The non-CO₂ climate impact of aviation strongly relies on the atmospheric conditions at the time and location of emissions. Therefore, it is possible to mitigate their associated climate impact by planning trajectories to re-route airspace areas with significant climate effects. Identifying such climate-sensitive regions requires specific weather variables. Inevitably uncertain weather forecasts can lead to inefficient aircraft trajectories if not accounted for within flight planning. The current study addresses the problem of generating robust climate-friendly flight plans under meteorological uncertainty characterized using the ensemble prediction system. We introduce a framework based on the concept of robust tracking optimal control theory to formulate and solve the proposed flight planning problem. Meteorological uncertainty effects on aircraft performance variables are captured using the formulated ensemble aircraft dynamical model and controlled by penalizing the performance index variance. Case studies show that the proposed approach can generate climate-optimized trajectories with minimal sensitivity to weather uncertainty.

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The optimization of aircraft trajectories involves balancing operating costs and climate impact, which are often conflicting objectives. To achieve compromised optimal solutions, higher-level information such as preferences of decision-makers must be taken into account. This paper introduces the SolFinder 1.0 module, a decision-making tool designed to identify eco-efficient aircraft trajectories, which allow for the reduction of the flight's climate impact with limited cost penalties compared to cost-optimal solutions. SolFinder 1.0 offers flexible decision-making options that allow users to select trade-offs between different objective functions, including fuel use, flight time, NOx emissions, contrail distance, and climate impact. The module is included in the AirTraf 3.0 submodel, which optimizes trajectories under atmospheric conditions simulated by the ECHAM/MESSy Atmospheric Chemistry model. This paper focuses on the ability of the module to identify eco-efficient trajectories while solving a bi-objective optimization problem that minimizes climate impact and operating costs. SolFinder 1.0 enables users to explore trajectory properties at varying locations of the Pareto fronts without prior knowledge of the problem results and to identify solutions that limit the cost of reducing the climate impact of a single flight.@en

The Modular Earth Submodel System (MESSy) provides an interface to couple submodels to a base model via a modular flexible data management facility. This paper presents the newly developed MESSy submodel, ACCF version 1.0 (ACCF 1.0), based on algorithmic Climate Change Functions version 1.0 (aCCFs 1.0), which describes the climate impact of aviation emissions. The ACCF 1.0 is coupled via the second version of the standard MESSy infrastructure. ACCF 1.0 takes the simulated atmospheric conditions at the location of emission as input to calculate the climate impact (in terms of average temperature response over 20 years (ATR20)) of aviation emissions, including CO2 and non-CO2 impacts, such as from NOx emissions (via ozone production and methane destruction), water vapour emissions, and contrail-cirrus. The online calculated ATR20 value per emitted mass fuel burn or flown-kilometer using ACCF 1.0 in the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model is presented. We perform quality checks of the ACCF 1.0 outputs in two aspects. Firstly, we compare climatological values calculated by the ACCF 1.0 to previous studies. Secondly, we evaluate the reduction of NOx-induced O3 effects through trajectory optimization, employing the tagging chemistry approach (contribution approach to tag species according to their emission categories and to inherit these tags to other species during the subsequent chemical reactions). Finally, we couple the ACCF 1.0 to the air traffic simulation submodel AirTraf version 2.0 and demonstrate the variability of the flight trajectories when the efficacy of individual effect is considered.@en

