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Climate and Air Quality Impact of Using Ammonia as an Alternative Shipping Fuel

Abstract: As carbon-free fuel, ammonia has been proposed as an alternative fuel to facilitate maritime decarbonization. Deployment of ammonia-powered ships is proposed as soon as 2024. However, NOx, NH3 and N2O from ammonia combustion could impact air quality and climate. In this study, we assess whether and under what conditions switching to ammonia fuel might affect climate and air quality. We use a bottom–up approach combining ammonia engine experiment results and ship track data to estimate global tailpipe NOx, NH3 and N2O emissions from ammonia-powered ships with two possible engine technologies (NH3–H2 (high NOx, low NH3 emissions) vs pure NH3 (low NOx, very high NH3 emissions) combustion) under three emission regulation scenarios (with corresponding assumptions in emission control technologies), and simulate their air quality impacts using GEOS–Chem High Performance global chemical transport model.

We find that the tailpipe N2O emissions from ammonia-powered ships have climate impacts equivalent to 5.8% of current shipping CO2 emissions. Globally, switching to NH3–H2 engines avoids 16,900 mortalities from PM2.5 and 16,200 mortalities from O3 annually, while the unburnt NH3 emissions (82.0 Tg NH3 yr-1) from pure NH3 engines could lead to 668,100 additional mortalities from PM2.5 annually under current legislation. Requiring NH3 scrubbing within current Emission Control Areas leads to smaller improvements in PM2.5-related mortalities (22,100 avoided mortalities for NH3–H2 and 623,900 additional mortalities for pure NH3 annually), while extending both Tier III NOx standard and NH3 scrubbing requirements globally leads to larger improvement in PM2.5-related mortalities associated with a switch to ammonia-powered ships (66,500 avoided mortalities for NH3–H2 and 1,200 additional mortalities for pure NH3 annually).

Our findings suggest that while switching to ammonia fuel would reduce tailpipe greenhouse gas emissions from shipping, stringent ammonia emission control is required to mitigate the potential adverse effects on air quality.

Showcasing advances and building community in modeling for sustainability (Intro to SPECIAL FEATURE: Modeling Dynamic Systems for Sustainable Development)

Abstract: We organized this Special Feature on “Modeling Dynamic Systems for Sustainable Development” to showcase the field’s recent advances. Much recent research in sustainability science has mobilized data and theory to better understand systems that include interacting people, technologies, institutions, ecosystems, and both social and environmental processes. A recent National Academies workshop and an Annual Review paper identified several challenges and open questions for the field, stressing the importance of developing and testing new theories to advance knowledge and guide action. However, there has been less attention in sustainability science towards integrating modeling with theory and data-focused approaches. Modeling is necessary for making projections about the dynamical implications of our present understanding of nature-society systems – which is essential to determining whether long term trends in nature-society interactions are consistent with sustainable development goals, and to analyze whether particular interventions (e.g. technologies, policies, behavior) are likely to change those interactions in ways that promote such goals.

The papers in this Special Feature highlight advances in simulating coupled nature-society systems. We believe that these techniques, if they were more widely adopted, could significantly improve the capacity of sustainability science researchers to test
theory, mobilize data, and inform action. Each contribution to the Special Feature addresses a specific area in which novel modeling approaches have demonstrated the capacity to advance theory and insight more broadly. The contributions were selected to be illustrative rather than comprehensive, and to facilitate connections across the communities they represent.

 

Mutual Reinforcement of Land-based Carbon Dioxide Removal and International Emissions Trading in Deep Decarbonization Scenarios

Abstract: Carbon dioxide removal (CDR) technologies and international emissions trading are both widely represented in climate change mitigation scenarios, but the interplay among them has not been closely examined.

By systematically varying key policy and technology assumptions in a global energy-economic model, we find that CDR and international emissions trading are mutually reinforcing in deep decarbonization scenarios.

This occurs because CDR potential is not evenly distributed geographically, allowing trade to unlock this potential, and because trading in a net-zero emissions world requires negative emissions, allowing CDR to enable trade. Since carbon prices change in the opposite direction as the quantity of permits traded and CDR deployed, we find that the total amount spent on emissions trading and the revenue received by CDR producers do not vary strongly with constraints on emissions trading or CDR. However, spending is more efficient and GDP is higher when both CDR and trading are available.

SPECIAL FEATURE: Modeling Dynamic Systems for Sustainable Development

Abstract: The Modeling Dynamic Systems for Sustainable Development Special Feature showcases recent advances in modeling that, if more widely adopted, could significantly improve the capacity of sustainability science researchers to test theory, mobilize data, and evaluate interventions. The contributors show how new methods and approaches for analyzing complex interactions in nature–society systems can help to link knowledge with action in society’s efforts to address the core challenges of sustainable development.

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