Does having more women in managerial positions improve firm environmental performance? We match firm-corporate governance characteristics with firm-level carbon dioxide (CO2) emissions over the period 2009-2019 to study the relationship between gender diversity in the workplace and firm carbon emissions. We find that a 1 percentage point increase in the percentage of female managers within the firm leads to a 0.5% decrease in CO2 emissions. We document that this effect is statically significant, also when controlling for institutional differences caused by more patriarchal and hierarchical cultures and religions. At the same time, we show that gender diversity at the managerial level has stronger mitigating effects on climate change if females are also well-represented outside the organization, e.g. in political institutions and civil society organizations. Finally, we find that, after the Paris Agreement, firms with greater gender diversity reduced their CO2 emissions by about 5% more than firms with more male managers. Overall, our results indicate that gender diversity within organizations can have a significant impact in combating climate change.