Regional Efficacy and Implications of Marine Cloud Brightening Applications (RegMCB)

• Applicant: Professorin Dr. Anna Possner
• Subject Area: Atmospheric Science
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 500932476

Regional Marine Cloud Brightening (RegMCB) is a solar radiation management technique considered by scientists and politicians to offset the induced warming due to anthropogenic climate change. While proven to work in theory, many uncertainties remain with regard to the efficacy of this approach, and its potential for unintended consequences. Meanwhile, field testing of small-scale MCB applications is already underway in Australia and in the planning by other countries.Our current understanding of the induced brightening by continuous emissions of sea spray into the lower troposphere remains incomplete. Our knowledge about the efficacy of this approach is largely based on either process models of limited spatial and temporal extent, or global climate models making broad-stroke assumptions of continuous, near-global MCB emissions. In this proposal we will address this gap in the literature by simulating conceivable RegMCB emission strategies on the multi-annual timescale. The aim of this proposal is to quantify the efficacy of regMCB within the Californian Stratocumulus Deck, as well as the critical level of induced cloud brightening beyond which regional unintended consequences can no longer be excluded.As part of this work we will build and evaluate a simplified version of ICON-HAM, a climate model with a complete parameterisation of aerosol microphysical processes, aerosol-radiation, and aerosol-cloud interactions. We propose to limit the full complexity of ICON-HAM for sea salt size distributions only, while prescribing all other aerosol species. We will evaluate this model studying different transitions within the Californian stratocumulus deck, which is one of the best sampled and understood stratocumulus decks worldwide.The aim of RegMCB is to better understand and quantify the utility and limitations of this technology at the scale of conceivable deployment. The fundamental scientific results obtained in this project can inform future decisions of regional testing and MCB deployment, while also improving our understanding of aerosol-cloud interactions in marine stratocumuli at the regional scale.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigators: Dr. Tom Goren; Professor Dr. Johannes Quaas
• Cooperation Partner: Professor Dr. Robert Wood