The ‘Common Carbon Metric’, Supported by UNEP, had been developed for ​

The correct answer is A. The Common Carbon Metric was developed under UNEP's Sustainable Buildings and Climate Initiative (SBCI) to measure energy use and greenhouse gas emissions from building operations in a standardised way. Its purpose is to let cities, developers and countries compare building-level carbon footprints on a common basis, which matters because buildings account for a very large share of global energy use and emissions.

• B is wrong: The metric is about buildings, not farming entities or emission trading markets.
• C is wrong: National carbon accounting is done through inventories under the UNFCCC and IPCC methods, not through this building-focused metric.
• D is wrong: It does not measure the world's fossil fuel emissions per unit time. That is a global emissions accounting question, handled through bodies like the IEA and the UNFCCC.

This links to GS-III on climate change mitigation and energy efficiency. In India, the Energy Conservation Building Code (ECBC) and the Energy Conservation Act, 2001 address the same building-sector emissions.

Trap: Students see the word 'carbon footprint' and pick C or D because they sound like national or global measures. Always check the scope of the tool named in the question.