This study aims to determine whether ESG funds can be used as an effective tool for environmental sustainability. ESG funds, which first appeared in the 2000s and were exported by environmentally friendly companies, are among the most effective tools for increasing firm value and managing environmental degradation. The causality relationship between the ESG funds, one of the environmentally friendly investment instruments, and the CO emission values, which are used as an environmental degradation criterion, was investigated in this study. The study used 209 daily data sets from July 31, 2020, to May 28, 2021. The symmetric developed by Hacker and Hatemi-J (Appl Econ 38:1489-1500, 2006), the asymmetric developed by Hatemi-J (Empir Econ 43:447-456, 2012), and time-varying asymmetric causality tests were used as models. According to the study results, while there is no symmetric causality between CO emissions and ESG funds, there is causality between CO emissions and ESG funds prices for negative shocks and between CO emissions and ESG funds trade volume for positive shocks. The results of a time-varying asymmetric causality test also support that this causality relationship varies by period. As a result, ESG funds can be used as a strategic financial tool to improve environmental quality during the COVID-19 period; however, this may vary for different sub-sample periods.
