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Greenhouse Gases

Last Updated on Sunday, 22 October 2017 16:15





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Greenhouse Gases

Carbon Dioxide is not the only greenhouse gas but it is the one most people associate with global warming since it is by far the most abundant and most obviously linked to the combustion of fossil fuels.

It is not even the the most potent greenhouse gas, A quick scan of the table below shows that it is the least! However there is so much of the stuff it exerts the major effect on the climate in terms of global warming. Each greenhouse gas has a different global warming potential (GWP) and persists for a different length of time in the atmosphere. The table converts all the atmospheric greenhouse gases into CO2 equivalents so they can be compared.

The three main greenhouse gases (along with water vapour) and their 100-year global warming potential (GWP) compared to carbon dioxide are:

  • 1 x Carbon Dioxide (CO2)
  • 25 x Methane (CH4) this means that Releasing 1 kg of CH4 into the atmosphere is about equivalent to releasing 25 kg of CO2
  • 298 x Mitrous Oxide (N2O) and releasing 1 kg of N2O into the atmosphere is about equivalent to releasing 298 kg of CO2

Water vapour is not considered to be a cause of man-made global warming because it does not persist in the atmosphere for more than a few days. But given that increased temperature increases water vapor concentrations I wonder if this is true??

There are other greenhouse gases which have far greater global warming potential but are much less prevalent. These are sulphur hexafluoride (SF6), hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).

There are a wide variety of uses for SF6, HFCs, and PFCs but they have been most commonly used as refrigerants and for fire suppression. Many of these compounds also have a depleting effect on ozone in the upper atmosphere.

The 100-year global warming potential for greenhouse gases reported by the United Nations Framework Convention on Climate Change (UNFCCC). The column on the right shows how much that chemical would warm the earth over a 100 year period as compared to carbon dioxide.
Greenhouse GasFormula100-year GWP
Carbon dioxideCO21
MethaneCH425
Nitrous oxideN2O298
Sulphur hexafluorideSF622,800
Hydrofluorocarbon-23CHF314,800
Hydrofluorocarbon-32CH2F2675
PerfluoromethaneCF47,390
PerfluoroethaneC2F612,200
PerfluoropropaneC3F88,830
PerfluorobutaneC4F108,860
Perfluorocyclobutanec-C4F810,300
PerfluoropentaneC5F1213,300
PerfluorohexaneC6F149,300

For perspective, sulphur hexafluoride is apparently used to fill tennis balls. The table shows that a release of 1 kg of this gas is equivalent to 22,800kg of CO2. So releasing 1kg of sulphur hexafluoride is about equivalent to driving 100,000km!

You will of then see the term CO2e describing greenhouse gas emissions, this is the total green house gas emission translated in terms of Kg CO2 greenhouse equivalence. So for example if you burn some diesel fuel you will emit Xkg CO2, Ykg CO2e CH4 and ZCO2e N2O and the total will be the Kg CO2e for burning diesel.

Total KgCO2e = Xkg CO2 + Ykg CO2e CH4 + ZCO2e N2O


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