The ocean is the only cumulative sink of atmospheric CO2. It has absorbed approximately 40% of the CO2 from fossil fuel burning and cement production, lowering atmospheric CO2 and limiting climate change. Here we will examine the regional and global mechanisms controlling the evolution of ocean uptake of this additional carbon from human activities (anthropogenic carbon, Cant) using ocean models and observations. Cant is rapidly injected into the deep ocean, sequestering it from the atmosphere for centuries. It is currently uncertain whether any of this sequestered Cant was absorbed from the atmosphere in the subpolar North Atlantic. Here we present evidence that the upper limb of the ocean’s overturning circulation supplies the subpolar North Atlantic with capacity to absorb Cant from the atmosphere. Using a coupled ocean model, we find that surface freshening of the subpolar North Atlantic reduces the volume available for Cant storage. We also investigate whether global ocean Cant uptake is reduced due to changing ocean circulation, this time across multiple emission scenarios, including scenarios with aggressive emission mitigation. Though it is clear that emission mitigation will reduce the magnitude of the ocean carbon sink, the mechanisms governing the decline in uptake have not been studied in detail. We find that the ocean sink becomes less efficient due to kinematic effects wherein Cant escapes from the surface ocean as atmospheric CO2 plateaus and then declines. In emission scenarios ranging from high to low emissions, projected changes in global Cant uptake due to ocean circulation are small. This is in contrast with the subpolar North Atlantic, where future circulation change plays a important role in the declining Cant uptake.

The rise of anthropogenic CO₂ emissions and the associated increasing levels of CO₂ in the atmosphere are expected to bring uninhabitable conditions on earth due to global climate change and numerous associated environmental crises. To reduce these impacts, warming must be kept to 1.5°C above pre-industrial levels. With the slow transition to more favorable energy generation methods with lower carbon emissions, it is clear that power plants utilizing fossil fuel combustion for electricity will not be reduced to an acceptable level. Thus, the deployment of negative emission and carbon capture, utilization, and storage (CCUS) technologies will be crucial to meet the 1.5°C target. The current state-of-the-art carbon capture technology is point source amine scrubbing, in which diluted aqueous amine solutions are used to absorb CO₂ from power plant flue gases. The CO₂ is captured at ~40°C by the formation of an amine/H₂O—CO₂ complexes. The absorbent solution, now containing CO₂, must be heated to release the CO₂ for further processing and to regenerate the amine for recycling. Though this technology is well-engineered and commercially available, there are some major drawbacks such as energy intensity mainly due to vaporization of the water during CO₂ separation from the amine, corrosivity of the amine material, and the need to transport the released CO₂ for further utilization or sequestration. To this end, dual function materials (DFM) were developed to address these issues. DFMs eliminate the need for the energy intensive regeneration of liquid amine solutions and transportation of CO₂. Comprised of both a capture and catalytic component co-dispersed on the same high surface area carrier, the DFM is able to selectively capture CO₂ from the effluent flue gas and catalytically convert it to methane (or renewable natural gas) with the introduction of preferably renewable H₂ in the same reactor. The DFM can operate isothermally at around 320°C by harnessing the sensible heat of typical power plant effluent flue gases. 