There is no doubt that the Earth's climate has become warmer over the twentieth century. There is still the ongoing debate as to whether these temperature increases are caused by natural variations or by human activity. Different groups of UK scientists have investigated both these variations. Mike Lockwood and colleagues from The Rutherford Appleton Laboratory (RAL) argue that the Sun's magnetic field has doubled over the century, and that this natural "solar forcing" has affected the climate (Nature 399-437). Where as Simon Tett and colleagues from the UK's Meteorological Office in Reading argue that while solar forcing has contributed to climate change, human activity has been responsible for the temperature changes over the past 50 years (Nature Journal 11 June 1999).
If this is the case and climate variations and change are caused by external forcings they may well be predictable and therefore able to tell us to what extent human activities have influenced these changes, particularly on a global scale because human activities, such as the emission of greenhouse gases or land-use change, do result in external forcing, therefore it is fair to say that the large-scale aspects of human-induced climate change are also partly predictable, potentially giving us the ability to calculate the extent to which climate change is caused by individual activities. (The Gaia Atlas 1995). Unfortunately the ability to do so is reduced because it is impossible to accurately predict population changes, economic changes, technological advancements, and other relevant characteristics of future human activity
The influence of human activities is much more complex than warming over the entire surface of the planet.Climate changes caused by human activities including the burning of fossil fuels; coal, oil, and natural gas as well as deforestation. These are superimposed on, and to some extent hidden by, natural climate variations. Natural changes in climate result from interactions such as those between the atmosphere and ocean, referred to as internal factors, and from external causes, such as variations in the sun's energy output and in the amount of material injected into the upper atmosphere by explosive volcanic eruptions.(The Gaia Atlas 1995)
The Industrial Revolution in the 19th century saw the large-scale use of fossil fuels for industrial activities. These industries created jobs and over the years, people moved from rural areas to the cities. More and more land that was covered with vegetation has been cleared to make way for houses. Natural resources are being used extensively for construction, industry, transport, and consumption. Consumerism has increased by leaps and bounds, creating mountains of waste. Also, our population has increased to an incredible extent, it now stands at figures estimated to be well over 5 billion and still increasing exponentially. All this has contributed to a rise in greenhouse gases in the atmosphere. Fossil fuels such as oil, coal and natural gas supply most of the energy needed to run vehicles as well as generating electricity for industries and households. It also produces nitrogen oxides and carbon monoxide which aren’t greenhouse gases but do have an influence on the chemical cycles in the atmosphere that produce or destroy greenhouse gases. Carbon dioxide is undoubtedly, the most important greenhouse gas in the atmosphere. Changes in land use pattern, deforestation, land clearing, agriculture, and other activities have all led to a rise in the emission of carbon dioxide. The UK is one of the very few countries in which emissions fell between 1990 and 2000. The only growing emissions sector is transport which is dominated by road transport. Air transport is, also, growing even faster at 5% per year, representing annual growth in emissions of 3%. Source: (United Nations framework Convention on Climate Change).
Methane is another important greenhouse gas in the atmosphere. A quarter of all methane emissions are said to come from domesticated animals. These animals produce methane during the cud-chewing process. Methane is also released from rice or paddy fields that are flooded during the sowing and maturing periods. When soil is covered with water it becomes anaerobic or lacking in oxygen. Under such conditions, methane-producing bacteria and other organisms decompose organic matter in the soil to form methane. Methane is also emitted from landfills and other waste dumps. If the waste is put into an or burnt in the open, carbon dioxide is emitted. Methane is also emitted during the process of oil drilling and coal mining. Methane has a direct influence on the question because as a result of human activity there will be increase greenhouse gases which will influence climatic change because of positive forcing.
The record below of temperature and atmospheric CO2 over the past 400,000, preserved in the ‘Vostok Ice Core’, shows the temperature record from the in blue together with CO2 levels in red, The vertical line on the right represents the change in CO2 associated with the industrial revolution .this gives specific proof that human activity is currently having an effect on climate that hasn’t occurred previously in Earths history.
Paleoclimate; CO2 / Temperature over the Past 400 Thousand years
There have been a series of large fluctuations in temperature (the ), accompanied by large changes in atmospheric CO2. It is thought that these large temperature fluctuations are triggered by Milankovitch cycles, (Mike Lockwood and colleagues from RAL). These cycles are not enough to explain the changes in temperature. The full explanation seems to be that the small change in temperature caused by the changing orbit are amplified by both natural and anthropogenic processes on earth. This cause CO2 to be released from the oceans and the biosphere, causing an increased greenhouse effect that is now increasing at an even greater rate because of human activity (New Scientist, 29 January, 2000)
Climate forcing results when an external factor imposes a change on the planet's heat balance. Aerosols produced by human activity can exert both positive and negative forcing, but it is believed that their overall effect is negative (positive forcing adds heat and tends to warm the climate, where as negative forcing removes heat and tends to cool the climate. The particles reflect sunlight back into space and also modify the properties of clouds, causing them to reflect more sunlight back into space. These patchy effects add up to a global impact that tends to offset climate warming caused by human-produced greenhouse gases, such as carbon dioxide. However, increasing concentrations of greenhouse gases in the atmosphere are leading to rapid changes in climate over fairly short periods and, if left unchecked climate change will increase indefinitely, exponentially and potentially catastrophically. The Earth as a whole could warm as result of increased greenhouse gas emissions, this alone could cause parts of it to cool e.g.; the North Atlantic thermohaline circulation (Gulf Stream) may divert south as a result of warming the Arctic, which would remove its heating effect from the UK and Northern Europe in general. This region might thus cool considerably.
This means that although the common perception of climate change is that of increased green house gases and global warming, there is the potential for there to be increased variations, greater aerosol levels and differences in climatic conditions as can be seen from the example above. Climate is a very complicated and finely balanced system encompassing many factors, if the above arguments were correct then Earth could be looking at a future of global cooling rather than warming, but what we can be sure of is the fact that we are most defiantly looking at a future of continued climatic unrest. Finally the extent to which human activity is responsible for climate change is very difficult to answer accurately. Scientists believe that it is involved to an extent however they are uncertain as to what extent this is, this is because there is far too little data for far too small a time span to judge to what extent human activities are influencing our climate.
We shall only learn the true extent humans have had on Earth’s climate over the coming decades as knowledge and understanding increases, until then the only certainty is that climate change is occurring.
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