November 2012J. CloyEXAM QUESTIONS AND MODEL ANSWERS

ATMOSPHERIC QUALITY AND GLOBAL CHANGE

PART 1 – ESSAY QUESTION

Answer ONE of the essay questions below

1. Using examples of existing emission inventories, describe the main purpose of emission inventories, what they contain and the methodology used to compile emission inventories. (50 marks)

Model Answer Introduction, inventories on national, international scale, NAEI, IPCC, EDGAR, …

Regulatory and reporting purpose, modelling, trend development

Source sectors and pollutants (air pollutants, greenhouse gases)

Activities and emission factors, bottom-up calculations

Measured vs. calculated

Conclusions

2. Using relevant examples, explain how environmental archives have been used to reconstruct past climate conditions and atmospheric air quality. Describe advantages and disadvantages associated with the use of environmental archives.

(50 marks)

Model Answer Introduction explaining how ice, moss, bark, peat bogs and lake sediments are

used as archives of environmental change.

Climate change reconstruction – e.g. vostok ice core (Ice Age maximums and the warm interglacials occur within a regular cyclic pattern), tree rings in fossilised trees, indicators of humification in peat bogs.

Atmospheric air quality – e.g. atmospheric metal deposition records in ice, peat, lake sediments, bark and moss.

Advantages: Ice - virtually no chemical transformation occurs after deposition has taken place. Moss, bark, tree rings – age is known so don’t need to use radiometric dating and also widespread globally (lake sediments also widespread).

Disadvantages – ice and peat limited to certain geographical locations. Chemical records in environmental archives such as peat and lake sediments can be disturbed by bioturbation, resuspension, chemical remobilisation. Peat and sediment cores need to be intact/uncompacted and free from disturbance e.g. core collection issues (also need undisturbed sampling sites). Ice records need to be preserved carefully and need to avoid contamination (very low concs).

Conclusions

3. Explain how modelling can be used to predict the impacts of climate change in terrestrial environments. Your answer should include an assessment of the strengths and weaknesses of different modelling approaches. (50 marks)

Model AnswerDifferent modelling approaches should be described including empirical and process-based models. In-class examples of these were provided which included that the DNDC model for describing trace gas emissions from soil and carbon footprinting models is an example of empirical modelling approaches. Other models of terrestrial systems could be described. The strength of the process-based model is its ability to predict responses to a range of complex interacting factors within the environment, however parameterisation of such models can be difficult and demand large datasets. Empirically-based models tend to be simpler to parameterise but are often less capable of predicting outcomes in complex and interactive environments.

PART 2- SHORT ANSWER QUESTIONS

Answer FIVE questions only

1. Describe the process and main air pollutants contributing to acidification and eutrophication of soils, ecosystems and surface waters. (10 marks)

Model Answer Gases are removed from the atmosphere by dry and wet deposition,

accumulating in soils and surface waters. Soil, freshwater and oceanic acidification by protons decreases pH and puts

ecosystems at risk. High nutrient loading causes eutrophication in soils and surface waters and

affects species composition. SO2, NOx and NH3 are the main contributors to soil acidification, the nitrogen in

NOx and NH3 causes eutrophication.

2. Describe the radiative balance that is present at the top of Earth's atmosphere when the planetary temperature is stable. Explain what is meant by "radiative

forcing" and describe the basic mechanisms of radiative forcing by anthropogenic aerosols in the troposphere. (10 marks)

Model AnswerFor the Earth to have a relatively constant, stable temperature there must be no net heat flow into our out of the climate system*. Sunlight is the dominant heat input*, amounting to 342 W/m2 on average at the top of the atmosphere*. About 30% of this sunlight, however, is reflected, both by the atmosphere and surface, back out to space (albedo)*. The emission of infrared (thermal) radiation by Earth must balance this net input, i.e., must equal on average 0.7x343 W/m2*. [Instead of numbers, students may refer to equations to obtain the equivalent marks: S(1-a)=sT^4 is then the radiative balance.] If a factor perturbs this balance, the amount of imbalance caused, prior to any climate adjustment to the forcing, is the radiative forcing*. RF is therefore a way of putting all climate perturbations on a common scale, equivalent to a change in sunlight that changes the radiative balance by the same amount*. Aerosols reflect sunlight, and therefore increase albedo, and exert a negative radiative forcing*. (They have a small greenhouse effect also, but we didn't discuss this in class.) Indirectly, they may brighten clouds by facilitating smaller droplet sizes, which is an indirect negative RF*. Particularly the latter indirect effect is the greatest uncertainty in radiative forcing relative to pre-industrial conditions*.

each * is a mark out of 10 available

3. What is meant by the term “global warming potential”? If a landscape produces 7,000 000 tonnes/yr of CO2 emissions, 400 000 tonnes/yr of CH4 emissions, and 700 tonnes/yr of N2O emissions, what is its Global Warming Potential in CO2e?

