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Carbon dioxide is the most common greenhouse gas but there are gases that are much more potent greenhouse gases.
The five main ones are:
Methane
Methane is the second biggest contributing greenhouse gas, and is
responsible for 20 percent of the human-induced greenhouse
effect.
It is about 23 times more powerful a greenhouse gas than
carbon dioxide, and has an atmospheric lifetime of roughly 12 years.
Sources of methane include decomposing organic waste (in nature and in
garbage dumps), and the raising of livestock.
It's also emitted during
the production and transport of coal and natural gas.
Globally, atmospheric
concentrations of methane have increased by about 150 percent since
1750, and are now at higher levels than in the last 400,000 years.
Once
in the atmosphere, methane decays into carbon dioxide over a period of
a few years.
Nitrous oxide
Nitrous oxide is 296 times more powerful a greenhouse gas than carbon
dioxide, and remains in the atmosphere for 114 years.
It is naturally
emitted from oceans and soil, and human-driven sources inlcude agriculture (mostly nitrogen fertilisation) and
industrial activities, and it is created during combustion of fossil
fuels and other organic matter.
Nitrous oxide also has a variety of
direct uses - including as an aerosol propellant and as an anaesthetic
("laughing gas").
Hydrofluorocarbons (HFCs)
HFCs make up only a small portion of greenhouse gas emissions, but they are extremely potent greenhouse gases.
Depending on the exact type of HFC, they are up to 20,000 times more
powerful greenhouse gasses than carbon dioxide, and have atmospheric
lifetimes of up to 260 years.
Some uses of HFCs are in refrigeration (both commercial and domestic),
in air-conditioning (homes, cars, offices etc), and they are also used
as foam blowing agents, solvents, fire fighting agents and aerosol
propellants.
HFC use and production surged after they were actively promoted as
replacement refrigerants when a phase out of the ozone depleting
chlorofluorocarbons (CFCs) was mandated by the Montreal Protocol.
But there are plenty of natural and benign alternatives commercially viable for
refrigeration.
When you buy a new fridge or air conditioner make sure its tagged with R600a, R290 and R744 -- these all using natural refrigerants.
See our section on HFC's (sometimes called F-gases).
Perfluorocarbons (PFCs)
PFCs are from 5,700 to 10,000 times more powerful greenhouse gases
than carbon dioxide, and have an
atmospheric lifetime of up to 50,000 years.
PFCs are by-products
of aluminium smelting. They are also used in semi-conductor
manufacture, and as substitutes for ozone-depleting chemicals.
Emissions of PFCs are small even compared to HFCs. However, given
their potency, long lifetimes and availability of alternatives already
on the market, PFCs should be urgently phased out.
Sulphur Hexafluoride
Sulphur Hexafluoride is the most potent greenhouse gas evaluated by the
Intergovernmental Panel on Climate Change.
It is 23,900 times more
powerful a greenhouse gas than carbon dioxide, and has an atmospheric
lifetime of 3,200 years.
It has a number of uses including in Nike Air shoes, car tyres, for
electrical insulation, semiconductor manufacture, and in the magnesium
industry.
Like PFCs, the effects of Sulphur Hexafluoride to date are fairly
small. However, since it is a very persistent and potent greenhouse
gas, there is concern about its continuing build up in the
atmosphere.
Given its potency, long lifetime and availability of
alternatives already on the market, Sulphur Hexafluoride should be
urgently phased out.
