ACACIA – Advancing the Science for Aviation and Climate

Aviation is an integrated part of the globalised society, with several hundred airlines transporting goods and people across the globe daily. Because of its dependence on fossil fuels, aviation is also a large source of CO₂ emissions. Today, aviation accounts for around 2.5% of annual global CO₂ emissions. But the emissions are increasing rapidly and even if the sector’s goal of carbon neutral growth is met, emissions from international aviation will likely consume a significant part of the carbon budget compatible with the 2°C climate target between 2015 and 2050. Further measures to reduce emissions are therefore urgently needed for the sector to align with the global climate goals of the Paris Agreement.

But CO₂ makes up only a part of aviation’s climate impact: aviation causes a broad range of non-CO₂ effects, both short- and long-lived, and of opposite signs, which means they can have both cooling and warming effects. These include changes in ozone and methane from NOx emissions, contrails, and indirect effects of aerosols on clouds. Current estimates suggest that including non-CO₂ effects increases the net climate impact of the sector by roughly a factor of two compared to the impact of CO₂ alone.

Future emission pathways consistent with limiting global warming to 1.5°C require reaching net-zero CO₂ emissions globally around 2050. For aviation, including non-CO₂ effects may provide additional contributions towards the Paris Agreement ambitions, apart from reducing fuel consumption. However, these non-CO₂ effects are also associated with much larger uncertainties. To understand the role that they play, as well as potential trade-offs, and to provide robust recommendations for decision-makers, the uncertainties must be reduced.

This is the overall objective of ACACIA. The project brings together experts from a broad range of disciplines – from laboratory experiments to global modelling and stakeholder dialogue – in order to provide the knowledge basis and strategic guidance for future implementation of mitigation options. The project will in particular focus on improving the scientific understanding of the impacts with the largest uncertainty (indirect effects of aerosols), providing an updated climate impact assessment and investigate how non-CO₂ effects may be included in international climate policy strategies.

Duration and funding:

ACACIA is a four-year (2020-2023) project funded by the EU (under the InCO flagship) and is led by the German Aerospace Center (Deutsches Zentrum fuer Luft - und Raumfahrt (DLR)).

Project partners:

German Aerospace Center (DLR, Germany), CICERO (Norway), Manchester Metropolitan University (UK), University of Reading (UK), University of Vienna (Austria), ETH Zurich (Switzerland), University of Leipzig (Germany), Delft University of Technology (TU Delft, Netherlands), Forschungszentrum Jülich (FZJ, Germany), French National Centre for Scientific Research (CNRS, France), Zurich University of Applied Sciences (ZHAW, Switzerland).