Global warming is a case in point. When the downside risks associated with such limits and thresholds are brought into estimates of sustainable development, the growth in wealth among the world’s wealthy nations will probably turn out to have been less than we now think.
但替代性是有限的：替代的成本（包括人类的创造性）总是在关键资源衰退之前就悄然提高了。全球变暖正好切中这一点。当我们在估算可持续发展水平时计入与这些极限相关的消极风险，则世界富国财富增长的结果可能并不如我们想象中那样好。