Carbon Dioxide

Carbon Dioxide (C0₂) is the most common greenhouse gas and poses the greatest concern. C0₂ is a naturally occurring gas as a major component of the carbon cycles. Biological processes repeatedly capture and store carbon in organisms, ocean deposits, and soils; the carbon is released into the atmosphere as C0₂ when plants decompose, only to be recaptured and sequestered again and the process repeats.

Human activity is generating and releasing new C0₂ into the atmposhere that was not previously in the carbon cycle. Natural carbon dioxide sinks are not able to keep up with the pace recapturing and binding this new source. This means that more and more C0₂ is accumulating in the atmosphere. When circulating naturally as a part of the carbon cycle, C0₂ stays in the atmosphere for around 150 years; that, however, is dependent on the amount of C0₂ in the atmosphere at the time and the biological processes in place to manage it. Now, with more C0₂ and fewer biological processes (due to deforestation and altered land use), the carbon cycle has been slowed down considerably.

Increases in C0₂ due to human activity are mostly caused by the burning of fossil fuels and land use changes, like deforestation and unsustainable agriculture, that result in the decreased ability for organisms and soil to capture and store carbon.

Methane

Methane (CH₄) is a chemical made up of carbon and hydrogen atoms. Methane is a very common, naturally-occurring greenhouse gas. It is found in deposits within the earth's crust. It also comes from the anaerobic decay or fermentation of organic matter. It is non-toxic, but it can cause harm to organisms by displacing the oxygen an organism breathes. Methane is also flammable at certain temperatures and pressures.

Methane is utilized as a fuel and in various industrial processes. It is being released into the atmosphere due to human activities of energy production and organic decomposition and fuel burning. In the atmosphere it acts as a greenhouse gas with a global warming potential 21 times stronger than CO₂; but also has a short atmospheric life.

Nitrous Oxide

Nitrous Oxide (N₂O) is a naturally occurring gas. It is colourless, non-flammable, and stable, but it also has a noticeably sweet odour and taste. When inhaled in small quantities, it causes mild euphoria. This is the reason for the other name for N₂O, “Laughing Gas”.

N₂O is used as an anaesthetic in surgical procedures, as a propellant in food aerosol products, as a leak detector for natural gas pipelines, an oxidant for the production of organic compounds, as an ingredient in rocket fuel, and in the manufacture of nitrates. While N₂O is naturally occurring, the N₂O we use for these purposes is manufactured.

N₂O is also created as a result of human activities. It is released into the atmosphere from the use of agricultural fertilizers and from livestock. While N₂O naturally exists in the atmosphere, the extra N₂O added to the atmosphere is increasing the greenhouse gas effect of the atmosphere. It has a Global Warming Potential of 310, which makes N₂O a powerful greenhouse gas.

Hydrofluorocarbons

Hydrofluorocarbons are a family of chemicals which share the characteristic of being composed of fluorine, hydrogen and carbon atoms. Hydrofluorocarbons are not naturally occurring in the environment. Their manufacture began a short time ago, in the 1990's. They are commonly manufactured for refrigeration/air-conditioning, foam blowing, general aerosols, metered dose inhalers (MDIs), solvent cleaning and fire fighting.

Hydrofluorocarbons have large global warming potentials (GWP) thousands of times more powerful than CO₂.

Sulphur hexafluoride

Sulphur hexafluoride is a heavy gas made up of sulphur and fluorine. It is odourless, colourless, non-toxic, and non-flammable. Sulphur hexafluoride has many commercial and industrial uses, including window manufacturing, as a tracer, as a medical substance, in magnesium casting, and in electronics.

Sulphur hexafluoride has a Global Warming Potential almost twenty-four thousand times stronger than CO₂. Small releases of sulphur hexafluoride can have a significant impact on the atmosphere.

Perfluorocarbons

Perfluorocarbons are a family of chemicals which share the characteristic of being composed of fluorine and carbon atoms. The chemicals in this family are chemically inert, thermally stable, non-toxic, and non-flammable. Perfluorocarbons are not naturally occurring in the environment. They are commonly manufactured for various medical and electronic purposes, and for paint and textile manufacturing. Perfluorocarbons are also commonly produced as by-product in aluminum manufacturing.

Perfluorocarbons tend to have extremely large global warming potentials (GWP), starting at 6500 GWP. They also spend extremely long periods of time in the atmosphere before completing a cycle, often thousands of years.

Water Vapour

Water vapour exists naturally in the atmosphere as a result of the hydrologic cycle. Water circulates from liquid water on the Earth into the atmosphere and back to the Earth through the processes of transpiration, evaporation and precipitation. As the Earth’s temperature rises, more and more water vapour will be stored in the atmosphere at any given moment, thus enhancing the greenhouse effect. Some human activities release water vapour to the atmosphere but this is insignificant compared to the natural hydrologic processes.

Ozone

Ozone, the triatomic form of oxygen (O₃), is a gaseous atmospheric constituent. It is created both naturally and by photochemical reactions involving gases resulting from human activities (photochemical smog). In high concentrations, at ground-level ozone can be harmful to a wide-range of living organisms including people. High up in the stratosphere, ozone is created by the interaction between solar ultraviolet radiation and molecular oxygen (O₂). Stratospheric ozone is a greenhouse gas and plays a decisive role in the stratospheric radiative balance.