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Browsing by Author "Hurrell, James W., advisor"

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    Assessing outcomes in stratospheric aerosol injection scenarios shortly after deployment
    (Colorado State University. Libraries, 2022) Hueholt, Daniel M., author; Hurrell, James W., advisor; Barnes, Elizabeth A., advisor; Conant, Richard T., committee member
    Current global actions to reduce greenhouse gas emissions are very likely to be insufficient to meet climate targets outlined under the Paris Agreement. This motivates performing research on possible methods for intervening in the Earth system to minimize climate risk while decarbonization efforts continue. One such hypothetical climate intervention is stratospheric aerosol injection (SAI), where reflective particles would be emitted into the stratosphere to cool the planet by reducing solar insolation. The climate response to SAI is not well understood, particularly on short-term time horizons frequently used by decision makers and planning practitioners to assess climate information. This knowledge gap limits informed discussion of SAI outside the scientific community. We demonstrate two framings to explore the climate response in the decade after SAI deployment in modeling experiments with parallel SAI and no-SAI simulations. The first framing, which we call a snapshot around deployment, displays change over time within the SAI scenarios and corresponds to the question "What happens before and after SAI is deployed in the model?" The second framing, the intervention impact, displays the difference between the SAI and no-SAI simulations, corresponding to the question "What is the impact of a given intervention relative to climate change with no intervention?" We apply these framings to annual mean 2-meter temperature, precipitation, and a precipitation extreme in the first two experiments to use ensembles of Earth system models that comprehensively represent both the SAI injection process and climate response, and connect these results to implications for other climate variables. The parallel SAI and no-SAI simulations in these experiments allow us to explore the climate response in the context of the response to SAI, the underlying greenhouse gas forcing scenario, and the noise from internal climate variability.
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    Assessing the impact of stratospheric aerosol injection on convective weather environments in the United States
    (Colorado State University. Libraries, 2023) Glade, Ivy, author; Hurrell, James W., advisor; Rasmussen, Kristen L., committee member; Anderson, Brooke, committee member
    Continued climate warming, together with the overall development and implementation of climate mitigation and adaptation approaches, has prompted increasing research into the potential of proposed solar climate intervention (SCI) methods, such as stratospheric aerosol injection (SAI). SAI would reflect a small amount of incoming solar radiation away from the Earth to reduce warming due to increasing greenhouse gas concentrations. Research into the possible risks and benefits of SAI relative to the risks from climate change is emerging. There is not yet, however, an adequate understanding of how SAI might impact human and natural systems. To date, little or no research has been done to examine how SAI might impact environmental conditions critical to the formation of severe convective weather over the United States (U.S.), for instance. We use parallel ensembles of Earth system model simulations of future climate change, with and without hypothetical SAI deployment, to examine possible future changes in thermodynamic and kinematic parameters critical to the formation of severe weather during convectively active seasons over the U.S. Southeast and Midwest. We find that simulated forced changes in thermodynamic parameters are significantly reduced under SAI relative to a no-SAI world, while simulated changes in kinematic parameters are more difficult to distinguish. We also find that unforced internal climate variability may significantly modulate the projected forced climate changes over large regions of the U.S.
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    Impact of forced and internal climate variability on changes in convective environments over the eastern United States
    (Colorado State University. Libraries, 2022) Franke, Megan E., author; Hurrell, James W., advisor; Rasmussen, Kristen L., committee member; Mueller, Nathan D., committee member
    Hazards from convective weather and severe storms pose a serious threat to the continental United States (CONUS). Previous studies have examined how future projected changes in climate might impact the frequency and intensity of severe weather using simulations with both convection permitting regional models and coarser-grid Earth system models. However, most of these studies have been limited to single representations of the future climate state with little insight into the uncertainty of how the population of convective storms may change. To more thoroughly explore this aspect, we utilize a large-ensemble of climate model simulations to investigate the forced response and how it may be modulated by internal variability. Specifically, we use daily data from an ensemble of 50 climate simulations with the most recent version of the Community Earth System Model (CESM) to examine changes in the severe weather environment over the eastern CONUS during boreal spring from 1870-2100. Our results indicate that the large-scale convective environment changed little between 1870 and 1990, but from then throughout the 21st century, convective available potential energy increases while 0-6 km vertical wind shear and convective inhibition decreases (increased stability). While the forced changes in these variables are robust both in space and time, we show that they are likely to be modified significantly by internal climate variability. This effect can either act to significantly enhance the forced response or conversely, suppress it in such a way that produces changes in the convective environment that are opposite to the forced response. The time evolution of bivariate distributions of convective indices illustrates that future springtime convective environments over the eastern CONUS will be characterized by relatively less frequent, but deeper and more intense convection. Future convective environments will also be less supportive of the most severe convective modes and their associated hazards.