Generally greenhouse effect occurs when solar radiation gets trapped in earth atmosphere. Solar radiation largely passes through the earth’s atmosphere and warm up the planetary surface. A certain portion of this radiation (approximately 30%) gets reflected directly back to the space. The rest of it gets absorbed by the planet surface and atmosphere. Once absorbed, this energy is released back in the atmosphere and space in the form of a slow moving energy known as infrared radiation. When some part of these infrared radiations gets trapped by certain gases in the atmosphere like water vapor, carbon dioxide, ozone, methane, nitrous oxide etc. and radiated back towards the earth surface, greenhouse effect occurs. These trapped infrared radiations increase the average surface temperature than what it would be in the absence of those gases. As these gases act like the glasses of a greenhouse to trap radiation and increase the heat inside; they are known as greenhouse gases.
Most of these greenhouse gases occurs naturally and without this natural greenhouse effect life on earth would not be feasible. Without this earth could be much colder than it is now: that is freezing minus 18 degree centigrade than the present 15 degree centigrade (source: Government of Canada). But over the past years, there is excessive accumulation of greenhouse gases has occurred in the atmosphere due to human activities and industrialization. This intensification of effect through human activities or anthropogenic factors is known as Enhanced Greenhouse Effect.
Over the last centuries, increased human civilization and industrialization have contributed heavily in the greenhouse gas emission and accumulation. The largest sources of greenhouse gas resulted from human activities include burning fossil fuel, transportation, industrialization and deforestations.
The major causes of greenhouse gas emissions are listed below:
Human civilization and industrialization need excessive use of fossil fuels, oil, coal and gas to meet the current energy demands. Based on Government of Canada’s statistics, about 80 % of total greenhouse gases are predominantly associated with the production or consumption of fossil fuels for energy purposes. Among that, about 44 % comes from stationary sources such as electricity generation, space heating, fossil fuel industries, manufacturing, construction, and mining. Other 27% comes from Domestic transportation of goods and people. The remaining 9% is from fugitive sources such as venting and flaring of waste fuel gases or escapes from mine openings. (Source: Government of Canada). Greenhouse gases are released in the atmosphere from the burning of the fossil fuels and it is one of the major causes of the greenhouse effect.
Using gasoline in the automobile engine leaves carbon dioxide in the atmosphere. In developed countries, people rely heavily on the personal vehicles and this contributes to the greenhouse gas emission considerably.
Industrial sector and industrial process activities also contribute a significant amount of greenhouse gas emission. Industrial process activities such as cement production, iron and steel blast furnace operation etc. produce many greenhouse gases including carbon dioxide, nitrous oxide and halocarbons. Some electrical and electronics industries also use greenhouse gases in the manufacturing and use of products such as refrigerators, air conditioners, foams and aerosols.
Rapid population growth and increased civilization required more lands and resources. Forests are being converted to croplands and trees are being cut down for making habitats as well as for meeting other industrial and commercials needs. Trees act as a natural carbon dioxide sink; increasing deforestation and diminishing green lands upset this natural balance, leaving more carbon dioxide in the atmosphere to enhance the greenhouse effect.
Farming practices like raising livestock or animal production contribute to greenhouse gas production. A large amount of methane generate during the normal digestive process of the herbivores. Ruminant animals like cattle thus generate the most methane. In addition, both methane and nitrous oxide are emitted during manure handling and management of the livestock. The amount of emission depends on the quantity and type of the manure and the manure management system. In addition, some agricultural activities including the use of fertilizers contribute to higher greenhouse gas emission like nitrous oxide.
The primary greenhouse gas and sources of greenhouse gas emissions in the United States are shown in the following figures, generated by the U.S. Environmental Protection Agency:
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