There are three main factors contributing to global warming or ‘the enhanced greenhouse effect’ (Kemp, D 1994). Firstly Carbon dioxide (CO2) accounts for over 60% of global warming. It is estimated that every year 7000 million tonnes of carbon is released into the atmosphere every year (Kemp, D 1994). It is stored in fossil fuels, such as coal and oil and released when they are burnt accounting for over 5 billion tonnes of CO2 emitted into the atmosphere every year (Keepin et al. 1986), it is also stored in trees and released with the burning after deforestation. This is a major concern, partly because the demand for land with an ever-growing population, leading to ever more deforestation, but also as plants reduce levels of CO2 during photosynthesis, as they retain it and release oxygen into the atmosphere. This is an example of where humans disturb natural sinks as the natural process that help the earth to reduce CO2 levels is disrupted. Fig.2 shows the flows and stores of a carbon cycle and the increased levels which contribute to global warming (Gribbin 1978, McCarthy et al. 1986).
Another main cause of global warming is the release of methane into the atmosphere. This accounts for 20% of the ‘enhanced greenhouse effect’, it comes primarily from agriculture, especially flooded rice paddies, and animal waste, both of which coincide with the increase of CO2 from deforestation as the pressure for land increases and more is cleared, so in turn the levels of greenhouse gases are heightened. It is difficult to make an accurate statement of how much this has affected global warming because the majority of this production is done in the developing world where research is limited, but the trend of increased global warming has followed that of the increase in rice cultivation (Watson et al 1990).
The final of the important factors that contribute to global warming is nitrous oxides, chlorofluorocarbons (CFCs) and ozone which together account for the final 20% of global warming. Although not as abundant as some of the other chemicals they are thought to be of the most dangerous. For example CFC-11 is 12,000 times as strong as CO2 (Houghton et al. 1990). These originate mainly from aerosol sprays, insulating foams and refrigeration appliances (Kemp, D 1994). Their widespread usage has been seen to stabilise since it’s peak in the early 1990s and the installation of the Montreal Protocol agreement in 1987 which called for the reduction of CFC use and production (Houghton, J 1994). As with CO2, though, they have a long atmospheric lifetime and it is obvious that they still contribute greatly to global warming.
We also have to consider the occurrence of what I mentioned as the ‘natural greenhouse effect’, and its main source is water vapour. Although not directly due to human activity it is augmented as a result of an increased greenhouse effect. The water vapour also adds to the thermal blanket that keeps the earth warm. As the temperature rises the air can hold more moisture, therefore there is an increase in water levels globally coinciding with global warming.
Of course there are those who choose to dispute the idea that global warming exists as a problem at all and among the many explanations there is the theory that it is all just in fact a natural occurrence, that the intensity from the sun has increased to correspond with that of global warming. But even though research in some areas is not as advanced and accurate as it could be there is undoubted evidence with the rapid increase of deforestation and intensification of agriculture to name just two examples, that show there is grounds for concern and to not address it would just be irresponsible.
There have been attempts to try to lower global warming especially concerning CFCs and the emissions of CO2 but it still remains a serious concern and it has been estimated that without any curb of the current trends the average temperature will rise by up to ¼°C every 10 years or 2½°C every century (Kemp, D 1994). Fig. 3 shows what is predicted will happen to greenhouse gas levels depending on whether we ‘carry on as we are’ or try to prevent it. (Houghton et al. 1990).
Therefore to conclude, although the ‘natural greenhouse effect’ does exist it is enhanced by the considerable role human activity has to play and although predictions have been made as to what the long term results will be, such as melting of polar ice caps which will cause coastal flooding and also a significant change in climate with more frequent tropical storms (UNFCCC), it can not be certain what positive feedbacks have already occurred.
Bibliography
Kemp, D. (1994) Global Environmental Issues: A Climatic Approach. 2nd
Edition. London: Routledge.
Houghton, J. (1994) Global Warming: The Complete Briefing. Oxford. Lion
United Nations Framework Convention on Climatic Change (UNFCCC). Official website.