Browsing by Subject "Global warming"

Now showing 1 - 9 of 9

A Climate Saved is a Climate Earned
(2020-12) Hirsh, Emily
Combined effects of global warming and a shutdown of the Atlantic meridional overturning circulation on West African and European climate
(2012-05) Brown, Meredith Guenevere Longshore; Cook, Kerry Harrison, 1953-; Fu, Rong; Dickinson, Robert E.; Jackson, Charles S.
The Atlantic meridional overturning circulation has a vast potential for abrupt climate change due to its large heat transport through the ocean and its nonlinear dynamics. Because of these unique properties, this paper investigates how the climate of West Africa and Europe will respond to a shutdown of the Atlantic meridional overturning circulation at the end of the 21st century. Here we use a regional climate model with 90-km grid spacing is forced by an idealized sea-surface temperature anomaly, based upon coupled atmosphere/ocean global model water hosing experiments, with a business-as-usual global warming scenario to discover how West African and European climate will change. In both the boreal spring and summer, cooling in the eastern Atlantic is associated with a strong intensification and eastward extension of the North Atlantic subtropical high over Europe throughout the depth of the atmosphere, a strengthening of the heat low over West Africa at low levels, and a weakening of the Saharan High in the upper atmosphere. Rainfall rates also decrease markedly throughout most of West Africa and Europe: in spring, rainfall rates decrease by 50-80% over Sahelian Africa, in summer rainfall over Europe decreases by up to 90%, while precipitation over West Africa is reduced by 40%.
Deciphering changes in rainfall events and the consequences over Texas under global warming
(2023-08-10) Tabassum, Sabiha; Yang, Zong-liang; Jackson, Charles S; Rempe, Daniella M; Niyogi, Dev; Passalacqua, Paola
The far-reaching impacts of global warming on precipitation patterns warrant our unwavering attention. As the atmosphere heats up, heightened water vapor levels lead to more intense and frequent severe weather, exacerbating the risk of floods. Conversely, shifts in rainfall distribution could incite prolonged droughts and diminished water access in specific regions. Given the societal and economic repercussions of these extremes, comprehending their evolving nature becomes paramount. This study employs General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to explore shifts in rainfall and their consequences for Texas amid global warming. In Chapter 2, I meticulously evaluate the performance of the CMIP6 GCMs in representing the observed rainfall characteristics over Texas. Subsequently, I scrutinize projections from the most accurate GCMs to estimate changes in extreme rainfall events. The analysis reveals a more pronounced increase in the annual maximum 5-day rainfall (Rx5day) in the near-future (2021-2050) than long-term (2071-2100) when compared to the historical period (1985-2014). In Chapter 3, I use a data driven approach to develop a statistical relationship between flood height at critical infrastructures and precipitation during historical tropical cyclones (TC) in Texas. This relationship is then extrapolated to anticipate future flood risks based on projected extreme rainfall. The findings illuminate heightened vulnerabilities to damage and disruptions from future TC-induced floods in specific areas. In Chapter 4, I assess prospective changes in streamflow within the Colorado River Basin (CRB) using GCMs selected based on their ability to represent the observed climatic characteristics over the CRB. The results signal substantial alternations in CRB streamflow and an escalated probability of extreme flow occurrences. Cumulatively, this dissertation underscores the urgency for adaptable strategies to confront the intricate challenges stemming from evolving Texas rainfall patterns in a warming climate.
Environmental controls on African rainfall variability
(2023-04-12) Zhao, Siyu; Cook, Kerry Harrison, 1953-; Vizy, Edward K.; Persad, Geeta; Okumura, Yuko; Heimbach, Patrick
Local African communities heavily depend on rain-fed agriculture, which are vulnerable to the impacts of extreme weather and climate variability/change. However, challenges remain in predicting African rainfall. For instance, climate models with cumulus convective parametrization lack the ability to explicitly simulate mesoscale convective systems that produce much of the total rainfall over West Africa. This study aims to improve our understanding of African rainfall variability, using state-of-the-art rainfall observations and convective-permitting (CP) ensemble simulations. This work is organized into three research projects. In the first project, we evaluate the influence of Walker circulations on East African Rainfall. Three Walker circulations are identified near East Africa, namely, the East African, the Indian Ocean, and the Congo Basin Walker Circulations. Less (more) precipitation occurs over equatorial East Africa during October – December with a strong (weak) Indian Ocean Walker Circulation. The rainfall anomalies are associated with anomalous mid-level divergence over equatorial East Africa that is likely induced by horizontal moist static energy advection. In the second project, we investigate how the observed shrinkage of Lake Chad since the 1970s affects the local climate using CP simulations. A smaller lake area enhances the local precipitation by limiting the spatial extent of daytime lake breezes, which would otherwise induce low-level subsidence/divergence and suppress local afternoon rainfall. In addition, a shallow planetary boundary layer over the large lake weakens turbulent vertical mixing, reducing low- to mid-level humidity and the likelihood of convection triggering compared to the small lake. In the third project, we analyze the roles of thermodynamic and dynamic controls on intense storms over the West African Sahel with climate change. Future-Warming simulations are run with initial/boundary conditions prescribed by the current-climate data plus CMIP6 multi-model mean anomalies. The 99th (99.9th) 24-hr precipitation increases from 42 (77) mm in the current climate to 59 (104) mm in the future over the analysis region (12°N-18°N, 9°W-20°E). Increased low-tropospheric moisture (gradient) is more closely associated with this rainfall intensification than enhanced low- to mid- level vertical wind shear. Both moisture and shear conditions are related to the storm area and propagating speed that affect local rainfall accumulation.
