Companies listed on the London Stock Exchange's Main Market are now first in the world to face a government mandate to report their greenhouse gas emissions—a compliance demand activists would like to see go global.

Deputy Prime Minister Nick Clegg was expected to make the government's announcement on June 20 at the +20 sustainability conference in Brazil. The roughly 1,600 firms listed on Britain's main stock market will be required to detail emissions data in earnings reports by an April 2013 deadline. The program will be reviewed by 2015 and could eventually expand to other companies

The U.K.-based Carbon Disclosure Project (CDP), a longtime proponent for a global corporate disclosure  system for gas emissions and climate change risk information, applauded the move. In a statement, it added that, “the UK must now take a position of global leadership by introducing regulation that ensures companies are required to make a full assessment of how climate change is expected to affect their business.”

The group is promoting a system that could be adopted by other nations for comparable reporting.  For the past five years, the Climate Disclosure Standards Board (a special project of CDP) — supported by the UK Department for Environment, Food and Rural Affairs — has worked to develop a reporting framework designed for compliance with mandatory climate change-related reporting.