CMI Annual Report 2022

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Critical Hydrogen Emission Intensity for Methane Mitigation PRINCIPAL INVESTIGATORS: MATTEO BERTAGNI, STEPHEN PACALA, FABIEN PAULOT AND AMILCARE PORPORATO At a Glance Hydrogen (H 2 ) energy will play a crucial role in decarbonizing some energy sectors to reach worldwide net-zero carbon emissions. However, atmospheric hydrogen interferes with greenhouse gases like methane, water vapor and ozone. This means that hydrogen losses across the supply chain may offset some of the climate benefits of hydrogen adoption. Hydrogen's interaction with atmospheric methane, the second most important greenhouse gas, is of particular importance because methane mitigation is recognized as the most effective solution for near-term climate change mitigation. The research explored the impact of hydrogen emissions on atmospheric methane, quantifying a critical hydrogen emission rate (HEI) above which methane increases despite reducing fossil fuel use. This information will help inform bp about the importance of minimizing hydrogen losses to limit hydrogen climate impact. Research Highlight The use of H 2 will be essential toward decarbonizing the energy and transport sectors where direct electrification may not be feasible, like heavy industry, heavy-duty road transport, shipping and aviation. H 2 fuel also offers a promising solution to reduce air pollution and store intermittent renewable energy. However, the impact of future hydrogen losses due to leakages, venting, purging and incomplete combustion are not clearly understood and may complicate hydrogen’s future role. H 2 is neither a pollutant nor a direct greenhouse gas. It is, however, an indirect greenhouse gas because it interferes with methane, water vapor and ozone in the atmosphere. Most recent evaluations give H 2 a global warming potential of around 10 for a 100-year time horizon and about 35 for a 20-year time horizon (Warwick et al., 2022) demonstrating that the potential climate impact of H 2 emissions is significant. The feedback of hydrogen on atmospheric methane is particularly important to climate change. Methane has been the second largest contributor to atmospheric warming since the beginning of the industrial era, and there are global efforts to mitigate its atmospheric level. Porporato’s group has been addressing this problem by developing a box model for the coupled atmospheric system of 39 Carbon Mitigation Initiative Twenty-second Year Report 2022
methane and hydrogen (Bertagni et al., 2022). The hydrogen and methane budgets are deeply interconnected for several natural and anthropogenic reasons (Figure 8.1). First, both gases are removed by the radical hydroxide (OH), the ‘atmosphere detergent’. An increase in the concentration of tropospheric H 2 would reduce the availability of OH for methane oxidation. This, in turn, would increase the amount of atmospheric methane. Second, methane oxidation leads to hydrogen formation. Third, hydrogen and methane are linked at the industrial level because most of the current and nearterm future H 2 production comes from steam methane reforming. Figure 8.1. Sketch of H 2 and CH 4 tropospheric budgets and their interconnections: 1) the competition for hydroxide (OH); 2) the production of H 2 from CH 4 oxidation; and 3) the potential emissions [minimum-maximum] due to a more hydrogenbased energy system. Flux estimates (Tg/year) are from Ehhalt et al. (2009) and Saunois et al. (2020). Arrows are scaled with mass flux intensity, the CH 4 scale being 10 times narrower than H 2 scale. The research finds that hydrogen displacement of fossil fuel energy can have very different consequences for atmospheric methane, depending on the amount of hydrogen lost and the methane emissions associated with hydrogen production. The research defines a critical hydrogen emission intensity (HEI) at which hydrogen losses completely offset the reduction in methane emissions as a result of lower fossil fuel use (Figure 8.2). For green H 2 , which is hydrogen obtained from renewable sources, the critical HEI is around 9%. This has an uncertainty of ±3%, which is related to how OH consumption is partitioned among the atmospheric gases and how much atmospheric H 2 is consumed by soil bacteria. For blue H 2 , which is hydrogen obtained from steam methane reforming coupled with carbon capture and storage, the critical HEI is much lower and greatly depends on the methane emissions associated with hydrogen production. Notably, if methane losses are above 1%, blue hydrogen displacement of fossil fuel energy offers no benefit for methane mitigation. Carbon Mitigation Initiative Twenty-second Year Report 2022 40
Page 1 and 2: Annual Report 2022
Page 3 and 4: Contents INTRODUCTION 1 RESEARCH -
Page 5 and 6: The Carbon Mitigation Initiative (C
Page 7 and 8: gases. Knowing how much hydrogen le
Page 9 and 10: Best Paper Awards 2022 Since 2010,
Page 11 and 12: Research - At a Glance REPEAT Proje
Page 13 and 14: Understanding Drivers of Hurricane
Page 15 and 16: How the Orography-Aware Land Model
Page 17 and 18: Research Highlight The Biden Admini
Page 19 and 20: Figure 1.2. Difference in sectoral
Page 21 and 22: Figure 2.1. Stylized project invest
Page 23 and 24: IRA Impacts on Prospective Economic
Page 25 and 26: Figure 3.1a. Levelized cost of fuel
Page 27 and 28: Figure 3.2a. Levelized cost of fuel
Page 29 and 30: India’s Deccan Traps Appear to Ha
Page 31 and 32: Figure 4.1a-d. Mapping the Deccan T
Page 33 and 34: Pore Structure and Permeability of
Page 35 and 36: Projecting the Expansion and Impact
Page 37 and 38: References Busecke, J.J.M., J. Resp
Page 39 and 40: 2022, 2023). This work has enabled
Page 41: Hsieh, T. L., G.A. Vecchi, W. Yang,
Page 45 and 46: The CMI Wetland Project: Understand
Page 47 and 48: particularly pronounced during the
Page 49 and 50: Land Conversion to Store Carbon: Th
Page 51 and 52: Understanding How Economic Incentiv
Page 53 and 54: The second part of our project dive
Page 55 and 56: may begin to convert to savanna bef
Page 57 and 58: Ongoing Research at the Pacala Lab
Page 59 and 60: Stanford Business School Dean Jon L
Page 61 and 62: Cipolla, G., S. Calabrese, A. Porpo
Page 63 and 64: Uden, S., and C. Greig, 2022. “Wh
Page 65 and 66: The cover and text pages of this re

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