the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Oct 2026
Climate-mediated surface ozone responses to simultaneous multi-regional marine cloud brightening
Abstract. Marine cloud brightening (MCB) has been proposed as a regional solar radiation modification strategy, yet its effects on atmospheric composition remain poorly understood. Here, using the Community Earth System Model version 1 (CESM1), we isolate the climate-mediated response of surface ozone (O3) with a three-stage experimental design. We first determine a sea salt injection rate of 11.4 Tg yr−1 in each of six oceanic regions, which is sufficient to offset the 1.0 W m−2 effective radiative forcing difference between SSP5-8.5 and SSP2-4.5 in 2050. We then simulate the coupled climate response and prescribe the resulting sea surface temperature and sea ice fields in atmospheric chemistry experiments without additional sea salt injection. The MCB injection decreases global annual mean sea surface temperature by 0.44 °C and increases Arctic sea ice concentration by 9.7 %. The resulting changes in temperature, moisture, radiation, boundary-layer mixing, and transport produce spatially heterogeneous surface O3 responses. After a machine learning bias correction, boreal summer surface O3 concentration decreases by 0.33 μg m−3 over China, remains nearly unchanged over Europe at +0.01 μg m−3, and increases by 0.12 μg m−3 over the United States. The subregional responses are more pronounced with decreases of 0.59 and 0.64 μg m−3 over western and eastern China and contrasting changes of −0.19 and +0.14 μg m−3 over western and eastern Europe. A comprehensive evaluation of MCB should therefore consider its consequences for regional air quality alongside its intended climate effects.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 03 Dec 2026)
- RC1: 'Comment on egusphere-2026-6197', Anonymous Referee #1, 11 Nov 2026 reply
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- 1
This manuscript addresses a worthwhile and relatively understudied aspect of MCB: the consequences of MCB-induced climate changes for surface ozone. The authors employ a three-stage experimental framework to first determine the sea salt aerosol injection rate required to achieve a target radiative forcing, simulate the coupled climate response, and subsequently examine the resulting changes in surface ozone using prescribed SST and SIC fields in atmospheric chemistry simulations. The study further applies machine-learning-based bias correction to the simulated ozone concentrations and uses SHAP analysis to identify meteorological variables associated with the regional ozone responses.
However, I have several concerns regarding the robustness of the reported ozone responses, the interpretation of the machine-learning results, and the extent to which the proposed physical mechanisms are supported by the analysis. In particular, the bias correction substantially modifies the magnitude of the simulated ozone responses, yet its reliability under the future MCB-modified climate is not adequately established. The subsequent statistical attribution of meteorological drivers also raises questions about the independence of the relationships identified. More generally, while the manuscript documents regional changes in ozone concentrations, I find that some of the conclusions regarding their physical drivers and broader air-quality implications extend beyond what is demonstrated.
I believe the manuscript could make a useful contribution to the literature, but these issues should be addressed before it can be considered for publication. My specific comments are attached.