Although rarely studied, international accounting standards shape what information regarding a firm's environmental performance is communicated to international financial markets. This article builds on scholarship describing the influence of international accounting standards on private financial markets to show that nominally technical choices regarding how to recognize and measure firms' environmental impacts hold the potential to reduce these impacts. Obscure accounting debates within the International Accounting Standards Board (IASB) mask important political choices about what a firm must disclose to investors about its environmental liabilities and risks. IASB decisions about how these appear on corporate balance sheets change the link between a firm's environmental performance and its economic value and, thereby, contribute to steering private financial markets toward rewarding sustainable behavior within the global economy. This analysis demonstrates the authority of the IASB as an overlooked source of global environmental governance.