Global warming first emerged as a cause of global concern in the 1980’s, a result of the apparent rise in global temperatures, believed to be due to human activities, such as burning of fossil fuels and destruction of forests. There is debate as to whether global warming exists, as it could merely be another example of changes in temperature the world has seen over millions of years.
It is important to distinguish global warming from the greenhouse effect. The greenhouse effect is a naturally occurring phenomenon, without which human life would not exist on the earth.
Many greenhouses gases exist naturally, and it is human actions that are increasing their concentrations within the lower atmosphere. It is believed that as the amount of greenhouse gases in the atmosphere increases, the amount of long-wave (infra-red) radiation in the lower atmosphere also increases, thus raising temperatures.
The table below outlines the major sources of greenhouses gases:
|Gas:||Source:||Use:||Way it increases global warming:|
|Water vapour||Oceans, lakes, rivers, reservoirs. Humans have little impact upon levels.||Absorbs limited outgoing radiation.||Water vapour and clouds are responsible for nearly 98% of the natural greenhouse effect.|
|Carbon dioxide||Burning of fossil fuels, and forests, breathing animals, less produced by southern hemisphere (less land).||Absorption of long wave radiation.||Approximately 50%.|
|Methane (CH4)||Much from break down of organic matter by bacteria (rice paddy fields) cows, swamps marshes.||As above.||Approximately 18%.|
|Ozone||Naturally from some oxygen atoms. Ozone in the troposphere is due to chemical reactions between sunlight and agents of pollution.||Filters short wave UV radiation.||Difficult to estimate.|
|CFCs||Fridges and aerosols.||25%, but increasing due to ability to survive within the atmosphere for 100 years.|
|Nitrous oxide||Nitrate fertilisers, transport and power stations (combustion).||Absorption of long wave radiation.||Approximately 6%.|
It is important to remember that whilst most publicity concentrates on the negative side of global warming it will undoubtedly have some positive consequences.
|Impact on:||Effect:||Consequence (-):||Consequence (+):|
|Health||Malaria and cholera increase, due to temperature increase.||More money needed to fight disease, strain on medical services, rise in death rate.|
|Vegetation||Shifting flora and fauna to different areas. Extinction of some species.||Spread of pests and disease, alteration in crop yields, may increase food shortages.||Canadian Prairies could become major wheat growing belt. Areas able to grow different crops, for example, citrus fruits in the UK.|
|Weather||More extreme climates in inland locations. More frequent and devastating hurricanes.||Unknown at present.||Unknown at present.|
|Ocean||Sea temperatures increase, sea levels rise, shift in ocean currents.||Changes in number of fish stocks and their location will impact the fish industry.||Increase in fish stocks in certain areas.|
|Landscape||Reduced snow cover in some areas. Glaciers melt in Antarctica.||Rise in sea levels.||Extended summer season in some landscapes due to higher temperatures, increasing revenue.|
|Hydrology||Reduction of wetland areas, as precipitation is reduced. In some places river flooding may increase.||Great pressure on water supplies. Problems for HEP schemes and irrigation.||Increased awareness of water conservation measures, less water wastage.|
|Population||Reduction of areas suitable for human habitation, for example. lowland Bangladesh.||Increased population densities increase possibility of disease and malnutrition.||Forced movement of population from densely populated coastal areas, to interior locations.|
|Climate||Location of jet stream may alter. Depressions may shift south, causing them to be more intense.||Better forecasting needed to warn people of approaching storms. Insurance premiums will increase.||More accurate weather forecasting developed.|
Predicted Effects of Global Warming for the year 2100
This diagram shows the likely increase of temperatures from the current levels.