Life cycle global warming emissions for natural gas
(2012-08) Randel, Tony Lynn; Allen, David T.; Crawford, Richard
Climate change is a topic of social and political commentary and controversy, and is a topic that will continue to be addressed by future scientists and laypersons alike. This report contains information and laboratory exercises for use in a greenhouse gas (GHG) and global warming potential (GWP) learning module, to be employed in secondary or entry level university engineering and environmental science curricula. Exercises include a hands-on experience with the greenhouse effect and calculations of GWP for 20-year and 100-year timeframes.
Petrophysical modeling and simulation study of geological CO₂ sequestration
(2014-05) Kong, Xianhui; Delshad, Mojdeh; Wheeler, Mary F. (Mary Fanett)
Global warming and greenhouse gas (GHG) emissions have recently become the significant focus of engineering research. The geological sequestration of greenhouse gases such as carbon dioxide (CO₂) is one approach that has been proposed to reduce the greenhouse gas emissions and slow down global warming. Geological sequestration involves the injection of produced CO₂ into subsurface formations and trapping the gas through many geological mechanisms, such as structural trapping, capillary trapping, dissolution, and mineralization. While some progress in our understanding of fluid flow in porous media has been made, many petrophysical phenomena, such as multi-phase flow, capillarity, geochemical reactions, geomechanical effect, etc., that occur during geological CO₂ sequestration remain inadequately studied and pose a challenge for continued study. It is critical to continue to research on these important issues. Numerical simulators are essential tools to develop a better understanding of the geologic characteristics of brine reservoirs and to build support for future CO₂ storage projects. Modeling CO₂ injection requires the implementation of multiphase flow model and an Equation of State (EOS) module to compute the dissolution of CO₂ in brine and vice versa. In this study, we used the Integrated Parallel Accurate Reservoir Simulator (IPARS) developed at the Center for Subsurface Modeling at The University of Texas at Austin to model the injection process and storage of CO₂ in saline aquifers. We developed and implemented new petrophysical models in IPARS, and applied these models to study the process of CO₂ sequestration. The research presented in this dissertation is divided into three parts. The first part of the dissertation discusses petrophysical and computational models for the mechanical, geological, petrophysical phenomena occurring during CO₂ injection and sequestration. The effectiveness of CO₂ storage in saline aquifers is governed by the interplay of capillary, viscous, and buoyancy forces. Recent experimental data reveals the impact of pressure, temperature, and salinity on interfacial tension (IFT) between CO₂ and brine. The dependence of CO₂-brine relative permeability and capillary pressure on IFT is also clearly evident in published experimental results. Improved understanding of the mechanisms that control the migration and trapping of CO₂ in the subsurface is crucial to design future storage projects for long-term, safe containment. We have developed numerical models for CO₂ trapping and migration in aquifers, including a compositional flow model, a relative permeability model, a capillary model, an interfacial tension model, and others. The heterogeneities in porosity and permeability are also coupled to the petrophysical models. We have developed and implemented a general relative permeability model that combines the effects of pressure gradient, buoyancy, and capillary pressure in a compositional and parallel simulator. The significance of IFT variations on CO₂ migration and trapping is assessed. The variation of residual saturation is modeled based on interfacial tension and trapping number, and a hysteretic trapping model is also presented. The second part of this dissertation is a model validation and sensitivity study using coreflood simulation data derived from laboratory study. The motivation of this study is to gain confidence in the results of the numerical simulator by validating the models and the numerical accuracies using laboratory and field pilot scale results. Published steady state, core-scale CO₂/brine displacement results were selected as a reference basis for our numerical study. High-resolution compositional simulations of brine displacement with supercritical CO₂ are presented using IPARS. A three-dimensional (3D) numerical model of the Berea sandstone core was constructed using heterogeneous permeability and porosity distributions based on geostatistical data. The measured capillary pressure curve was scaled using the Leverett J-function to include local heterogeneity in the sub-core scale. Simulation results indicate that accurate representation of capillary pressure at sub-core scales is critical. Water drying and the shift in relative permeability had a significant impact on the final CO₂ distribution along the core. This study provided insights into the role of heterogeneity in the final CO₂ distribution, where a slight variation in porosity gives rise to a large variation in the CO₂ saturation distribution. The third part of this study is a simulation study using IPARS for Cranfield pilot CO₂ sequestration field test, conducted by the Bureau of Economic Geology (BEG) at The University of Texas at Austin. In this CO₂ sequestration project, a total of approximately 2.5 million tons supercritical CO₂ was injected into a deep saline aquifer about ~10000 ft deep over 2 years, beginning December 1st 2009. In this chapter, we use the simulation capabilities of IPARS to numerically model the CO₂ injection process in Cranfield. We conducted a corresponding history-matching study and got good agreement with field observation. Extensive sensitivity studies were also conducted for CO₂ trapping, fluid phase behavior, relative permeability, wettability, gravity and buoyancy, and capillary effects on sequestration. Simulation results are consistent with the observed CO₂ breakthrough time at the first observation well. Numerical results are also consistent with bottomhole injection flowing pressure for the first 350 days before the rate increase. The abnormal pressure response with rate increase on day 350 indicates possible geomechanical issues, which can be represented in simulation using an induced fracture near the injection well. The recorded injection well bottomhole pressure data were successfully matched after modeling the fracture in the simulation model. Results also illustrate the importance of using accurate trapping models to predict CO₂ immobilization behavior. The impact of CO₂/brine relative permeability curves and trapping model on bottom-hole injection pressure is also demonstrated.
