School of Earth Sciences - Theses
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Energy transition in liberalised electricity markets: Lessons from Australia
Renewable energy generation is being added to global electricity supply at a remarkable pace. A primary driver for this expansion has been the extraordinary cost reductions achieved by the sector, in large part in response to both explicit and implicit climate policy measures and objectives. While a globally consistent and coherent climate policy remains elusive, research and development efforts, deployment policies and industrial policy motivated by the need to dramatically reducing carbon emissions have all contributed to the recent success of the renewable energy industry. In December 2015, a historic global climate agreement was devised under the auspices of the United Nations Framework Convention on Climate Change at the 21 st Conference of the Parties in Paris. This agreement includes a global goal to hold average temperature increase to well below 2C and pursue efforts to keep warming below 1.5C above pre-industrial levels. According to the International Energy Agency, the average CO 2 intensity of electricity will need to fall from 0.411t/MWh in 2015 to 0.015t/MWh by 2050 (IEA 2016). Any future scenarios that meet this objective will necessarily involve significantly increased penetrations of renewable energy (Holz and Von Hirschhausen 2013). While many studies have concluded that such a substantial de-carbonisation of the electricity sector with renewable technologies is feasible, to date such studies have tended to focus on the technical viability of systems with high penetration of renewables to reliably supply electricity. In Australia alone 1 , there are now several such studies that show that 100% renewable energy systems are technically capable of meeting our electricity requirements (AEMO 2013a; Elliston, MacGill, and Diesendorf 2013; Wright and Hearps 2010). Challenges remain, but the questions are now shifting from technical viability to economic feasibility (Riesz 2012). Notwithstanding this, reaching high penetration of renewable energy requires more than technical or economic feasibility. There is a particular need for careful consideration of market design (IEA 2016). In this thesis, I explore the way market design issues are impacting the penetration of renewable energy in the context of the National Electricity Market (NEM) in Australia, with a particular focus on the experience in South Australia. Three different aspects of energy market design are considered in this thesis. Firstly, I consider how the current market design values energy arbitrage and storage. Secondly, I consider how specific market rules related to dispatch and settlement intervals impact the technology mix and capabilities, and effect the efficiency of the market itself. Finally, I consider how new technologies impact on secondary markets such as frequency control which have typically been provided by thermal generation. The thesis begins with a review of the energy-only market structure and design. This includes discussion of the ‘capacity cycle’ from both a historic and forward looking perspective, and how it is impacted by renewable technologies. The suitability of traditional ‘capacity overhang’ heuristics in a system where older technologies are displaced or replaced by fundamentally different technologies is discussed. I also explore the interaction with historical problems that remain contested and unresolved for energy-only markets, such as the so-called ‘missing money problem’, as well as the viability of energy-only markets in high penetration renewable energy systems. The second chapter specifically looks at the contextual settings of the Australian NEM, and in particular, the South Australian (SA) market region. Considered in isolation to the NEM, South Australia has an exceptionally high penetration of renewable energy, even by international standards, making this region a noteworthy case study in energy system transition. The historical and geographical context in which SA sits is nonetheless critical to understand both its place in the NEM and how it has responded to date. As such, this chapter includes an overview of the SA market, and important characteristics including energy mix, the size of the market, the impacts of the recent exit of coal generation and resultant changes in market concentration. The third chapter focuses on the way increasing renewable energy generation and price volatility give rise to opportunities for storage technologies in an energy-only market, using the NEM and SA as an example. In particular, I demonstrate that the main driver for storage options in an energy-only market is price volatility which, in turn, is dependant on capacity requirements to meet particular reliability settings. I show that storage technology economics are very similar to the economics of traditional forms of peak generation in this respect, and common hedging and contracting strategies used by peak generators would be suitable to finance storage assets. The analysis suggests that in energy only markets storage may also derive a competitive advantage over traditional peaking assets by deriving revenue from arbitrage opportunities, in addition to capacity payments. A case study involving Pumped Hydro Energy Storage (PHES) demonstrates that in certain circumstances, it may already have a competitive advantage over Open Cycle Gas Turbines (OCGT). The fourth chapter looks at a particular market-market design element, and investigates how this impacts the different technologies, and the efficiency of dispatch in the market. Specifically, I examine a particular characteristic of the NEM in which physical dispatch (which occurs on a 5-minute interval basis) is misaligned with financial settlement (which occurs on a 30-minute interval basis), and the incentives and outcomes that result. Drawing on the analysis and methods from the previous chapter, the effect and value of aligning these intervals is evaluated for storage technologies. The impact on other technologies, including demand side response and the costs to the system of ‘gaming’ this particular rule is also estimated. I find that market rules have a significant impact on the operation of an energy-only market under transition. The fifth chapter examines how, in a high penetration renewable market, storage technologies are able to contribute to security of supply, allowing for changes in traditional market management strategies. Specifically, I look at how lithium-ion batteries have participated in the existing frequency control framework, and the implications for the provision of system security in the longer term. The final chapter summarises and concludes the thesis, including a discussion of further avenues for analysis. A range of outputs have been generated as part of this thesis. In particular, chapter 3 was published as a journal article, while the analysis in chapter 4 was submitted and contributed to the Australian Energy Market Commission, as part of its assessment of a rule change. Finally, the analysis draws heavily on market data from the Australian Energy Market Operator (AEMO). In undertaking this analysis, substantial amounts of the publicly available data provided by AEMO have been curated in a large database that continues to be updated in real time. This database now exists as the ‘openNEM’ project - an online resource that is now both open access and opensource. Further details are provided in appendix F. Prior to this thesis I was the lead author of a journal article that investigated the merit order effect of rooftop solar in Australia (McConnell et al. 2013), and was co-author of a paper published in the Journal of Environmental Sociology (Haines and McConnell 2016) and another in the electricity journal (Sandiford et al. 2015). Whilst these are not included or part of this thesis, these work have informed my knowledge of the research area.
