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Greenhouse Effect & Global Warming: Role of Methane & Chlorofluorocarbons
Temperature of the earth has risen by approximately 1 degree Fahrenheit in the last century. During the past 100 years global sea levels have risen 4 to 8 inches. This is the phenomenon that is known as ‘Global Warming’. Global Warming has serious implications on human civilization and that could be devastating! Every one of us should be aware about this phenomenon so that we can save our beloved ‘Earth’ that’s going to be destroyed much earlier than its actual life span.
The Greenhouse Effect:
We all know that greenhouse is a mechanism by which the growth of certain plants can be ensured. The infrared radiation that is trapped inside the greenhouse helps maintain an elevated temperature level before it finally released to the outside world. Sun’s energy is not sufficient to make the earth warm enough for living. The reason the earth is just at the right temperature for humans and other species to grow is because of the phenomenon called the ‘greenhouse effect’. This phenomenon is responsible for maintaining earth’s temperature at an average of 15 degree Centigrade. Without it the temperature would be minus 20 degree Centigrade, so cold that humanity would have never been able to evolve.
The greenhouse effect changes the way the sun impacts the earth. Carbon dioxide and other gases in the atmosphere act like the glass in a greenhouse, trapping the heat from the sun. As more greenhouse gases are added to the atmosphere, more heat is trapped and the world’s climate grows warmer.
The greenhouse gases are trace gases that alter the heating rates in the atmosphere by allowing incoming solar energy to pass through but trapping the heat emitted back by the surface of the earth. Absorption of radiation is a property of a wide range of gas molecules including carbon dioxide (CO2), methane (CH4), chlorofluorocarbons (CFCs), nitrous oxide (N2O) and sulfur dioxide (SO2). These are all long lived greenhouse gases.
Carbon dioxide contributes about 50 per cent to the greenhouse effect. The primary source of CO2 is the usage of fossil fuels. Since prehistoric times people have burnt wood and other plant remains to produce heat and light. After wood became scarce the use of coal started followed by oil and gas. Apart from the burning of fossil fuels land-use change is another way of accumulation of CO2 in the atmosphere. Before the ‘Industrial Revolution’ the rise in the concentration of CO2 was largely ascribed to deforestation and agricultural land use. 20 per cent of the total released CO2 has been contributed by land-use change even today. Due to deforestation soil erosion has increased substantially which again has led to the concentration of CO2.
The concentration of methane (CH4) is also rising rapidly in the atmosphere. It is produced by anaerobic respiration in a wide variety of environments such as stomachs of animals, swamps, paddy fields, water logged soils to name a few. Methane is removed from the atmosphere by reaction with hydroxyl (OH) radicals in the air. But the problem is with the increasing population of the world agricultural activity is bound to increase, which results in increased methane emission. Since 1960s methane in the atmosphere increased by 1% per year – twice as fast as the build up of CO2. Since methane molecule is 20 times more effective in trapping the heat than CO2 molecules methane is a serious threat too! In terms of contribution to the greenhouse effect methane comes second after CO2. Methane molecules survive 10 years in the atmosphere. As the world continue to warm large amount of methane stored in the frozen Tundra of the north and also on the seabed may be released.
Nitrous oxide (N2O) contributes about 6 per cent to the greenhouse effect at present. It comes from both natural and man-made processes. 45 per cent of N2O comes from man-made sources like fuel consumption, using nitrogenous fertilizers, burning rain forests and animal wastes. Chlorofluorocarbons (CFCs) are extremely effective greenhouse gases. Although there are lower concentrations of CFCs in the atmosphere than CO2 they are able to trap more heat. Actually a CFC molecule is 10,000 times more effective in trapping heat than a CO2 molecule. CFC molecules survive 110 years because they are very stable and decay slowly. CFCs are accumulating slowly in the stratosphere where they are broken by the sun’s ultraviolet ray, releasing chlorine atoms. Chlorine attacks the ozone layer and creates holes in the ozone layer. One chlorine atom can destroy 100,000 ozone molecules. It is necessary to phase out the production of CFCs totally at the earliest.
Although sulfur dioxide (SO2) is a greenhouse gas, it has a cooling effect. SO2 released in gaseous state is converted in aerosol particles that absorb short wave radiations and are the main condensation nuclei for water vapor, which ultimately becomes the source of clouds. Water vapor too is one of the most important greenhouse gases but its role is a bit complicated. When water vapors condenses into clouds it can either absorb long wave radiation from the ground causing further warming or reflect radiation from the sun causing a cooling effect. Which of these predominates depends on the type of clouds and its height in the atmosphere.
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Effects of Global Warming:
Because of the combined effect of greenhouse gases, global warming is happening at a rapidly increasing rate. If no substantial action is taken the greenhouse effect could lead to the rise in average global temperature by anywhere between 1.5 degree Centigrade to 4.5 degree Centigrade by as early as 2030. Experts from the IPCC (Inter-governmental Panel on Climate Change) confirmed that the 1990s have been the hottest decade since recording of climate change began 150 years ago. According to them eleven of the twelve years in the period 1995 – 2006 rank among the top 12 warmest years in the instrumental record. They also found that average temperatures had risen by approximately 0.74 degree Centigrade since 1900. Forecasts for the future are even more alarming!
Temperature will increase more in the two poles and less at the tropical area. There will also be more warming in the winter than summer. Such increase will make the world hotter than it has been for more than 100,000 years. Storms, cyclones, hurricanes, gales and typhoons will become more frequent and stronger. In the same way continental heartland will face droughts. With sea level rising at a rate of 1 to 2 mm each year due to the melting of the polar ice and mountain glaciers it could lead to major flooding in the coastal and low lying areas of the world.
As our economies continue to grow more fuel consumption will happen than ever before! On current trend the world’s use of energy is set to almost double in the first thirty years of this century with about 90 per cent of the growth likely to be met by oil, gas and coal. Things have already started to heat up and the number of droughts, storms, floods, heat waves is on the rise! So it is extremely important to slow down global warming as much as possible. This means using less fossil fuel, elimination of CFCs altogether and slowing down deforestation. This can be best done by energy conservation, optimal use of public transport mainly through renewable energy such as solar, wind and wave energy.