Aviation significantly contributes to anthropogenic radiative forcing with both CO (Formula presented.) and non-CO (Formula presented.) emissions. In contrast to technical advancements to mitigate the climate impact, operational measures can benefit from short implementation times and thus are expected to be of high relevance in the near future. This study evaluates the climate mitigation potential of nine operational improvements, covering both in-flight and ground operations. For this purpose, an innovative approach is presented to compare the results of measure-specific case studies, despite the wide differences in the underlying modeling assumptions and boundary conditions. To this end, a selection of KPIs is identified to estimate the impact of the studied operational improvements on both climate and the stakeholders of the air transport system. This article presents a comparative method to scale the results of the individual studies to a comparable reference, considering differences in traffic sample size as well as CO (Formula presented.) and non-CO (Formula presented.) climate effects. A quantitative comparison is performed for operational improvements belonging to the same category, i.e., trajectory-related, network-related, and ground-related measures, and a qualitative comparison is carried out among all considered operational improvements. Results show that the in-flight operational improvements are more effective in mitigating the impact on climate with respect to ground operations. However, the latter generally have a weaker impact on the aviation industry and a higher maturity level. Further research could expand this study by assessing the effects of implementation enablers, such as actions at the regulatory level, to facilitate the acceptance of the studied measures in the aviation industry.

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Aviation contributes to about 3.5% of the total anthropogenic climate change when including non-CO2 effects, e.g., contrail formation and the impact of NOx emissions on ozone and methane. Among various non-CO2 effects, the contrail-cirrus radiative forcing is the largest (~2/3) with large uncertainties. The most critical affecting factor is the huge weather-induced variability of the radiative impact of individual contrails, which imposes challenges on formulating adequate mitigation measures and develop policy-driven implementation schemes, stressing relevance of reliable forecasts. The newly funded EU project BeCoM intends to address the uncertainties related to the forecasting of persistent contrails and their weather-dependent individual radiative effects. The project will focus on: 1) obtaining a larger and higher resolution database of relative humidity and ice supersaturation at cruise levels for assimilation into numerical weather prediction (NWP) models; 2) providing more adequate representation of ice clouds in their supersaturated environment in the NWP models; and 3) validation of the predictions to determine and reduce the remaining uncertainties of contrail forecasts. To facilitate the assimilation and validation process, a novel hybrid artificial intelligence algorithm will be developed. Based on the contrail prediction, the project will develop a policy framework for effective contrail avoidance through a trajectory optimization approach. The results will enable a better understanding of contrail’s climate impact and formulate recommendations on how to implement strategies to enable air traffic management to reduce aviation's climate impact.@en

Aviation is an important contributor to the global economy, satisfying society’s mobility needs. It contributes to climate change through CO₂ and non-CO₂ effects, including contrail-cirrus and ozone formation. There is currently significant interest in policies, regulations and research aiming to reduce aviation’s climate impact. Here we model the effect of these measures on global warming and perform a bottom-up analysis of potential technical improvements, challenging the assumptions of the targets for the sector with a number of scenarios up to 2100. We show that although the emissions targets for aviation are in line with the overall goals of the Paris Agreement, there is a high likelihood that the climate impact of aviation will not meet these goals. Our assessment includes feasible technological advancements and the availability of sustainable aviation fuels. This conclusion is robust for several COVID-19 recovery scenarios, including changes in travel behaviour.

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Air traffic contributes to anthropogenic global warming by about 5% due to CO₂ emissions and non-CO₂ effects, which are primarily caused by the emission of NO_x and water vapor as well as the formation of contrails. Since-in the long term-the aviation industry is expected to maintain its trend to grow, mitigation measures are required to counteract its negative effects upon the environment. One of the promising operational mitigation measures that has been a subject of the EU project ATM4E is climate-optimized flight planning by considering algorithmic climate change functions that allow for the quantification of aviation-induced climate impact based on the emission’s location and time. Here, we describe the methodology developed for the use of algorithmic climate change functions in trajectory optimization and present the results of its application to the planning of about 13,000 intra-European flights on one specific day with strong contrail formation over Europe. The optimization problem is formulated as bi-objective continuous optimal control problem with climate impact and fuel burn being the two objectives. Results on an individual flight basis indicate that there are three major classes of different routes that are characterized by different shapes of the corresponding Pareto fronts representing the relationship between climate impact reduction and fuel burn increase. On average, for the investigated weather situation and traffic scenario, a climate impact reduction in the order of 50% can be achieved by accepting 0.75% of additional fuel burn. Higher mitigation gains would only be available at much higher fuel penalties, e.g., a climate impact reduction of 76% associated with a fuel penalty of 12.8%. However, these solutions represent much less efficient climate impact mitigation options.

