**6. Discussions**

The results of this paper show that the economic cost of carbon neutralization is very large. If we want to make up for this part of the economic loss, we need an additional TFP growth of about 0.564–0.568% per year.

How difficult is the 0.564–0.568% annual additional TFP growth? According to Park (2012) [62], the TFP growth in most Asian countries (such as China, Japan, Korea, Thailand, Pakistan, and India) will range from 0.95% to 2.66% during 2010–2030. Additionally, the US's TFP growth ranged from 0%–3% during 2000–2020 [63]. Although we could not find the literature about the long-term TFP growth projection, it is certain that China's TFP growth will no longer be higher than China is used to, and the annual growth rate may range from 1% to 2.5%. Thus, the additional 0.568% TFP growth means that the TFP growth should increase by 22.72% to 56.8%.

The paper also finds other examples in the literature identifying Porter's hypothesis from which to take references. Zhao and Sun (2016) [64] argued that flexible control policies meet the weak Porter hypothesis using 2007–2012 enterprise-level data. Lin and Chen (2020) [65] supported the strong Porter hypothesis in the non-ferrous metal industry using province-industry level data in China. Zhou et al. (2021) [66] found that the weak version hypothesis for China's revised environmental protection law does not hold using the listed company's data. Lanoie et al. (2008) [67] found an average of 3% TFP growth in the Quebec manufacturing sector brought by environmental regulation. Their study has data for six years, so the annual additional TFP growth is about 0.5%, which is similar to this study; however, rather than for the manufacturer, this study is for the whole society. Other examples in the literature on testing the hypothesis also prove how hard it can be made in the context of carbon neutrality.
