3. Electronic Theses and Dissertations (ETDs) - All submissions

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Start date: 2020Subject: search.filters.subject.Climatic changes

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    Volcanic forcing: modelling impacts on southern hemisphere temperatures
    (2021) Harvey, Pamela
    Considerable recent research attention has focussed on volcanic forcing effects on global climate, perhaps due to its cooling effects in what is otherwise an era of global warming. In an attempt to contemplate ways to combat the global warming phenomenon, geoengineering options have been considered, such as the idea to manipulate the climate by injecting sulphate aerosols into the stratosphere and thus simulate a volcanic forcing effect. This was of course a very controversial suggestion, and many argue that attempting to resolve global warming in this way could do more harm than good. The fact is, that there are still too many unknown variables and potential outcomes as a consequence of volcanic forcing on climate, such that the impact of manipulating climate to combat global warming cannot be fully appreciated at this stage. Instead, the focus remains on identifying research gaps and addressing these. While much research attention has focussed on understanding climatic responses to volcanic forcing over the Northern Hemisphere (NH), very little attention has focussed on the Southern Hemisphere (SH) in this regard. This PhD thus aims to address this research gap and establish, in some measure of detail, the temperature responses to major volcanic eruptions over terrestrial regions of the SH. Initially, near-surface temperature responses to eight major eruptions (Krakatau, 1883; Tarawera, 1886; Santa Maria, 1902; Colima, 1913; Quizapu, 1932; Agung, 1963; El Chichón, 1982; Pinatubo 1991) are investigated. Four eruptions (Krakatau, Santa Maria, Agung and Pinatubo) are identified as having caused significant temperature responses over the SH, and thereafter the temperature responses to these eruptions are established at a variety of spatial (hemispheric, continental and sub-regional) and temporal (annual, seasonal and monthly) scales. Model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are used as the main data source to study these climatic impacts. However, a reanalysis dataset (20th Century Reanalysis V2) provided by the NOAA/OAR/ESRL PSL station data, as well as station data for some sub-regions, iv were used to test the reliability of CMIP5 model outputs in its ability to simulate volcanic forcing effects on SH climate. Results from the CMIP5 ensemble used in this study suggest that significant cooling occurs in the SH following four of the eight eruptions (Krakatau, Santa Maria, Agung and Pinatubo), although the response is weaker than what the models suggest for the NH, as expected. The strongest temperature response follows the Krakatau eruption, which emitted the largest amount of SO2 into the lower stratosphere. The weakest responses would follow after either Santa Maria or Agung, varying with the region or the season studied. Overall, it is found that stronger responses occur during austral autumn, followed by austral winter, while the weakest responses occur during austral spring. Exploring the responses at a continental scale reveals that Australia experiences strongest cooling anomalies, which peak earlier (av = 5 months) than both southern African (SAF) and southern South American (SSA) anomalies, while SSA experiences weakest anomalies which also have the most delayed peak response (av = 9 months). Temperature responses in six sub-regions of SAF and eight sub-regions of Australia are then explored to establish responses at a much finer spatial scale. Results show that more northern regions experience stronger cooling than southern regions. Variations of responses appear at the smaller scale, as some regions experience strongest cooling response in one season while other regions experience strongest cooling in another season. Responses can vary depending on the latitude and magnitude of the eruption, the time of year of the eruption, as well as the condition of the atmosphere at the time of the eruption. Investigating variations in the responses to individual eruptions at different spatial and time scales highlights the necessity of studying the impacts of volcanic forcing on an individualistic eruption basis, rather than based on a composite of eruptions. Comparing CMIP5 results to reanalysis and station data reveals that uncertainties exist in the observed temperature responses. It is possible that at least some results are overestimated, as has been found in other CMIP5 studies investigating v volcanic forcing. However, as found in this thesis, at times CMIP5 in fact underestimates the temperature response based on comparisons with reanalysis data (in the Australian sub-regions following the Agung and Pinatubo eruptions). Expecting climate models to perform close to 100% accurately is unrealistic, as large uncertainties also exist when using both reanalysis and station-based instrumental data. Notwithstanding the challenges and limitations when using CMIP5, such model outputs provide a reasonable sense of expected temperature pattern following major volcanic eruptions. Hopefully, such model outputs will continue to improve with the newly established CMIP6
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    Perspectives on the effectiveness of green buildings in climate change mitigation: a study of the City of Johannesburg
    (2021) Makgalemele, Malesotse Cecilia
    It has been proved that anthropogenic activities globally have resulted in accelerated climate change and global warming, beginning with the industrial revolution, through the release of greenhouse gases of which Carbon Dioxide is the most prevalent. Estimations indicate that up to 40% of greenhouse gases are emitted from the construction and building sector hence the urgency for climate change mitigation. The aim of this study was to determine the effectiveness of retrofitted certified green buildings of office use in the City of Johannesburg in terms of climate change mitigation during their operational lifecycle. The study utilized semi-structured interviews which were conducted with various stakeholders as well as existing literature. Their purpose was to gather the information needed to examine the various perspectives on green buildings in terms of climate change mitigation. Parallel to the human perceptions, energy consumption data was also collected from the property companies and meteorological data was collected from the South African Weather Services. These two data sets as well as calculated Carbon emission data were analysed against each other to examine whether climate, particularly temperature, impacted how buildings consume energy and emit Carbon emissions. The empirical evidence suggests that despite factors contributing to increased energy consumption and Carbon emissions in buildings existing, retrofitting and certifying existing office buildings in the City of Johannesburg generally mitigates this. The process of certification, like the majority of the legislation and institutional frameworks in existence countrywide governing green buildings, is voluntary and act more as a guide. Challenges in governance and implementation of legislation present an obstacle to realising the full potential of green buildings. Generally, the building sector in the country has been positively impacted by the green building phenomena with incentives from various economic sectors playing a significant role and other potential ones identified
