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Published February 8, 2019 | Supplemental Material
Journal Article Open

Aerosol-driven droplet concentrations dominate coverage and water of oceanic low level clouds


A lack of reliable estimates of cloud condensation nuclei (CCN) aerosols over oceans has severely limited our ability to quantify their effects on cloud properties and extent of cooling by reflecting solar radiation—a key uncertainty in anthropogenic climate forcing. We introduce a methodology for ascribing cloud properties to CCN and isolating the aerosol effects from meteorological effects. Its application showed that for a given meteorology, CCN explains three-fourths of the variability in the radiative cooling effect of clouds, mainly through affecting shallow cloud cover and water path. This reveals a much greater sensitivity of cloud radiative forcing to CCN than previously reported, which means too much cooling if incorporated into present climate models. This suggests the existence of compensating aerosol warming effects yet to be discovered, possibly through deep clouds.

Additional Information

© 2019 American Association for the Advancement of Science. Received 19 September 2018; accepted 3 December 2018. Published online 17 January 2019. Funding: This research was supported by the Joint NSFC-ISF Research Program (No. 41561144004), the National Natural Science Foundation of China (No. 41575136). Y.Z. is supported by the U.S. Department of Energy (DOE) Atmospheric System Research program (DE-SC0018996). T.G. received funding from the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement 703880. M. W. is supported by the National Natural Science Foundation of China (No. 41575073, 41621005, and 91744208) and by the Jiangsu Collaborative Innovation Center of Climate Change. S.Y. is supported by the Department of Science and Technology of China (No. 2016YFC0202702, 2018YFC0213506, and 2018YFC0213503), National Research Program for Key Issues in Air Pollution Control in China (No. DQGG0107), and National Natural Science Foundation of China (No. 21577126 and 41561144004). Author contributions: D.R. designed this study; Y. Zhu acquired and processed the data; D.R. and Y. Zhu carried out analyses, interpreted data, and wrote the manuscript; M.W. contributed to the comparisons with other studies and to the discussion; Y. Zheng supported the calculations of cloud base updrafts and contributed to the discussion; and T.G. and S.Y. contributed to the discussion. Competing interests: All authors have no competing interests. Data and materials availability: The MODIS data for this study are obtained from NASA (https://search.earthdata.nasa.gov).

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