ITS4.4/ERE1.10

Urban areas are major contributors to global greenhouse gas (GHG) emissions. To address climate change, many cities have developed climate action plans (CAPs) as strategic roadmaps to reduce their emissions and strive for emission neutrality and climate resilience by 2050 or before. It has been more than a decade since the first of these plans were put in place, and it is now important to evaluate these plans and to access whether city-level climate ambitions will be realised or perhaps need adjustment to pursue for improvements in climate resilience over time

 This work aims to further our understanding of urban GHG emissions, by completing existing urban carbon emissions data with blue-green contributions to the urban carbon cycle. In a previous study, it was found that the inclusion of blue-green emissions in urban carbon accounting in Stockholm, Sweden had a significant impact on that region’s ability to reach net zero emissions in the coming decades (Page et al., 2021). In this study, we complete the urban emissions data for cities across the European Union (EU) in order to assess if, and for which types of cities, the inclusion of blue-green emissions in the GHG accounting is similarly relevant.

Furthermore, we will use data about the CAPs produced and implemented by these cities together with the completed GHG emissions in order to assess whether the actions and plans made by many European cities have actually had any impact on the emissions from these cities. The inclusion of blue-green emissions and sequestrations in this assessment is particularly important, as many of the strategies included in CAPs impact blue-green areas, such as the implementation of nature-based solutions (NBS).

Conclusions will be drawn about the role of green-blue areas in urban GHG emissions, the role which CAPs have played in reducing emissions in European cities, and how and where these could potentially be adapted to further reduce future GHG emissions in urban areas.

Keywords: Sustainable cities; Greenhouse Gas Emissions; Nature-based Solutions; Climate Action Plans

References:

Page J, Kåresdotter E, Destouni G, et al. (2021) A more complete accounting of greenhouse gas emissions and sequestration in urban landscapes. Anthropocene 34: 100296. DOI: 10.1016/j.ancene.2021.100296.

How to cite: Page, J., Pan, H., and Kalantari, Z.: Completing Urban GHG Emissions Data to Assess the Effectiveness of Climate Action Plans in Europe, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5175, https://doi.org/10.5194/egusphere-egu22-5175, 2022.

Urban areas are notable sources of atmospheric CO₂ and cities are currently setting up climate programs with the aim of carbon neutrality in the near future. For example, two major cities in Southern Finland, Helsinki and Turku, have set their targets for 2035 and 2029, respectively. Carbon neutrality can be achieved by reducing carbon emissions, compensating them, and / or strengthening carbon sinks in urban vegetation and soils, the last of which is often deemed the most cost-efficient option. However, the current understanding of biogenic carbon cycling in urban environments is based on dynamics observed in more well-known ecosystems such as forests and agricultural lands. Urban ecosystems differ from non-urban areas in terms of temperature, precipitation and water cycling, pollution, and the level of human-induced disturbance. Thus, there is a need for observations on urban carbon to accurately model and estimate the carbon sinks and stocks in urban green space.

We aimed to monitor urban biogenic carbon cycle with an extensive field campaign carried out around the SMEAR III ICOS station in 2020–2022, accompanied by a few satellite sites around the capital region of Finland. In this presentation, we will show soil carbon pools and the dynamics of soil respiration at five different types of urban green space: a managed park lawn with and without trees, small urban forest, apple orchard, and street tree site. Soil respiration was measured with both regularly repeated manual chamber measurements and automatic chambers throughout two growing seasons. Soil carbon stock was estimated by soil samplings conducted in 2020 and 2021. We investigate the role of different drivers in soil CO₂ emission at the various urban green space types and compare those to corresponding metrics measured in non-urban areas. In addition, we test the applicability of Yasso model to simulate the soil carbon dynamics in urban areas.

How to cite: Karvinen, E., Järvi, L., Viskari, T., Havu, M., Kuuri-Riutta, O., Rauhamäki, P., Soininen, J., and Kulmala, L.: The potential of urban soils for carbon neutral cities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7868, https://doi.org/10.5194/egusphere-egu22-7868, 2022.

