The researchers’ activities of “Investigation of the theory and techniques required for assessing the climate impacts of marine cloud brightening geoengineering” are linked to those of IAMAS (International Association of Meteorology and Atmospheric Sciences).
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“Investigation of the theory and techniques required for assessing the climate impacts of marine cloud brightening geoengineering” is a key project under the National Key Research and Development Program of China. It started in November 2024 and will end in October 2029.
The four PIs are:
- Professor Chuanfeng Zhao from Peking University
- Professor Rui Li from the University of Science and Technology of China
- Professor Minghuai Wang from Nanjing University
- Professor Long Cao from Zhejiang University
The goal is to clarify the theoretical and technical aspects associated with marine cloud brightening, including developing key technical to observe aerosol-low cloud interaction, developing parameterization of aerosol-low cloud interaction for climate models, assessing the global and regional impacts and providing policy-making advice.
There are four key scientific questions that they would like answer:
- How to observe key parameters related to aerosol-low cloud interaction using remote sensing techniques?
- How does low clouds, especially marine stratus clouds, respond to aerosols in observation?
- How to use observed cloud responses to improve aerosol-cloud interaction modeling?
- What are the global and regional benefits and risks if we implement cloud seeding over different ocean regions?
They are addressed through extensive field observations, developing remote sensing techniques, analysis of observational results, developing model parameterization and performing climate model simulations.
Why is this research important?
As global warming becomes increasingly evident, it is almost impossible to reach the 1.5 degree warming goal by the end of this century. Geoengineering has thus been proposed as a potentially effective means to overcome global warming. Marine cloud brightening, which aims to distribute aerosols such as sulfate particles into marine clouds or simply above the oceans in order to increase the reflectivity of the clouds, is one popular geoengineering technique. However, how will clouds will respond to aerosol seeding with different types, amounts and in different regions, and how changes in clouds affect global and local climate, is still unclear. This information is critical to evaluate the pros and cons of this technique, as well as designing detailed implementation strategy. It is thus very important to perform research in these areas in order to clarify the possible effects and consequences of marine cloud brightening. This research is also very important in understanding aerosol-cloud interaction, the major source of uncertainty in climate projection.
What is one key discovery and its challenges?
One key discovery till now is that marine stratus clouds respond very nonlinearly to aerosols and seeding in different regions seems to show different or even opposite effects. Cloud albedo increases evidently with small amount of aerosol seeding, but then stay stable or even decline. Seeding in the remote tropical oceans seems to be most effective compared to seeding over North Pacific or North Atlantic. However, these findings need to be verified with more extensive observations and model simulations.
The key challenge is the observation of cloud development with aerosols, which is almost impossible with satellite measurements. Clouds and aerosols cannot be simultaneously observed using passive sensors, nor are their vertical structure known. Their find is based on 3 years of collocated CALIPSO lidar and Cloudsat radar measurements, and they analyze the relationship between cloud backscatter and aerosol extinction. They still lack in situ observations which is their next plan. Another challenge is that even with these observations, it is critical to improve the parameterization of cloud microphysics in climate models to make them better agree with measurements. There are many processes and parameters involved, and most of which lack direct observations.
About eight ECS are involved, and there will likely be more in the next year since we are recruiting postdocs.
Don’t miss next week’s blog posts featuring interviews with ECS participating in the “Investigation of the theory and techniques required for assessing the climate impacts of marine cloud brightening geoengineering” project!