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    Long-term reconstruction of rainfall and fire for the Kavango-East and Zambezi regions, Namibia and the impact of people on past fire regimes
    (2020) Hamilton, Tamryn
    African savanna structure is driven by climate and fire, which have been well documented in modern observations and palaeo-studies, but is lacking on intermediate (decades to centuries) timescales where much of the ecosystem dynamics occur. Long term rainfall and fire records were generated from environmental proxies from the semi-arid Kavango-Zambezi region of South-Central Africa. The records were radiocarbon dated in high resolution and modelled with Bayesian accumulation models to generate ~600year chronologies. The proxy time series were analysed in time-frequency space to elucidate the relationship between rainfall and fire at different timescales within local and regional fire histories. Wavelet analysis shows periods of time in the past when fire had a positive relationship with rainfall, and also a negative relationship, and a switch from local to regional-scale fire response to rainfall is observed in the Little Ice Age (1700-750). A shift to regionally dominated fire regime thereafter is attributed to human population increase and associated land-use change. The results show that over time savanna landscapes can shift between load-limited and moisture-limited fire regimes and that savanna structure has been affected by human activities both directly, and via changes in fire regimes
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    SYMBIOSEAS - Connecting man and sea: preserving our oceans through built form
    (2020) Cachalia, Ayesha
    Currently our oceans are at great risk of losing species and habitats due to global warming, pollution and over fishing. Marine conservationists are fighting to maintain the biodiversity in our oceans however, these efforts are futile if the global population does not acknowledge the damaging impact of their activities on the ocean. It is through awareness and understanding of marine life that humans can be more conscious of their actions. Human interaction with the ocean is limited and often superficial. This research works towards establishing a meaningful connection between man and sea through a multitude of interactions. To achieve this in the form of a building proposal, a site in Hermanus was chosen due to pre-existing eco-tousrim infrastructure which supports the cause. In this environment it is possible to create up-close encounters with marine life, in nature, providing a more intimate experience than what is already available. The proposed design, facilitating meaningful access to the ocean, includes a shark research centre and a much needed visitor centre, connected by an education centre which includes an underwater observatory. A journey through these spaces, ending in the local historic harbour, will be the source of different experiential relationships between people and the ocean
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    A Palaeolimnological determination of a regional industrial signal in the sediments of Mpumalanga Highveld Pans
    (2020) Spratt, Jesse Patrick
    Fresh water endorheic wetlands are a scarce resource in South Africa and are threatened by human activities such as mining, abstraction, farming and other industry. The Mpumalanga Lake District (MLD) is a unique region comprising of over 300 endorheic pans differing in type. This provided the ideal regional setting for a pilot palaeolimnological study. The overall aim was to identify a regional industrial signal for anthropogenic influence by understanding the uniqueness of these pans through a palaeolimnological approach using historical lake sediments. A historical sediment record was established in order to identify any temporal changes in physiochemical characteristics over the last approximately 130 years. Four sites were selected so as to analyse a spatial aspect of contamination and to compare physical characteristics of pans in the MLD. Sediment samples were collected in the form of four lake sediment cores which were sub-sampled at 0.5 cm in order to understand down core trends. A bathymetric approach was adopted in which GPS, depth and water quality data were obtained in order to understand the physiochemical characteristics and morphology of these pans. Analyses performed included radio-isotopic dating through 210Pb, organic carbon content analysis through Loss on Ignition methods, sediment grain size analysis using laser diffraction and the analysis of the composition of major elements in these lake sediments using x-ray fluorescence (XRF) spectrometry. Bathymetry data was used to produce maps representing the physical morphological characteristics of these pans. Sediment data including major elements, organic carbon content and grain size data was analysed statistically and represented graphically in order to understand down core trends. Identified was the uniqueness of these pans and the MLD region as a whole. The pans differed in size, depth and in terms of the sediment properties of organic carbon, carbonate and sediment grain size distribution. Results showed a distinct difference between sites TPE compared to the other three sites in terms of bathymetry and limnology. It was determined that there are multiple fluctuations throughout the sediment record which represents a seasonal variation in climatic conditions. An attempt to observe trends of environmental and climatic change was made with varied success. An identification of a possible regional industrial signal was made with respect to major element compositional changes however the distinction between natural and anthropogenic sources was difficult to determine
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