There is growing awareness of the role that agricultural soils can play for climate change mitigation. Agricultural management that increases soil organic carbon (SOC) stocks constitutes a nature-based solution for carbon dioxide removal. As soils store about twice the amount of carbon found in the atmosphere, even small relative increases could significantly reduce global warming.

However, increasing SOC requires management changes that come with costs to the farmers. In this regard, soil carbon certificates could provide a much-needed financial incentive: Farmers register their fields with commercial providers who certify any SOC increase achieved during a set period of time. The certificates are then sold on the voluntary carbon-offset market. We analysed the suitability of soil carbon certificates for climate change mitigation from the perspectives of soil sciences, agricultural management, and governance. In particular, we addressed questions of quantification, additionality, permanence, changes in emissions, leakage effects, transparency, legitimacy and accountability, as well as synergies and trade-offs with other societal targets.

Soil properties and the mechanisms by which carbon is stored in soils have strong implications for the assessment. Soils have a limited storage capacity, and SOC is not sequestered but its SOC stocks are the dynamic result of plant derived inputs and losses mainly in the form of microbial respiration. The higher the SOC stock, the higher the annual carbon inputs that is needed to maintain it. If carbon friendly management is discontinued, elevated SOC levels will therefore revert to their original level.

We found that while changes in agricultural management that increase SOC are highly desirable and offer multiple-co benefits with climate change adaptation, soil carbon certificates are unsuitable as a tool. They are unlikely to deliver the climate change mitigation they promise as certificate providers cannot guarantee permanence and additionality of SOC storage over climate relevant time-frames. Where the certified carbon storage is non-permanent or fails to meet criteria of additionality, the use of such certificates to advertise products as “carbon-neutral” may be construed as false advertising.

How to cite: Paul, C., Don, A., Bartkowski, B., Wiesmeier, M., Weigl, S., Mayer, S., Steffens, M., Wolf, A., Dönmez, C., and Helming, K.: Suitability of soil carbon certificates for climate change mitigation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10433, https://doi.org/10.5194/egusphere-egu22-10433, 2022.

Calls are rising for ecosystems, or green infrastructure, to complement engineered infrastructure for more effective disaster risk reduction and climate governance. Key international framework agreements, including the Sendai Framework for Disaster Risk Reduction 2015-2030 and the 2021 Glasgow Pact, noted the importance of ensuring the integrity of all ecosystems in addressing climate change and disaster risk. For example, vegetation can stabilize slopes to reduce mountain hazards and sand dunes, mangroves, and/or seagrasses can reduce the impacts of coastal storms.  However, there are gaps in the scientific evidence on this topic with few comprehensive, peer-reviewed studies to support decision-making on green infrastructure for disaster risk reduction.

This study systematically reviews 529 English-language articles published between 2000 and 2019. The objective was to catalogue the extent of knowledge and confidence in the role of ecosystems in reducing disaster risk. The main question this review addresses is: What is the evidence of the role that ecosystem services and/or functions contribute to disaster risk reduction? We modified the review methodology established by the Intergovernmental Panel on Climate Change to identify the robustness of evidence and level of agreement on the role of ecosystems in attenuating most common types of hazards.

The data demonstrate very robust links on the role of ecosystems in forest fire management, urban flooding and slope stabilization to reduce mountain hazards in a cost-effective manner. The study also highlights how ecosystems provide multiple services and functions in addition to regulating hazards, e.g., provisioning services for reducing vulnerability. The review highlights several research gaps, notably a geographic concentration of studies on urban areas of Europe and North America, and insufficient policy-relevant research on coastal, dryland, and watershed areas, especially in Asia, Africa and Latin America. To conclude, more attention should be paid to filling these research gaps and developing performance standards, which would provide policy-makers with increased confidence in investing in green infrastructure for disaster risk reduction and climate governance.

