Despite the importance of the Carbon Disclosure Project (CDP), the question of how firms' voluntary carbon disclosure influences capital markets and shareholder value remains unanswered. Using the event study methodology with a sample of firms from the CDP Korea 2008 and 2009, this paper investigates market responses to firms' voluntary carbon information disclosure. The results suggest that the market is likely to respond negatively to firms' carbon disclosure, implying that investors tend to perceive carbon disclosure as bad news and thus are concerned about potential costs facing firms for addressing global warming. In addition, the study examines the moderating effect of frequent carbon communication on the relationship between carbon disclosure and shareholder value. The results suggest that a firm can mitigate negative market shocks from its carbon disclosure by releasing its carbon news periodically through the media in advance of its carbon disclosure. Copyright © 2013 John Wiley & Sons, Ltd and ERP Environment.