5.2 Greenhouse effect - IBDPBiology-Dnl

Pp 122 - 130

Assessment Statements  5.2.1 Draw and label a diagram of the carbon cycle to show  

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the processes involved. 5.2.2 Analyse the changes in concentration of atmospheric carbon dioxide using historical records. 5.2.3 Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect. 5.2.4 Outline the precautionary principle. 5.2.5 Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect. 5.2.6 Outline the consequences of a global temperature rise on arctic ecosystems.

Draw and label a diagram of the carbon cycle to show the processes involved.  You must be able to draw

and label the complete carbon cycle.  The details of the carbon cycle should include the interaction of living organisms and the biosphere through the processes of photosynthesis, cell respiration, fossilization and combustion.

Roles of living organisms in the carbon cycle  plants fix carbon dioxide during photosynthesis  producing carbon compounds such as sugars  carbon compounds in plants are eaten by primary consumers (herbivores)  carbon compounds in primary consumers are eaten by secondary consumers & passed along the food chain  carbon compounds are digested & absorbed by consumers  carbon dioxide is released by cell respiration in plants & animals  plants & animals die and are decomposed by saprotrophic bacteria & fungi  carbon dioxide released by cell respiration in bacteria & fungi (decomposers)  enzymes are released to digest carbon compounds in organic matter  forest fires (combustion) releases carbon dioxide  humans burn fossil fuels adding carbon dioxide to the atmosphere

Changes in atmospheric carbon dioxide concentration over time

 increase in machinery & industrialization has caused rise in levels of atmospheric carbon dioxide concentrations since the 1880’s.  human activities such as the burning of

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fossil fuels & transportation have all contributed to the increase. scientists estimate the levels have increased by over 25% as compared to the levels before industrialization. scientists take measurements by looking at the concentration of carbon dioxide in bubbles of air trapped in Antarctic ice at different dates. this data shows that before the 1880’s the carbon dioxide concentrations remained fairly steady at about 270 ppm for about 2000 years. concentration begins rising after 1880 and is now more than 100 ppm higher than in 1880.

Global trend in Greenhouse Gases

Relationship between the rise in the concentration of atmospheric CO2 & the enhanced greenhouse effect  CO2 is a greenhouse gas  increases in CO2 enhance the greenhouse effect  greenhouse effect is a natural phenomenon but

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not its increase Earth receives short wave radiation from the sun These waves reflected from Earth as longer wave radiation, infra red or heat CO2 (greenhouse gases) absorb longer wave radiation, infra red & heat global warming happened during same period as the rise in CO2 CO2 concentration correlated positively with global temperature this causal link between CO2 concentration & global temperature is accepted by most scientists However, there is no proof that man-made increases in CO2 have caused global warming

Relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect.  water vapour, carbon dioxide,

methane & oxides of nitrogen are greenhouse gases which occur naturally in low concentration in the atmosphere  human activity has increased the normal level of these gases in the atmosphere in recent years  incoming shorter wave radiation from the Sun is re-radiated as longer wave radiation  mainly in the form of heat which is captured by the greenhouse gases

 this trapping of radiations

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increases the atmospheric temperature at a higher rate than normal creating a positive imbalance in global temperature which threatens ecosystems, climatic patterns & ocean patterns Earth’s history had many fluctuations in greenhouse gases levels & global temperature some scientists are skeptical about enhanced greenhouse effect

The enhanced greenhouse effect

Causes and consequences of the enhanced greenhouse effect  burning of fossil fuels such coal,

 global warming causes melting

oil & gas releases carbon dioxide  deforestation & loss of ecosystems reduces uptake carbon dioxide by plants  methane is emitted from cattle, melting permafrost & decomposing waste at dump sites  accumulation of greenhouse gases cause heating of the atmosphere leading to global warming

of ice caps, glaciers, permafrost, sea level rise, flooding & droughts  global warming also causes changes in ocean currents, produce more powerful hurricanes & extreme weather conditions  there is also changes in species distributions, migration patterns, increased decomposition rates, increases in pest & pathogen species, loss of ice habitats

The precautionary principle  those proposing something must prove that      

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it causes no harm before they start to do it objectors do not have to prove that there will be harm activities that threaten the environment are banned trials (tests) must be done first before changes are made precautionary principle is applied when possible consequences are severe precautionary principle should be used in the case of global warming action should be taken to reduce CO2 emissions before proved it is the cause of global warming where there are threats of serious or irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation

Precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect  Supporters of the precautionary

principle advocate for action now to reduce greenhouse gases before it is too late. Anyone producing greenhouse gases should be required to prove that those gases will not have harmful effects.  Those on the opposite side of this issue such as farmers, manufacturers and transportation providers, argue that if there is no proof that greenhouse gases are the cause then they should not have to invest money in new technologies to reduce such gases.

 The global consequence is that unless all

countries take precautionary measures, which can be more expensive than the traditional methods, the polluting competitors will offer products at a reduced price and drive the ecologically conscious companies out of business.  A global effort to support the ecologically friendly companies could drive their less ecologically friendly competitors out of business.  Most scientists believe that the old saying “an ounce of prevention is worth a pound of cure” is relevant here. A more sustainable future is something worth investing in.  There are also many ethical issues at play here and the future generations to consider. The time for more sustainable development is here. Humans are not only impacting each other but all organisms within the biosphere.

Consequences of a global temperature rise on arctic ecosystems  Global warming seems to have the

largest & most obvious effects right now on the arctic ecosystems.  The Arctic includes the areas of North America, Greenland, Iceland, Norway and Russia which are north of the Arctic Circle.  It also includes Arctic Ocean which is covered by a huge mass of ice surrounding the North Pole.  Over the century there have been many changes in the ecosystems in this area noted by scientists and the people who live there.

 changes in the arctic ecosystems include the following:  increased amounts of ice melting each year.  melting of glaciers & breaking of polar ice

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sheets into icebergs that will eventually melt the Arctic ice cap may disappear altogether. permafrost will begin melting during the summer which means the rate of decomposition will increase resulting in the release of more carbon dioxide. species will have to move north which will alter food chains and disrupt animals in the higher trophic levels. many marine species could face extinction due to their sensitivity to temperature changes in the ocean. Polar bears & other ice dwelling organisms will lose their habitat where they feed and breed. warmer temperatures will increase the threat of pests and disease such as malaria. the rise in sea levels will flood low-lying areas. extreme weather events (storms) will become more frequent.