Voluntary environmental programs have proven to be a viable tool of pollution abatement, supplementing the command-and-control approach and market-based policies such as emissions trading and taxes. These voluntary initiatives aim to achieve pollution reduction through several channels, including procedural changes, raw material changes, product and packaging redesign, and innovation in pollution control technologies. The ISO 14001 standard is such a voluntary program; first introduced in 1996 by the International Organization for Standardization (ISO), it has steadily grown since and has been widely adopted by organizations around the world. In this paper, we empirically study the effects of the ISO 14001 standard on carbon emissions using a panel dataset of Korean manufacturing firms. As the largest contributor to the warming of the earth's atmosphere, carbon emissions are the focus of national and international efforts to curb climate change. The Korean manufacturing industry is responsible for about 40% of greenhouse gases in the country and has experienced rapid growth in ISO 14001 certified facilities. Our econometric results indicate that ISO 14001 certification spurs a significant reduction in carbon emissions among certified firms, after accounting for its potential endogeneity with an instrumental variable strategy. The empirical results suggest that wider ISO 14001 certification among carbon-intensive industries can be a credible pathway to help achieve the Korean government's goal of cutting domestic carbon emissions by 37% by 2030. •Impact of ISO 14001 certification on carbon emissions at the firm level.•Econometric analysis based on panel data of South Korean firms for the 2011–14 period.•The South Korean manufacturing industry is responsible for about 40% of greenhouse gases in the country.•The results show that ISO adoption spurs a 34% reduction in carbon emissions on average.•The reductions are larger in the first years after certification but linger for a number of years.