How to cite: Sudmeier-Rieux, Dr. K. and the Co-authors: Ecosystems for disaster risk reduction: what is the scientific evidence?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9109, https://doi.org/10.5194/egusphere-egu22-9109, 2022.

Globally, urban areas will face multiple water-related challenges in the near future. The main challenges are intensified droughts leading to water scarcity, increased flood risk due to extreme rainfall intensification, increased total water demand due to an increasing urban population, amplified urban heat island intensities due to urban sprawl, and reduction in urban carbon sink due to plant water stress. Urban greening is an excellent option for mitigating flood risk and excess urban heat. Meanwhile, rainwater harvesting (RWH) systems can cope with water supply needs and urban water management. In this study, we investigated how urban greening and RWH can work together to mitigate the aforementioned risks. We evaluate the joined-up management approach under climate projections for 30 cities in the USA spanning a variety of climates, population densities and urban landscapes. By incorporating a new RWH module in the urban ecohydrological model UT&C and flexible operational rules of reusing harvested water for domestic use and urban green space irrigation, we tested 4 intervention approaches: control, RWH installation, urban greening supported by RWH, and urban greening supported by traditional irrigation (i.e., supplying via mains water). Each intervention approach was evaluated using our adapted version of UT&C and forced by the last generation convection-permitting model simulations of current (2001-2011) and end-of-century (RCP8.5) climate from Weather Research and Forecasting (WRF). The volume of RWH is assumed to be 2000L per household for all cities. Results showed that neither urban greening nor RWH could contribute significantly to reducing the expected increase in canyon temperature, because of the strong change in background climate (i.e., increases in average atmospheric temperature). However, RWH alone can sufficiently reduce the intensifying surface flood risk and effectively enhance water conservation, and urban greening can significantly increase the carbon sink of cities especially in dry regions, and if supported by traditional irrigation. Those results vary with the background climate: the benefits of urban greening, either supported by RWH or traditional irrigation, on canyon temperature reduction and carbon sink improvement increased with average air temperature and decreased with wetness index respectively; the benefits of RWH on runoff reduction and water conservation are both positively dependent on local annual precipitation.

How to cite: Zhang, Z., Paschalis, A., Mijic, A., Dobson, B., and Butler, A.: Assessing co-benefits of urban greening coupled with rainwater harvesting management under current and future climates across USA cities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7324, https://doi.org/10.5194/egusphere-egu22-7324, 2022.

Abstract

The challenges posed by the growth of urbanization in Egypt and the development of new cities play an essential role in applying the circular economy (CE) in the construction materials sector and the priorities for promoting sustainable construction activities in the future. Therefore, the construction sector has many adverse environmental impacts on energy and natural resources consumption. Starting from materials production, operation until disposal to landfills. Consequently, the industry is considered one of the most consumers of non-renewable resources and producer of CO2 emissions. On the other hand, applying Nature-based solutions (NbS) to enhance sustainability by protecting the ecosystems and maintaining economic benefits plays a vital role, especially for new Egyptian cities. The research aims to investigate the role of applying NbS for achieving CE in construction materials and eliminate its negative impact in the scope of three factors:  green building materials, waste management systems, renewable energy use. The current research attempts to answer how NbS can improve the CE and reduce environmental impacts of the construction materials sector. Therefore, the SOWT analysis investigated the strengths, opportunities, weaknesses, and threats of using the NbS strategies for three different construction sites in Egypt. Furthermore, the survey questionnaire was applied to identify the interactions between the parameters derived from 40 participants such as consultants, architecture engineers, civil engineers, site engineers, project managers and review the previous research efforts. As a result, a conceptual framework was created for the construction materials considering reduce, reuse, recycle, recovery, and disposal, to identify the impact of the implementation of NbS on achieving sustainable development strategies in the Egyptian construction sector. The result showed that the NbS could effectively promote the construction sector and achieve environmental and economic benefits, which consequently help the transition to CE. Therefore, there is the necessity for developing new sustainable policies and cooperation between public and private sectors to support the investments of sustainable strategies in the construction materials market and increase Egyptian society's awareness of the benefits of NbS in economic, environmental, and social aspects.

