Quantifying the Multiscale Effects of Subtropical Marine Cloud Brightening on the Tropical Cloud Continuum

• Applicant: Dr. Fabian Hoffmann
• Subject Area: Atmospheric Science
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 523314332

Earth's climate is changing, causing global and regional changes in sea level height, extreme weather events, precipitation, and water availability, among others. International mitigation efforts to reduce greenhouse gas emissions are urgently needed. If these efforts fail, an intervention in the form of climate engineering might be inevitable. One of the most promising pathways is marine cloud brightening (MCB): the deliberate enhancement of marine cloud reflectance by local injections of aerosol particles that serve as cloud condensation nuclei. Unfortunately, the impacts of such action are highly uncertain due to the multiscale nature of MCB, covering aerosol-cloud microphysics (< 10^-5 m), cloud field organization (10^3 - 10^4 m), and the resultant global impacts (> 10^6 m). Although the underlying physics are not independent, their scales are often separated to assess this problem in today's numerical models and with today's computing resources. Here we propose innovative numerical approaches to account for processes on all relevant scales to examine the effects of local MCB injections in the subtropics, where they are most effective, and their implications for the tropical cloud regimes downwind. We will test the hypothesis that a substantial fraction of the climate system response to MCB will be found in the transitions, interactions, and potential compensations between different cloud regimes in the investigated region. This avenue for studying the impact of MCB on the climate system has the potential to transform our understanding of clouds in the climate system well beyond the focus on MCB.

• DFG Programme: Research Grants
• International Connection: Israel, USA
• Cooperation Partners: Dr. Matthew Christensen; Dr. Graham Feingold
• International Co-Applicant: Dr. Guy Dagan