Introduction

The increasing interest in quantification of greenhouse gas emissions comes as a result of growing public awareness of global warming. Many global metropolitan cities and organizations are estimating their greenhouse gas emissions and developing strategies to reduce their emissions. As per Intergovernmental Panel on Climate Change (IPCC), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydro fluorocarbons (HFCs), per fluorocarbons (PFCs) and sulfur hexafluoride (SF6) are the major greenhouse gases. Among the GHG’s, carbon dioxide is the most dominant gas causing global warming which accounts for nearly 77% of global total CO2 equivalent greenhouse gas (GHG) emissions (IPCC 2007c). Climate change is a serious threat for all the countries. Concentration of (GHG’s) in the atmosphere has increased rapidly due to anthropogenic activities resulting in significant increase in the temperature of the earth. Increase in the concentration of these greenhouse gases results in global warming. Observations over India show that in the last 100 years the mean annual surface air temperature has increased by 0.4°C (Hingane et al., 1985). So there exists a need for a global parameter to assess the global greenhouse gas emissions. ‘Carbon footprint’ can thus be defined as a measure of the impact of human activities on the environment in terms of the amount of greenhouse gases produced. The total greenhouse gas emissions from various anthropogenic activities are expressed in terms of carbon dioxide equivalent, which indicate the carbon footprint of a region. Carbon dioxide equivalent (CO2e) is a unit for comparing the radiative forcing of a GHG to that of carbon dioxide. It is the amount of carbon dioxide by weight that is emitted into the atmosphere that would produce the same estimated radiative forcing as a given weight of another radiatively active gas. Carbon dioxide equivalents are calculated by multiplying the weight of the gas being measured by its estimated global warming potential.

In the year 1996, Intergovernmental Panel on Climate Change (IPCC) published Guidelines for National Greenhouse Gas Inventories to estimate national greenhouse gas emissions from various sources> (IPCC 1996 Guidelines). IPCC has also developed Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories (GPG 2000) and the Good Practice Guidance for Land Use, Land-Use Change and Forestry (GPGLULUCF). All these inventories taken together provide internationally agreed methodologies that countries currently use to estimate greenhouse gas inventories. Many researchers have estimated Indian> emission inventories of different gases from various sources and for different years (Mitra 1991, ADB 1994, Parashar et al., 1994, 1997, ALGAS 1998, Gupta et al., 1999, Garg, Bhattacharya and Shukla., 2001a, Mitra A P et al., 2004). In the year 2004, effort was made to assess greenhouse gas emissions from anthropogenic origin from sectors like Energy, Agriculture, Industry, Land Use, Land Use Change and Forestry and Waste and efforts were also made to assess the climate change impacts and vulnerability of key sectors of economy in India’s Initial National Communication to the UNFCCC (NATCOM, 2004). The base year for the studies were taken as 1994 using 30% country specific and 70% default emission factor.

This paper focuses on calculation greenhouse gases (eq CO2) in the major cities of India (population above 10 million as per 2011 census) namely Delhi and Greater Mumbai Chennai and Bangalore from key sectors. The total Carbon dioxide equivalent emissions are compared with their economic activity, measured in terms of GDP. The emissions from methane and nitrous oxide are expressed in terms of carbon dioxide equivalents using their respective global warming potential values as shown in the Table 1.

Table 1. Major greenhouse gases and their Global Warming Potential