5% Ru, 6.1% “Na₂O”/Al₂O₃ was shown to be a very robust, demonstrating stable performance after 50 cycles of capture and catalytic conversion with simulated flue gas. In addition to point-source capture, negative emission technologies like direct air capture (DAC) are required to mitigate climate change. Thus, we investigate the use of DFM for a new application – the direct air capture of CO₂ and subsequent catalytic methanation. Furthermore, for such applications, the loading of Ru was dramatically decreased to alleviate the economic burden for commercialization and wide-scale deployment. This thesis demonstrates the flexibility of the DFM as a carbon capture technology for direct air capture of CO₂ at ambient air temperatures and subsequent methanation (DAC-M) at temperatures in excess of 200°C. Recognizing the energy intensity of isothermal DAC-M operation, the capture and conversion cycles were modified for temperature-swing operation, with adsorption occurring at 25°C, followed by heating up to 300°C in H₂ for methanation. Short-term aging was conducted on 1% Ru, 10% Na₂O/Al₂O₃ in a packed bed configuration for 10 cycles of adsorption in dry air conditions (400ppm CO₂ in air) and methanation. The sample was also tested in humid adsorption conditions (400ppm CO₂, ~2% H₂O/air) to better simulate ambient environments. These tests showed that the DFM is able to operate in a temperature swing mode and exhibits a higher, stable CO₂ adsorption capacity in humid conditions unlike other capture technologies using amines and physical adsorption methods, which show a significant decline in capture capacity. We were able to establish that the DFM has great potential for DAC-M. Consequently, these materials are moving towards advanced process development with our engineering partners under the sponsorship of DOE. Critical parameters such as pressure drop, heating rate, and methanation temperature are primary parameters that must be optimized. New low Ru loading DFMs, 0.5% Ru and 1% Ru DFM, were aged with simulated power plant flue gas (7.5% CO₂, 4.5% O₂, 15% steam, balance N2) for over 50 cycles of capture and catalytic conversion to CH4 (and water) in a packed bed configuration. These conditions of continuous operation at 320°C with 15% steam and 4.5% O₂ are far more severe than for DAC which adsorbs low levels of CO₂ from air at ambient air conditions (0-40°C with 2-5% moisture). Therefore, these power plant effluent test conditions can be considered accelerated aging for DAC-M. A reduced level of 0.5-1% Ru DFM was tested under simulated power plant effluent conditions on several Al₂O₃ structures, particularly tablets and ring tablets for scale-up of the technology. These tests showed a subtle but gradual deactivation of the material. Characterization with CO chemisorption and in-situ FT-IR indicated that the Ru component is deactivated – most likely by sintering – due to the presence of O₂ and H₂O in the flue gas. Microreactor studies show that in the presence of O₂ and H₂O, adsorption capacity is reduced and the rate of methanation is decreased. Upon removing O₂ and H₂O from the adsorption step, the adsorption capacity is restored but the rate and selectivity of methanation declines steadily, indicating that the deactivation is irreversible. Interestingly, the DFM with higher Ru loading showed more stable performance suggesting that higher catalytic content is required for more improved stability. Fortunately, Ru can be leased and recycled, reducing the capital economic burden of higher Ru loadings. Additionally, we expect that given the milder conditions for capture in DAC scenarios, low Ru loaded DFMs will be more stable. Initial DAC-M data substantiates this stability, but longer aging times are required for confirmation. Furthermore, stability may be favored with the use of higher concentration H₂. Finally, this thesis also investigates the use of other Ru+sorbent/carrier combinations for DAC and the apparent enhancement of adsorption arising from the use of a reactive sorbent (e.g., addition of Ru). After screening Al₂O₃-supported Na₂O, CaO, MgO, and BaO in combination with 1% Ru, we are able to show that Ru+Na₂O/Al₂O3 has the best adsorption capacity. This material, relative to the other alkaline oxides studied, shows a unique enhancement in the CO₂ adsorption capacity compared to the bare supported sorbent (Na₂O/Al₂O₃). The enhancement effect is shown to be an asymptotic function of an increasing Ru loading, plateauing after 3% Ru. ZrO₂-supported Ru+Na₂O is also tested but does not show favorable adsorption capacity, indicating that Al₂O₃ is also a crucial component of the DFM formulation. This technology is the subject of a provisional patent application.

