Global Warming

Year 11 Senior Geography Essay - New South Wales, Australia. Mark: 20/20 (A).

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 increases in carbon dioxide, although on a much smaller scale, through the burning and decaying of vegetation. The reduction in vegetation also means that there are fewer plants to absorb the gas. Methane has various sources including herbivorous animals such as sheep and cattle that release it as a byproduct of digestion, rice paddies, land fills and forest fires. It can also enter the atmosphere from natural gas fields and coal mines. There are various sources of nitrous oxide including the use of fertilisers, the combustion of fossil fuels and motor vehicle emissions. Chloroflurocarbons and halons were invented in the 1920's as coolants. They have been used in refrigerators, air conditioners, plastic foams (bubbles) and aerosol cans. Water vapour is the most important greenhouse gas. Human activities are not directly changing the level of water vapour in the atmosphere. However, increases in other greenhouse gases are likely to raise the earth's temperature and thus increase evaporation and therefore the level of water vapour. This would further increase global warming.

There is an increasing body of evidence to suggest that global warming is taking place. Some examples include that temperature measurements taken in the traditional way - by thermometers in meterological stations - show that the world warmed by about 0.5 degrees celcius during the twentieth century, 1995 was the world's hottest year since reliable records began around 140 years ago - prior to this 1990 was the hottest year, The Australian Bureau of Meterorology records show that Australia has been warming since the early 1950 by 0.1 degrees celcius to 0.2 celcius a decade, five Antarctic ice shelves have retreated dramatically over the past 50 years and others have broken up, at Macquarie Island just north of Antarctica sea temperatures have risen by more than 1 degree celcius since 1912, pine trees in northern Finland have taken root in tundra areas at the rate of about 40 metres per year in an apparent response to warmer temperatures, tropical corals which are sensitive to water temperatures are beginning to suffer losses in many regions, Siberia is now warmer than at any time since the Middle Ages and the northern interior of India has been experiencing life-threatening heatwave conditions in consecutive years throughout the 1990's.

There are many possible impacts of global warming on a regional scale. These include that there could be an increase in the intensity and frequency of heavy rainfall in some regions, there could be a change in the frequency and intensity of natural disasters such as tropical cyclones and droughts, changes in temperature and the pattern and intensity of rainfall may affect the structure and functioning of ecosystems, the regional and subregional changes in rainfall and temperature patterns may alter the production possibilities in