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The aerodynamic formation flight, which is also known as aircraft wake-surfing for efficiency (AWSE), enables aircraft to harvest the energy inherent in another aircraft’s wake vortex. As the thrust of the trailing aircraft can be reduced during cruise flight, the resulting benefit can be traded for longer flight time, larger range, less fuel consumption, or cost savings accordingly. Furthermore, as the amount and location of the emissions caused by the formation are subject to change and saturation effects in the cumulated wake of the formation can occur, AWSE can favorably affect the climate impact of the corresponding flights. In order to quantify these effects, we present an interdisciplinary approach combining the fields of aerodynamics, aircraft operations and atmospheric physics. The approach comprises an integrated model chain to assess the climate impact for a given air traffic scenario based on flight plan data, aerodynamic interactions between the formation members, detailed trajectory calculations as well as on an adapted climate model accounting for the saturation effects resulting from the proximity of the emissions of the formation members. Based on this approach, we derived representative AWSE scenarios for the world’s major airports by analyzing and assessing flight plans. The resulting formations were recalculated by a trajectory calculation tool and emission inventories for the scenarios were created. Based on these inventories, we quantitatively estimated the climate impact using the average temperature response (ATR) as climate metric, calculated as an average global near surface temperature change over a time horizon of 50 years. It is shown, that AWSE as a new operational procedure has a significant mitigation potential on climate impact. For a global formation flight scenario, we estimated the average relative change of climate response to range between 22% and 24% while the relative fuel saving effects sum up to 5-6%.

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Aviation can reduce its climate impact by controlling its CO2-emission and non-CO2 effects, e.g. aviation-induced contrail-cirrus and ozone caused by nitrogen oxide emissions. One option is the implementation of operational measures which aim to avoid those atmospheric regions that are in particular sensitive to non-CO2 aviation effects, e.g. where persistent contrails form. Quantitative estimates of mitigation potentials of such climate-optimized aircraft trajectories are required, when working towards sustainable aviation. Results are presented from a comprehensive modelling approach which is working towards identifying such climate-optimized aircraft trajectories. The overall concept relies on a multi-dimensional environmental change function concept, which is capable of providing environmental impact information to air traffic management (ATM) and which in principal could include the noise and air quality impacts. A one-day case study with a weather situation containing regions with high contrail impacts for European air traffic estimated an overall climate impact reduction of about 30% for an increase of costs of 0.5%, relying on best estimate for climate impact information. The climate impact reduction and mitigation potential varies strongly with individual routes. By using a range of different climate metrics, the robustness of proposed mitigation trajectories is assessed. Sustainable ATM needs to integrate comprehensive environmental impacts and associated forecast uncertainties into route optimisation in order to identify robust eco-efficient trajectories. @en

Aviation can reduce its climate impact by controlling its CO₂-emission and non-CO₂ effects, e.g., aviation-induced contrail-cirrus and ozone caused by nitrogen oxide emissions. One option is the implementation of operational measures that aim to avoid those atmospheric regions that are in particular sensitive to non-CO₂ aviation effects, e.g., where persistent contrails form. The quantitative estimates of mitigation potentials of such climate-optimized aircraft trajectories are required, when working towards sustainable aviation. The results are presented from a comprehensive modelling approach when aiming to identify such climate-optimized aircraft trajectories. The overall concept relies on a multi-dimensional environmental change function concept, which is capable of providing climate impact information to air traffic management (ATM). Estimates on overall climate impact reduction from a one-day case study are presented that rely on the best estimate for climate impact information. Specific weather situation that day, containing regions with high contrail impact, results in a potential reduction of total climate impact, by more than 40%, when considering CO₂ and non-CO₂ effects, associated with an increase of fuel by about 0.5%. The climate impact reduction per individual alternative trajectory shows a strong variation and, hence, also the mitigation potential for an analyzed city pair, depending on atmospheric characteristics along the flight corridor as well as flight altitude. The robustness of proposed climate-optimized trajectories is assessed by using a range of different climate metrics. A more sustainable ATM needs to integrate comprehensive environmental impacts and associated forecast uncertainties into route optimization in order to identify robust eco-efficient trajectories.

