Chen, YingHaywood, JimWang, YuMalavelle, FlorentJordan, GeorgePeace, AmyPartridge, DanielCho, NayeongOreopoulos, LazarosPlatnick, StevenGrosvenor, DanielField, PaulAllan, RichardLohmann, Ulrike2023-10-132023-10-132023-09-22https://doi.org/10.21203/rs.3.rs-3291831/v1http://hdl.handle.net/11603/30148With global warming currently standing at approximately + 1.2 °C, climate change is a pressing global issue. Marine cloud brightening (MCB) proposes injecting aerosols into marine clouds to enhance their reflectivity and thereby planetary albedo. However, because it is unclear how aerosols influence clouds, especially cloud cover, both climate projections and the effectiveness of MCB remain uncertain. Here, we use volcanic eruptions to quantify the aerosol fingerprint on tropical marine clouds. We observe a large enhancement in reflected sunlight, mainly due to an aerosol-induced increase in cloud cover. This observational evidence of a strong aerosol impact suggests that the Earth’s climate is highly sensitive to external forcing mechanisms, but also that mitigation of global warming via MCB is more plausible than current climate models suggest. Our results suggest that the best efficacy for MCB practice is to seed clouds in humid and stable meteorological conditions.20 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domain Mark 1.0http://creativecommons.org/publicdomain/mark/1.0/Text