Module Contact: Dr A Manning, ENV Copyright of the University of East Anglia Version 1

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1 UNIVERSITY OF EAST ANGLIA School of Environmental Sciences Main Series UG Examination THE CARBON CYCLE AND CLIMATE CHANGE ENV-3A31 Time allowed: 2 hours Answer TWO questions, ONE question from EACH section. Answer EACH question in a SEPARATE answer book. All questions have equal weighting. Provided: 2 answer books Notes are not permitted in this examination. Do not turn over until you are told to do so by the Invigilator. ENV-3A31 Module Contact: Dr A Manning, ENV Copyright of the University of East Anglia Version 1

2 2 SECTION A 1 a) Write down the mass balance equation for a species, A, in the box-model system shown above, in terms of the mass of A (MA), and the fluxes of A into and out of the box (FIN and FOUT) respectively. [20%] b) If the system above is in equilibrium, explain how you can calculate the residence time ( ) of A in this box-model system. Write down an equation for, in terms of the above quantities. [20%] c) The above diagram represents a simplified version of the pre-industrial global carbon cycle. The boxes represent the reservoirs of carbon in the atmosphere, ocean, land vegetation, soils and sediments, respectively. The numbers in each box represents the mass of carbon in that reservoir (units = Pg C). The arrows represent the fluxes of carbon between the reservoirs (units = Pg C yr -1 ) Calculate the residence time of carbon in each of the reservoirs (in units of years) and fill in the table below (in your answer book). [25%] Question 1 continued over the page

3 3 RESERVOIR Atmosphere Land vegetation Soils Ocean Sediments RESIDENCE TIME (Units = years) d) Outline a set of processes that could account for a carbon cycle-climate feedback between the atmospheric and land reservoirs. State whether it is a positive or negative feedback, and why. [15%] e) Outline the processes that control the transfer of carbon between atmospheric and sedimentary reservoirs on geologic timescales of > 10 8 years. [20%] 2 Critically discuss the evidence for our understanding of how increasing ocean acidification will influence the planktonic processes of photosynthesis, calcification and N2 fixation. Discuss the implications of this evidence for the projected plankton community structure and cycling of carbon. [100%] 3 a) What is the difference between the terms precision and accuracy? [10%] b) i) Describe briefly a typical method for calibrating a CO2 or O2 analyser. [20%] ii) Describe the general concept behind an international intercomparison programme for atmospheric measurements, and mention briefly why these programmes are important. [20%] c) Give three examples of carbon-based geo-engineering techniques being considered to mitigate climate change, and discuss a key advantage OR disadvantage of each technique. [30%] d) What is the primary reason why production of biofuels is not a practical alternative, on a large scale, in a country such as the UK? What is a key advantage AND key disadvantage of solar water heating compared to solar electricity generation? Overall, which of these two uses of solar power is recommended for the UK? [20%] TURN OVER

4 4 SECTION B 4 a) Given that the global atmospheric mole fraction of nitrous oxide (N2O) is 325 ppb, what is the global atmospheric N2O burden in Tg N? Note that the global atmosphere contains x moles of dry air and the relative molecular mass of N is 14 g mol -1. [25%] b) The atmospheric lifetime of N2O is 110 years. Given this, your answer in a) above, and assuming N2O sources and sinks are at equilibrium, what is the value for global N2O sources/sinks in units of Tg N / yr? [15%] c) What is meant by the term atmospheric CO2 airborne fraction? There are two slightly different definitions; please define both. [20%] d) According to the 2013 IPCC Working Group I report, to remain below a 2 C global average surface warming threshold, we should not emit more than 1,000 Pg C from fossil fuel burning. In the post-industrial era, we have already emitted about half (500 Pg C) of this allocation. Calculate what the atmospheric CO2 mole fraction will be after burning the total allocation of 1000 Pg C. You can assume that the average airborne fraction remains constant at its present average value of 57%, and that the global average atmospheric CO2 concentration after emission of the first 500 Pg C was 395 ppm. [40%] TURN OVER

5 5 5 Discuss in detail the atmospheric CO2 and O2/N2 data shown in the figure. Your answer should include discussion of the processes that give rise to the various features illustrated by the data. [100%] 6 a) Discuss some of the expected or hypothesised changes to the terrestrial carbon sink under a changing climate. [40%] b) The carbon sinks in the Southern Ocean and North Atlantic Ocean have reportedly been undergoing changes in recent years. Discuss these findings as they have been reported in the literature. [35%] c) List three key differences between the contemporary ocean carbon sink and the contemporary terrestrial carbon sink. [25%] END OF PAPER