Clouds are a very important, yet not well understood feedback factor in climate change and they contribute to the effective radiative forcing (ERF) from aerosol-cloud interactions (ACI). The uncertainty in ERFaci is larger than for any other forcing agent. Also, feedbacks between the terrestrial and marine biosphere and the atmosphere involving ACI are thought to play an important role in regulating climate change but their relevance remains poorly quantified. The EU project BACCHUS studies to quantify key processes and feedbacks controlling ACI, by combining advanced measurements of cloud and aerosol properties with emphasis on ice nucleating particles and the ice phase in clouds with state-of-the-art numerical modelling. It investigates the importance of biogenic versus anthropogenic emissions for ACI in regions that are key regulators of Earth's climate (Amazonian rain forest) or are regarded as tipping elements in the climate system (Arctic). BACCHUS will advance the understanding of biosphere aerosol-cloud-climate feedbacks that occur via emission and transformation of biogenic volatile organic compounds, primary biological aerosols, secondary organic aerosols and dust. Integration of new fundamental understanding gained in BACCHUS in Earth Systems Models allows to reduce the uncertainty in future climate projections. In this session we invite submissions from all BACCHUS relevant topics.