Mitigating anthropogenic climate change with aqueous green energy: Direct air carbon dioxide capture and storage powered by ocean thermal energy conversion
Date
2023
Authors
Olim, Sophia
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Publisher
University of Victoria
Abstract
In the 2015 Paris Accords, 196 nations agreed to keep global warming below 2°C and to pursue efforts to limit it to below 1.5°C. The Earth has already warmed by around 1.1°C since preindustrial times ( Masson-Delmotte et al., 2022; Shukla et al., 2022). If worldwide fossil fuel combustion was immediately eliminated, the direct and indirect net cooling effect of atmospheric aerosol loading would rapidly dissipate. The aerosol cooling realised since the preindustrial era would be eliminated, resulting in an additional warming of around 0.6°C and taking the Earth rapidly to an around 1.7°C warming. In 2018 the Intergovernmental Panel on Climate Change noted the requirement of widespread negative emissions technology in order to meet this 1.5°C target (Masson-Delmotte et al., 2022; Rumjaun et al., 2018).
In direct air CO2 capture and storage (DACCS), CO2 is scrubbed from the atmosphere and injected into underground geological formations (Keith et al., 2018). Carbon dioxide is a potent greenhouse gas and is the focus of many negative emissions technologies. Ocean thermal energy conversion (OTEC) is a form of electricity production that exploits the temperature difference between deep and shallow ocean waters, analogous to land-based heat pumps. OTEC requires a temperature gradient of at least 18°C and is most efficient in the tropics, due to the high temperature gradient between shallow warm water (around 25 metres deep) and deep cold waters (around 1000 metres deep) (Nihous, 2005). The UVic Earth System Climate Model (UVic ESCM) is used to explore the feasibility of using OTEC to power DACCS as a negative emissions technology in order to help mitigate anthropogenic climate change.
Once this CO2 has been removed from the atmosphere, it needs to be injected where it can remain safely stored. In marine environments, sedimentary basins along continental shelves, such as depleted oil and gas fields, are the most geologically sound choice for this (Celia et al., 2015; Strutt et al., 2003). In order to maximise OTEC power production while limiting the need to transport this energy away from the source, offshore OTEC plants are used to power DACCS in two selected oil and gas basins of suitable size in the tropics. OTEC power production of 3 TW of electricity powering DACCS can result in a global relative decrease of 277 parts per million CO2 by 2100 and a relative temperature decrease of 1.18°C, compared to diagnosed emissions from the IPCC 2018 “business as usual” RCP 8.5 scenario.
There are potential negative impacts to implementing OTEC on a large scale including changes in ocean temperatures, biological productivity, precipitation patterns, and atmosphere-ocean variability (Rau and Baird, 2018; Devault and Péné-Annette, 2017; Rajagopalan and Nihous, 2013; Nihous, 2005). While these must be considered, this combination of green energy and negative emission technology offers an exciting new approach to help mitigate anthropogenic climate change.
Supervisors: Andrew Weaver and Michael Eby
Description
Keywords
ocean thermal energy conversion (OTEC), direct air carbon dioxide capture and storage (DACCS), net zero emissions, aqueous green energy, carbon capture, carbon storage