The greenhouse effect, caused by heat trapping gases in the atmosphere, is essential to life on earth. The present day levels of atmospheric greenhouse gases, combined with some of the most potent man-made global warming gases, are threatening to amplify this greenhouse effect to dangerous environmental levels.
Greenhouse Gases and the Greenhouse Effect
Atmospheric gases such as water vapor, carbon dioxide, methane and others produce a “greenhouse effect” on the planet Earth. In Essentials of Meteorology: An Invitation to the Atmosphere, published by Cengage Learning in 2008, the author, C. Donald Ahrens explains that without these heat trapping gases in the atmosphere, the Earth would be up to 30 degrees Celsius cooler than it actually is.
While Ahrens states that, “It is the atmospheric greenhouse effect, then, that keeps the temperature of our planet at a level where life can survive. The greenhouse effect is not just a "good thing" - it is essential to life on earth”, he goes on to show that because this greenhouse effect is a finely tuned natural occurrence, undue interference with the levels of greenhouse gases in the atmosphere can have a devastating environmental effect on the climate of the planet.
Atmospheric Levels of Greenhouse Gases
Climate Change 2007: The Physical Science Basis, by the Intergovernmental Panel on Climate Change and published by Cambridge University Press in 2007 lists the levels of greenhouse gases in the atmosphere. These are:
- Water vapor is by far the most abundant of the greenhouse gases, making up about 3% of the atmosphere or 30,000 parts per million (ppm). Although responsible for up to 70% of global warming, because 99.99% of water vapor is of natural origin, this greenhouse gas is not amenable to man-made mitigation efforts.
- Carbon dioxide is the largest of the anthropogenic greenhouse gases. The present day level of carbon dioxide in the atmosphere is 387ppm, an increase of 107ppm (man-made) since pre-industrial times.
- Levels of methane, natural and man-made, are at 1,774 parts per billion (ppb) with 1,040ppb added since 1750.
- Nitrous Oxide levels are at 314ppb with 44ppb added since 1750.
- Combined levels of CFC gases such Freon-11 and Freon-12, which were used in refrigeration and air conditioning processes until banned under the Montreal Protocol as damaging to the ozone layer, are still at 1070 parts per trillion (ppt).
- HFC gases, or F-Gas as they are collectively known, replaced CFC gases and are now at combined levels approaching 100ppt.
- Sulfur hexafluoride levels are at 5ppt.
CFC, HFC and Sulfur hexafluoride gases are entirely man made and did not exist prior to industrialization.
Most Potent Greenhouse Gases
Chapter Two of Climate Change 2007 explains how the global warming potential (GWP) of atmospheric gases is measured. Since carbon dioxide is the most common of the anthropogenic greenhouse gases, it is given a GWP of 1 and all other greenhouse gases are measured against this. As different gases have different atmospheric lifetimes the GWP of a greenhouse gas is usually measured over a 100 year period.
- Sulfur hexafluoride, with a GWP of 23,900 is the most potent of the greenhouse gases. It has an atmospheric lifetime of 3,200 years.
- HFC-23, an F-Gas, has a GWP of 11,700 with an atmospheric lifetime of 270 years.
- PFC-116, another type of F-Gas has a GWP of 9,200 with an atmospheric life of 10,000 years.
- Freon-12, a CFC gas has a GWP of 8,100 and a life of 100 years.
- Hexafluoropropane, an F-Gas used in fire extinguishers has a GWP of 6,300 and an atmospheric life of 240 years.
- Nitrous Oxide has a GWP of 310 and a lifetime of 114 years.
- Methane has a GWP of 21 and a lifetime of 12 years.
While man-made greenhouse gas levels could be controlled, rising temperatures caused by increasing levels of carbon dioxide may allow the atmosphere to hold much more water vapor, over which mankind has no control, thus causing further global warming, with the possible release of natural sinks of methane, creating a runaway greenhouse effect, with dire environmental results.
Laurence O'Sullivan - Larry O'Sullivan, Irish short story and freelance Article writer now living in Thailand. I am Irish, 55 years old and am now living in ...
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