(10 marks)

Model AnswerGlobal warming potential: an index defining the radiative effect over a given time period of a gas relative to that of CO2

CalculationTotal CO2-eq = tonnes CO2(GWP[CO2]) + tonnes CH4(GWP[CH4]) + tonnes N2O(GWP[N2O])= 7,000,000 (1) + 400,000 (25) + 700 (298) = 17,208,600 metric tonnes CO2-eq

[GWPs CO2 = 1, N2O=298, CH4=25]

4. Solar energy arrives at the earth from the sun at 15,000 times the rate we use it. Discuss how latitude, season, time of day and atmospheric factors affect our

ability to capture solar energy and use it to meet the energy demands of mankind. (10 marks)

Model AnswerSolar energy is not always available where we need it and when we need it. It is a very diffuse source of energy and must be captured and concentrated. The intensity of solar radiation at any point on the planet depends on the distance from the equator, the time of year and the time of day. When the sun is low in the sky the radiation arriving from the sun is spread over a larger area. It also has further to travel through the atmosphere before arriving on the earth’s surface. A collector of a given size will therefore collect less energy than when the sun is directly overhead. The intensity of solar radiation arriving at a collector also depends upon the amount absorbed by cloud cover, atmospheric pollution and physical obstructions and on the amount reflected by surrounding land/sea and clouds.

5. Describe the layers of the earth’s atmosphere and include in your answer a brief description of the physical properties of each layer. (10 marks)

Model AnswerThe troposphere extends from the earth's surface to an average of 12 km. The pressure ranges from 1000 to 200 millibarsThe temperature generally decreases with increasing height up to the tropopause (top of the troposphere). The layer ends at the point where temperature no longer varies with height. This area, known as the tropopause, marks the transition to the stratosphere. The stratosphere extends from 12 km – 46 The air is much drier above the tropopause, in the stratosphere.

6. Explain why the Kyoto protocol was adopted and what it aims to achieve in terms of greenhouse gas emissions from industrialized countries in the reporting period between 2008-2012?

(5 marks)

and

Describe the three market-based Kyoto mechanisms. (5 marks)

Model AnswerPart 1.The Kyoto Protocol was adopted at the third Conference of the Parties to the UNFCCC (COP 3) in Kyoto, Japan, on 11 December 1997. The Protocol shares the objective and institutions of the Convention. The major distinction between the two, however, is that while the Convention encouraged industrialized countries to stabilize GHG emissions, the Protocol commits them to do so. The near-term challenge for industrialized countries is to achieve the Kyoto targets, i.e., a reduction in overall emissions of six greenhouse gases (or families of gases) by an average of 5.2 per cent below 1990 levels in 2008 – 2012.

Part 2.Countries with commitments under the Kyoto Protocol to limit or reduce greenhouse gas emissions must meet their targets primarily through national measures. As an additional means of meeting these targets, the Kyoto Protocol introduced three market-based mechanisms, thereby creating what is now known as the “carbon market.” The three Kyoto mechanisms are: Emissions Trading (known as .the carbon market), the Clean Development Mechanism (CDM) and Joint Implementation (JI). The carbon market spawned by these mechanisms is a key tool in reducing emissions worldwide. It was worth 30 billion USD in 2006 which increased to 176 billion USD in 2011.

7. Explain the importance of the oceanic carbon sink relative to other carbon sinks in the Global carbon cycle? (5 marks)

and

What processes are responsible for driving the ocean carbon cycle? (5 marks)

Model AnswerPart 1.The carbon cycle can be viewed as a set of reservoirs (four main reservoirs in the global carbon cycle – atmosphere, oceans, reserves of fossil fuels, terrestrial ecosystems (vegetation and soils), each of which holds a form of carbon (such as calcium carbonate in rocks or CO2 in the atmosphere), with carbon moving at various natural rates of transfer between these reservoirs. The total amount of carbon in the system is fixed by very long-term geophysical processes such as the weathering of rock. Human actions that affect the carbon cycle, such as fossil fuel combustion and deforestation, change the rate at which carbon moves between important reservoirs. C sinks are found both on land and in the oceans,

and evidence suggests that the land based sink is strengthening. Oceans dominate the global carbon cycle over time scales of decades to millennia. Oceans are continuing to sequester C but could eventually reach saturation point.

Part 2.Ocean sink driven by the solubility pump (dissolution of CO2, increases with increasing atmospheric CO2 concentration) and biological pump (most active in warmer productive waters). Solubility pump - CO2 is taken up in the cold waters of high latitudes and transported towards the equator, and the biological pump, whereby phytoplankton remove carbon from the upper ocean and transport a significant fraction of this to the deeper ocean. Higher concentrations of CO2

enhance the solubility pump although higher temperatures may partially offset this and may also increase ocean stratification which, in turn, slows the transfer of carbon to the deep ocean. The biological pump is also sensitive to nutrient transport from terrestrial systems, thus the ocean and terrestrial carbon cycles are intimately linked. The overall controlling mechanisms probably involve physical and chemical reorganization of the ocean and changes in nutrient inventories.

See diagram on J.Cloy Week 2 lecture slide 17.