WARMING OF EARTH AND ITS CAUSES
- Global warming has been and is being caused due to a various number of factors. Global warming is basically a change in the climatic conditions of the earth. These climatic conditions vary due to various reason, external and internal. Changes to climatic conditions and therefore Global Warming can be caused to to natural or man-made circumstances also. Some of the factors causing global warming are volcanic emissions and solar activity.
According to the solar variation theory,the sun has been gaining strength and is at it's strongest since a sixty years. Therefore, it may now be acting as a cause of global warming. Sunspots are also said to be a cause or catalyst for Global Warming. Recent reports suggest that the number of sunspots in an area directly affects the amount of time the nearby earth takes to cool. The sun is the main source of energy to the earth. The earth absorbs about seventy percent of the earth's solar flux. This solar flux increases the temperature of the earth's atmosphere, land and oceans.
Orbital forcing is also said to be one of the natural causes of Global Warming. The reports show the effect of the slow tilting of the earth's axis on the climate of the earth.The greenhouse effect is said to be the most important factor regarding global warming. When infrared radiation from the atmosphere increases the temperature of the earth's surface, it is termed as the greenhouse effect. The greenhouse effect has increased the earth's temperature by about twenty four percent.
Carbon dioxide contributes about twelve percent of the greenhouse effect, while water vapor contributes thirty six percent of the greenhouse effect. Methane causes five to ten percent of Global Warming, while Ozone makes around three to seven percent of the greenhouse effect possible.
Solar variation is said to be another reason of Global Warming. The changes in the amount of radiant energy emitted by the Sun are known as solar variation. This solar variation has been correlated with the changes in the Earth's climate and temperature.
Along with the natural causes of Global Warming, scientists have also contributed rapid industrialization to the increase of Global Warming today.Humans had first affected global warming some eight thousand years ago, with the start of agriculture. Due to the clearing of the forests for agriculture, the amount of carbon dioxide in the atmosphere increased drastically.
Scientists are of the opinion that industrialization releases various gases like carbon-dioxide and methane which are known to contribute to Global Warming. Deforestation is also said to increase global warming. Trees contain a high level of carbon, and therefore their cutting creates an increase of carbon in the atmosphere. Humankind also contributes to the increase of carbon dioxide by the burning of fossil fuels. The contribution of humankind to global warming due to the burning of fossil fuels has increased by about eighty percent in the past twenty years.
If the greenhouse effect didn't exist, the temperature of the earth would be around twenty seven Celsius less. Some scientists are of the opinion that human life would be impossible on planet earth if the temperature would be so less.
- Causes of global warming » The greenhouse effect
The average surface temperature of Earth is maintained by a balance of various forms of solar and terrestrial radiation. Solar radiation is often called “shortwave” radiation because the frequencies of the radiation are relatively high and the wavelengths relatively short—close to the visible portion of the electromagnetic spectrum. Terrestrial radiation, on the other hand, is often called “longwave” radiation because the frequencies are relatively low and the wavelengths relatively long—somewhere in the infrared part of the spectrum. Downward-moving solar energy is typically measured in watts per square metre. The energy of the total incoming solar radiation at the top of Earth’s atmosphere (the so-called “solar constant”) amounts roughly to 1,366 watts per square metre annually. Adjusting for the fact that only one-half of the planet’s surface receives solar radiation at any given time, the average surface insolation is 342 watts per square metre annually.
The amount of solar radiation absorbed by Earth’s surface is only a small fraction of the total solar radiation entering the atmosphere. For every 100 units of incoming solar radiation, roughly 30 units are reflected back to space by either clouds, the atmosphere, or reflective regions of Earth’s surface. This reflective capacity is referred to as Earth’s planetary albedo, and it need not remain fixed over time, since the spatial extent and distribution of reflective formations, such as clouds and ice cover, can change. The 70 units of solar radiation that are not reflected may be absorbed by the atmosphere, clouds, or the surface. In the absence of further complications, in order to maintain thermodynamic equilibrium, Earth’s surface and atmosphere must radiate these same 70 units back to space. Earth’s surface temperature (and that of the lower layer of the atmosphere essentially in contact with the surface) is tied to the magnitude of this emission of outgoing radiation according to the Stefan-Boltzmann law.
