Delhi Metro has been certified by the United Nations as the first metro rail-based system in the world to get carbon credits for contributing to the fight against climate change by help reducing pollution levels in the city by 6.3 lakh tons every year. It also has earned carbon credits of worth 47 crores annually for the next seven years. 

A carbon credit is a term for any tradable certificate or permit representing the right to emit one tonne of carbon dioxide. Carbon credits and carbon markets are a component of national and international attempts to mitigate the growth in concentration of greenhouse gases.

About 18 lakh people travel by the metro rail which is completely non-polluting and environment-friendly. But for the metro, these people would have travelled by cars, buses, two or three-wheelers which would have resulted in emission of greenhouse gases.

Thus, the DMRC has helped in reduction in emission of harmful gases into the atmosphere and the United Nations-body administering the Clean Development Mechanism (CDM) under the Kyoto Protocol has certified carbon credits to DMRC for reducing emissions.