Policymakers in China have paid attention to SO2 emissions reduction since the 1990s, as adverse environmental effects such as acid rain devastated large parts of the country. Shen empirically tests the “political regulation wave” theory based on temporal patterns in SO2 regulation between 2001 and 2010. During this time, reduction targets were nonbinding during 2001-5 but binding during 2006-10. Since SO2 emissions management entails a low level of ambiguity, regulatory efforts translate well into regulatory effectiveness. Results based on official data from statistical yearbooks and on satellite-based statistics concur that top prefectural leaders whose prefectures received high reduction targets were incentivized to produce an incremental yet steady decrease in regulation during 2001-5 to accommodate economic and stability goals, consistent with theoretical predictions. Later, when binding SO2 reduction targets became tied to local leaders’ career prospects, they fostered a more consistent regulatory implementation during their tenures.

Here we grasp the tool in this side of our box with the most promise to exert a material cooling impact on the planet in the foreseeable future. It also however comes with the greatest likelihood of problematical unintended consequences. Volcanoes provide a helpful analog for how SAI might operate and demonstrate that aerosols suspended in the atmosphere can and do immediately and substantially cool the earth. The mechanics of recreating such a volcano effect in a deliberate fashion are explained and situated in both space and time. It is also noted that relative to any other climate intervention or solution, SAI would be stunningly cheap, giving rise to the prospect of the “free driver” hypothesis. In addition to exerting force upon the climate variable (temperature), it may well interfere with ones we do not, such as rainfall. The problematical dynamics of stopping such a program (“termination shock”) are explored, as are difficulties that would arise in seeking to attribute observed climate impacts in an engineered climate to their causes. SAI is presented as an enigma to be explored rather than a remedy to be implemented.