The 'Common Carbon Metric', supported by UNEP, has been developed for

Answer: (a) assessing the carbon footprint of building operations around the world

UNEP’s Sustainable Buildings and Climate Initiative developed the Common Carbon Metric to measure energy use and emissions from building operations.

The idea

Buildings use about a third of the world’s energy for lighting, cooling, heating and appliances. To compare a building in Delhi with one in Berlin you need one common way to measure. The Common Carbon Metric gives that: energy used and greenhouse gas emitted per square metre (or per person) per year while the building is in use.

Building is in use → Electricity and fuel are consumed → Converted to kg of CO₂ equivalent → Divided by floor area → Buildings anywhere can be compared

Why the others are wrong

(c) A whole country’s emissions are counted in its national greenhouse gas inventory, prepared with IPCC guidelines. That needs data from every sector, not from buildings alone.

The trap

The word “carbon” makes (c) or (d) feel broader and safer. The metric is only for buildings.

Also know

A building has two kinds of carbon: operational (from using it) and embodied (from the cement, steel and construction). The metric covers the first kind. In India the Energy Conservation Building Code comes from the Bureau of Energy Efficiency, and GRIHA is the national green-building rating. The Global Alliance for Buildings and Construction was launched at COP21 in Paris.