5.2: The greenhouse effect

Question 1

Draw and label a diagram of the carbon cycle to show the processes involved:

Answer 1

There are a number of processes by which carbon can be cycled between these pools:

• Photosynthesis: Atmospheric carbon dioxide is removed and fixed as organic compounds (e.g. sugars)
• Feeding: In which organic carbon is moved from one trophic level to the next in a food chain
• Respiration: All organisms (including plants) metabolise organic compounds for energy, releasing carbon dioxide as a by-product
• Fossilization: In which carbon from partially decomposed dead organisms becomes trapped in sediment as coal, oil and gas (fossil fuels)
• Combustion: During the burning of fossil fuels and biomass
  In oceans, carbon can be reversibly trapped and stored as limestone (storage happens more readily at low temperatures)

Question 2

Analyse the changes in concentration of atmospheric carbon dioxide using historical records:

Answer 2

Recent Trends:

• Atmospheric carbon dioxide concentrations have been measured at the Mauna Loa atmospheric observatory in Hawaii from 1958 and has since been measured at a number of different locations globally
• The data shows that there is an annual cycle in CO2 concentrations which may be attributable to seasonal factors, but when data from the two hemispheres is incorporated, it suggests that atmospheric CO2 levels have risen steadily in the past 30 years

Long Term Estimates:

• Carbon dioxide concentration changes over a long period of time have been determined by a variety of sources, including analysing the gases trapped in ice (and thus providing a historical snapshot of atmospheric concentrations)
• Data taken from the Vostok ice core in Antarctica shows that fluctuating cycles of CO2 concentrations over thousands of years appear to correlate with global warm ages and ice ages
• It is compelling to note that CO2 levels appear to be currently higher than at any time in the last 400,000 years

Question 3

Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.

Answer 3

1. The incoming radiation from the sun is short wave ultraviolet and visible radiation.
2. Some of this radiation is absorbed by the earths atmosphere.
3. Some of the radiation is reflected back into space by the earths surface.
4. The radiation which is reflected back into space is infrared radiation and has a longer wavelength.
5. The greenhouse gases in the atmosphere absorbe some of this infrared radiation and re-reflect it back towards the earth.
6. This causes the green house effect and results in an increase in average mean temperatures on earth.
7. A rise in greenhouse gases results in an increase of the green house effect which can be disastrous for the planet.

Question 4

Outline the precautionary principle:

Answer 4

The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead.

Question 5

Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect.

Answer 5

There is strong evidence that shows that green house gases are causing global warming. This is very worrying as global warming has so many consequences on ecosystems. If nothing is done, and the green house gases are in fact causing the enhanced green house effect, by the time we realize it, it will probably be too late and result in catastrophic consequences. So even though there is no proof for global warming, the strong evidence suggesting that it is linked with an increase in green house gases is something we can not ignore. Global warming is a global problem. It affects everyone. For these reasons, the precautionary principle should be followed. Anyone supporting the notion that we can continue to emit same amounts or more of the green house gases should have to provide evidence that it will not cause a damaging increase in the green house effect.

Question 6

Outline the consequences of a global temperature rise on arctic systems:

Answer 6

• Changes in arctic conditions (reduced permafrost, diminished sea ice cover, loss of tundra to coniferous forests)
• Rising sea levels
• Expansion of temperate species increasing competition with native species (e.g. red fox vs arctic fox)
• Decomposition of detritus previously trapped in ice will significantly increase greenhouse gas levels (potentially exacerbating temperature changes)
• Increased spread of pest species and pathogens (threatening local wildlife)
• Behavioural changes in native species (e.g. hibernation patterns of polar bears, migration of birds and fish, seasonal blooms of oceanic algae)
• Loss of habitat (e.g. early spring rains may wash away seal dens)
• Extinction and resultant loss of biodiversity as food chains are disrupted