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1.1 Climate Change ​​



There have been evident signs of warming in the global climate, with observations of increases in average air and ocean temperatures, rising sea levels, as well as widespread melting of snow and ice. These phenomena are depicted in Figure 1 , which illustrates the observed changes in global average surface temperature, sea levels and snow cover.





















































Figure 1. Observed changes in (a) global average surface temperature; (b) global average sea level from tide gauge (blue) and satellite (red) data; and (c) Northern Hemisphere snow cover for March-April. All differences are relative to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. ​IPCC, 2007



These changes have resulted in significant impacts on the natural environment and on human activities. For example, there has been significant biodiversity loss through species extinction in tropical areas in Latin America, more frequent flooding in coastal countries like Bangladesh and Mauritius as well as more extreme drought conditions in Australia.  These conditions will only further be exacerbated with increased warming.



The increase in concentration of greenhouse gases is the main contributing factor to the observed increase in temperatures, with CO2 being the anthropogenic emission with the largest contribution. (IPCC, 2007). IPCC models indicate that there is a likely increase in the global temperature of 1.1-6.4K this century and a global average sea level rise of 0.18-0.59m. (IPCC, 2000). Therefore, the IPCC recommends the implementation of policies to create incentives to reduce climate change. 



There is a potential increase in global energy demand of more than 45% by 2030 (IEA, 2008),  and given that our current infrastructure is still heavily dependent on fossil fuels, it is likely that the use of fossil fuels will continue well into the future. An estimated 28 Gt CO2/year (IEA, 2008) is emitted from the use of fossil fuels, hence climate mitigation strategies should account for the emission of CO2 from fossil fuel use.

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1.2 Carbon Capture and Sequestration

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Carbon Capture and Sequestration is a set of technologies that aim to reduce the impact on climate change by capturing the CO2 emitted from fossil fuel combustion, and subsequently compressing it and injecting it into geological strata. According to the wedge theory by Socolow and Pacala, one of the possible "wedges"  to stabilize carbon emissions involves the deployment of carbon capture and storage (Socolow and Pacala, 2006)​.

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​However, problems with CCS include the high cost and energy penalty associated with the CO2 capture step. Currently, a close-to-market technology for CO2 capture is post-combustion scrubbing of flue gases using amine-based solvents such as MEA. However, there are numerous problems with this technology. These include solvent degradation at high temperatures and irreversible reactions with SO2 and NO2 in the flue gas to form corrosive salts. (Blamey et. Al, 2010). Another close-to-market technology is oxyfuel combustion , whereby coal is burned in a mixture of pure O2, producing a CO2 rich emission stream (eg: Schwarze pump in Germany). However, a large air separator is necessary to produce the O2 required, incurring high capital costs. 



Therefore, much research has been done to develop cheaper CO2 capture methods as well as cheaper solvents with higher absorption capacities and greater resistance to degradation. One promising alternative technology is the “Calcium Looping Cycle”, which uses solid CaO-based solvents to remove CO2 from flue gases.





References:​



[1] Blamey, J., Anthony, E. J., Wang, J., Fennell, P. S., The calcium looping cycle for large-scale CO2 capture. Progress in Energy and Combustion Science 36(2),2010

[2] IEA. World energy outlook, 2008. Paris, France: IEA; 2008.

[3] IPCC, Climate change 2007: synthesis report. Contribution of Working Groups I, II and III to the fourth assessment report of the intergovernmental panel on climate change. In: Pachauri KP, Reisinger A, editors. IPCC: Geneva, Switzerland; 2007.

[4] IPCC, Intergovernmental panel on climate change special report on emissions scenarios. Nakicenovic N, Swart R, editors. IPCC: Geneva, Switzerland; 2000.