This study investigates the effect of greenhouse gas (GHG) emissions on firm value for Korean firms and provides possible explanations behind this effect. To mitigate selection issues regarding voluntary disclosure, we use the Korean government's adoption of TMS in 2011, which requires only heavy GHG emitters to disclose their GHG emissions information. Using the Difference-in-Differences (DID) methodology, we find a significant decline in value among treated firms after the enactment of mandatory disclosure for heavy GHG emitters. This decrease can be attributed, at least in part, to an increase in firm risk perceived by investors. Furthermore, foreign ownership decreased for the treated firms following the mandatory emissions information disclosure for heavy GHG emitters, suggesting that reduced demand for stocks from foreign investors also contributes to lowered firm value. In summary, our study highlights that investors actively use GHG emissions information, and they penalize heavy GHG emitters for potential future liabilities associated with carbon emissions. The implications of our research shed light on the role of GHG emissions information in shaping firm value, risk perception, and investor behavior within the Korean context.