Periodic Reporting for period 1 - ACACIA (Advancing the Science for Aviation and ClimAte)
Reporting period: 2020-01-01 to 2021-06-30
The global society is suffering from the impacts of climate change and global warming. Measures and methods have to be developed and implemented to reduce the anthropogenic climate footprint, including aviation’s share. On the way forward to a greener aviation system huge investments are needed. In order to take the best and most effective decisions, they must be based on robust scientific results.
A particularity of aviation is its major share of non-CO2 effects to climate impact; in fact, non-CO2 effects contribute about two thirds, carbon dioxide itself only about one third, according to a recent assessment. However, while the climate impact from CO2 emissions can be estimated from the fuel burn, the impact of the non-CO2 effects is associated with larger uncertainties.
Non-CO2 effects comprise i. a. the emission of nitrogen oxides (NOx) which modifies the abundances of the greenhouse gases ozone (O3) and methane (CH4). The generation of contrails and contrail cirrus is an obvious effect of aviation. The emitted particles (soot and liquid aerosol droplets) might perturb cloud formation and thus cloud properties far away from the place of their emission. The latter effects are called indirect cloud effects, and while they might have a strong cooling contribution to climate change, almost nothing is currently known about the involved processes.
The ACACIA project aims at improving scientific understanding of those impacts that have the largest uncertainty. It formulates concepts for international measurement campaigns with the goal to constrain numerical models and theories with data. Implementation work is performed on putting all aviation effects on a common scale which will eventually allow providing an updated climate impact assessment. Uncertainties are treated in a transparent way, such that trade-offs between different mitigation strategies can be evaluated explicitly. Finally, the project strives for the knowledge basis necessary to allow strategic guidance for future implementation of mitigation options, that is, to give robust recommendations of no-regret strategies for achieving reduced climate impact of aviation.
ACACIA will further be exploring how changes to aviation might help to bring emissions and impacts in line with the goals of the Paris Agreement. Due to a better understanding of aviation's non-CO2 climate effects, the project will during a later phase deliver necessary input for an eco-efficient planning of flight trajectories, which will allow a substantial reduction of the aviation-induced climate change at the same transport capacity. The project will then also deliver guidelines for the design of future aircraft, which are more adapted to a climate friendly transport.
Regarding non-CO2 effects, the models have been evaluated against the IAGOS/MOZAIC dataset using an improved methodology. The thermodynamic condition for contrail formation can be predicted quite reliably. But underestimation of frequency and degree of ice supersaturation in weather and climate models leads to very low reliability in forecasting of contrail persistence. Subsequent work with the same data showed that the forecast of ice supersaturation is improved considerably if the threshold for saturation is reduced. The evaluation of the various participating global models for ozone, carbon monoxide, water vapour and NOy is underway. The preliminary assessment shows encouraging results.
The work of searching in the database JULIA for atmospheric conditions that favour the formation of contrails/contrail cirrus was conducted. Literature on past measurement campaigns studying aviation and aerosol/cloud effects, cirrus clouds and mineral dust was used to set up a matrix for aerosol and cirrus parameters. Atmospheric situations favourable for aviation-induced effects were identified in simulations with the global aerosol-climate model ECHAM6-HAM. The effect of soot activation on the radiative forcing appears insignificant in these simulations.
Several important new assessments of aviation climate impact have appeared with major contributions and leadership of authors from the ACACIA consortium. The project also started to analyse different types and sources of uncertainty in modelling results including the monitoring of literature for substantially new insights that could be translated into reduced uncertainties.
For dissemination and communication, a project webpage was created (https://www.acacia-project.eu/) an internal team site, and emailing lists. Several scientific presentations at international conferences and workshops were performed. The project clustered with the partner EU projects Great, ClimOp, and Alternate. Exchange and collaboration are ongoing. Thematic stakeholder exchange involving industry and regulation takes place inter alia with the members of the Advisory Board. Several scientific papers were published including contributions to the IPCC report. The project was also invited to an Expert Discussion in the German Federal Chancellery related to the topic 'Green Deal’ in Jan 2021.