The world's built environment consumes as much as 40 percent of global energy use. That makes for a massive carbon footprint, but until recently, the building sector didn't have a universal framework to measure carbon emissions produced during a building's operations.

The Common Carbon Metric (CCM) was developed to fill that void, and now the International Organization for Standardization (ISO) is deciding whether to use it as a basis for a new international standard for measuring and reporting energy use and emissions from building operations.

This may one day lead to the development of international baselines that governments and the construction industry may use to set policies and improve efficiencies in the sector.

"The metric is a first step," said Ben Thompson, Sustainable Business Program Manager at Autodesk, one of several companies that participated in the first phase of CCM testing. "Once everyone can agree on the metric and approach, people can start setting goals and making policy."

The Sustainable Buildings and Climate Initiative of the United Nations Environment Programme (UNEP) developed the CCM, which is now in its second phase of testing. UNEP plans to release preliminary results in October. The organization cites several compelling reasons for why we need a consistent way to measure and report the emissions of operating buildings:

• Day-to-day use of a building is responsible for 80 percent to 90 percent of its life cycle carbon footprint, largely due to energy consumption from heating, cooling, lighting, appliances and ventilation
• Existing technologies and design principles can reduce energy use by 30 percent to 50 percent by 2020
Emissions from building may rise to 11.1 billion metric tonnes of CO2 in 2020, compared to 8.6 billion tonnes in 2004.

But as the old saying goes, you can't manage what you don't measure, Thompson said. "With a standardized approach, cities and companies can start moving past measuring and toward reporting actual savings."

The CCM measures performance in two ways: a top-down approach that uses estimated data for a whole portfolio of buildings or city; a bottom-up approach that assesses the performance of an individual building based on more granular data. The metrics that can be tracked by CCM are:

Energy intensity
• Kilowatt hours per square meter per year
• Kilowatt hours per occupant per year

Carbon intensity
• Kilogram of CO2e per square meter per year
• Kilogram of CO2e per occupant per year

Autodesk tried both top-down and bottom-up approaches, but preferred the bottom-up approach because it is well-suited for the wealth of data the company already collects from its operations. Autodesk discovered that as a whole, its entire portfolio performed better than a smaller sample of larger buildings.

A potential ISO standard based on the CCM wouldn't happen for years. The proposal will be put on the agenda of ISO members within a year, and then the standards for energy consumption and emissions would be drafted if approved. Once finalized, the standards may be adopted within three years, according to UNEP.

There are some regional methodologies used to measure emissions from buildings, according to Andrea Traber, a Principal of Sustainable Use, Americas, at Kema, an energy consulting and certification firm. An international standard, however, would be of value for companies that must track operations on different continents. Quantifiable data that can be verified by a third party may also support carbon credit programs.

"Consistency and the value of a third-party, independent, unbiased standard is really important," Traber said. "I really do believe that. If one standard can become a guiding light, that could solve a lot of problems."