"April 2004" / Includes bibliographical references (leaves 308-327) / 354 leaves : ill. (some col.), maps, plates (col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Soil and Land Systems, 2004

Of all the strategies to reduce carbon emissions, carbon dioxide (CO₂) geological sequestration is an immediately available option for removing large amounts of the gas from the atmosphere. However, our understanding of the transition behavior between Forchheimer and Darcy flow through porous media during CO₂ injection is currently very limited. In addition, the kinetic mass transfer of SO₂ and CO₂ from CO₂ stream to the saline and the fully coupling between the changes of porosity and permeability and multiphase flow are two significant dimensions to investigate the brine acidification and the induced porosity and permeability changes due to SO₂ co-injection with CO₂. Therefore, this dissertation develops a multiphase flow, contaminant transport and geochemical model which includes the kinetic mass transfer of SO₂ into deep saline aquifers and obtains the critical Forchheimer number for both water and CO₂ by using the experimental data in the literature. The critical Forchheimer numbers and the multiphase flow model are first applied to analyze the application problem involving the injection of CO₂ into deep saline aquifers. The results show that the Forchheimer effect would result in higher displacement efficiency with a magnitude of more than 50% in the Forchheimer regime than that for Darcy flow, which could increase the storage capacity for the same injection rate and volume of a site. Another merit for the incorporation of Forchheimer effect is that more CO₂ would be accumulated in the lower half of the domain and lower pressure would be imposed on the lower boundary of the cap-rock. However, as a price for the advantages mentioned above, the injection pressure required in Forchheimer flow would be higher than that for Darcy flow. The fluid flow and contaminant transport and geochemical model is then applied to analyze the brine acidification and induced porosity and permeability changes due to SO₂ co-injection. The results show that the co-injection of SO₂ with CO₂ would lead to a substantially acid zone near the injecting well and it is important to include the kinetic dissolution of SO₂ from the CO₂ stream to the water phase into the simulation models, otherwise considerable errors would be introduced for the equilibrium assumption. This study provides a useful tool for future analysis and comprehension of multiphase Darcy-Forchheimer flow and brine acidification of CO₂ injection into deep saline aquifers. Results from this dissertation have practical use for scientists and engineers concerned with the description of flow behavior, and transport and fate of SO₂ during SO₂ co-injection with CO₂ in deep saline aquifers.

This thesis estimates the impacts of rooftop photovoltaic (PV) capacity on electricity generation and CO2 emissions in America's Pacific Northwest. The region's demand for electricity is increasing at the same time that it is attempting to reduce its greenhouse gas emissions. The electricity generated by rooftop PV capacity is expected to displace electricity from fossil fueled electricity generators and reduce CO2 emissions, but when and how much? And how can this region maximize and focus the impacts of additional rooftop PV capacity on CO2 emissions? To answer these questions, an hourly urban rooftop PV generation profile for 2009 was created from estimates of regional rooftop PV capacity and solar resource data. That profile was compared with the region's hourly fossil fuel generation profile for 2009 to determine how much urban rooftop PV generation reduced annual fossil fuel electricity generation and CO2 emissions. Those reductions were then projected for a range of additional multiples of rooftop PV capacity. The conclusions indicate that additional rooftop PV capacity in the region primarily displaces electricity from natural gas generators, and shows that the timing of rooftop PV generation corresponds with the use of fossil fuel generators. Each additional Wp/ capita of rooftop PV capacity reduces CO2 emissions by 9,600 to 7,300 tons/ year. The final discussion proposes some methods to maximize and focus rooftop PV impacts on CO2 emissions, and also suggests some questions for further research.