 Keywords, Nature-based solution, Construction materials, Circular Economy, Egypt 

How to cite: Marey, H., Szabó, G., and Kozma, G.: Using the Nature-Based Solutions for Applying Circular Economy for the Construction Materials Sector in Egypt, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7997, https://doi.org/10.5194/egusphere-egu22-7997, 2022.

Nitrous oxide (N₂O) emitted from agricultural soils makes up a significant part of the collective agricultural greenhouse gas (GHG) emissions. These emission are to a large extent caused directly or indirectly by the application of nitrogenous fertilizer and there is a strong demand for mitigation strategies.

Nitrous oxide is produced in the soil in a range of different processes but mainly in microbial nitrification and denitrification. A number of factors exert influence on these microbial processes in the soil, most notably the oxygen concentration, availability of ammonium and nitrate, available organic matter and diffusivity, and fairly advanced process-based simulation models are often used in attempts to simulate the amount of N₂O emitted. Here we propose using more a simplistic modelling approach to provide a novel risk assessment tool for nitrogenous fertilizer applications to be implemented in Danish farmers field management programmes.

At SEGES Innovation we have unique database access to field activity data from Danish farmers - e.g. crop sequence, fertilizer applications, residue handling, soil texture - covering more than 85 % of the Danish cultivated area. Based on these data and field specific climate data, a soil water balance model (Plauborg et al. 1995) and soil organic carbon model (Taghizadeh-Toosi et al. 2014) are running in daily timesteps for all fields in the database. These models provide, respectively, the daily level of WFPS in the soil and the organic matter turnover rate in the soil simulated during the weather forecast period of 10 days. Those two outputs are combined with a simulated soil temperature in a simplified version of the NGAS-model (Parton et al. 1996) to give a rough simulated N₂O-emission for any planned fertilizer application throughout the weather forecast period.

The risk assessment tool exhibits this daily simulated N₂O-emission as a risk evaluation of fertilizer application to the farmer in field management programmes, where future field activities are entered and logged. The objective is to lower the GHG emission by reducing the number of fertilizer applications right at peak N₂O-emission conditions, once the farmers are presented with this information.    

How to cite: Vestergaard Poulsen, H., Bruun, S., Skov Nielsen, C., and Kolind Hvid, S.: N2O-emission risk assessment tool for nitrogenous fertilizer applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11878, https://doi.org/10.5194/egusphere-egu22-11878, 2022.

Facing the dual threats of climate and socio-economic changes, how the social-ecological systems (SES) in the Tibet Autonomous Region can seize the opportunity of ecological restoration to enhance the quality of the environment while improving the relationship between human and nature is of great significance to promote the regional sustainable development. Thus, regarding human as the key component, we used Ostrom’s SES framework as an analytical fundation to analyze the impact of the implementation of ecological engineering on local human-policy-resource connection. We distributed questionnaires for local residents, distinguished experimental groups (EG, n=325) and control groups (CG,n =165), and used a network approach to construct indicators for assessing effectiveness of ecological engineering, including overall connectivity and evenness. Meanwhile, random forest regression was used to explore the background variables of the dominant connection and accordingly proposed subsequent directions for optimal governance. We found that interviewees in areas where ecological engineering was implemented had more positive perceptions of the importance of ecosystem services, the relationship between ecological conservation and well-being, attitudes toward ecological engineering, and the impact of measures. The overall connectivity and evenness of EG were significantly higher than that of CG. The implementation of ecological engineering enhanced the connection between local people and the environment, but caused some inconvenience to local residents’ livelihoods. Besides, elevation and annual precipitation were the background variables that dominated the overall connectivity. The overall connectivity was lower in alpine steppes with elevation of around 4000 m and semi-arid areas with annual precipitation around 400-500 mm. The implementation of ecological engineering played a positive role in alleviating human-nature relationship in tensions and promoting collective governance of common pool resources, but the governance process still involved risks. Safeguarding and improving the residents’ livelihoods and enhancing the regional weak SES coupling due to geographical constraints are the future directions for optimal governance.

