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 gases in its atmosphere. If it had none, the difference between daytime and night time temperatures would be extreme with an average temperature of -18 degrees Celsius, as opposed to 14 degrees we have today.
Over the past two centuries human activities have been increasing the concentration of various greenhouse gases in the atmosphere. Following is a brief summary of the most important gases and their sources.
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 a bout 100 years. Most of the CO2 released today is emitted 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 the CO2 we release is absorbed by the land and oceans.
Methane accounts for around a seventh of human-caused warming. It’s 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 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 (N2O)
Nitrous oxide accounts for around eight percent 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. Nitrous oxide is released naturally by bacteria living in soils, but humans substantially increase the rate at which this happens through the addition of fertilizers. Livestock manure is a particularly potent source of this greenhouse gas. Other sources of N2O include power plants and certain industrial processes.
The F-gases are a family of synthetic chemicals used as solvents, refrigerants and aerosol propellants, among other things. They include hydroflourocarbonos, perflourinated carbons and sulphur hexafluoride. F-gases are among the most powerful of all grenhouse gases – thousands of times more potent that CO2. Thankfully, they are not emitted in particularly large quantities.
Other greenhouse gases: water vapour (H2O) and ozone (O2)
There are two other significant greenhouse gases whose relationship both to human activity and global warming is somewhat more complex. The first is water, taking the form of clouds and humidity. Water vapour makes up roughly 1% of the Earth’s atmosphere. It accounts for the majority of the ‘natural’ greenhouse effect and has a greater warming impact than all the human-produced gases put together.
Ozone is an unstable version of oxygen and it exists in the upper atmosphere (the ozone layer) but can also be created by the reaction between sunlight and ground-level pollution.
(Sources: The Rough Guide to Green Living by Duncan Clark 2009)
- Rough Guide to Green Living
- The Greenhouse Effect
- Greenhouse Gases: Worldwide Impacts (Global Warming (Facts on File))
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