Working in the environment team for large coal fired power station, I often get into the debate about the Green house effect or "Global Warming". Quite often in my debates I often here the other person claim “The Green house effect is all a big lie, it was only the other week I heard on the news that the hole in the ozone layer is getting smaller” or “didn't we change the gas in our refrigerators years ago to stop global warming?” The difference between the Greenhouse effect and the hole in the Ozone Layer has been a point of confusion for many people. So do you know the difference?

The Greenhouse Effect

The Greenhouse effect was proposed by Joseph Fourier in 1824 and first investigated quantitatively by Swedish scientist Svante Arrhenius in 1896. The Earth receives energy from the sun in the form of visible and invisible radiation, including light. The earth absorbs around 70% of this radiation and reflects the remaining 30% back out into outer space. The greenhouse effect is the process of increasing the amount of radiation being absorbed by the earth, while decreasing the amount that is reflected. So how are we absorbing more radiation? Most of the visible radiation is absorbed, or reflected by the earth it self. Ever been to the beach or snow on a really sunny day? That glare in your eyes is the sun's light being reflecting back into outer space. The invisible radiation or "infrared waves", however, are reflected by the atmosphere, not by the ground. The amount of reflection depends on the concentration of gases such as water vapour, carbon dioxide and methane in the atmosphere. Increasing the concentrations of these components, increases the amount of invisible radiation the earth is absorbing. So how bad is it? With simple laboratory tests, Arrhenius, predicted that a doubling the carbon dioxide concentration in the atmosphere, the temperature will rise by about 5oC. This a large enough rise to cause serious havoc with the worlds environments, such as melt glaciers, cause an increase in storm severity and prolong droughts.

The Hole in the Ozone Layer

While global action to reduce carbon dioxide emissions is still only in the infant stages, the story about the hole in the ozone layer is becoming better every day. That's because the hole is shrinking. The atmosphere above the earth is made up of many layers. The lowest layer, reaching between 11 to 20km above the earths surface is the troposphere. This is the region where the green house gases are being trapped. Higher up above. Above this region is the stratosphere, ranging from 11km to 50km above the earths surface. In this region the ozone layer can be found. While the ground absorbs the visible radiation, the greenhouse gases in the troposphere absorb the infrared radiation, the ozone layer in the stratosphere reflects, ultraviolet (UV) radiation.

Ozone, O3, is composed of three oxygen atoms joined together to make a single molecule. This molecule is specially designed to absorb a different kind of radiation again, ultra violet (UV) radiation. Absorbing UV radiation is of great importance to us humans as it is the main cause of skin cancers.

So how does the hole in the ozone layer differ from the greenhouse effect? The biggest difference is that the hole in the ozone layer is caused by O3 molecules disappearing, while the green house effect is caused by the amount of carbon dioxide molecules increasing in the atmosphere. Another difference is that the hole in the Ozone layer is a good news story! The hole in the ozone layer was chiefly caused by another group of chemicals called “organohalgen compounds” especially “chlorofluorocarbons” (CFCs). These chemicals were once found in everything from spray cans to refrigerator and air-conditioning gas. One highly stable CFC gas molecule could break down at least 100,000 ozone molecules.

So to stop a massive increase in sun cancer around the world, governments acted. In 1987 an international treaty was signed, the Montreal Protocol, which limited CFC production, before banning it all together in 1996. Since that date, scientists have reported the rate of decline in the layer has slowed dramatically, and some have even reported the hole is repairing itself.

So now you have no excuse to confuse the two phenomena! The difference between the hole in the ozone layer and the green house effect is first is being caused by a disappearing ozone gas, and the second is being caused by to much carbon dioxide! While the ground absorbs the visible radiation, the greenhouse gases absorb the infrared radiation in the troposphere, the ozone layer reflects a different type of radiation, ultraviolet (UV) radiation.

Peter Welsummer - Editor: The Nature Garden

About the Author: Peter Welsummer is the editor of www.thenaturegarden.com. Learn how to garden in tune with nature with a collection of DIY gardening and environmental articles.