Geologic expressions of faulting and earthquake strong ground motions in intraplate bedrock terrains
Australian earthquakes offer unique opportunities to investigate environmental and landscape effects of reverse rupturing faults. All historic surface-rupturing earthquakes have occurred in arid, low-relief, bedrock dominated areas with little to no anthropogenic influence. Environmental earthquake effects identified following the 2016, reverse-mechanism, MW 6.1 Petermann earthquake in remote central Australia are categorised with the Environmental Seismic Intensity scale, the first application of this scale for an Australian earthquake. The intensity and distribution of environmental damage demonstrates strong asymmetry due to fault geometry, with damage increasing towards the surface rupture rather than epicentral region. The direction and distances of 1,437 co-seismically displaced rock fragments (chips) in the near-field of the Petermann earthquake provide a dense proxy-record of strong ground motions, both along- and across-rupture. Chips record preferred azimuths of displacement that are attributed to rupture fling effects. This unprecedented geological proxy-record of the distribution, directivity and intensity of strong ground motions has important implications for hazard analysis in the near-field of reverse earthquakes. Fine-scale mapping of the 2016 Peterman surface rupture and secondary fractures using field, drone-derived and remote-sensing datasets indicates surface rupture characteristics vary with changes in surface geology. Deformation zones are wider and less recognizable in granular materials (e.g. dunes, alluvium) compared with those in proximal bedrock. Kinematic analysis of bedrock fractures indicates sinistral-reverse faulting, consistent with published focal mechanisms, and a maximum compressive stress orientation generally consistent with the inferred regional SHMax orientation. Trenching and 10Be cosmogenic nuclide erosion rates provide preliminary evidence of absence for prior rupture on the Petermann faults within the last 200 to 400 kyrs. The 2016 earthquake is therefore hypothesized to be the first to rupture this fault in the near surface. Analyses of geological and geophysical data from ten moderate magnitude (MW 4.7 – 6.6) historical surface-rupturing earthquakes in cratonic Australia indicate that rupture likely propagated along pre-existing Precambrian bedrock structures. Six of seven events show evidence of multi-fault rupture across 2 to 6 discrete faults of greater than 1 km length, placing these events as some of the most structurally complex earthquake ruptures identified globally for this magnitude. No unambiguous geological evidence for preceding surface-rupturing earthquakes is present. This raises important questions regarding the recurrence behaviour of intraplate stable continental region faults, with implications for seismic hazard analysis. In summary, this thesis explores observational, seismic, and remote-sensing data of surface rupturing earthquakes in Australia to provide new (i) data regarding the recurrence patterns of Australian earthquakes (ii) insights into basement controls on these earthquakes (iii) and methods to quantify seismic directionality behaviour common to reverse earthquakes globally. These contribute to better understanding the why, what, when, where of intraplate earthquakes, and how seismic hazard varies across diverse tectonic and crustal environments.
