5.2: The greenhouse effect

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  1. Atmospheric carbon dioxide concentrations follow an annual cycle. Describe this cycle.
    Atmospheric carbon dioxide follows an annual cycle related to the growth cycle of plants, e.g. in autumn and winter when deciduous plants lose their leaves the rate of photosynthesis decreases and atmospheric carbon dioxide levels in those areas rise, while in spring and summer high rates of photosynthesis take carbon dioxide from the air.
  2. What is the greenhouse effect?
    The greenhouse effect is the warming of the planet due to greenhouse gases in the atmosphere absorbing reflected in infra-red wavelengths (longer wavelength radiation),  reflecting some of these longer wavelengths back towards Earth and heating the atmosphere.
  3. Identify some greenhouse gases.
    Greenhouse gases are a natural part of the atmosphere and include water vapor, carbon dioxide, methane, ozone, oxides of nitrogen, and artificial chemicals, e.g. halocarbons.
  4. What has led to the enhanced greenhouse effect?
    Human activities, e.g. burning fossil fuels such as coal, oil and natural gas, clearing the land for agriculture or urban development, are increasing the concentrations of greenhouse gases in the atmosphere. This is contributing to an increased rate of warming. Humans have mainly impacted on carbon dioxide, methane and nitrous oxide levels.
  5. Explain why water and carbon dioxide are greenhouse gases while nitrogen gas (78% of atmosphere) and oxygen gas (21% of atmosphere) are not greenhouse gases.
    The greenhouse gases consist of three or more atoms. Nitrogen gas and oxygen gas are diatomic with a balanced centre of charge and mass. Thus nitrogen and oxygen tend not to interact with infra-red electromagnetic radiation to change to an excited vibrational state. The molecules of green house gases are not electrically neutral in all places and can be excited by a passing infra-red photon (or IR wave). Energy is transferred from the photon to the molecule and thus the greenhouse gases absorb the reflected heat.
  6. Outline how concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen are determined.
    Direct measurement of concentrations of atmospheric greenhouse gases began in 1958 with measurements of atmospheric carbon dioxide.  Analysis of polar ice cores provides earlier data, e.g. back 1 million years.
  7. Discuss how the concept of global warming potential (GWP) can show the relative contributions of the different gases to the greenhouse effect.
    Global warming potential (GWO) is a value which shows how, for a given change in volume of a greenhouse gas, there will be a net change in the downward flow of energy (radiative forcing) that is determined by the length of time the gas lasts in the atmosphere. For example, although water is a major greenhouse gas, it recycles quickly and water vapour does not stay in the atmosphere beyond a few days. Methane lasts around 12 years in the atmosphere, carbon dioxide lasts for several hundred years and though methane has a higher radiative force its shorter time in the amosphere reduces its GWP. Some flurocarbons have massive GWP values due to the length of time they last in the atmosphere.
  8. What is the precautionary principle?
    The precautionary principle presents the principle that a person or body must prove their action will not cause harm, before they take that action. It is a moral and political principle aimed to protect the public and the environment from actions taken when there is scientific uncertainty about all outcomes of taking a particular action.
  9. Discuss why the precautionary principle operates in the reverse of the normal situation.
    In the normal situation, those who are protecting the environment or the public have to show how an action has caused sever or irreversible harm. The precautionary principle takes the burden of proof away from those protecting an area or public place and place it on those who wish to take the action. Those who wish to take the action must prove the action will not cause harm, before they take the action.
  10. Identify some policies/protocols which incorporate the precautionary principle.
    The precautionary principle has been incorporated into several policies, e.g. the Montreal Protocol, the Rio Declaration of the United Nations, the Maastricht Treaty of the European Union, the Wingspread statement on the Precautionary Principle at Wisconsin and the Cartagena protocol on Biosafety.
  11. Outline some areas of application of the precautionary principle.
    • 1. Reducing or preventing the emission of greenhouse gases
    • 2. Introduction of transgenic species which disturbs ecological equilibrium and could threaten biodiversity
    • 3. Food safety, the effect of additives, disease potential 
    • 4. Medicine - new techniques and new drugs can have serious side effects 
    • 5. Release of toxic substances can affect human and other populations
    • 6. Resource exploitation can cause lad degradation, permanently remove habitats and alter natural ecosystems.
  12. Discuss some criticisms of the precautionary principle.
    Some critics believe the precautionary principle is impractical as all actions will have some negative aspect and the negative aspects of not taking the action are not considered. Some critics point out how the principle is often selectively applied, often for political reasons rather than scientific reasons. e.g. it is applied to new technology rather than the old technology it replaces. Some critics believe the precautionary principle can be misused by pressure groups to force a particular action that may not necessarily be the most scientifically accurate or needed action.
  13. Outline some actions that would be taken if the precautionary principle was applied to the threat of enhanced greenhouse gases.
  14. Describe the arctic ecosystem.
  15. Discuss how climate change is affecting sea ice in the arctic.
  16. Explain how a change in the extent, thickness and distribution of sea ice in the arctic affects arctic ecosystems.
  17. Discuss how climate change is affecting the permafrost in the arctic.
  18. Discuss how climate change can affect forest communities in arctic regions.
  19. Discuss how human activities, in response to rises in temperature and less ice in the arctic, can impact on arctic ecosystems.
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5.2: The greenhouse effect
2013-12-25 03:55:51

5.2: The greenhouse effect
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