Greenhouse Gases

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Carbon Dioxide's concentration is said to be around .037% and there are a number of gases that are so small in concentration, even compared to Carbon Dioxide, that they are called trace gases. The most important of these trace gases to us are Methane CH4, Nitrous Oxide N20, and CFC's or chloroflouro-carbons because of the way they act as greenhouse gases.

So greenhouse gases are gases that absorb radiation being given off by the earth and re-emit it back to the earth keeping the air near the ground warmer than if the greenhouse gases were not present.

Carbon Dioxide
A clear, odourless gas that is non-toxic to humans, CO2 neither fouls the air, impairs visibility, nor contributes to respiratory disease. CO2 is the basic building block of the planetary food chain, and rising concentrations help most plants grow faster and bigger, use water more efficiently and resist pollution and other environmental stresses. The ecological benefit of an atmosphere richer in CO2 is universal, because all animals depend, directly or indirectly, on plants as a food source.

It seems that the CO2 level as well as the levels of other greenhouse gases are always going up and down between a certain levels for the past millions of years.

Research in to ice core samples give us insight in to CO2 levels up to 400,000 years ago and patterns have been noticed as well as maximum and minimum levels. This information shows us that CO2 has ranged between around 200 ppm (parts per million) to 300 ppm and it seems to range over 100,000 years or so from one to the other. This research shows us that 10,000 to 15,000 years ago the CO2 concentration was 300 ppm and based on the ice core data and the historical pattern the earth will slowly decrease the CO2 level for 100,000 years to 200 ppm and then rise quickly again for thousands of years to 300 ppm starting the cycle over again.

The current level of CO2 is around 380 ppm. There are sign in the last 10,000 years that hint towards a falling CO2 level from 300 ppm but that all changed in the last couple hundred years with the industrial revolution and the burning of fossil fuels. The most dramatic change being in the 1990 where the CO2 level rose more than any other recorded decade.

CO2 comes from many different sources and its concentration rises and falls every year following the seasons and the amount of plant life doing photosynthesis. CO2 also comes from clearing forests because CO2 is released when burning vegetation or from decaying vegetation. Although vegetation and oceans absorb the extra CO2 it is estimated that 25 to 50 percent stays in the atmosphere.

Methane
A clear gas, non-toxic to humans with a distinct odour.

Methane is found in far less a concentration than CO2, but it is 20 to 30 times more effective in absorbing the long wave infrared radiation given off by the earth. So even though it is a trace gas, it still has a strong effect. Methane is produced by anaerobic bacteria, which thrive in moist and wet areas where the oxygen content is low. This includes swamps, wetlands, bogs, rice paddies, and in the stomach of certain grazing animals like sheep and cows. It has been recorded that Methane concentration has doubled in the last couple hundred years and this matches the recent huge population growth and consumption of rice and widespread use of domesticated animals.

Nitrous Oxide
Nitrous Oxide, N2O, not only is a greenhouse gas that is more effective than Methane at absorbing radiation from the earth but also has a lifetime of around 150 years. The amount of N2O in the atmosphere is very small and its amount is not growing as fast as Methane or CO2, but it is increasing and is monitored because of its long lifetime.

Nitrous oxide is believed to be increasing as a result agricultural activity and the fact that nitrogen fertilizers are very commonly used. N2O is also released in the combustion of fossil fuels at high temperatures.

CFC's: Chlorofluorocarbons
A trace greenhouse gas that is not naturally present in the atmosphere. CFC's are manufactured chemicals discovered in the 1920's and used in greater quantity in the 1950's to present. Even though it is not natural to the atmosphere CFC's are attributed with the same contribution to the greenhouse effect as methane. The current use of CFC's is not declining and there is not a strong plan to eliminate the use either. Even if we were to stop using CFC's right now the effects would not stop because the CFC molecule can last in the atmosphere for decades.

Aerosols
Tiny solid and liquid particles suspended in the atmosphere consisting of soil, smoke, sea salt, dust and sulphuric acid produced from things like waves crashing, dust storms, and volcanoes. Other particles like water vapour attach and detach to aerosols all the time and can be in the form of ice if it is cold enough. Solar radiation also hits these aerosols in the air and the radiation is either reflected back out of the atmosphere or scattered in multiple directions within the atmosphere. Radiation from the earth heading outward is also reflected back towards the earth or scattered within the atmosphere.

Human generated aerosols are thought to be in similar amount to naturally generated aerosols. The human generated aerosols are commonly a result of sulphur dioxide being emitted during fossil fuel combustion and burning vegetation and chemical reactions in the atmosphere convert the sulphur dioxide to sulphate aerosols, the material that produces acid precipitation.

Aerosols make clouds better reflectors because the aerosols attract water and create more cloud droplets within a cloud. If a cloud has a greater number of small droplets within it, less radiation can penetrate it. By reducing the amount of solar radiation that reaches the planet aerosols help create a cooling effect for the planet. The extent of this and effects though are uncertain, and the hope that aerosols will help offset the effects of global warming is yet to be seen.

Water Vapour
Water vapour is a very important element to the atmosphere and us all. Sunlight, chlorophyll, water, and carbon dioxide are the base necessities for plant life to go though photosynthesis. Without water life would not exist on this planet. The hydrosphere includes all the water on the planet whether it be frozen in a glacier or in a cloud about to be rained down to earth. This process of water evaporating, condensing in the air, and raining down on land is essential. So water vapour being the main source of clouds and water vapour is very important.

Water vapour acts as a greenhouse gas and absorbs heat being given off by the earth as well as reflects solar energy back before entering the atmosphere. So it plays a big role in the earth's temperature having the ability to halt radiation both coming to the planet and being given off. As well when water vapour goes through a change of state it absorbs or releases heat and it is this latent energy release that contributes to weather.