Greenhouse Effect is a term for the role the atmosphere plays in helping warm the earth’s surface. The atmosphere is largely transparent to incoming short-wave (or ultraviolet) solar radiation, which is absorbed by the earth’s surface.
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The earth receives energy from the sun, which warms the earth’s surface. As this energy passes through the atmosphere, a certain percentage gets scattered. Some part of this energy is reflected back into the atmosphere from the land and ocean surface. The rest (70%) actually remains behind to heat the earth. In order to establish a balance, therefore, the earth must radiate some energy back into the atmosphere. As the earth is much cooler than the sun, it does not emit energy as visible light. It emits through infrared or thermal radiation. However, certain gases in the atmosphere form a sort of blanket around the earth and absorb some of this energy emitted back into the atmosphere. Without this blanket effect, the earth would be around 30 o C colder than it normally is. These gases like carbon dioxide, methane, and nitrous oxide, along with water vapour, comprise less than one per cent of the atmosphere. They are called ‘greenhouse gases’ as the working principle is same as that which occurs in a greenhouse. Just as the glass of the greenhouse prevents the radiation of excess energy, this ‘gas blanket’ absorbs some of the energy emitted by the earth and keeps temperature levels intact. This effect was first recognized by a French scientist, Jean-Baptiste Fourier, who pointed out the similarly in what happens in the atmosphere and in a greenhouse. Hence he terms the “greenhouse effect.”
This gas blanket has been in place ever since the creation of the earth. Since the industrial revolution human activities have been releasing more and more of these greenhouse gases into the atmosphere. This leads to the blanket becoming thicker and upsets gases are called ‘sources’ and those that remove them are known as ‘sinks’. A balance between ‘sources’ and ‘sinks’ maintains the levels of these greenhouse gases. Humankind upsets this balance when new sources that interfere with the natural sinks are introduced. Carbon dioxide is released when we burn such fuels as coal, oil and natural gas. And, when we destroy forests, the carbon stored in the trees escapes as carbon dioxide into the atmosphere. Increasing agricultural activities, changes in land-use patterns, and other sources lead to rising levels of methane and nitrous oxide. Industrial processes also release artificial and new greenhouse gases like CFCs (chlorofluorocarbons), while automobile exhaust fumes lead to ozone generation. The resulting enhanced greenhouse effect is more commonly referred to as global warming or climate change.
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Global warming is a result of the increase of thickness of the greenhouse gas layer or increase in concentration of GHGs that are released into the atmosphere through human activity. Increased greenhouse gas concentrations may be resulting in more heat being trapped in the atmosphere and increasing global temperatures emitted by the cars we drive, the furnaces we use to heat our homes, and the industries that produce oil and gas, create electricity, and develop products for the world’s marketplace. These greenhouse gases are completely human-caused. They harm stratospheric ozone, and so are not as directly responsible for global warming as carbon dioxide is. The question of reducing their presence in the stratosphere is being taken care of in another global convention, the Montreal Protocol. These gases are particularly effective in absorbing long wave radiation from the earth’s surface and preventing heat from escaping. Although the views and opinions of people across the world vary on issues relating to the cause of global warming and its possible impacts, there is a common understanding that it is a cause for major global concern and must be addressed immediately.