5.2 The Greenhouse Effect

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

There are four main 'pools' of carbon in the environment:

• Atmosphere                        • Biosphere                        • Sediments                        • Ocean

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)

The Carbon Cycle

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

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

Recent and Long-term Changes in Carbon Dioxide Concentration

                   Mauna Loa CO2 Data  (last 50 years)                                                      Vostok Ice Core Data - CO2 vs Temperature (last 400,000 years)    


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

The greenhouse effect is a natural process whereby the earth's atmosphere behaves like a greenhouse to create the moderate temperatures to which life on earth has adapted (without the greenhouse effect, temperatures would drop significantly every night)

  • The incoming radiation from the sun is short-wave ultraviolet and visible radiation
  • Some of this radiation is reflected by the earth's surface back into space as long-wave infrared radiation
  • Greenhouse gases absorb this infrared radiation and re-reflect it back to the earth as heat, resulting in increased temperatures (the greenhouse effect)

The Greenhouse Effect

The enhanced greenhouse effect refers to the suggested link between the increase in greenhouse gas emissions by man and changes in global temperatures and climate conditions

The main greenhouse gases are water vapour, carbon dioxide (CO2), methane (CH4) and oxides of nitrogen (e.g. NO2)

While these gases occur naturally, man is increasing greenhouse gas emissions via a number of processes, including:

• Deforestation (less trees)                       • Industrialisation (more combustion)                        • Increased farming / agriculture (more methane)

With increases in greenhous gas emission, it is thought that the atmospheric temperature may increase and threaten the viability of certain ecosystems, although this link is still being debated

5.2.4  Outline the precautionary principle

The precautionary principle states that when a human-induced activity raises a significant threat of harm to the environment or human health, then precautionary measures should be taken even if there is no scientific consensus regarding cause and effect

  • Because the global climate is a complex phenomena with many emergent properties, and is based on time frames well beyond human lifespans, it is arguably impossible to provide appropriate scientific evidence for enhanced global warming before consequences escalate to potentially dire levels
  • According to the precautionary principle, the onus falls on those contributing to the enhanced greenhouse effect to either reduce their input or demonstrate their actions do not cause harm - this makes it the responsibility of governments, industries, communities and even the individual
  • The precautionary principle is the reverse of previous historical practices whereby the burden of proof was on the individual advocating action

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

Arguments for Action

  • Risks of inaction are potentially severe, including increased frequency of severe weather conditions (e.g. droughts, floods) and rising sea levels
  • Higher temperatures will increase the spread of vector-borne diseases
  • Loss of habitat will result in the extinction of some species, resulting in a loss of biodiversity
  • Changes in global temperature may affect food production, resulting in famine in certain regions
  • The effects of increased temperatures (e.g. rising sea levels) could destroy certain industries which countries rely on, leading to poverty
  • All of these consequences could place a far greater economic burden on countries than if action were taken now
  • These factors would increase competition for available resources, potentially leading to increased international tensions

Arguments for Inaction

  • Cutting greenhouse emissions may delay economic growth in developing countries, increasing poverty in these regions
  • Very difficult to police - what level of action would be considered sufficient on a global scale in the current absence of scientific consensus?
  • Boycotting trade with non-compliant countries could negatively effect economies and create international tensions
  • No guarantee that human intervention will be sufficient to alter global climate patterns
  • Money and industrial practices that may be used to develop future technologies may be lost due to restrictions imposed by carbon reduction schemes
  • Carbon reduction schemes will likely result in significant job losses from key industries, retraining workers will require significant time and money

5.2.6  Outline the consequences of a global temperature rise on arctic ecosystems

Increases in global temperature pose a credible threat to arctic ecosystems, including:

  • 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