As the Intergovernmental Panel on Climate Change (2018) testifies, the world is a long way from halting climate change, let alone reverting it. The existence of adaptation and mitigation technologies did not prove sufficient, their adoption being respectively faulted or hindered by the presence of externalities. In this work, we study how externalities, whether positive or negative, lead the system away from Pareto-dominant (social optimum) states, towards Pareto-dominated ones. We show that adoption gaps, i.e. differences between socially optimum vs current adoption shares, of both (mal)adaptation and mitigation technologies are caused by the externalities emitted. In particular, over-adoption may occur for maladaptive technologies, whereas under-adoption may occur in case of mitigation. We employ a model with two regions at different stages of development and also derive relevant considerations on possible counterproductive effects of green policies and environmental dumping.

正如政府间气候变化专门委员会（2018 年）所证明的那样，世界距离阻止气候变化还有很长的路要走，更不用说逆转了。适应和缓解技术的存在证明是不够的，它们的采用分别受到外部性存在的错误或阻碍。在这项工作中，我们研究外部性，无论是积极的还是消极的，如何引导系统从帕累托主导（社会最优）状态转向帕累托主导状态。我们表明，（不良）适应和缓解技术的采用差距，即社会最优与当前采用份额之间的差异是由排放的外部性引起的。特别是，适应不良的技术可能会被过度采用，而在缓解的情况下可能会出现采用不足的情况。