We investigate whether female representation on bank boards influences lending to polluting firms. Using confidential credit register data matched with firm-level greenhouse gas emissions, we isolate credit supply effects. Our findings reveal that banks with more gender-diverse boards lend less to more polluting firms, particularly those with the highest emission levels. These results are robust to endogeneity concerns as well as a range of alternative model specifications and econometric variations. Evidence from a European Central Bank large exposures data set confirms that this effect holds across different lending contexts. We also find that gender-diverse boards are less likely to initiate new lending relationships with highly polluting firms, suggesting an effect on both the intensive and extensive margins of credit allocation.