Origin(s) and evolution of granitic melts: theoretical considerations and field examples from Mount Isa, Australia
Felsic igneous rocks are formed from a variety of processes including: (1) partial melting and melt extraction from source regions in the crust and mantle, (2) host-rock assimilation, (3) magma mixing, and (4) fractional crystallisation. These processes do not generally occur in isolation, but often overlap in space and time. As a result determining the relative contributions of these processes to granite petrogenesis remains challenging. Here, a combination of geochemical proxies, mineral chemistry, and field data were used to assess the key parameters that have contributed to the origin and magmatic evolution felsic melts of the Proterozoic Mount Isa Inlier of northern Australia. An evaluation of the available geochemical data for the main granite suites of the western Mount Isa Inlier provides insight into the crustal evolution of the eastern margin of the proto-North Australian Craton (NAC). The 1860 Ma Kalkadoon Suite are geo- chemically similar to I-type granites of the Lachlan Fold Belt but exhibit anomalously low-Mg#, Na2O, as well as anomalously high-K2O, LREE, and Th/U for an I-type gran- ite. The modified I-type character of the Kalkadoon Suite reflects the high-geothermal gradient nature of the compressional 1890–1840 Ma Barramundi Orogeny. The 1740 Ma Wonga and the 1680–1650 Ma Sybella suites are compositionally similar to Lachlan Fold Belt A-type granites, but exhibit extreme enrichment in U and Th. The Sybella Suite is also extremely enriched in F and LREE. The anomalous geochemistry of these two suites reflects the interaction of mantle derived melts with an incompatible element-enriched ensialic crust. Part of the Sybella Suite, the zoned Queen Elizabeth Granite exhibits complex textural relationships which record incremental emplacement, differentiation, deformation, mix- ing and crystallisation of compositionally distinct magmatic phases during active rifting in the western Mount Isa Inlier. Emplacement of voluminous porphyritic to equigranular syenogranite was followed by emplacement of a leucogranite phase along the northern and eastern margins of the pluton. A high-strain zone developed contemporaneously with intrusion and crystallisation of an enclave-rich monzogranite phase in the paleo-floor zone of the pluton during continued extensional deformation. Intermingled doleritic, hybrid granitoid, and pegmatite lithologies along the western edge of the pluton highlight the bimodal character of the Queen Elizabeth Granite magmatism. Late-stage melt-drainage networks link the development of pegmatitic segregations in the marginal leucogranite phase to the accumulation of voluminous pegmatite bodies within the adjacent Mica Creek Pegmatite Field. Mineral compositional data highlight the mineral-scale variability of the main granite phases of the Queen Elizabeth Granite. Major minerals host most of the Rb, Ba, and Sr. Accessory minerals including allanite, titanite, zircon, and monazite are the major hosts of Y, Th, U, and REE. Hornblende contains a significant proportion of the HREE budget in the main syenogranite phase of the Queen Elizabeth Granite. Combined in situ zircon U-Pb-Hf-O isotopic analysis of pre-1600 Ma felsic igneous rocks from western Mount Isa Inlier provide insights into the magmatic evolution of the eastern margin of the proto-NAC during the Paleoproterozoic. Barramundi-aged granitoids are dominantly sourced from reworking of ca. 2.5 Ga, isotopically evolved continental crust. Zircon isotope data suggest that the Sybella Batholith was emplaced during two magmatic cycles at 1680–1670 Ma and 1660–1650 Ma with each cycle associated with a broad trend towards increasing juvenile mantle input with time. The geochemical, isotopic, and field data are consistent with the presence of a long-lived, mantle driven, transcrustal magmatic plumbing system active within the eastern proto- NAC crust during the late Paleoproterozoic. This mantle driven model contrasts with existing models that rely on derivation of A-type melts from protoliths within the crust and directly links bi-modal magmatism, crustal assimilation, sedimentation, and extensional tectonics within the western Mount Isa Inlier during the Paleoproterozoic.
The role of health co-benefits in the development of climate change mitigation policies in Australia, the European Union, China and the United States
Governments are yet to commit to action on climate change commensurate with the likelihood and severity of predicted impacts. The human health consequences of a changing climate are substantial, already being felt and will be exacerbated without ambitious and urgent action. Acting to mitigate climate change can result in ancillary benefits to health outcomes, also known as health co-benefits. Numerous studies over the past two decades have estimated the monetised value of a range of health co-benefits that may result from the implementation of mitigation measures. These studies conclude that accounting for health co-benefits can partially, if not fully, offset abatement costs. Despite this economic rationale for climate action, numerous climate change and health scholars have questioned the influence of health co-benefits on final policies. To date, there has been limited research investigating the political traction of health co-benefits. To begin to address this knowledge gap, this thesis examines the role of health co-benefits in climate change mitigation policy-making in four Parties to the United Nations Framework Convention on Climate Change. To do so, I first review literature on i) the political economy of health and climate change; ii) the science-policy interface; and iii) power in policy-making in order to identify areas where barriers for the consideration of health co-benefits in climate change mitigation policies may exist. Next, I outline the methods and analytical approach used. I then examine the role of health co-benefits in climate change mitigation policies through the development of case studies for Australia and the European Union. Next, I present results of my analysis of select Chinese and American climate change policy documents published between 2007 and 2017. The key finding of this research is that while health co-benefits are often a driver of air pollution mitigation policies, their consideration in the development of climate change mitigation policies is context- and policy-dependent. In considering the implications of this finding, I discuss key factors influencing the political traction of health co-benefits in the context of existing literature and possible policy implications. This thesis concludes by outlining contributions of this research to the literature and suggesting future research opportunities. The significance of this research is its extension of the burgeoning literature on health co-benefits and climate change mitigation policy-making from a social science perspective. Further, this thesis articulates implications for policy and identifies potential opportunities to enhance the political traction of health co-benefits in climate change mitigation policies at a time when strong climate action is so desperately needed.
