Carbon dioxide is the most common greenhouse gas, but other greenhouse gases are much more potent in smaller concentrations.
The five main ones are:
Methane is the second-biggest contributing greenhouse gas, responsible for 20% of human-induced global warming.
It is 23 times more powerful 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.
Atmospheric concentrations of methane have increased by about 150% 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.
Not to be confused with nitrogen oxides, nitrous oxide is 296 times more powerful a greenhouse gas than carbon dioxide, and remains in the atmosphere for 114 years.
While nitrous oxide is naturally emitted from oceans and soil, its human-derived sources include agriculture (mostly nitrogen fertilisation) and industrial activities. It is also created during the combustion of fossil fuels and other organic matter.
Nitrous oxide also has a variety of direct uses, including as an aerosol propellant and an anaesthetic (laughing gas).
Fluorinated gases (F-gases)
Fluorinated gases make up only a small portion of greenhouse gas emissions, but they are extremely potent. The most common F-gases are hydrofluorocarbons (HFCs).
Depending on the exact type of F-gas, they are up to 20,000 times more powerful than carbon dioxide, and have atmospheric lifetimes of up to 260 years. Currently, HFCs contribute 4% of global greenhouse gas emissions. But their concentration in the atmosphere is growing faster than other greenhouse gases.
The most recent science shows that if we only focus on reducing CO2 and do nothing about HFCs, they will be responsible for 28-45% of climate change by 2050. Even if we did nothing about CO2, HFCs would still be responsible for 10-20% of climate change by 2050.
HFCs are used in refrigeration (both commercial and domestic) and in air-conditioning (homes, cars, offices, etc), as well as foam-blowing agents, solvents, fire-fighting agents, and aerosol propellants.
However, there are natural, benign, and commercially viable alternatives for refrigeration. Greenpeace invented the first natural refrigerant that neither depletes the ozone nor damages the planet. Read more about Greenfreeze, an innovative new technology.
If you buy a new fridge or air conditioner, make sure it is tagged with R600a, R290 and R744 – these all use natural refrigerants.
PFCs are 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 manufacturing and as substitutes for ozone-depleting chemicals.
Emissions of PFCs are small even compared to HFCs. However, given their potency, long lifetimes, and available alternatives already on the market, PFCs should be urgently phased out.
Sulphur hexafluoride is the most potent greenhouse gas evaluated by the Intergovernmental Panel on Climate Change. It is 23,900 times more powerful than carbon dioxide and has an atmospheric lifetime of 3,200 years.
It has a number of uses, including in Nike Air shoes, car tires, electrical insulation, semiconductor manufacturing, 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.
Learn more about climate science:
The greenhouse effect
Super greenhouse gases: F-gases
Deforestation and climate hange
Scientific consensus on climate change