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Given the comparably high impact of aircraft emissions, especially their non-CO2 effects, on climate in the order of 5%, aviation stakeholders are required to act to reduce the warming effects of air traffic. Besides new operational procedures, like e.g. climate-optimized routing, this demands the development of completely new global-warming optimized aircraft by aircraft manufacturers. The European Clean Sky 2 project "Global-Warming Optimized Aircraft Design" (GLOWOPT) aims at providing aircraft designers an innovative tool to perform aircraft design studies for minimum climate impact, which we call Climate Functions for Aircraft Design (CFAD). The CFAD will substantially change the way aircraft are designed, while maintaining compatibility to existing Multidisciplinary Design Optimization (MDO) methods. The functions need to integrate a lot of information on the typical aircraft usage, including the routes the aircraft will be operated on. This is because, besides the amount of emissions, the impact of aviation non-CO2 effects, such as NOx, H2O as well as contrails, on climate is highly dependent on location (i.e. latitude, longitude) and altitude. So, the representative operating profile of the aircraft needs to be considered in a characteristic route and fleet model. This work will present the interdisciplinary GLOWOPT approach, which comprises expertise on aircraft design, operations, atmospheric physics and climate. Conceptual thoughts on how the complexity of the operating profile in combination with the geographically variable climate impact of aircraft emissions will be reduced such that it can be used in an aircraft design process are given. @en

Air traffic contributes to anthropogenic global warming by about 5% due to CO2 emissions (about 1/3) and non-CO2 effects (about 2/3) primarily caused by emissions of NOx and water vapour as well as the formation of contrails. Since aviation is expected to maintain its trend to grow over the next decades, mitigation measures are required counteracting its negative effects upon the environment. One of the promising operational mitigation measures which has been subject of the EU project ATM4E, is climate-optimized flight planning using algorithmic climate change functions describing the climate sensitivity as a function of emission location and time. The methodology developed for the use of algorithmic climate change functions in trajectory optimization is described and results of its application to the planning of about 13,000 intra-European flights on one specific day are presented. The optimization problem is formulated as bi-objective continuous optimal control problem with climate impact and fuel burn being the two objectives. Results on individual flight basis indicate that there are three major classes of different routes which are characterized by different shapes of the corresponding Pareto-fronts. For the investigated scenario, results show a climate impact mitigation potential of about 73% which is related with a fuel penalty of 14.5%. However, a climate impact reduction of 50% can already be achieved with 0.75% additional fuel burn. @en

The WeCare project (Utilizing Weather information for Climate efficient and eco efficient future aviation), an internal project of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR), aimed at finding solutions for reducing the climate impact of aviation based on an improved understanding of the atmospheric impact from aviation by making use of measurements and modeling approaches. WeCare made some important contributions to advance the scientific understanding in the area of atmospheric and air transportation research. We characterize contrail properties, show that the aircraft type significantly influences these properties, and how contrail-cirrus interacts with natural cirrus. Aviation NOx emissions lead to ozone formation and we show that the strength of the ozone enhancement varies, depending on where within a weather pattern NOx is emitted. These results, in combination with results on the effects of aerosol emissions on low cloud properties, give a revised view on the total radiative forcing of aviation. The assessment of a fleet of strut-braced wing aircraft with an open rotor is investigated and reveals the potential to significantly reduce the climate impact. Intermediate stop operations have the potential to significantly reduce fuel consumption. However, we find that, if only optimized for fuel use, they will have an increased climate impact, since non-CO2 effects compensate the reduced warming from CO2 savings. Avoiding climate sensitive regions has a large potential in reducing climate impact at relatively low costs. Taking advantage of a full 3D optimization has a much better eco-efficiency than lateral re-routings, only. The implementation of such operational measures requires many more considerations. Non-CO2 aviation effects are not considered in international agreements. We showed that climate-optimal routing could be achieved, if market-based measures were in place, which include these non-CO2 effects. An alternative measure to foster climate-optimal routing is the closing of air spaces, which are very climate-sensitive. Although less effective than an unconstrained optimization with respect to climate, it still has a significant potential to reduce the climate impact of aviation. By combining atmospheric and air transportation research, we assess climate mitigation measures, aiming at providing information to aviation stakeholders and policy-makers to make aviation more climate compatible.@en

