Global Warming Potential – An Introduction

Six Green House GasesThere 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:

GHG

Molecular Formula

Atmospheric Lifetime (Years)

Global Warming Potential

Carbon dioxideCO2

50-200

1

MethaneCH4

12 (+/-3)

21

Nitrous oxideN2O

120

310

Sulphur hexafluorideSF6

3200

23900

HFC’s

HFC-23CHF3

264

11700

HFC-32CH2F2

5.6

650

HFC-41CH3F

3.7

150

HFC-125C2HF5

32.6

2800

HFC-134C2H2F4

10.6

1000

HFC-134aC2H3F4

14.6

1300

HFC -143C2H3F3

3.8

300

HFC -143aC2H3F3

48.3

3800

HFC -152aC2H4F2

1.5

140

HFC -227eaC3HF7

36.5

2900

HFC -236faC3H2F6

209

6300

HFC -245caC3H3F5

6.6

560

HFC -4310meeC5H2F10

17.1

1300

PFCs

PFC-14CF4

50000

6500

PFC-116C2F2

10000

9200

PFC-218C3F8

2600

7000

PFC-3-1-10C4F10

2600

7000

PFC-c318c-C4F8

3200

8700

PFC-4-1-12C5F12

4100

7500

PFC-5-1-14C6F14

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.

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