Aviation aims to reduce its climate effect by adopting trajectories that avoid regions of the atmosphere where aviation emissions have a large impact. To that end, prototype algorithmic climate change functions (aCCFs) can be used, which provide spatially and temporally resolved information on aviation's climate effect in terms of future near-surface temperature change. These aCCFs can be calculated with meteorological input data obtained from, e.g., numerical weather prediction models. We present here the open-source Python library called CLIMaCCF, an easy-to-use and flexible tool which efficiently calculates both the individual aCCFs (i.e., aCCF of water vapor, nitrogen oxide (NOx)-induced ozone production and methane depletion, and contrail cirrus) and the merged non-CO2 aCCFs that combine all these individual contributions. To construct merged aCCFs all individual aCCFs are converted to the same physical unit. This unit conversion needs the technical specification of aircraft and engine parameters, i.e., NOx emission indices and flown distance per kilogram of burned fuel. These aircraft- and engine-specific values are provided within CLIMaCCF version V1.0 for a set of aggregated aircraft and engine classes (i.e., regional, single-aisle, wide-body). Moreover, CLIMaCCF allows the user to choose from a range of physical climate metrics (i.e., average temperature response for pulse or future scenario emissions over the time horizons of 20, 50, or 100 years). Finally, we demonstrate the abilities of CLIMaCCF through a series of example applications.@en

Aviation contributes to 3.5% of anthropogenic climate change in terms of Effective Radiative Forcing (ERF) and 5% in terms of temperature change. Aviation climate impact is expected to increase rapidly due to the growth of air transport sector in most regions of the world and the effects of the COVID-19 pandemic are expected to only have a temporary effect on this growth. While efforts have been made to curb CO2 emissions, non-CO2 effects that are at least equally significant according to recent research, require more attention. The EU Horizon 2020 project ClimOp considers a comprehensive approach to tackling the climate impact of aviation using novel operational measures. One such measure is climate-optimised flight planning, where small deviations can be made in aircraft trajectories to minimise their overall climate impact. Algorithmic Climate Change Functions (aCCFs) are used to estimate the climate impact of local non-CO2 effects such as nitrogen oxide (NOx) emissions (via ozone (O3) formation and methane (CH4) depletion), aviation water vapour (H2O) and contrails using weather variables directly as inputs. By using these functions in an air traffic optimisation module, climate sensitive regions are detected and avoided leading to climate-optimised trajectories. Here, we focus specifically on evaluating the effectiveness of reducing the aviation NOx induced climate impact via O3 formation, using only O3 aCCFs for the optimisation strategy. This is achieved using the chemistry climate model EMAC (ECHAM5/MESSy) and various submodels. A summer and winter day, characterised by high spatial variability of O3 aCCFs are selected, following which, air traffic over the European airspace is optimised with respect to climate as well as operating cost. The air traffic is laterally and vertically optimised separately to enable an evaluation of the horizontal and vertical pattern of O3 aCCFs. It is shown that despite the significant impact of the synoptic situation on the transport of emitted NOx, the climate-optimised flights lead to lower O3 Radiative Forcing (RF) compared to the cost-optimised flights. The study finds that while O3 aCCFs can reduce the climate impact, there are certain discrepancies in the prediction of O3 impact from aviation NOx emissions, as seen for the selected summer day. Although the aCCFs concept is a rough simplification in predicting future pathways of emissions and subsequent climate impact, we could show that it enables a reasonable first estimate. Further research is required to better describe the aCCFs allowing an improved estimate in O3-RF reduction for optimisation approaches.@en

Climate impact of anthropogenic activities is more and more of public concern. But while CO₂ emissions are accounted in emissions trading and mitigation plans, emissions of non-CO₂ components contributing to climate change receive much less attention. One of the anthropogenic emission sectors, where non-CO₂ effects play an important part, is aviation. Hence, for a quantitative estimate of total aviation climate impact, assessments need to comprise both CO₂ and non-CO₂ effects (e.g., water vapor, nitrogen dioxide, and contrails), instead of calculating and providing only CO₂ impacts. However, while a calculation of CO₂ effects relies directly on fuel consumption, for non-CO₂ effects detailed information on aircraft trajectory, engine emissions, and ambient atmospheric conditions are required. As often such comprehensive information is not available for all aircraft movements, a simplified calculation method is required to calculate non-CO₂ impacts. In our study, we introduce a simple calculation method which allows quantifying climate assessment relying on mission parameters, involving distance and geographic flight region. We present a systematic analysis of simulated climate impact from more than 1000 city pairs with an Airbus A330-200 aircraft depending on the flight distance and flight region to derive simplified but still realistic representation of the non-CO₂ climate effects. These new formulas much better represent the climate impact of non-CO2 effects compared to a constant CO₂ multiplier. The mean square error decrease from 1.18 for a constant factor down to 0.24 for distance dependent factors and can be reduced even further to 0.19 for a distance and latitude dependent factor.