Earth’s energy budget is further complicated by the greenhouse effect. Trace gases with certain chemical properties—the so-called greenhouse gases, mainly carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—absorb some of the infrared radiation produced by Earth’s surface. Because of this absorption, some fraction of the original 70 units does not directly escape to space. Because greenhouse gases emit the same amount of radiation they absorb and because this radiation is emitted equally in all directions (that is, as much downward as upward), the net effect of absorption by greenhouse gases is to increase the total amount of radiation emitted downward toward Earth’s surface and lower atmosphere. To maintain equilibrium, Earth’s surface and lower atmosphere must emit more radiation than the original 70 units. Consequently, the surface temperature must be higher. This process is not quite the same as that which governs a true greenhouse, but the end effect is similar. The presence of greenhouse gases in the atmosphere leads to a warming of the surface and lower part of the atmosphere (and a cooling higher up in the atmosphere) relative to what would be expected in the absence of greenhouse gases.
It is essential to distinguish the “natural,” or background, greenhouse effect from the “enhanced” greenhouse effect associated with human activity. The natural greenhouse effect is associated with surface warming properties of natural constituents of Earth’s atmosphere, especially water vapour, carbon dioxide, and methane. The existence of this effect is accepted by all scientists. Indeed, in its absence, Earth’s average temperature would be approximately 33 °C (59 °F) colder than today, and Earth would be a frozen and likely uninhabitable planet. What has been subject to controversy is the so-called enhanced greenhouse effect, which is associated with increased concentrations of greenhouse gases caused by human activity. In particular, the burning of fossil fuels raises the concentrations of the major greenhouse gases in the atmosphere, and these higher concentrations have the potential to warm the atmosphere by several degrees.
The amount of solar radiation absorbed by Earth’s surface is only a small fraction of the total solar radiation entering the atmosphere. For every 100 units of incoming solar radiation, roughly 30 units are reflected back to space by either clouds, the atmosphere, or reflective regions of Earth’s surface. This reflective capacity is referred to as Earth’s planetary albedo, and it need not remain fixed over time, since the spatial extent and distribution of reflective formations, such as clouds and ice cover, can change. The 70 units of solar radiation that are not reflected may be absorbed by the atmosphere, clouds, or the surface. In the absence of further complications, in order to maintain thermodynamic equilibrium, Earth’s surface and atmosphere must radiate these same 70 units back to space. Earth’s surface temperature (and that of the lower layer of the atmosphere essentially in contact with the surface) is tied to the magnitude of this emission of outgoing radiation according to the Stefan-Boltzmann law.
Earth’s energy budget is further complicated by the greenhouse effect. Trace gases with certain chemical properties—the so-called greenhouse gases, mainly carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—absorb some of the infrared radiation produced by Earth’s surface. Because of this absorption, some fraction of the original 70 units does not directly escape to space. Because greenhouse gases emit the same amount of radiation they absorb and because this radiation is emitted equally in all directions (that is, as much downward as upward), the net effect of absorption by greenhouse gases is to increase the total amount of radiation emitted downward toward Earth’s surface and lower atmosphere. To maintain equilibrium, Earth’s surface and lower atmosphere must emit more radiation than the original 70 units. Consequently, the surface temperature must be higher. This process is not quite the same as that which governs a true greenhouse, but the end effect is similar. The presence of greenhouse gases in the atmosphere leads to a warming of the surface and lower part of the atmosphere (and a cooling higher up in the atmosphere) relative to what would be expected in the absence of greenhouse gases.
It is essential to distinguish the “natural,” or background, greenhouse effect from the “enhanced” greenhouse effect associated with human activity. The natural greenhouse effect is associated with surface warming properties of natural constituents of Earth’s atmosphere, especially water vapour, carbon dioxide, and methane. The existence of this effect is accepted by all scientists. Indeed, in its absence, Earth’s average temperature would be approximately 33 °C (59 °F) colder than today, and Earth would be a frozen and likely uninhabitable planet. What has been subject to controversy is the so-called enhanced greenhouse effect, which is associated with increased concentrations of greenhouse gases caused by human activity. In particular, the burning of fossil fuels raises the concentrations of the major greenhouse gases in the atmosphere, and these higher concentrations have the potential to warm the atmosphere by several degrees.
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