Among the various transport modes aviation’s impact on climate change deserves special attention. Due to typical flight altitudes in the upper troposphere and above, the effect of aircraft engine emissions like e.g. water vapour, nitrogen oxides and aerosols on radiative forcing agents is substantial. The projected doubling of aircraft movements in the next 15 years will lead to an increase of aviation’s impact on climate and requires immediate mitigation options. Besides technological measures also new operational strategies are widely discussed; one of these concepts which has been subject of several studies in the past is Intermediate Stop Operations (ISO). It is based on the idea to reduce the stage length of flights by performing one or more intermediate landings during a mission. Here, we analyse the ISO concept by combining different models, which include a realistic traffic simulation taking into account operational constraints and ambient conditions, like e.g. wind, the calculation of engine emissions and the integration of a climate response model.We analyse the ISO concept for today’s worldwide aircraft fleet, including its influence on global emissions distributions as well as the impact on climate change by taking into account CO2 and non-CO2 effects, arising from contrail-cirrus, water vapour and nitrogen oxide emissions. We show in agreement with earlier findings that due to shorter flight distances the amount of fuel burnt over the mission can be reduced by roughly 5% on average globally. For the first time, we quantify the climate impact of ISO, where the flight trajectory is optimised for fuel use and the aircraft is not redesigned for the ISO procedure. We find an increased warming effect, which arises from nitrogen oxide and water vapour emissions, which are released at higher cruise altitudes and which over-compensate reduced warming effects from CO2 and contrail-cirrus. However, we expect a climate impact reduction for ISO even with existing aircraft, avoiding the higher flight altitude in the first flight segment and hence reducing the fuel savings. Thus, climate impact benefits could be achieved if lower fuel savings were acceptable. Moreover, this negative climate impact is found for the particular case of introducing ISO using the current wide-body fleet. It does not necessarily apply to the adoption of ISO using aircraft redesigned for a shorter range.

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Aviation guarantees mobility, but its emissions also contribute considerably to climate change. Therefore, climate impact mitigation strategies have to be developed based on comprehensive assessments of the different impacting factors. We quantify the climate impact mitigation potential and related costs resulting from changes in aircraft operations and design using a multi-disciplinary model workflow. We first analyze the climate impact mitigation potential and cash operating cost changes of altered cruise altitudes and speeds for all flights globally operated by the Airbus A330-200 fleet in the year 2006. We find that this globally can lead to a 42% reduction in temperature response at a 10% cash operating cost increase. Based on this analysis, new design criteria are derived for future aircraft that are optimized for cruise conditions with reduced climate impact. The newly-optimized aircraft is re-assessed with the developed model workflow. We obtain additional climate mitigation potential with small to moderate cash operating cost changes due to the aircraft design changes of, e.g., a 32% and 54% temperature response reduction for a 0% and 10% cash operating cost increase. Hence, replacing the entire A330-200 fleet by this redesigned aircraft (Macr = 0.72 and initial cruise altitude (ICA) = 8000 m) could reduce the climate impact by 32% without an increase of cash operating cost. @en

Air traffic is an important part of our mobility with an increasing rate in transport volume of around 5% per year. Air traffic also contributes to anthropogenic warming by around 5%. Here we present a climate impact assessment tool AirClim and give an overview on the recent technology assessments. Finally, we present a best practice for a robust climate impact assessment, which combines a comprehensive four-layer approach to model the air traffic system with AirClim and includes aspects of atmospheric uncertainties, sensitivities, and verification procedures.@en

Impacts of commercial aircraft operation upon the environment, which are caused primarily from emissions of CO2, NOx and the formation of contrails, are matter of growing concern, as aviation is one of the fastest developing industrial sectors worldwide and the awareness of its effects is expanding. Recent research has focused on the cost-benefit potential of different mitigation strategies, which optimize flight trajectories with respect to climate and economy, but most of these mitigation strategies cannot be implemented in the near future due to technical challenges.The objective of this paper is to present an interim mitigation strategy, which bridges this time period. In analogy to military exclusion zones, climate restricted airspaces (CRA) are defined based on 3-D climate change functions, characterizing the environmental impact caused by an aircraft emission at a certain location. Regions with climate costs greater than a threshold value are closed in the corresponding month; others are cleared for air traffic. To estimate the cost-benefit potential of this strategy, a preliminary analysis is conducted on the route from Helsinki (EFHK) to Miami (KMIA). Affected flight trajectories are re-routed optimally around resulting CRA with regard to monetary costs for varying threshold values. Therefore, flight simulation algorithms are developed, which solve a non-linear optimal control problem. For each optimized flight trajectory corresponding average temperature response (ATR) and cash operating costs (COC) are expressed relative to a reference great circle trajectory with constant Mach number and compared with the climate mitigation potential of climate optimized trajectories.@en

Trajectory optimisation is one option to reduce air traffic impact on environment. A multidimensional environmental assessment framework is needed to optimize impact on climate, local air quality and noise simultaneously. An interface between flight planning and environmental impact information can be established with environmental cost functions. In a feasibility study such multidimensional assessment can be applied to the European Airspace. The project ATM4E within the frame of SESAR2020 has spelled out the objective to develop such a concept and to study changing traffic flows due to environmental optimisation. @en