Presentation: Global Warming - Lone Star Impacts
(Environmental Science Institute, 2009-12-11) Environmental Science Institute; North, Gerald R.
The risk of ending a solar radiation management program abruptly
(2009-12) Agrawal, Shubham; Bickel, J. Eric; Lasdon, Leon
Climate change as a result of anthropogenic activities calls for reduction of greenhouse gas emissions to avoid dangerous consequences on society. However, abatement of emission is a costly process and adversely affects the economic growth. Recent proposals, therefore, suggested a different approach i.e. Geoengineering. Instead of controlling emissions, Geoengineering modifies the climate by changing global energy fluxes either by increasing the amount of outgoing infrared radiation through reduction of greenhouse gases (GHGs) or by decreasing the amount of solar radiation falling upon the earth’s surface by increasing the albedo (reflectivity) of the atmosphere. Most popular geoengineering strategies are Air Capture (AC) and Solar Radiation Management (SRM) and many economic studies have shown large net monetary benefits with their application. But, these studies neglected the risks which can arise due to potential failure to sustain SRM after few decade of its deployment. There is a concern that application of SRM will lead to increase in concentration of carbon-dioxide in atmosphere and its abrupt turning off can lead to rise in temperature and thereby huge monetary losses. In this report, consequences of abruptly turning off of SRM have been analyzed. A modified version of DICE (Dynamic Integrated model of Climate and the Economy) model that incorporates negative SRM forcing and a two phase optimization procedure has been used for the study. Different outcomes such as net change in NPV of climate damage and abatement costs, maximum mean temperature of earth surface, increase in temperature, emissions control rate, carbon taxes, etc due to abrupt ending of SRM have been analyzed. Results show that application of SRM with a risk of abrupt turnoff is still more profitable compared to not using it at all.
Understanding preciptation changes over West Africa and North America under global warming and identifying a Congo Basin Walker circulation
(2015-05) Neupane, Naresh; Cook, Kerry Harrison, 1953-; Dickinson, Robert E.; Fu, Rong; Jackson, Charles S.; Scanlon, Bridget R.
Studies have shown that the Atlantic Ocean affects West African rainfall. However, the response of the West African monsoon to Atlantic warming is not understood clearly. My dissertation explores this by analyzing idealized simulations with a regional climate model. Below 1.5 K warming of the Atlantic, rainfall increase by 30-50% over the Sahel. In contrast, above 2 K, rainfall decreases substantially. Atlantic warming is accompanied by decreases in low-level geopotential heights in the Atlantic decreasing the large-scale meridional geopotential height gradient across West Africa. This leads to easterly wind anomalies in the Sahel. Below 2 K, these easterly anomalies allow moisture transport to the Sahel. Above 2 K, the easterly anomalies reverse the westerly flow and reduce precipitation in the Sahel. Models predict increases of precipitation in the future under global warming. Theoretical understanding of this is founded in the Clausius-Clapeyron equation. I compare precipitation from the theory with the model simulations over the U.S. for the mid-21st century and investigate the physics of the departure of the model from theory. In the spring and fall precipitation increases, up to 30%/ K, and the modeled precipitation matches the theoretical prediction. In contrast, rainfall lowers and prediction fails in the summer. These differences are associated with the soil moisture distributions. Associated with the increased soil moisture, model follows theoretical prediction in the spring and fall, while reduced soil moisture is associated with failure of the theoretical prediction in the summer. The Gulf of Guinea in the eastern Atlantic shows subsidence. This subsidence becomes well established in the low-level from July-September. Using observations, I contribute to understanding its cause and relationship with the regional precipitation and circulation. This subsidence is associated with the subsiding-branch of a Congo basin Walker circulation identified here. The circulation has a rising-branch over the Congo basin, and is driven by temperature gradient. Basin temperature remains almost uniform throughout the year, but in association with the Atlantic cold tongue formation, Guinean temperature cools up to -4 K in the summer. This gradient drives the circulation. A strong Walker circulation is associated with enhanced northward moisture transport.