This paper examines the relationship between board diversity and firms’ decisions to voluntarily disclose information about their greenhouse gas (GHG) emissions. We focus on board ancestral diversity as a relatively new dimension of (deep-level) board structure and document that it has a positive and statistically significant effect on a firm's scope and quality of voluntary GHG emission disclosure. The effect goes beyond the impact of more common (surface-level) dimensions of board diversity and remains robust after addressing endogeneity concerns. In line with the theoretical conjecture that diversity enhances a board's advising and monitoring capacity, we find that the impact of diverse boards is stronger in more complex firms and in firms with low levels of institutional ownership. Overall, our findings provide evidence for board diversity being a relevant governance factor in corporate environmental decision making.