One of the main concerns about climate change has been the effect that greenhouse gases such as carbon dioxide, methane, nitrous oxide, fluorinated gases, and ozone – produced by industrial activities – are having on the climate. They exert their effect by trapping heat in the atmosphere.
The above image show the rise in the global levels of three of these gases since 1750.
Global Warming Potential (GWP)
Different greenhouse gases have different effects on global warming. The two main factors are:
- How long they remain in the atmosphere (lifetime)
- Their ability to absorb energy (radiative efficiency)
The global warming potential index has been developed to enable a comparison to be made between the effect different greenhouse gases on global warming. The results are expressed in the form of how much energy the emission of 1 ton of a particular greenhouse gas will absorb over a given period of time (normally 100 years), compared to the emission of 1 ton of carbon dioxide. The larger the GWP figure the great the potential damage to the environment.
The UNited Nations publish a table of the relative GWPs of the important greenhouse gases. The list of GWPs for a 100 year period below is an extract from this table:
- Carbon dioxide: GWP =1
- Methane: GWP =21
- Nitrous oxide: GWP = 310
- HFC-23: GWP = 11,700
- Perfluoromethane: GWP = 6,500
- Sulfur hexafluoride: GWP = 23,900
We can now look at each of these types of greenhouse gases in turn: