Green house gases (GHGs) such as carbon dioxide (CO2) emission increase the Earth’s ambient temperature with the rapid increase of urbanization and industrialization as well as rapid growth of human population. Kolkata Metro City has an area of 185 km2 and consists of 4,572,876 populations with a density of 24,718 persons/km2 in 2001. Main sources of CO2 emission are vehicular exhaust, emission from small-scale industries, emission from commercial and domestic fuel burning, human respiration, soil respiration, etc. The specific objective of this article is to estimate the CO2 emission from different sources mainly from the sections of automobile exhaust, small-scale industries, human respiration, and soil respiration. Other emission sources have not been discussed here due to nonavailability of existing data. In Kolkata, vehicular exhaust emitted 257.63 t CO2/day in 2005, small-scale industries emitted 64.65 t CO2/day, and human respiration emitted 3.16 × 103 t CO2/day in 2001. Measurement of soil respiration as conducted in two gardens in and around the city was 1.23 × 10-6 t CO2/m2/day in Botanical Garden and 5.09 × 10-6 t CO2/m2/day in Banobitan. The vehicular pollution has to be minimized through emission control by the strict regulations in conjunction with increasing environment-friendly technologies. CO2 emission from small-scale industries in Kolkata has already been reduced by applying process change and alternative fuel use. Human respiration is also contributing to increase the GHG-CO2 level in the atmosphere with the rapid increase of human population. There is also an urgent need to control human population that will help to conserve and protect natural resources in all respects.