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One possibility to reduce the climate impact of aviation is the avoidance of climate-sensitive regions, which is synonymous with climate-optimised flight planning. Those regions can be identified by algorithmic Climate Change Functions (aCCFs) for nitrogen oxides (NOx), water vapour (H2O) as well as contrail cirrus, which provide a measure of climate effects associated with corresponding emissions. In this study, we evaluate the effectiveness of reducing the aviation-induced climate impact via ozone (O3) formation (resulting from NOx emissions), when solely using O3 aCCFs for the aircraft trajectory optimisation strategy. The effectiveness of such a strategy and the associated potential mitigation of climate effects is explored by using the chemistry–climate model EMAC (ECHAM5/MESSy) with various submodels. A summer and winter day, characterised by a large spatial variability of the O3 aCCFs, are selected. A one-day air traffic simulation is performed in the European airspace on those selected days to obtain both cost-optimised and climate-optimised aircraft trajectories, which more specifically minimised a NOx-induced climate effect of O3 (O3 aCCFs). The air traffic is laterally and vertically re-routed separately to enable an evaluation of the influences of the horizontal and vertical pattern of O3 aCCFs. The resulting aviation NOx emissions are then released in an atmospheric chemistry–climate simulation to simulate the contribution of these NOx emissions to atmospheric O3 and the resulting O3 change. Within this study, we use O3-RF as a proxy for climate impact. The results confirm that the climate-optimised flights lead to lower O3-RF compared to the cost-optimised flights, although the aCCFs cannot reproduce all aspects of the significant impact of the synoptic situation on the transport of emitted NOx. Overall, the climate impact is higher for the selected summer day than for the selected winter day. Lateral re-routing shows a greater potential to reduce climate impact compared to vertical re-routing for the chosen flight altitude. We find that while applying the O3 aCCFs in trajectory optimisation can reduce the climate impact, there are certain discrepancies in the prediction of O3 impact from aviation NOx emissions, as seen for the summer day. Although the O3 aCCFs concept is a rough simplification in estimating the climate impact of a local NOx emission, it enables a reasonable first estimate. Further research is required to better describe the O3 aCCFs allowing an improved estimate in the Average Temperature Response (ATR) of O3 from aviation NOx emissions. A general improvement in the scientific understanding of non-CO2 aviation effects could make climate-optimised flight planning practically feasible@en

The aviation industry is an essential contributor to total anthropogenic climate change, and the ever-growing demand for air transport requires serious attention. While efforts have been made to curb CO2 emissions, non-CO2 effects that are even more significant according to recent research have not been given enough attention. The EU Horizon 2020 project ClimOp steps in to follow a more holistic approach to tackling the climate impact of aviation using novel operational measures. One such measure is climate-optimised flight planning, where small deviations can be made in aircraft trajectories to minimise their overall climate impact. Algorithmic Climate Change Functions (aCCFs) are used to estimate the climate impact of local non-CO2 effects such as Nitrogen oxide (NOx) emissions (via Ozone formation and Methane depletion), aviation water vapour, and contrails by using meteorological inputs directly. By plugging these functions directly into an aircraft trajectory optimization module, climate sensitive regions are detected and avoided leading to climateoptimised trajectories. While a preliminary verification conducted specifically for NOx-ozone aCCFs showed positive signs, this research entails a more detailed verification procedure, which provides a deeper insight into its capability in predicting the impact of aviation NOx emissions on atmospheric changes in ozone. Air traffic simulation is performed concerning a subset of one-day European flights on the specifically chosen days characterized by high variability of NOx-ozone aCCFs. The air traffic on these days is optimized for cost and climate. A subsequent chemistry simulation captures the NOx effects from these re-routing procedures, and the climate impact of both scenarios can thereby be directly compared. It is expected that the results will confirm the effectiveness of NOx-ozone aCCFs in producing climate-friendly trajectories. @en

