Are GHGs Considered "Pollution"?
Pollution is a tricky concept to explain. According to some scientists, pollution occurs when any amount of a residual has been introduced into the environment. However, pollution has also been defined as something that happens when the quality of the environment has been degraded to such a degree as to cause damage.
Using the latter definition, we can classify pollution as the excess product (in gas, solid or fluid form) which nature is unable to absorb through osmosis. In the case of climate change, this is defined as any gas which exists in our environment in excess of what nature produces.
For example, tetrafluoromethane (also known as Freon-14) exists in nature, in very small amounts. However, it is the production of more Freon-14 (which we use in refrigerators and freezers to keep things cold) and the release of that gas into the environment (when you throw your old fridge out) that causes pollution and contributes to climate change.
The most common GHG is water vapour. However, three others are of special relevance to climate change because they are very commonly produced by human activities:
- Carbon dioxide (CO2) is released into the atmosphere through natural processes of plant and animal life, but the deliberate burning of fossil fuels and other materials by humans now accounts for the majority of atmospheric CO2. It is the main contributor to climate change and accounts for approximately two thirds of the GHGs produced by human activities. Photosynthesis, the process by which plants take in CO2, and converts it into oxygen, reducing the amount of this greenhouse gas in the atmosphere.
- Methane (CH4) is not as abundant as CO2 but is 21 times more effective at trapping heat. It is created when vegetation is burned, is digested or rots in an oxygen-free environment — buried in a landfill, for example. Wetlands, rice paddies, animal digestive processes and decaying garbage are the greatest sources of CH4 in our atmosphere.
- Nitrous oxide (N2O) occurs naturally in the environment, but human activities are increasing the quantities. This gas is most often released when chemical fertilizers and manure are used in agriculture.