Indiana University-Purdue University Indianapolis (IUPUI) / Carbon dioxide (CO2) level in the atmosphere has increased steadily since Pre-Industrial times. The need for a better understanding of the effects of elevated CO2 on plant physiology and growth is clear. Previous studies have focused on how plants are affected by either elevated CO2 or salinity, one of many environmental stresses for plants. However, little research has been focused on the interaction of these two factors. In my project, three common grass species were exposed to both elevated CO2 and salinity, so that the effects of either of these factors and the interaction of the two on these species could be examined. The CO2 levels were set to 400 µmol mol-1, close to the current concentration, or 760 µmol mol-1, projected to be reached by the end of this century. Salt solutions of 0, 25, 50, 75, and 100 mM NaCl with CaCl2 at lower rates (1% of each respective molarity for NaCl) were used to water the grasses, which are unlikely to experience prolonged exposure to salt conditions beyond this range in their natural habitats. The three common grass species studied in my experiment were Kentucky bluegrass (Poa pratensis L.) and red fescue (Festuca rubra L.), both C3 cool season grasses, as well as buffalo grass (Buchloe dactyloides (Nutt.) Engelm.), a C4 warm season grass. Each treatment had five replicates, bringing the total number of experimental pots to 150. Various growth parameters were monitored, and all data was statistically analyzed for statistical significance. My results showed that elevated CO2 had a stimulating effect on most growth parameters, particularly when plants were given more time to grow. In a 100-day growth experiment, CO2 affected the number and dry biomass of plants of all species, regardless of their C3 or C¬4 photosynthetic pathways. Salinity consistently inhibited germination and growth at all stages, from germination through plant emergences, numbers of established plants, and dry biomasses at harvest. Interactive effects of CO2 and salinity did occur, though often in seemingly specific instances rather than forming clear and consistent trends. My findings suggested that growth of common grasses would be enhanced by the rising level of CO2 in the atmosphere, but the effect would be modified by environmental stresses, such as salinity.

The terrestrial water, energy and carbon cycles are tightly coupled through land-atmosphere (L-A) interactions, not only regulating local plant physiological activities and also modulating regional and global climate. With ongoing anthropogenic greenhouse gas emissions, many of these interactions can be modified and complicated. To better anticipate and adapt to future climate, it is of great importance and necessity to deepen and refine our understanding of the complex L-A interactions. In this dissertation, three topics are investigated across the ecosystem, regional and global scales respectively, throughout which, the critical role of dryness or drying in the context of global warming is highlighted. 𝐂𝐡𝐚𝐩𝐭𝐞𝐫 𝟏: Evapotranspiration (ET) is a key component that connects the continental water, carbon and energy cycles and a proxy that measures the coupling strength between the biosphere and atmosphere. A wide range of biophysical factors, which usually exhibit nonlinearity and strong covariation, collectively modulate ET and complicate the overall understanding of ET dynamics. In the first study, the causal discovery frameworks PCMCI+ and Latent PCMCI are utilized with integrated priori physical knowledge to identify the dominant drivers and constraints of ET in the growing seasons across sites, with a particular focus on the role of site dryness degree. The Dryness Index (DI), defined as the ratio of annual mean net radiation to precipitation, has been introduced to assess the water availability relative to energy supply at different locations. By analyzing the daily observations from 115 flux tower sites and satellite remote sensing, it has been discovered that the feedbacks around ET are mediated by the degree of dryness: at sites with adequate water supply (using PCMCI+, the DI value averaged from such sites is 1.33), the atmospheric conditions, including incoming solar radiation and atmospheric demand for water (indicated by vapor pressure deficit, VPD), prevail in driving ET; in contrast, in semi-arid and arid areas where the water stress is high (using PCMCI+, the DI value averaged from such sites is 3.32), soil water content is the primary factor to constrain ET due to the plant regulation of stomatal conductance as part of the water conservation strategy. Additionally, as DI increases across sites, the sign of the contemporaneous causal relationship between VPD and ET can reverse from positive—indicating that atmospheric demand for water drives ET—to negative—reflecting that plant stomatal closure limits ET in response to the dryer atmosphere. 