The geochemistry and petrogenesis of MARID and PIC xenoliths
MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) and PIC (Phlogopite-Ilmenite-Clinopyroxene) rocks are rare mantle samples, most often occurring as xenoliths in kimberlites. Both MARID and PIC xenoliths contain high modal abundances of phlogopite, which does not occur in the “depleted mantle” – i.e. the residue that represents the protolith of Archean mantle roots, complementary to the formation of continental crust. Consequently, these rocks are frequently interpreted as the products of extreme mantle metasomatism. Previous studies of these rocks have focussed on acquiring isolated datasets on small sample suites. This approach has made it difficult to explore possible relationships within the spectrum of metasomatised, phlogopite-rich xenoliths, even from a single locality. It therefore remains unclear how MARID and PIC rocks are formed (whether by metasomatism of peridotites, or by melt crystallisation in mantle veins). The nature of MARID parental melts/fluids also remains unidentified. Finally, MARID geochemical compositions (e.g., high K2O content) and “enriched mantle” radiogenic isotope signatures are often cited as evidence for their presence in the source of mantle-derived potassic magmas, such as lamproites. This study seeks a greater understanding of the causes and effects of mantle metasomatism by studying the petrographic, geochemical, and isotopic (radiogenic Sr-Nd-Hf-Pb and stable N-O-S-Tl) features of 26 MARID and PIC samples from southern African kimberlites (Kimberley) and orangeites (Newlands). Previous inferences of a genetic link between PIC rocks and kimberlite melts are substantiated by clinopyroxene trace element compositions in equilibrium with kimberlite melts, and the similar radiogenic isotopic compositions of PIC clinopyroxene (87Sr/86Sri = 0.7037–0.7041) and southern African Cretaceous kimberlites (87Sr/86Sri = 0.7032–0.7048). Based on petrographic observations of kimberlite groundmass minerals (e.g., calcite, perovskite) as inclusions in secondary clinopyroxene rims, PIC rocks must be the result of kimberlite metasomatism, and not the melt source for kimberlite magmas. Furthermore, PIC rocks appear to be closely related to some phlogopite-bearing peridotites and wehrlites from the lithospheric mantle beneath Kimberley, due to similarities in their mineral geochemical compositions. It can therefore be inferred that these lithologies are the result of variable degrees of interaction between kimberlite melts and the lithospheric mantle. This study also presents mineralogical, geochemical, and isotopic evidence that kimberlites infiltrate and affect the mineral and bulk-rock compositions of the MARID rocks that they host, complicating interpretations of MARID genesis. By filtering out such contamination effects, new interpretations regarding these rocks can be reached. Although many studies support a magmatic genesis, the ranges in primary MARID mineral major element compositions presented in this thesis overlap with those in extremely metasomatised peridotites, opening the possibility of MARID genesis by metasomatic overprinting of peridotite protoliths. Some lherzolites studied herein have similar geochemical and isotopic signatures to MARIDs, suggestive of a common parental metasomatic fluid. Prior to kimberlite infiltration, MARID rocks appear to have had “enriched mantle” radiogenic isotopic signatures, which may indicate that the source of MARID parental melts contained recycled material – comprising both oceanic and continental crust, based on stable isotope considerations. Finally, bulk-rock reconstructions of MARID compositions were conducted to eliminate secondary features, from which the trace element composition of MARID-derived melts was modelled. These melts closely match the compositions of mantle-derived magmas, such as orangeites, lamproites, and some ultramafic lamprophyres, suggesting that MARID-veined mantle could indeed be the source of alkaline ultramafic magmas in intracontinental settings.
