Topic 9

Topic 9

The Greenhouse Effect
1. Greenhouse gases such as water vapour, methane and carbon dioxide stop heat escaping from the Earth into space. An increased greenhouse effect can lead to global warming and climate change.
  1. Human activities are causing the release of large amounts of carbon dioxide. These activities include: deforestation - cutting down trees for fuel, farms, buildings and roads increased use of energy (and so an increased use of fossil fuels). As the percentage of carbon dioxide in the atmosphere has increased, so in general has the Earth’s mean temperature.
2. Some sources of greenhouse gases are natural and some are man-made
  1. Natural gases are made by- Decomposing plant material,Evaporation from oceans, lakes and rivers and Respiration by plants and animals, forest fires, volcanoes
    1. It is not just human activities that can affect weather patterns and climate. Ash and gases released by volcanic eruptions also go into the atmosphere. They reflect radiation from the Sun back into space, causing cooling. This, and other effects, can make it difficult for scientists who study the atmosphere and global warming.
  2. Man made sources of gas are made by- Rice paddy fields, cattle, coal mines,Burning hydrocarbon fuels and Making cement, burning fossil fuels
3. This Diagram shows shows how the Greenhouse Effect Works
4. Increased global warming will lead to climate change – changes in the average weather experienced over 30 years or more. Climate change may make it impossible to grow certain food crops in some regions. Melting polar ice, and the thermal expansion of sea water, could cause rising sea levels and the flooding of low-lying land.
Air Pollution
1. The atmosphere surrounding the Earth is a mixture of gases. In some places, human activities have added other gases to the atmosphere, which are called pollutants.
2. The gases in dry air
  1. Nitrogen 78 per cent
  2. Oxygen 21 per cent
  3. Argon 1 per cent
3. The atmosphere also contains a small but important amount of carbon dioxide, approximately 0.04 per cent, and tiny amounts of a few other gases.
  1. In addition to these gases, the air also contains water vapour. The percentage of water vapour varies from one location to another, and according to weather conditions
    1. The burning of fuels releases a large amount of carbon dioxide into the atmosphere. This is thought to cause global warming.
The Early Athmosphere
1. Scientists believe that the Earth was formed about 4.5 billion years ago. Its early atmosphere was probably formed from the gases given out by volcanoes.
  1. It is believed that there was intense volcanic activity for the first billion years of the Earth's existence.
2. The early atmosphere was probably mostly carbon dioxide, with little or no oxygen
  1. There were smaller proportions of water vapour, ammonia and methane
    1. As the Earth cooled down, most of the water vapour condensed and formed the oceans.
    2. It is thought that the atmospheres of Mars and Venus today, which contain mostly carbon dioxide, are similar to the early atmosphere of the Earth.
3. volcanoes release high quantities of carbon dioxide. Iron-based compounds are present in very old rocks that could only have formed if there was little or no oxygen at the time.

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