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On March 21, 2022, the SEC proposed a rule that would make corporate greenhouse gas (“GHG”) emissions reporting mandatory. That decision may break the impasse over whether corporate social responsibility reporting should be designed solely for the benefit of investors — single materiality — or for the benefit of investors and the public — double materiality. In corporate greenhouse gas disclosure, the materiality debate pitted the double-materiality Corporate Greenhouse Gas Protocol (“GHG Protocol”) against the single-materiality Sustainability Accounting Standards Board (“SASB”) standards. SASB capitulated in November 2021 by joining a single-materiality alliance that accepts the GHG Protocol. The SEC’s proposed rule tracks the GHG Protocol. Mandatory reporting to some version of the GHG Protocol now appears inevitable in the United States.

The GHG Protocol is the dominant reporting standard, but dozens of other protocols, standards, and frameworks, including SASB’s, authorize deviations. This Article presents the first comprehensive study of voluntary corporate GHG reporting. The study consists of two parts: (1) a review of the complex array of protocols, standards, and frameworks that govern voluntary GHG reporting and (2) an empirical analysis of the 2020 GHG disclosures of two hundred randomly selected S&P 500 companies. The review reveals several loopholes in the GHG Protocol, including options for converting other gases to CO2 equivalents, options for setting firm boundaries, the ability to exclude categories of emissions, and the omission of biogenic CO2 emissions from the reports. The empirical analysis, however, reveals little evidence of companies exploiting the loopholes. The empirical analysis shows an eighty-one percent reporting rate for Scope 1 and Scope 2 emissions.

Public use of the GHG data will be possible only through rankings by trusted intermediaries. This Article proposes methods for ranking S&P 500 companies based on corporate GHG emissions reports. It demonstrates those methods by ranking the studied companies.