Which organization is known for establishing sustainability reporting standards?

The Global Reporting Initiative (GRI) is recognized for its significant role in developing sustainability reporting standards. These standards provide a framework for organizations to measure and communicate their economic, environmental, and social impacts, fostering transparency and accountability in sustainability practices.

GRI's guidelines help companies report on their sustainability performance in a consistent manner, which can then be compared across organizations and industries. By establishing these standards, GRI encourages organizations to take a comprehensive approach to sustainability, considering not only their direct activities but also their broader impact on stakeholders and the environment.

Other organizations mentioned have different focuses. For instance, the Forest Stewardship Council is primarily concerned with sustainable forest management and certification, while the Future-Fit Business Benchmark assesses a company's overall fitness regarding sustainability but does not establish a reporting standard per se. The Union of Concerned Scientists is focused on scientific research and advocacy, rather than creating reporting standards. Thus, GRI stands out as the correct answer due to its direct contribution to the field of sustainability reporting.