How to cite: Wang, Y., Liu, Y., Wu, X., Wang, X., Yao, Y., and Fu, B.: The implementation of ecological engineering in Tibet has strengthened the local human-policy-resource connection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1956, https://doi.org/10.5194/egusphere-egu22-1956, 2022.

Limiting global warming to 1.5°C by the end of the century currently seems to be an ambitious target which will potentially be accompanied by a period of temperature overshoot. Achieving this climate goal might require massive carbon dioxide removal on large scales. Regardless of the feasibility of such removals, their effects on biogeochemical cycles and climate are not well understood. Changes in atmospheric CO2 concentration ([CO2]) and climate alter the CO2 exchange between the atmosphere and the underlying carbon reservoirs of land and ocean. Carbon-concentration and carbon-climate feedback metrics are useful tools for quantifying such changes in the carbon uptake by land and ocean, currently acting as a sink of carbon. We investigate the changes in carbon feedbacks under overshoot scenarios that could influence mitigation pathways to achieve the temperature goal. An ensemble of Coupled Model Intercomparison Project 6 (CMIP6) Earth system models that conducted an idealized ramp-up and ramp-down experiment (1pctCO2, with increasing and later decreasing [CO2] at a rate of 1% per year) has been used and compared against a scenario simulation involving negative emissions (SSP5-3.4-OS). The analyses are based on results from biogeochemically coupled (where land and ocean respond to rising CO2 levels but the climate is kept constant) and fully coupled simulations. For the positive emission phases, the model-mean global average carbon-climate feedback looks roughly similar between the SSP5-3.4-OS and the 1pctCO2 simulations, with a gradual monotonic decreasing behavior in absolute values which translates to a reduction in land and ocean uptakes. The carbon-concentration feedback in SSP5-3.4-OS is larger than in the 1pctCO2 simulations over the ocean. Both the ocean and land simulate an increase in carbon uptake during the ramp-up, while during the ramp-down, their uptakes show a hysteresis behavior. This feature is more prominent in the idealistic 1pctCO2 experiment with a higher [CO2] growth rate and without land use change effects than in the more realistic SSP5-3.4-OS scenario. Also, the time evolution of the global annual carbon-concentration and carbon-climate feedbacks seem to be very similar over natural land areas. In addition, changes in carbon fluxes are compared over the high latitude permafrost and non-permafrost regions in the Northern Hemisphere. Over land, the carbon-concentration feedback metric is decomposed into different terms to investigate the contributions from changes in live vegetation carbon pools and soil carbon pools. This indicates that the feedback is dominated by the residence time of carbon in vegetation and soil. Furthermore, building on previous studies, feedback metrics are also calculated using an alternative approach of instantaneous flux-based feedback metrics to further compare differences between models. The difference between the two approaches can be seen more obviously in the geographical distribution of the two feedbacks, especially for the negative emission phases of the 1pctCO2 experiment.

How to cite: Asaadi, A., Schwinger, J., Lee, H., Tjiputra, J., Arora, V., Séférian, R., Liddicoat, S., Hajima, T., Santana-Falcòn, Y., and Jones, C.: Carbon cycle feedbacks in an idealized and a scenario simulation of carbon dioxide removal in CMIP6 Earth system models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8269, https://doi.org/10.5194/egusphere-egu22-8269, 2022.