𝐂𝐡𝐚𝐩𝐭𝐞𝐫 𝟐: As summer heatwaves and droughts are becoming more frequent and intense, such as in Western Europe, there is a growing interest in unraveling the physical mechanisms behind their occurrences and their changes. Soil desiccation is critical for the intensification and propagation of heatwaves, but its relative importance compared to other well-known large-scale atmospheric mechanisms, such as persistent atmospheric blocking systems and horizontal warm advection, remains elusive, especially in the context of a changing climate. In the second study, we utilize machine learning along with intervention experiments to estimate the respective contributions of soil water content 𝐶_𝑠𝑤𝑐 and atmospheric circulation 𝐶_𝑎𝑡𝑚 to daily maximum temperature in Western Europe, with a particular focus on the 2022 summer events. Our results reveal that during the two unparalleled heatwave events that occurred in June and July of 2022, the impact 𝐶_𝑠𝑤𝑐 on the heatwave intensity was on average approximately 40% of 𝐶_𝑎𝑡𝑚, and was comparable to 𝐶_𝑎𝑡𝑚 in continental dry-to-wet transition regions. Reviewing heatwaves in recent three decades, the percentage of heatwave areas that are significantly influenced by soil moisture-air temperature coupling has increased by 11.4% per decade. Additionally, for regions that have experienced heatwaves in at least 5 out of the past 33 years, about 21.7% areas, mostly in the transition zones, witness a significant increase in 𝐶_𝑠𝑤𝑐; while only 2.5% exhibit a substantial increase in 𝐶_𝑎𝑡𝑚. Furthermore, we find within the transitional climates, the intensification of heat extremes is mainly resulted from soil moisture depletion rather than atmospheric anomalies; while in (dry) Spain and the (wet) northern areas of central Europe, it is the variations in atmospheric circulation and soil desiccation that jointly fuel the persistent heatwaves. Our study emphasizes the observation-based large and increasing importance of soil moisture coupling in intensifying summer heatwaves and provides insights into future climates in extra-tropical regions like Western Europe, where a warmer and drier future is projected. 𝐂𝐡𝐚𝐩𝐭𝐞𝐫 𝟑: Earth system models (ESMs) and climate simulations are extensively employed to study the dynamics of climate and project long-term changes in the climate system. Despite their widespread use, large uncertainties persist among these models regarding the estimation of the continental gross primary productivity (GPP) and land carbon sink, which compromise the reliability of projections concerning future atmospheric carbon dioxide (𝐶𝑂₂) concentrations and the assessment of how terrestrial ecosystems respond to and might mitigate some of global warming. In ESMs, convection and clouds are one major source of such uncertainties—they are not only the most uncertain factors in the modeling of ``physical'' climate and also significantly affect the land carbon cycle through complex interactions involving radiation, moisture, and thermal pathways. In the third study, to isolate the role of clouds on the terrestrial carbon cycle, two models—the Community Earth System Model (CESM) and its super-parameterized counterpart (SPCESM, abbreviated as SP), which only differ in their representation of convection and clouds, are analyzed under present-day climatology to assess the impact of cloud representations on GPP. Compared with CESM, SP shows a 12.8% decrease in total cloud fraction within the 60°𝑆 ∼ 60°𝑁 range, which results in a notable GPP decline of 5.6 𝑃𝑔𝐶 𝑦𝑟⁻¹. This divergence, equivalent to 4.4% of terrestrial GPP in CESM, is comparable to the inter-annual variability in GPP and the uncertainty of GPP observed across climate models with diverse representations, extending beyond just cloud-related processes. Further analysis decomposes the GPP divergence between CESM and SP into two additive components and demonstrates that three-quarters of the difference is attributed to the negative impact from reduced cloud cover on light use efficiency (LUE) from CESM to SP, while the remaining one quarter is due to the positive impact from enhanced photosynthetically active radiation (PAR). An explainable machine learning model equipped with SHAP values further identifies two primary mechanisms underlying the lower LUE estimation in SP. Firstly, diminished clouds lead to higher air temperatures and reduced precipitation, creating a drier environment that prompts plants to regulate stomatal conductance to minimize water loss through transpiration, thereby suppressing the exchange rate of 𝐶𝑂₂ between biosphere and atmosphere. Secondly, the reduction in diffused radiation restricts the photosynthesis of shaded leaves. Combined, these two mechanisms reduce plant LUE, outweigh the beneficial impacts of increased PAR on photosynthesis, and ultimately lead to the declined terrestrial biosphere productivity in SP. Overall, we identify the representation of clouds as a key process for the terrestrial carbon cycle.