Mobility is becoming more and more important to society and hence air transportation is expected to grow further over the next decades. Reducing anthropogenic climate impact from aviation emissions and building a climate-friendly air transportation system are required for a sustainable development of commercial aviation. A climate optimized routing, which avoids climate-sensitive regions by re-routing horizontally and vertically, is an important measure for climate impact reduction. The idea includes a number of different routing strategies (routing options) and shows a great potential for the reduction. To evaluate this, the impact of not only CO2 but also non-CO2 emissions must be considered. CO2 is a long-lived gas, while non-CO2 emissions are short-lived and are inhomogeneously distributed. This study introduces AirTraf (version 1.0) that performs global air traffic simulations, including effects of local weather conditions on the emissions. AirTraf was developed as a new submodel of the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model. Air traffic information comprises Eurocontrol's Base of Aircraft Data (BADA Revision 3.9) and International Civil Aviation Organization (ICAO) engine performance data. Fuel use and emissions are calculated by the total energy model based on the BADA methodology and Deutsches Zentrum für Luft- und Raumfahrt (DLR) fuel flow method. The flight trajectory optimization is performed by a genetic algorithm (GA) with respect to a selected routing option. In the model development phase, benchmark tests were performed for the great circle and flight time routing options. The first test showed that the great circle calculations were accurate to −0.004 %, compared to those calculated by the Movable Type script. The second test showed that the optimal solution found by the algorithm sufficiently converged to the theoretical true-optimal solution. The difference in flight time between the two solutions is less than 0.01 %. The dependence of the optimal solutions on the initial set of solutions (called population) was analyzed and the influence was small (around 0.01 %). The trade-off between the accuracy of GA optimizations and computational costs is clarified and the appropriate population and generation (one iteration of GA) sizing is discussed. The results showed that a large reduction in the number of function evaluations of around 90 % can be achieved with only a small decrease in the accuracy of less than 0.1 %. Finally, AirTraf simulations are demonstrated with the great circle and the flight time routing options for a typical winter day. The 103 trans-Atlantic flight plans were used, assuming an Airbus A330-301 aircraft. The results confirmed that AirTraf simulates the air traffic properly for the two routing options. In addition, the GA successfully found the time-optimal flight trajectories for the 103 airport pairs, taking local weather conditions into account. The consistency check for the AirTraf simulations confirmed that calculated flight time, fuel consumption, NOx emission index and aircraft weights show good agreement with reference data.@en

This paper describes AirTraf ver. 1.0 for climate impact evaluations that performs global and long-Term air traffic simulations with respect to aircraft routing options. AirTraf was developed as a new submodel of the EClIAM5/MESSy Atmospheric Chemistry (EM AC) model. The real flight plan, Eurocontrol's Base of Aircraft Data (BADA) and ICAO engine performance data were employed. Fuel and emissions were calculated by the total energy model based on the BADA methodology and DLR fuel flow correction method. The flight trajectory optimization was performed by the Genetic Algorithm (GA). The Air Traf simulation was demonstrated on-line with the tlight time routing option for a specific winter day. 103 trans-Atlantic flight plans were used, assuming Airbus A330-301 aircraft. The results confirmed that AirTraf properly works on-line and GA successfully found the time-optimal flight trajectories, reflecting local weather conditions.@en

Among the various transport modes aviation's impact on climate change deserves special attention. Due to typical flight altitudes in the upper troposphere and above the effect of aircraft engine emissions like carbon dioxide, water vapour, nitrogen oxides and aerosols on radiative forcing agents is substantial. The projected duplication of aircraft movements in the next 15 years will lead to an increase of aviation's impact on climate and requires immediate mitigation options. Besides technological measures also new operational strategies arc widely discussed; one of these concepts which has been subject of several studies in the past is Intermediate Stop Operations (ISO). It is based on the idea to reduce the stage length of flights by performing one or more inter-mediate landings during a mission. Due to shorter flight distances the amount of fuel burnt over the mission can be reduced, as the amount of fuel necessary to transport a certain percentage of the fuel for a long distance can be omitted. Besides fuel cost saving implications, many previous studies anticipate a strong reduction of the environmental impact compared to direct flight operations. So far, none of them has actually quantified this impact in a realistic scenario. While for the amount of emitted species which arc produced proportional to fuel burn, a reduction is straightforward, this is not the case for other species. Moreover, the geographic location and altitude of the emissions have to be taken into account for a sound climate impact assessment. The paper presents results of the ecological analysis of the ISO concept for today's worldwide aircraft fleet, including its influence on global emissions distributions as well as the impact on climate change. A method is described that comprises of different models for a realistic traffic simulation taking into account operational constraints and ambient conditions, like e.g. wind, the calculation of engine emissions and the integration of a climate response model.@en