The Green Wave Crash: Why Did Clean Technology Patenting Drop After 2010?

将经济增长与温室气体排放脱钩是避免灾难性的全球平均变暖水平比工业化前水平高出2摄氏度，而不放弃经济增长的唯一途径。根据政府间气候变化专门委员会(2018)，必须在2050年前将温室气体排放减少到净零，以减轻气候变化的最坏影响。如果要在不对经济和生计造成巨大损害的情况下实现这一目标，低碳技术的创新及其广泛传播是至关重要的(例如，Stavins 2007，Anadon和Holdren，2009；Popp等人，2010)。随着有效缓解全球变暖措施的窗口逐渐关闭(政府间气候变化专门委员会，2018年)，低碳技术创新比以往任何时候都更加重要。那么，在经历了近20年的持续增长后，为什么低碳技术专利的份额有所下降？了解清洁创新下降的原因是制定适当的政策回应以补救这一问题的关键先决条件。其目的是在观察到的下降及其原因之间建立可信的联系。使用最新汇编的数据集，我们探索了文献中观察到的清洁创新下降的最令人信服的解释，即信贷限制、能源价格和环境政策严格。这些驱动因素中，哪一个扮演着最重要的角色，将决定哪种政策最适合扭转这一趋势。

Decoupling economic growth from greenhouse gas emissions is the only way to avoid catastrophic global average warming levels above 2 degrees compared to pre-industrial levels, without forgoing economic growth. According to the IPCC (2018), greenhouse gas emissions must be reduced to net zero by 2050 to mitigate the worst effects of climate change. Innovation in low-carbon technologies and their widespread diffusion are essential if this goal is to be met without inflicting vast damage on the economy and, consequently, livelihoods (e.g. Stavins 2007, Anadon and Holdren, 2009; Popp et al., 2010). As the window for effective global warming mitigation measures gradually closes (IPCC, 2018), low-carbon technology innovation is more important now than ever. Why then, has there been a drop in the share of low-carbon technology patents after almost two decades of sustained growth? Understanding the causes of the drop in clean innovations is a key prerequisite for developing an appropriate policy response that could remedy the problem. The aim is to establish a credible link between the observed decline and its causes. Using a newly compiled dataset, we explore the most compelling explanations for the observed decline in clean innovation found in the literature, namely credit constraints, energy prices and environmental policy stringency. Which of these drivers plays the most important role will determine which policy is best suited to reverse the trend.