Carbon dioxide removal (CDR) has become part of the portfolio of solutions to mitigate climate change. In combination with emission reductions, CDR may be critical to achieving the goal of limiting global warming to below 2°C, as outlined in the Paris Agreement. Due to its potential high productivity and environmental co-benefits, macroalgae cultivation has recently become a prominent ocean-based CDR strategy. However, estimates of the CDR potential of large-scale deployment are highly limited. Here we simulate idealized global deployment of macroalgae-based CDR using the NEMO-PISCESv2 ocean biogeochemical model at high spatial resolution (0.25° nominal horizontal resolution). Macroalgae growth is confined to the upper 100m of the water column in Exclusive Economic Zones (EEZ) free of sea ice and with an appropriate nitrate/phosphate regime. Although the loss of dissolved inorganic carbon (DIC) through macroalgal growth enhances the flux of atmospheric carbon into the ocean, this increase in carbon uptake is less than the rate of macroalgal production. In the absence of any nutrient limitation on growth, the enhancement in ocean carbon uptake is only 73-77% of the carbon lost from the water column due to macroalgal production. However, when macroalgae nutrient limitation/uptake is additionally accounted for, the increase in ocean carbon uptake accounts for only 41-42% of the potential carbon lost through macroalgae production. These inefficiencies are due to ocean transport replacing part of the DIC lost in the upper water column with DIC from depth, the influence of local nutrient concentrations on the vertical profile of macroalgal production, and feedbacks on the nutrient resources available for phytoplankton net primary production. CDR efficiency is shown to scale near-linearly between scenarios assuming 1% to 10% of the global EEZ area is cultivated for macroalgae. The efficiency of macroalgal CDR shows significant regional variability, with much of the enhancement in ocean carbon uptake (43%-46%) occurring outside EEZs, posing potential difficulties to national scale accounting.

How to cite: Berger, M., Bopp, L., Ho, D. T., and Kwiatkowski, L.: Assessing global macroalgal carbon dioxide removal potential using a high-resolution ocean biogeochemistry model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4699, https://doi.org/10.5194/egusphere-egu22-4699, 2022.

To achieve the ambitious but necessary climate targets set by the Paris Agreement, the IPCC model pathways for limiting global warming to 1.5°C compared to pre-industrial levels make apparent the need for safeguarding and enhancing the natural global carbon sink – including via carbon dioxide removal (CDR). A range of ocean-based CDR approaches, also termed “negative emissions technologies” (NETs), has been proposed to make use of the ocean’s potential to take up carbon dioxide from the atmosphere and store it in water, biomass, and sediments. The governance framework in place to regulate CDR in the ocean, at this time, is limited to the direct and articulate regulation of ocean fertilization. Meanwhile, other NETs such as ocean alkalinity enhancement and artificial upwelling emerge, but a comprehensive and foresight-oriented regulation for the testing or even deploying at larger scale is missing. Specifically, there is large uncertainty on unintended (positive and negative) effects of these technologies on the condition of the ocean, in addition to enhanced carbon uptake and storage, and how these may impede on or support other global sustainability goals. The deployment of NETs in the ocean poses additional governance complexities relating to unknowns, uncertainties, and transboundary issues. In a study that is part of the EU H2020-project OceanNETs, we explore to what extent the current global governance framework directly or indirectly regulates emerging ocean-based NETs and reflect on the particularities and requirements for their comprehensive governance. The analysis considers the gaps, challenges, needs, and opportunities for comprehensive governance of ocean-based NETs. 

How to cite: Neumann, B. and Röschel, L.: Global governance of ocean-based negative emission technologies. Exploring gaps, challenges, and opportunities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-893, https://doi.org/10.5194/egusphere-egu22-893, 2022.

There are many uncertainties surrounding solar radiation management (SRM), which cannot all be quantified and reduced using models, laboratory experiments or observations of natural analogs such as volcanic eruptions, ship tracks, or dust storms. While there is broad consensus both in- and outside the scientific community that better understanding of the climate system is beneficial to policy makers and society, the value of improved knowledge of SRM has been highly controversial. Yet, it is evident that SRM research can contribute to quantifying and reducing important uncertainties pertaining to fundamental knowledge on the workings of the Earth system, while also providing essential specific knowledge on positive and negative impacts of SRM to inform future decisions.

