This study investigates how abnormally hot temperatures affect firms’ environmental behavior in China. We find that firms exposed to abnormally hot temperatures participate in more environmental engagement. We also find that this improvement effect is driven mainly by environmental concerns, including public concerns, CEOs, and governments. Our results remain intact after an array of robustness tests. Further analysis shows that the effect of abnormally hot temperatures on corporate environmental engagement is more pronounced in SOEs, heavily polluting firms, and firms located closer to local environmental protection agencies. Moreover, the positive impact of environmental engagement on firm value is stronger when firms are exposed to abnormally hot temperatures. Overall, this study sheds light on the potential stimulation of firms’ environmental actions by global warming, which is yet to be fully understood.