Inverse modeling of regional CO2 surface fluxes in the Latrobe Valley/ Otway basin
Carbon dioxide (CO2) is the most important greenhouse gas (GHG) attributable to human activity. Many natural components are responsible for the carbon emissions in the atmosphere. Therefore, large uncertainties exist in the current carbon budget. Using the atmospheric transport model and inverse techniques, we can estimate the carbon sources and sinks from the atmospheric CO2 measurements. The current global network is quite efficient in constraining the global carbon emissions. However, to obtain detailed knowledge about the controlling processes and better understanding of the carbon cycle, estimates of regional fluxes are important. To constrain the regional fluxes, it is important to capture the right signals at the right time. Therefore, continuous monitoring of atmospheric CO2 has been an essential part of the project. An optimal network design indicates the best location for the atmospheric monitoring units to be placed in the given domain. For our network design study, we have used the Lagrangian Particle Dispersion Model (LPDM), driven by mean wind velocity, turbulent kinetic energy and potential temperature. The necessary fields to drive LPDM are taken from Weather Research Forecasting (WRF) Model. Since, the input fields for LPDM are dependant on the output of the WRF model. On that account, it is important to choose an appropriate planetary boundary layer (PBL) scheme, which can produce all the required fields to drive LPDM. Scarcity of measurements and inaccurate representation of vertical transport within the planetary boundary layer in atmospheric transport can also lead to large uncertainties. Therefore, selection of an appropriate planetary boundary layer scheme to represent realistic atmospheric transport is indispensable. This study covers three main aspects: 1. Comparison between different planetary boundary layer schemes available in the Weather Research Forecasting (WRF) model. 2. Obtain an optimal network to constrain the greenhouse gas emissions in the Latrobe Valley. 3. Constraining the carbon sources and sinks in the Otway basin. We have used Bayesian synthesis inversion and incremental optimization to obtain an optimal network. The stations towards the central Latrobe Valley and east of the given domain would be able to constrain emissions from the power plants and major towns in the Latrobe Valley. As a proof of concept, we demomstrate the methodology using observations. We constrain emissions in the Otway Basin. For inversion, we adapt Bayesian synthesis approach. We further assessed the inverted fluxes with the flux tower data. Once we have data for the Latrobe Valley, we can use the same approach to estimate carbon fluxes.
A study on pore scale processes using a new multicomponent reactive-transport model
A new multi-component reactive transport model at the pore-scale is developed using a Java interface which combines COMSOL® and PhreeqC. The model solves for flow, transport and chemical reactions at the mineral-fluid boundaries on 2D and 3D domains extracted from porous rocks. Kinetically controlled reactions at the mineral-fluid boundaries are implemented on actual pore geometries derived from natural porous rocks. In order to carry out reactive transport simulations, the following workflow has been developed and applied. A spatial representation of the pores network and the solid grains in a natural porous rock using a micro- CT scanner. The digital images are then converted into three-dimensional unstructured meshes comprising tetrahedral and triangular elements. Boundary conditions are next assigned on the mesh and the mathematical equations representing flow, transport and reactions are solved on the finite element mesh. In order to optimize the image sample resolution, the effects of micro-CT scan resolution on the porosity and the pore-size distribution on two natural porous media: 1) Berea Sandstone and 2) Mt. Gambier Limestone are explored. The porosity and the pore-size distribution extracted from the digital images at a voxel resolution of 2.5 μm and 7 μm are compared to the properties derived from NMR analysis. It was concluded that a micro-CT resolution of 7 μm was sufficient for an accurate representation of the pore network in both natural rocks. This finding helped to define the micro-CT image resolution that should be used later in this study. The local Pè number which is a ratio of the advective and the diffusive flow was also quantified on the two rock samples in order to understand the heterogeneity of the fluid flow in the samples. The second part of this work focuses on the implementation of kinetically controlled reactions at the boundaries between the minerals and fluids. A calcite system is modelled combining the flow and transport of an acidic fluid and dissolution at the calcite mineral boundaries. The transition state theory is used to derive the calcite dissolution rate. This rate controls the flux of the Ca2+ ions species from the reactive boundaries into the aqueous phase. The model is then validated using the results of the experiment conducted by Li and colleagues, 2008. Fluid with a pH 4 and 5 were flushed through a calcite cylindrical domain at an injection rate of 4.72 and 9.39 μL/min. A match with an acceptable degree of error was obtained between the experimental results and the simulated results obtained from this pore-scale model at variable flow rates and different strengths of the acid, thus validating the results from the reactive transport model. The third part of this thesis focuses on the scaling relation between the physical and the chemical parameters at the local scale. The investigation of the effects of changing local flow properties on the chemical properties are presented and it was observed that the pressure difference and the local flow velocity scale linearly with a variable flow rate in the pore domain. The pH and the Ca2+ ion concentrations are inversely proportional to the flow rates i.e. the pH and the Ca2+ ion concentration decrease as the flow rates are increased. The reaction rates increase linearly but show a plateau trend in the higher flow rate regime suggesting that the reaction rates become flow dominated. It was concluded that the chemical parameters are observed to be non-conservative in nature and are highly dependent on the flow and structural regime of the pore space. The fourth part of this work uses pore-scale models to better understand the formation of dissolution patterns in natural porous media. In a system dominated by dissolution, broadly two types of patterns can be observed 1) face dissolution and 2) wormhole formation, small core flood experiment was conducted using the Mt. Gambier Limestone with a reactive fluid flushed through it for four hours. The changing pore geometry as recorded by micro-CT imaging at the initial time, after two hours and after four hours of injection. A pore-scale model based on the changing pore geometry