Global Warming Potential – An Introduction

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 CO_2.

Following table shows GWPs of six green house gases:

GHG	Molecular Formula	Atmospheric Lifetime (Years)	Global Warming Potential
Carbon dioxide	CO2	50-200	1
Methane	CH4	12 (+/-3)	21
Nitrous oxide	N2O	120	310
Sulphur hexafluoride	SF6	3200	23900
HFC’s
HFC-23	CHF3	264	11700
HFC-32	CH2F2	5.6	650
HFC-41	CH3F	3.7	150
HFC-125	C2HF5	32.6	2800
HFC-134	C2H2F4	10.6	1000
HFC-134a	C2H3F4	14.6	1300
HFC -143	C2H3F3	3.8	300
HFC -143a	C2H3F3	48.3	3800
HFC -152a	C2H4F2	1.5	140
HFC -227ea	C3HF7	36.5	2900
HFC -236fa	C3H2F6	209	6300
HFC -245ca	C3H3F5	6.6	560
HFC -4310mee	C5H2F10	17.1	1300
PFCs
PFC-14	CF4	50000	6500
PFC-116	C2F2	10000	9200
PFC-218	C3F8	2600	7000
PFC-3-1-10	C4F10	2600	7000
PFC-c318	c-C4F8	3200	8700
PFC-4-1-12	C5F12	4100	7500
PFC-5-1-14	C6F14	3200	7400

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.

Know more about Black Carbon, Global Warming and India