Global warming is the progressive gradual rise of the earth's surface temperature thought to be caused by the enhanced greenhouse effect and responsible for changes in global climate patterns. The greenhouse effect is a term used to describe the roles of water vapour, carbon dioxide, and other trace gases in keeping the Earth's surface warmer than it would be otherwise. The diagram below shows the greenhouse effect:
These "radiatively active" gases are relatively transparent to incoming shortwave radiation, but are relatively opaque to outgoing longwave radiation. The latter radiation, which would otherwise escape to space, is trapped by these gases within the lower levels of the atmosphere. The subsequent reradiation of some of the energy back to the surface maintains surface temperatures higher than they would be if the gases were absent. There is concern that increasing concentrations of greenhouse gases, including carbon dioxide, (the carbon dioxide emissions are primarily caused by the use of fossil fuels for energy) methane, and manmade chlorofluorocarbons, may enhance the greenhouse effect (this is called the enhanced greenhouse effect) and cause global warming. There are several important factors that have caused the increase in greenhouse gases over the past 200 years. Fossil fuels - coal, oil and natural gas - contain carbon. When they are burnt as a source of energy, they release carbon dioxide. The global demand for energy, primarily from fossil fuels, has grown to an average annual rate of approximately two per cent for almost two centuries - although the demand for energy varies considerably over time and among different regions. The burning of fossil fuels on a global scale produces around 20 billion tonnes of carbon dioxide each year. About half of these emissions are absorbed by oceans and plants. The rest stays in the atmosphere. Deforestation also contributes to... [continues]
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