was compared to the results obtained by the chemical analysis of the effluent and the digital image analysis. There was a minor overestimation of the concentration and the reaction rates simulated from the model compared to the effluent analysis. The image-based porosity change showed possible wormhole formation with the dissolution of calcite also observed away from the inlet face. The local reaction rates were calculated from the model along the injection plane and it was concluded that the high reaction rate areas decreased in abundance near the outlet as compared to the inlet, which is characteristic of wormhole formation. The importance of local dissolution rates in a multi-mineral system is the last part of this study. A scenario where two fluids with different CO2 concentrations interact with low porosity, low permeability interval in a siliciclastic reservoir is simulated. QEMSCAN® analysis was used to extract the spatial location of the minerals present in the siliciclastic rock sample. The reaction kinetics of five major minerals present in the rock were implemented and the calculated local dissolution rates showed several orders of magnitude difference. This points out the high degree of heterogeneity in the local reaction rates depending on the injection fluid and the type of mineral.
Application of computational modelling to the dynamic and geometric controls on slab earthquakes
The rupture mechanisms of intermediate depth earthquakes have led to a view that subducting slabs often exhibit either bulk extension or shortening in the upper mantle. Additionally, bending-related deformation has been invoked to explain the distribution and orientation of seismicity in double seismic zones. However, to date there is no clear understanding of why bending is more or less prominent in different settings. The primary aim of this research is to explore the relationship between intermediate depth seismicity and subduction dynamics, utilising thermo-mechanical modelling. I show that bending, in conjunction with strong thermal restrictions, can produce diverse seismic expression. For instance, flat slab geometries induce zones of positive bending rate within sub- horizontal, low-curvature sections of the slab. This gives rise to downdip extension in the upper part the flat slab, consistent with prevalent normal faulting in flat slab settings in Mexico, Peru and Chile. Deeper earthquakes on the lower side of the bending neutral plane are much less common. Overall, this leads to an apperent state of bulk downdip stretching. These examples, along with other settings explored in this study, suggest that bending has a more prevalent role than previously recognised. Another key theme of this research is how changes in mantle wedge flow can influence slab morphology and the configuration of volcanic arcs. These insights intersect with the seismicity problem due to the strong geometric control on slab bending rates. Systematic differences in the style of slab seismicity, either side of the Pacific, may be largely explicable in terms of these geometric differences. The framework I develop for intermediate depth seismicity is consistent with the idea that slabs are largely supported by mantle drag and transmit relatively little in-plane stress.
The impact of climate extreme events on global agricultural yields
Climate extreme events, such as droughts, heat waves, cold spells or heavy precipitation events, pose significant risks to food production and the livelihoods of farmers. Understanding the effect of such events on crop yields is crucial to predict the response of agricultural production to climate change and inform adaptation processes. This PhD research investigated the effect of temperature and precipitation extremes on the yields of four major crops — maize, rice, soybeans, and wheat — over the years 1961–2008, using a global, high-resolution yield dataset and global, gridded data on past weather conditions and climate extremes. First, a bibliographic network-type literature review was conducted to provide an overview of the research landscape. The number of publications focusing on climate and agriculture significantly increased after 2005, reflecting an increased awareness of the challenges related to climate change impacts as well as effects of extreme events on food production. An overview of the most influential publications and research clusters is presented and the main challenges faced by the agricultural sector, as identified in the literature, are summarised. The second part of this thesis analysed the effects of growing season climate variability and extremes (warm and cold temperature extremes, drought and heavy precipitation) on yield anomalies of maize, rice, soybeans, and spring wheat at the global scale, using random forests, a machine learning algorithm. The findings suggest that globally, 20–49% (range over all crops) of the variability of yield anomalies is explained by variations in growing season climate, including climate extremes. Excluding climate extreme indicators from the statistical models decreases the explained variance by 18–43% (range over all crops). This decrease represents more than half of the explained variance for maize, rice, and soybeans, highlighting the importance of climate extremes for understanding yield fluctuations. Yield anomalies are more strongly associated with temperature-related climate variables than with precipitation-related predictors. However, irrigation modulates the impacts of high temperatures on yield anomalies, reflecting the convoluted effects of water and temperature stress. By developing a composite indicator, regions were identified that are most strongly influenced by climate extremes and at the same time major contributors to global crop production, and hence may be the focus of adaptation efforts. The final analysis presented in this study focused on the effects of temperature extremes on maize yields more specifically. The first part assessed the effect of growing degree days above 30°C (GDD30+) — a commonly used, plant-critical temperature threshold — on maize yields across major producing regions. Most detrimental effects are found for rainfed yields in Europe, North America and Oceania, i.e. regions with highly industrialised agricultural systems. The strength of the negative relationship between GDD30+ and maize yield depends on a region’s mean climate and climate variability, with most negative yield effects found in colder and drier regions and regions with low temperature and precipitation variability. The second part determined region- and irrigation-specific temperature thresholds above which adverse yield effects accumulate. These thresholds range from 20°C in Europe to 26°C in Asia and North America. In summary, this study shows that the effects of high temperatures on maize production differ considerably between producing regions, with important implications for the adaptation of maize production systems to climate change and temperature extremes.