The aviation industry is an essential contributor to total anthropogenic climate change, and the ever-growing demand for air transport requires serious attention. While efforts have been made to curb CO2 emissions, non-CO2 effects that are even more significant according to recent research have not been given enough attention. The EU Horizon 2020 project ClimOp steps in to follow a more holistic approach to tackling the climate impact of aviation using novel operational measures. One such measure is climate-optimised flight planning, where small deviations can be made in aircraft trajectories to minimise their overall climate impact. In order to achieve this, algorithmic Climate Change Functions (aCCFs) are used to estimate the climate impact of local non-CO2 effects such as Nitrogen oxide (NOx) emissions (via Ozone formation and Methane depletion), aviation water vapour, and contrails by using meteorological inputs directly. By plugging these functions directly into an aircraft trajectory optimisation module, climate sensitive regions are detected and avoided leading to climate optimised trajectories. While a preliminary verification conducted specifically for NOx-ozone aCCFs showed positive signs, this research entails a more detailed verification procedure, which provides a deeper insight into its capability in predicting the impact of aviation NOx emissions on atmospheric changes in ozone. Air traffic simulation is performed concerning a subset of one-day European flights on the specifically chosen days characterised by high variability of NOx-ozone aCCFs. The air traffic on these days is optimised for cost and climate. A subsequent chemistry simulation captures the NOx effects from these re-routing procedures, and the climate impact of both scenarios can thereby be directly compared. It is expected that the results will confirm the effectiveness of NOx-ozone aCCFs in producing climate-friendly trajectories.@en

Air traffic contributes to global warming through CO2 and non-CO2 effects, including the impact of NOx emissions on atmospheric ozone and methane, formation of contrails, and changes in the amount of stratospheric water vapour. The climate impact of non-CO2 effects is highly dependent on the background atmospheric conditions at the time and location of emission. Therefore, there is the potential of mitigating the climate impact of aviation by optimizing the aircraft trajectories. In the present paper, we focus on the properties of alternative trajectories which have the potential to minimize the climate impact of NOx emissions, under a multitude of weather patterns. This study aims at enhancing the understanding of the relation between NOx-climate impacts and routing strategies, by employing the European Center Hamburg general circulation model (ECHAM) and the Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model. To this end, we conduct 1-year simulations with the air traffic submodel AirTraf 2.0, coupled to the EMAC model. We optimize 85 European flights, considering the atmospheric conditions at the time and location of the flight, to calculate the expected climate impact from the emitted species through a set of prototype algorithmic Climate Change Functions (aCCFs). The mean flight altitudes of NOx-climate optimal trajectories showed seasonal and latitudinal dependencies. We found that the potential of reducing ozone effects from aviation NOx is subjected to a strong seasonal cycle, reaching a minimum in summer. @en

Climate-optimized routing is an operational measure to effectively reduce the climate impact of aviation with a slight increase in aircraft operating costs. This study examined variations in the flight characteristics among five aircraft routing strategies and discusses several characteristics of those routing strategies concerning typical weather conditions over the North Atlantic. The daily variability in the North Atlantic weather patterns was analyzed by using the European Center Hamburg general circulation model (ECHAM) and the Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model in the specified dynamics mode from December 2008 to August 2018. All days of the ten complete winters and summers in the simulations were classified into five weather types for winter and into three types for summer. The obtained frequency for each of the weather types was in good agreement with the literature data; and then representative days for each weather type were selected. Moreover, a total of 103 North Atlantic flights of an Airbus A330 aircraft were simulated with five aircraft routing strategies for each representative day by using the EMAC model with the air traffic simulation submodel AirTraf. For every weather type, climate-optimized routing shows the lowest climate impact, at which a trade-off exists between the operating costs and the climate impact. Cost-optimized routing lies between the time-and fuel-optimized routings and achieves the lowest operating costs by taking the best compromise between flight time and fuel use. The aircraft routing for contrail avoidance shows the second lowest climate impact; however, this routing causes extra operating costs. Our methodology could be extended to statistical analysis based on long-term simulations to clarify the relationship between the aircraft routing characteristics and weather conditions.

