There are six Green House Gases (GHGs) and each has a different potential of trapping heat from the atmosphere. The concept of global warming potential (GWP) has been developed in order to enable comparison of the ability of different GHGs to trap heat in the atmosphere. This is termed as radiative forcing (Radiative forcing refers to the amount of heat-trapping potential for a GHG, measured in units of power per unit of area). Greenhouse gases differ in their effect on the Earth’s radiation balance depending upon their concentration; residence time in the atmosphere; and physical properties with respect to absorbing and emitting radiant energy.
Carbon dioxide (CO2) is present in a concentration of 0.03% in the atmosphere and is a principal anthropogenic greenhouse gas. For standard use, GHG emissions are measured in one tonne of carbon dioxide equivalent. It is taken as the reference gas against which other greenhouse gases are measured and therefore has a Global Warming Potential of one (1). For example: 1 tonne of Nitrous oxide (N2O) has a GWP of 310, indicating that its radiative forcing is 310 times that of CO2.
Following table shows GWPs of six green house gases:
Atmospheric Lifetime (Years)
Global Warming Potential
Source: IPCC Second Assessment Report
a – 100 years time horizon
b- The Methane GWP includes the direct effects and those indirect effects due to the production of tropospheric ozone and stratospheric water vapour. The indirect effect due to the production of CO2 is not included.
Note: The GWP of a GHG accounts for both the immediate radiative forcing due to an increase in the concentration of the gas in the atmosphere, and the lifetime of the gas.
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