Exploiting a unique measure of takeover vulnerability principally based on state legislations, we investigate how corporate carbon reduction efforts are influenced by the takeover market, which is widely regarded as a crucial instrument of external corporate governance. Our results show that more takeover exposure brings about significantly greater efforts to reduce carbon emissions. A rise in takeover susceptibility by one standard deviation improves carbon reduction performance by 12.81%. The findings corroborate the notion that the takeover market, acting as an external governance mechanism, compels managers to adopt policies that benefit shareholders in the long run. Our results imply that carbon emissions are a crucial corporate outcome as it is subject to the pressure from the takeover market. Companies should pay a close attention to this matter. Further analysis robustly validates the results, including propensity score matching, entropy balancing, an instrumental variable analysis, and heteroscedastic identification. Our measure of takeover vulnerability is plausibly exogenous and thus probably reveals a causal effect, rather than a mere association.