60 second guide to... Greenhouse gases
Their emissions are a major cause of global warming. Here's our essential guide to greenhouse gases
The temperature of any planet is determined partly by the gases in its atmosphere. So-called ‘greenhouse gases’ act like a blanket, absorbing heat that would otherwise escape to space, thereby warming up the planet’s surface. This phenomenon is known as the greenhouse effect.
The Earth has always had greenhouse gases in its atmosphere - if it had none, the difference between daytime and night-time temperatures would be extreme. Overall, the planet would be much colder, with an average temperature of -18ºC, as opposed to the much more habitable 14ºC we have today.
Over the past two centuries, human activities have been increasing the concentration of greenhouse gases in the atmosphere - this is the cause of climate change (read more: 60 second guide to Climate Change).
Directly emitted greenhouse gases
The following greenhouse gases are the ones emitted directly by human activities and which the Kyoto Protocol covers. They account for less than 0.05 per cent of the atmosphere, but are nonetheless pivotal to determining the temperature of the planet.
Carbon dioxide (CO2)
Carbon dioxide accounts for around three quarters of the total human impact on the climate. The gas typically persists in the atmosphere for around a hundred years, which means today’s emissions will continue to have a warming effect throughout the 21st century.
Most CO2 is released by the burning of fossil fuels in power stations, vehicles and buildings, but deforestation and cement manufacture are also significant sources. At present, around half of human CO2 emissions are absorbed by the land and oceans. However, in the future, scientists expect more of our CO2 to remain in the atmosphere, thereby accelerating global warming.
Methane (CH4)
Methane accounts for around a seventh of human-caused warming and it is more potent than CO2 but doesn’t persist in the atmosphere for as long. Overall, a kilogram of methane causes a warming impact around 20–25 times greater than a kilogram of CO2.
Significant sources of methane include sheep and cows (which belch the gas from their ruminant stomach systems), rice paddies, landfill sites and the production of fossil fuels. Methane is basically the same as the natural gas we use for cooking and heating, though once it’s burned on a stove or a boiler, it combines with oxygen to become CO2.
Nitrous oxide (N20)
Nitrous oxide accounts for around 8 per cent of human emissions. Relatively small amounts of the gas are emitted, but each kilogram causes a warming effect hundreds of times greater than a kilo of CO2.
N2O is released by bacteria living in soils. Humans increase the rate of emissions by various agricultural practices, especially the use of nitrogen fertilizer and the raising of livestock.
‘F-gases’
The F-gases are a family of synthetic chemicals used as solvents, refrigerants and aerosol propellants, among other things. They include hydrofluorocarbons, perfluorinated carbons and sulphur hexafluoride.
F-gases are among the most powerful of all greenhouse gases – thousands of times more potent than CO2. Thankfully, they’re not emitted in particularly large quantities.
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