Our study examines the impact of environmental policy stringency on CO2 emissions in the OECD and BRICS countries. CO2 emissions are measured using two indicators – production-based accounting (PBA) and consumption-based accounting (CBA). We analyse not only the main EPS index but also its three components: market-based instruments, non-market-based instruments, and technology support policies. The estimation procedure used in the study is the Method of Moments-Quantile Regression (MMQR), which allows us to demonstrate policies' effectiveness and assess the policies' role in high, medium, and low-emission countries. The results reveal that an increase in environmental policy stringency leads to a reduction in CO2 per capita in the OECD and BRICS countries. However, environmental policy stringency has a stronger impact on reducing PBA emissions than on reducing CBA emissions. The main finding is that EPS has a stronger impact in countries with lower per capita carbon emissions (i.e. lower quantiles) than in countries with high per capita pollution. Market-based instruments are the most effective when considering the three components of the EPS index. Interestingly, in countries with lower CO2 emissions per capita, both market-based and non-market-based policy instruments are most effective in reducing CO2 emissions, while the largest CO2 emitters per capita reduce their emissions through technology support.