Australian rainfall and El Niño diversity: past variability and context for recent changes
The climate system integrates internally and externally induced variability at various time scales as a result of interactions between the ocean and atmosphere. The influence of external forcing on the climate system and with it the structural changes of climate variability, in particular on seasonal and longer time-scales, is difficult to examine due to high natural variability and short observational records. The interplay between high and low-frequency variability restricts our understanding of the full range of climate variability and our ability to contextualise changes. This thesis explores and evaluates the potential to use seasonal paleoclimate information to advance our knowledge of natural climate variability and the multi-century context of recent changes in the Australasian and tropical Pacific region. Climate modes of variability including the El Niño -Southern Oscillation influence Australian rainfall and make Australian rainfall highly variable at interannual timescales. Multi-century reconstructions of past climate variability are developed for Australian rainfall at bi-seasonal resolution. The rainfall reconstruction is based on local paleoclimate proxies and teleconnected links between remote paleoclimate proxies, climate modes of variability and Australian rainfall. In a multi-century context, the recent drying trends in parts of southern Australia, as well as the tendency towards wetter conditions in northern Australia, are found to be unusual. The cool and warm season rainfall reconstructions allow the documentation of distinct characteristics of past major droughts in terms of their spatial extent, duration, intensity, and seasonality. Using coral data at seasonal resolution, two El Niño index reconstructions illustrate the sequence of diversity of past eastern and central Pacific El Niño events for the last 400 years. The distinct spatio-temporal signatures of both types of El Niño are exploited, and together with a novel machine learning approach, the diversity of past El Niño events is reconstructed and compared to recent changes. The recent increase in the frequency of central Pacific El Niño events relative to eastern Pacific El Niño events during the late 20th century appears unusual. The most recent 30-year period includes more intense eastern Pacific events compared to the past four centuries. To further investigate the changes and interactions between Australian rainfall and El Niño diversity, observations and climate model simulations are compared to the multi-century reconstructions. A number of climate models taking part in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are identified that simulate spatially distinct El Niño behaviour. Identification of El Niño events reveals a lack of model agreement about projected changes of El Niño diversity. The probability of infrequent El Niño characteristics is evaluated and point towards an under-representation of central Pacific events that are followed by eastern Pacific events in the observational records. Future simulations in climate models indicate that this El Niño transition as observed most recently in 2014-2016, could become less common. Based on the rainfall and El Niño reconstructions, the general drying impacts of El Niño is consistent for both types. Despite the strength asymmetry between eastern and central Pacific El Niño events, the impact on Australian rainfall is of a similar order of magnitude but also highlights a strong variable nature of the different types of El Niño and Australian hydroclimate. The context of recent changes provided by the reconstructions in this thesis advances our knowledge of natural climate variability in the Australasian and tropical Pacific region and offers new insights into the future climate of the region.
