The correct answer is assessing the carbon footprint of building operations around the world.

• The Common Carbon Metric is the calculation used to define the measurement, reporting, and verification for GHG emissions associated with the operation of buildings types of particular climate regions.
• Common Carbon Metric provides the foundation for accurate performance baselines to be drawn, national targets set, and carbon traded on a level playing field.
• The purpose of a Common Carbon Metric for buildings is to give the sector that represents 40% of the world’s energy consumption and related 1/3rd of global greenhouse gas (GHG) emissions.
• The building sector has more potential to deliver quick, deep and cost-effective GHG mitigation than any other.
• Significantly increasing building energy efficiency can be achieved in the short term.
• Energy consumption in both new and existing buildings could be cut by an estimated 30-50% by 2020 through readily available technologies, design, equipment, management systems, and alternative generation solutions. 
  This can be funded through investments that quickly pay back and result in significant environmental, social, and economic benefits.
• A universal measuring stick for building emissions a Common Carbon Metric provides the foundation for accurate performance baselines to be drawn, national targets set, and carbon traded on a level playing field.
• While all stages of a building’s life-cycle (including construction and demolition) produce carbon emissions, the building’s operational phase accounts for 80-90% of emissions resulting from energy use mainly for 
  heating, cooling, ventilation, lighting and appliances.
• Therefore, this is the stage of the building’s life-cycle that is the focus of the Common Carbon Metric.