UC Irvine

Stabilizing global climate will require major transformations to energy and food systems, including drastic reductions in the use of fossil fuels, improvements in energy and material efficiencies, extensive electrification of energy end uses, sustainable intensification of agriculture, and carbon management. Although progress has been made in researching these topics in recent years, several research questions central to framing global energy and agriculture policies deserve further study. In this dissertation, I explore several relevant research topics with the goal of contributing to our understanding of the opportunities and challenges for achieving net-zero emissions energy and food systems, including (1) the characteristics of modeled net-zero CO2 emissions energy systems; (2) the potential for seaweed farming to deliver globally-scaled carbon removal and emissions mitigation; and (3) potential solutions for hard-to-abate greenhouse gas emissions from the global food system. In scenarios that successfully reach net-zero CO2 emissions by the end of this century, renewable energy sources account for 60% of primary energy at net-zero on average (compared to ~14% today), with slightly less than half of that renewable energy derived from biomass. Meanwhile, electricity makes up approximately half of final energy consumed (compared to ~20% today), highlighting the extent to which solid, liquid, and gaseous fuels remain prevalent in the scenarios even when emissions reach net-zero. Residual emissions and offsetting negative emissions are not evenly distributed across world regions, which may have important implications for negotiations on burden-sharing, human development, and equity. Sinking farmed seaweed to the deep sea is a potential method to remove carbon from the atmosphere (i.e., negative emissions), and sequestering a gigaton of CO2 per year with this method may cost as little as $480/tCO2 on average. Instead, using farmed seaweed for products that avoid a gigaton of CO2-equivalent greenhouse gas emissions annually – by substituting for more emissions-intensive food or feed sources – could return a profit of $50/tCO2-eq. However, these costs depend on low farming costs, high seaweed yields, and assumptions that almost all carbon in seaweed is removed from the atmosphere (i.e., competition between phytoplankton and seaweed is negligible) and that seaweed products can displace products with substantial embodied non-CO2 GHG emissions, such as agricultural goods. Modern agriculture is extremely emissions-intensive, and sweeping systemic changes will be needed to reach net-zero. Shifting diets away from beef would have an outsized impact on decreasing the average emissions intensity of caloric production, and closing yield gaps is a top priority to increase production without increasing agricultural land area. Promising methods are being developed to suppress GHG emissions from enteric fermentation, soils, and rice paddies, although further research is needed to determine the long-term efficacy and scalability of solutions globally. Stopping deforestation is also a top priority, which will require aggressive policy action to enact strict land-use regulations. Ultimately, achieving net-zero emissions energy and food systems will entail an accelerated and coordinated global effort across multiple economic sectors.