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An operational measure to aim for mitigation of aviation climate impact that is inspired by migrant birds is to fly in aerodynamic formation. This operational measure adapted to human aircraft would eventually save fuel and is, therefore, expected to reduce the climate impact of aviation. As this method changes beside the total emission also the location of emission it is necessary to assess its climate impact with a climate response model to assure a benefit for climate. Therefore, the climate response model AirClim was adopted to account for saturation effects occurring for formation flight. The results for case studies comprising typical air traffic scenario show that on average the fuel consumption can be decreased by 5%, the climate impact, however, can be reduced by up to 24%. @en

A climate-optimized routing is expected as an operational measure to reduce the climate impact of aviation, whereas this routing causes extra aircraft operating costs. This study performs some air traffic simulations of nine aircraft routing strategies which include the climate-optimized routing, and examines characteristics of those routings. A total of 103 trans-Atlantic flights of an Airbus A330 is simulated for five weather types in winter and for three types in summer over the North Atlantic by using the chemistry-climate model EMAC with the air traffic simulation submodel AirTraf. For every weather type, the climate-optimized routing shows the minimum climate impact, whereas a trade-off exists between the costs and the climate impact. The cost-optimized routing lies between time- and fuel-optimized routings, and minimizes the costs. The aircraft routing for minimum contrail formation shows the second-lowest climate impact, whereas this routing also causes extra costs. @en

Aviation contributes to climate change, and the climate impact of aviation is expected to increase further. Adaptations of aircraft routings in order to reduce the climate impact are an important climate change mitigation measure. The air traffic simulator AirTraf, as a submodel of the European Center HAMburg general circulation model (ECHAM) and Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model, enables the evaluation of such measures. For the first version of the submodel AirTraf, we concentrated on the general setup of the model, including departure and arrival, performance and emissions, and technical aspects such as the parallelization of the aircraft trajectory calculation with only a limited set of optimization possibilities (time and distance). Here, in the second version of AirTraf, we focus on enlarging the objective functions by seven new options to enable assessing operational improvements in many more aspects including economic costs, contrail occurrence, and climate impact. We verify that the AirTraf setup, e.g., in terms of number and choice of design variables for the genetic algorithm, allows us to find solutions even with highly structured fields such as contrail occurrence. This is shown by example simulations of the new routing options, including around 100 North Atlantic flights of an Airbus A330 aircraft for a typical winter day. The results clearly show that AirTraf 2.0 can find the different families of optimum flight trajectories (three-dimensional) for specific routing options; those trajectories minimize the corresponding objective functions successfully. The minimum cost option lies between the minimum time and the minimum fuel options. Thus, aircraft operating costs are minimized by taking the best compromise between flight time and fuel use. The aircraft routings for contrail avoidance and minimum climate impact reduce the potential climate impact which is estimated by using algorithmic climate change functions, whereas these two routings increase the aircraft operating costs. A trade-off between the aircraft operating costs and the climate impact is confirmed. The simulation results are compared with literature data, and the consistency of the submodel AirTraf 2.0 is verified.@en

An operational measure that is inspired by migrant birds aiming toward the mitigation of aviation climate impact is to fly in aerodynamic formation. When this operational measure is adapted to commercial aircraft it saves fuel and is, therefore, expected to reduce the climate impact of aviation. Besides the total emission amount, this mitigation option also changes the location of emissions, impacting the non-CO₂ climate effects arising from NO_x and H₂O emissions and contrails. Here, we assess these non-CO₂ climate impacts with a climate response model to assure a benefit for climate not only due to CO₂ emission reductions, but also due to reduced non-CO₂ effects. Therefore, the climate response model AirClim is used, which includes CO₂ effects and also the impact of water vapor and contrail induced cloudiness as well as the impact of nitrogen dioxide emissions on the ozone and methane concentration. For this purpose, AirClim has been adopted to account for saturation effects occurring for formation flight. The results of the case studies show that the implementation of formation flights in the 50 most popular airports for the year 2017 display an average decrease of fuel consumption by 5%. The climate impact, in terms of average near surface temperature change, is estimated to be reduced in average by 24%, with values of individual formations between 13% and 33%.