In 2016, a group of SRM experts gathered at the Institute for advanced sustainability studies in Potsdam for a workshop to formulate a set of low environmental impact SRM experiment proposals. We present these as a non-exhaustive set of possible experiments with no measurable environmental side effects that could provide valuable information that cannot be obtained from models or lab experiments. Both perturbative and non-perturbative experiments are proposed for different SRM methods including marine cloud brightening, stratospheric aerosol injection and cirrus cloud thinning.

It was found that in the time period between 2016 and now several of the research questions addressed in the experiment proposals have been answered by unrelated experimental environmental science studies, whereas no experimental studies have been carried out in the context of SRM. This finding shows that there is significant overlap in high priority research questions and outcomes of non-SRM and SRM environmental research. In addition, it shows that non-controversial environmental science experiments can provide similar SRM-relevant knowledge as dedicated SRM-experiments. Given that one of the main arguments against SRM research is the potential danger of the acquired knowledge, the finding that obtained knowledge of non-SRM and SRM experiments can be similar raises the question which effect the declared relationship to SRM on outdoors research proposal review and regulation should be.

How to cite: Futerman, G., Janssens, M., de Vries, I., Dykema, J., Parker, A., and Hunt, H.: Governance and science implications of low environmental impact outdoors solar radiation management experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7797, https://doi.org/10.5194/egusphere-egu22-7797, 2022.

There are many uncertainties surrounding solar radiation management (SRM), not in the least concerning the technological feasibility of hypothetical deployment scenarios. In sulfate stratospheric aerosol injection (SAI) scenarios, the radiative effectiveness of the aerosol is governed by its size distribution. In turn, aerosol size distribution is governed by the aerosol-precursor injection rate and injection plume conditions. Hence, uncertainties in cost and environmental impact of aircraft-based sulfate stratospheric aerosol injection (SAI) are primarily determined by uncertainties in injection plume conditions. In addition, the climate impacts and side effects of SAI as simulated by climate models depend on the prescribed initial conditions concerning aerosol characteristics, which also hinge on injection plume dynamics and microphysics.

Up to now, studies into aircraft-based SAI have used simplified plume models, which estimate plume dynamics with considerable uncertainty, and which do not account for effects of the local plume dynamics on the microphysical processes. Here, we work towards reducing this uncertainty by using full computational fluid dynamics representations of plume dynamics within simulations incorporating state-of-the-art microphysics models for the computation of aerosol size distributions in aircraft engine plumes.

In order to anchor our approach in the current literature, we first consider simplified problems with the objective of validating our methodology using existing results. These experiments confirm the attainability of favourable initial aerosol size distributions under roughly the same conditions as shown with other lower-fidelity models. However, our results retain disagreement with respect to previous studies concerning the exact aerosol growth behaviour, highlighting a sensitivity to model choice which may also explain apparent contradictions in those previous studies. 

We then consider a RANS computational fluid dynamic representation of an engine plume. This differs from the simplified plume representation in several ways, including realistic local variations in temperature, vorticity, and eddy viscosity resulting from the inflow determined using a state-of-the-art engine model. This representation is currently being employed in combination with the previously validated microphysical models to simulate realistic aerosol size evolutions for aircraft-based delivery scenarios.

We anticipate our results to (1) provide a higher-confidence foundation on which to base the discussion concerning technological feasibility of SAI-based SRM and (2) constrain the uncertainty range of inputs for model and impact studies, improving reliability of simulations of (desired and undesired) effects of potential SRM scenarios and thereby informing the scientific and public debate.  

How to cite: Tluk, A., de Vries, I., Janssens, M., and Hulshoff, S.: Towards higher fidelity simulations of aerosol growth in aircraft plumes for feasibility and impact assessment of sulfate stratospheric aerosol injection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7923, https://doi.org/10.5194/egusphere-egu22-7923, 2022.