双管齐下，在调整过程中，财政刺激和巩固都是必要的。
但是这些还不够。最重要的是可行的总需求增长结构的转变以及恢复已经被破坏的经济发展基础，这意味着结构重组以及增加投资的必要性。
But the opposite of the excessive-consumption model – excessive reliance on investment to generate aggregate demand – is also a self-limiting growth pattern. When the private and social returns of investment diminish too much, growth cannot be sustained indefinitely, even though rising investment rates can sustain aggregate demand for a while. Altering this growth pattern is a significant part of the challenge that China now faces.
Rising inequality in either opportunity or outcomes (and often both) also poses threats to the sustainability of growth patterns. While people in a wide range of countries accept some degree of market-determined income variation, based on differential talents and personal preferences, there are limits. When they are breached, the typical result is a sense of unfairness, followed by resistance and, ultimately, political choices that address the inequality, though sometimes in counter-productive, growth-impeding ways.
Perhaps the largest long-run sustainability issue concerns the adequacy of the global economy’s natural-resource base: output will more than triple over the coming two or three decades, as high-growth developing economies’ four billion people converge toward advanced-country income levels and consumption patterns. Existing economic-development strategies will require significant adaption to accommodate this kind of growth.
Some adaptation will occur naturally, as rising energy and other commodity prices generate incentives to economize or seek alternatives. But the un-priced environmental externalities – global warming and water depletion, for example – will require serious attention, not myopic, reactive mindsets and approaches.
All of these self-limiting growth patterns tend to have three things in common. First, in one or several dimensions, some part of the economy’s base of tangible, intangible, and natural-resource assets is being run down. I would include social cohesion as part of the asset base: it is the one that is depreciated by excessive inequality.
Measurement issues play an important role here. It is easier to run down something that is partly invisible because it is not regularly or effectively measured. Expanded measurement of the dimensions of economic, social, and environmental performance is necessary to broaden awareness of sustainability issues.
Second, unidentified self-limiting growth patterns produce very bad results. Expectations come to exceed reality, and resetting the system to a sustainable growth pattern is difficult. After all, past investment shortfalls have to be made up and future-oriented investments undertaken simultaneously – a double burden that must be borne by the current generation. An inability to resolve the distributional and fairness problem can produce gridlock, paralysis, and prolonged stagnation.
Finally, many of these flawed growth patterns involve fiscal distress. Contrary to the prevailing wisdom nowadays, some degree of Keynesian demand management in the transition to a more sustainable growth pattern is not in conflict with restoring fiscal balance over a sensible time period. On the contrary, applied both individually and together, fiscal stimulus and consolidation are necessary parts of the adjustment process.
But they are not sufficient. The crucial missing pieces are a shift in the structure of accessible aggregate demand and restoration of those parts of the economy’s asset base that have been run down, implying the need for structural change and investment.