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This paper studies the impacts on flight trajectories, such as lateral and vertical changes, when avoiding the formation of persistent contrails for transatlantic flights. A sophisticated Earth-System Model (EMAC) coupled with a flight routing submodel (AirTraf) and a contrail submodel (CONTRAIL) is used to optimize flight trajectories concerning the flight time and the flight distance through contrail forming regions (contrail distance). All the trajectories are calculated taking into account the effects of the actual and local meteorological parameters, e.g., wind, temperature, relative humidity, etc. A full-year simulation has been conducted based on a daily flight schedule of 103 transatlantic flights. The trade-off between the flight time and contrail distance shows a large daily variability, meaning for the same increase in flight time, the reduction in contrail distance varies from 20% to 80% depending on the daily meteorological situation. The results confirm that the overall changes in flight trajectories follow a seasonal cycle corresponding to the nature of the potential contrail coverage. In non-summer seasons, the southward and upward shifts of the trajectories are favorable to avoid the contrail formation. In summer, the northward and upward shifts are preferred. A partial mitigation strategy for up to 40% reduction in contrail distance can be achieved throughout all the seasons with a negligible increase in flight time (less than 2%), which represents a reasonable trade-off between flight time increase and contrail avoidance.@en

For the first time, the algorithmic Climate Change Functions (aCCFs) for ozone, methane, water vapor, and persistent contrails have been developed within the ATM4E project to provide information on the climate sensitive regions, which can be conveniently implemented for the climate based flight routing. These aCCFs need to be verified before they are implemented. In this paper, we focus on the verification of the ozone aCCFs to enable the prediction of the short-term NOx effects from aviation en-route. The verification is conducted from two aspects. Firstly, the climatology of the ozone aCCFs is calculated based on a one-year simulation and verified by the existing literature. Secondly, the effectiveness of the ozone aCCFs for optimizing aircraft trajectories concerning the climate impact is verified by the comprehensive climate-chemistry model calculation. @en

Comprehensive assessment of the environmental aspects of flight movements is of increasing interest to the aviation sector as a potential input for developing sustainable aviation strategies that consider climate impact, air quality and noise issues simultaneously. However, comprehensive assessments of all three environmental aspects do not yet exist and are in particular not yet operational practice in flight planning. The purpose of this study is to present a methodology which allows to establish a multi-criteria environmental impact assessment directly in the flight planning process. The method expands a concept developed for climate optimisation of aircraft trajectories, by representing additionally air quality and noise impacts as additional criteria or dimensions, together with climate impact of aircraft trajectory. We present the mathematical framework for environmental assessment and optimisation of aircraft trajectories. In that context we present ideas on future implementation of such advanced meteorological services into air traffic management and trajectory planning by relying on environmental change functions (ECFs). These ECFs represent environmental impact due to changes in air quality, noise and climate impact. In a case study for Europe prototype ECFs are implemented and a performance assessment of aircraft trajectories is performed for a one-day traffic sample. For a single flight fuel-optimal versus climate-optimized trajectory solution is evaluated using prototypic ECFs and identifying mitigation potential. The ultimate goal of such a concept is to make available a comprehensive assessment framework for environmental performance of aircraft operations, by providing key performance indicators on climate impact, air quality and noise, as well as a tool for environmental optimisation of aircraft trajectories. This framework would allow studying and characterising changes in traffic flows due to environmental optimisation, as well as studying trade-offs between distinct strategic measures@en