Geoengineering, intentional large-scale manipulation of the Earth-system, has been proposed as a means to ameliorate the impacts of global warming. There are two approaches; Carbon Dioxide Removal (CDR) geoengineering which would reduce C02 concentrations and address the cause of climate change, and Solar Radiation Management geoengineering which would cool the planet by reducing the amount of sunlight absorbed by the planet without affecting CO2 concentrations. This thesis reviews geoengineering and investigates the direct and indirect climate effects of SRM geoengineering. The sunshade geoengineering scheme, which would reduce the solar insolation, is investigated in depth in this thesis. Sunshade gcoenginecring may be implemented at a range of C02 concentrations and it would also offer control over the amount of insolation that reaches the planet. Both of these aspects of sunshade geoengineering are investigated using a climate model and it is found that sunshade geoengineering would ameliorate most of the effects of elevated C02 but would cause heterogeneous changes in climate; globally reducing precipitation and leaving many regions with a climate markedly different from the pre-industrial. The regional climate effects of sunshade geoengineering are found to vary linearly with both the solar insolation reduction and the C02 forcing applied. An off-line ice-sheet model is used to investigate the indirect climate effects of different strengths of sunshade geoengineering on the Greenland Ice-Sheet at quadrupled CO2 levels, to determine whether sunshade geoengineering could stabilize the ice-sheet and reduce sea-level rise. It is found that the ice-sheet would eventually collapse at quadrupled C02 levels but that strong sunshade geoengineering can stabilize the entire ice-sheet or at weaker implementations, part of the ice-sheet could be maintained. A comparison is made between the urban, crop and desert surface albedo geoengineering schemes, which would have a highly heterogeneous radiative forcing effect, and sunshade gcocngineering, which would have a more homogeneous radiative forcing effect. This comparison shows that regional geoengineering forcing, if it is relatively weak, may provide local and regional cooling and other benefits but for stronger land albedo forcing there are large shifts in precipitation, including substantial reductions in monsoon precipitation, which could prove to be more harmful than the effects of global warming. Finally, to determine the robustness of the results in this thesis, a perturbed parameter ensemble is developed, tested and then used to investigate the effects of parametric uncertainty on the sunshade geoengineering climate effects. The perturbed parameter results agree with much of what was found in other parts of the thesis about sunshade geoengineering but finds that there is uncertainty in the resid- ual warming at the poles, the magnitude of the northward shift of the ITCZ, and that the standard climate model may have overestimated the effectiveness of sunshade geoengineering at maintaining the Greenland Ice-Sheet. Overall, I find that SRM geoengineering could offer a considerable amelioration of the impacts of global warming; however, the climate would differ substantially from a low-C02 climate, and there would be winners and losers as a result. Regional SRM geoengineering would have very heterogeneous climate impacts, potentially causing large problems but could offer a large degree of control over the climate. 'Whether the political risks that control over the climate could bring would outweigh the potential climate benefits, is an open question.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:573384 |
| Date | January 2012 |
| Creators | Irvine, Peter J. |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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