The energy business system: transformation, social innovation & disruptive smart grid business models
A radical shift from a high- to a low-carbon energy system is not occurring at the speed required to address climate change. One reason for this, is that conventional energy firms are locked into producing shareholder profit with fossil-intensive business models that are still operable in current markets. This PhD thesis employs systems thinking to analyse lock-in of the energy business system (EBS) and then adopts design thinking to propose disruptive innovations that can accelerate low-carbon transitions. Dynamics of the EBS transition are evaluated in an interdisciplinary way and across systems scales, from the Earth system to the distribution edge of the electrical power system. Conceptual frameworks that combine complex system and transition theory are developed to evaluate the global EBS in an Earth system context and to analyse the role of business models in the decarbonisation of the electricity sector. Previous research suggests that strategies for escaping EBS lock-in include incorporation of environmental liability to shareholders, carbon taxation and other economic measurements to alter market conditions. The systems analysis presented here suggests that to ensure environmental resilience the EBS’s fundamental purpose and governance need revision. I theorise that more social innovation in business models could influence business trajectory in the energy sector. Instead of maximising shareholder profit, social innovations can shift business purpose towards long-term social and environmental value-creation using emerging market-based tools. A business model analysis of the electricity sector is used to identify opportunities for EBS disruption from social innovations. I find that, in general, social and environmentally driven low-carbon projects often struggle to achieve scale and commercial advantage. However, recent business model innovations in smart grids can provide such projects with the required competitive position. Specifically, Virtual Power Plant technology has emerged as an energy management system that allows aggregation and coordination of multiple distributed energy resources. Aggregation can include diverse resources such as photovoltaics, batteries, electric vehicles and windfarms. Coordination can achieve improved physical and market performance as a functional unit within the electricity market. Using theoretical model development and illustrative examples, I highlight how emerging opportunities such as peer-to-peer Internet platforms and blockchain technology, also have significant potential as tools to enable disruptive business models, through decentralised value creation using assets from online participants. Building from the systems thinking analysis of the EBS lock-in, the second part of this PhD thesis uses design thinking to propose and further develop a new business model termed a ‘social virtual energy network’ (SVEN). As an urban social electricity-trading network, a SVEN is designed to help accelerate the decarbonisation of the power system and influence paradigm shifts in EBS governance. Two iterations in the design of the SVEN concept are presented and critiqued based on insights derived from the first part of the thesis. The first iteration focuses on the role of virtual power plants and tariff design for business feasibility, and the second on blockchain and user interfaces for mainstream market adoption. Through systems analysis, this study argues that an adequate response to climate change requires a paradigm shift in the EBS. Using a systems design approach, the thesis provides a vision for the architecture of a democratic open energy economy where users and their distributed energy resources have an active role in the value chain of the EBS. The findings and proposals of this work are relevant to debates about the most effective ways of accelerating targeted innovations to achieve a low-carbon energy system.
Governing geoengineering sustainably: a scenario exercise to inform Australian geoengineering policy development
Geoengineering, the technofix to climate change, is a complex, contentious and high-stakes proposal. Yet in the absence of credible long-term global emissions reduction, the idea cannot be overlooked. To ensure that geoengineering contributes to sustainable environmental and social outcomes, a forward-looking, inclusive and reflexive decision-making framework is needed. Instead, Australia’s history on climate policy reflects a short- sighted, impulsive and polarised approach. The motivation of this project is therefore to inform sustainable geoengineering governance in Australia. Within a sustainable governance context, scenarios are often used in the management of long-term, complex, and uncertain issues. This thesis investigates how a scenario exercise can inform sustainable geoengineering governance in Australia. The sustainability focus justifies an interdisciplinary mixed-methods approach. The thesis begins by surveying the present before interrogating the future and is presented as a compilation of five papers. First, the thesis explores from an Earth System Governance perspective what global geoengineering governance exists and how this might evolve. The analysis characterises geoengineering governance as governance-by-default where there is no purposive regulation—decisions are guided by existing norms and driven by the motivations of engaged academics. Given the influence of these actors, the research examines, through a systematic quantitative review, the types of geoengineering governance frameworks proposed in academic and non-academic literature. The study finds that the challenges of geoengineering governance can be likened to issues in other policy domains but suggests that normalising the debate thusly could obscure major threats and novel opportunities. Next, a meta-analysis of geoengineering scenarios is undertaken. It finds that the treatment of geoengineering within these scenarios does not align with sustainability concepts. An emphasis on technological solutions ignores the interdependence of nature and society and conceals alternative options; a focus on global effects and actions disregards local or regional issues; and scenarios portray only a narrow range of perspectives. Finally, an inductive and deductive scenario design method is proposed and demonstrated, producing four scenarios that are analysed in several ways: their key determinants are compared to those of scenarios in the geoengineering literature; they are studied individually and collectively to identify causal relationships and early warning signals; shared learning throughout scenario process is explored; and finally, they are used to stress-test climate policies and inform robust strategies. Proposed Australian climate strategies are found not to be robust. Policies are based on the expectation of enduring government legitimacy and that technological solutions obviate the need for behavioural change. The geoengineering strategy proposed for Australia is engagement nationally and internationally on geoengineering issues in a technologically and ideologically neutral manner and investment in transparent and inclusive research. The contributions of this thesis are several. It establishes that geoengineering governance is not tracking on a sustainable trajectory globally. It suggests that the role of scenarios, already central to geoengineering scholarship and governance design, can be expanded. It proposes and demonstrates a successful scenario development and analysis method. It begins a cross-sectoral Australian geoengineering conversation. It makes specific policy recommendations; and in doing so, it opens up the scope of policy options.