This paper begins with a tribute to William Nordhaus, focusing on the two questions that have motivated his life’s work. The first is by how much carbon dioxide emissions should be reduced over time. The second is how to reach and enforce an agreement among sovereign nations to limit carbon dioxide emissions. Nordhaus was awarded the Nobel Prize for his efforts to answer the first question. I argue here that the answer to this question has been solved to a satisfactory extent, not only by economists, but by diplomats, and that the greatest need now is to answer the second question. I also present a simple model that extends previous research into this second question, a model in which countries choose both whether to abate and whether to adapt. Like all previous research on this topic, including Nordhaus’s own, the model doesn’t provide a neat solution, only another perspective on one of the most vexing questions in all of human history: how to prevent a tragedy of the commons of global proportions and with profound and possibly catastrophic consequences.

中文翻译：

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堤防与风车：气候条约和适应

本文首先向威廉·诺德豪斯致敬，重点关注激发他毕生工作的两个问题。首先是随着时间的推移应该减少多少二氧化碳排放量。二是如何在主权国家之间达成和执行限制二氧化碳排放的协议。诺德豪斯因回答第一个问题而获得诺贝尔奖。我在此主张，这个问题的答案已经得到了令人满意的解答，不仅是经济学家，而且是外交官，而现在最需要的是回答第二个问题。我还提出了一个简单的模型，将先前的研究扩展到第二个问题，在这个模型中，各国选择是否减少和是否适应。就像之前关于这个主题的所有研究一样，包括诺德豪斯自己的研究，