Este trabalho objetiva contribuir com o planejamento da geração de energia elétrica por meio da utilização de geração fotovoltaica de forma distribuída, ou seja, instalada e em operação em paralelo junto com a rede de distribuição de energia elétrica. Utiliza-se uma abordagem hipotético-dedutiva, buscando hipóteses, na forma de questões orientadoras, que serão testadas por meio do tratamento dos dados coletados e sua posterior análise e interpretação. O método de procedimento é o estudo de caso, sendo escolhida a cidade de Curitiba e o restante dos municípios compreendendo sua Região Metropolitana. A partir da elaboração da revisão na literatura, visando constituir a fundamentação teórica desta pesquisa, é elaborado um breve inventário estatístico e do aspecto de geração de energia elétrica da cidade de Curitiba, no contexto do estado do Paraná. Os procedimentos metodológicos envolvem a simulação de cenários de inserção de geração fotovoltaica distribuída, considerando diferentes níveis de penetração, e seus efeitos sobre curvas de carga reais para a cidade de Curitiba. Foram selecionados 12 dias, considerados críticos, para a análise que contemplou a contribuição fotovoltaica em termos da redução do consumo de energia elétrica, redução de emissões de CO2 e, por fim, capacidade do sistema fotovoltaico em reduzir a demanda máxima do sistema elétrico. Constatou-se que o intervalo de capacidade instalada em energia solar fotovoltaica situa-se entre 40,80 MWp e 55,68 MWp, desconsiderando exceções, e remete a valores de máximo Fator Efetivo de Capacidade de Carga (FECC), para condição de irradiação máxima e irradiação típica, no inverno e verão. Dessa forma, este intervalo é considerado apropriado do ponto de vista do aumento da capacidade do sistema elétrico, devido à presença de geradores fotovoltaicos distribuídos. Além disso, o referido intervalo além de aumentar em mais de 50% a capacidade do sistema elétrico, acarreta em redução anual do consumo de energia elétrica entre 50,8 GWh e 69,4 GWh, além de evitar a emissão de 18.501 toneladas de CO2-eq a 25.251 toneladas de CO2-eq, sendo, portanto, um importante vetor para o aumento da oferta de energia elétrica, aumento da capacidade do sistema elétrico e, por fim, redução de emissões de Gases do Efeito Estufa, principalmente o CO2. / This study aims to deepen knowledge in the item electricity generation planning through the use of distributed generation using solar photovoltaic energy, which means that photovoltaic systems are able to operate in parallel with the electricity distribution network. A hypothetical-deductive approach was developed, seeking hypotheses in the form of guiding questions, which will be tested by treatment of the collected data and their analysis and interpretation. The method of procedure is the case study, being applied to the Metropolitan Region of Curitiba. The literature review aims to be the theoretical basis of this research, therefore it mainly consists of a brief statistical and electrical energy inventory of the city of Curitiba in Paraná state. The methodological procedures involve the simulation of different scenarios for distributed PV generators by varying their Penetration Level, so that the effects on actual load curves for the region analyzed were quantified. 12 critical days were selected to the analysis that included the photovoltaic contribution in terms of reducing electrical energy consumption, reducing CO2 emissions and, finally, the capacity of the photovoltaic systems to reduce the maximum demand of the electrical system of the city. It was concluded that the most appropriate PV Penetration Level, in terms of power, regards with 40,80 MWp up to 55,68 MWp, disconsidering exceptions. This result leads to maximum values of Effective Load Carrying Capacity (ELCC), for maximum and typical solar radiation, during the seasons of winter and summer. In result, this proposed interval represents the better peak shaving capability of PV, because of its higher ELCC parameter. Furthermore, in addition to increase more than 50% in the capacity of the electrical system, there is an annual amount of energy generated about 50.8 GWh and 69.4 GWh, which represents 18,501 to 25,251 tons of CO2-eq avoided. For this reason, solar PV energy is an extremely important and feasible strategy to enhance the electricity generation, the capacity of the electrical system and to reduce greenhouse gases emission, especially CO2.