Physical science research needed to evaluate the viability and risks of marine cloud brightening

Feingold, Graham; Ghate, Virendra P.; Russell, Lynn M.; Blossey, Peter; Cantrell, Will; Christensen, Matthew W.; Diamond, Michael S.; Gettelman, Andrew; Glassmeier, Franziska; Gryspeerdt, Edward; Haywood, James; Hoffmann, Fabian; Kaul, Colleen M.; Lebsock, Matthew; McComiskey, Allison C.; McCoy, Daniel T.; Ming, Yi; Mülmenstädt, Johannes; Possner, Anna; Prabhakaran, Prasanth; Quinn, Patricia K.; Schmidt, K. Sebastian; Shaw, Raymond A.; Singer, Clare E.; Sorooshian, Armin; Toll, Velle; Wan, Jessica S.; Wood, Robert; Yang, Fan; Zhang, Jianhao; Zheng, Xue

doi:10.1126/sciadv.adi8594

Cited by 5 publications

(4 citation statements)

References 129 publications

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“…This statement is by no means an endorsement of MCB as a viable climate intervention method. Much more solid research is needed at this stage to determine the viability of MCB and to quantify the potential risks associated with it (Feingold et al, 2024).…”

Section: Discussionmentioning

confidence: 99%

Cloud water adjustments to aerosol perturbations are buffered by solar heating in non-precipitating marine stratocumuli

Zhang,

Chen,

Yamaguchi

et al. 2024

Preprint

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Abstract. Marine low-level clouds are key to the Earth’s energy budget due to their expansive coverage over global oceans and their high reflectance of incoming solar radiation. Their responses to anthropogenic aerosol perturbations remain the largest source of uncertainty in estimating the anthropogenic radiative forcing of climate. A major challenge is the quantification of the cloud water response to aerosol perturbations. In particular, the presence of feedbacks through microphysical, dynamical and thermodynamical pathways at various spatial and temporal scales could augment or weaken the response. Central to this problem is the temporal evolution in cloud adjustment, governed by entangled feedback mechanisms. We apply an innovative conditional Monte Carlo subsampling approach to a large ensemble of diurnal large-eddy simulation of non-precipitating marine stratocumulus to study the role of solar heating in governing the evolution in the relationship between droplet number and cloud water. We find a persistent negative trend in this relationship at night, confirming the role of microphysically enhanced cloud-top entrainment. After sunrise, the evolution in this relationship appears buffered and converges to ∼ -0.2 in the late afternoon. This buffering effect is attributed to a strong dependence of cloud-layer shortwave absorption on cloud liquid water path. These diurnal cycle characteristics further demonstrate a tight connection between cloud brightening potential and the relationship between cloud water and droplet number at sunrise, which has implications for the impact of the timing of advertent aerosol perturbations.

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Section: Discussionmentioning

confidence: 99%

Cloud water adjustments to aerosol perturbations are buffered by solar heating in non-precipitating marine stratocumuli

Zhang,

Chen,

Yamaguchi

et al. 2024

Preprint

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“…For example, if marine cloud brightening (MCB) were to be attempted our findings imply a strong, regionally-dependent masking of MCB detectability by the natural variability in cloud radiative effect, and that an ambitious seeding strategy might be required. The low detectability of the radiative perturbation from IMO2020 at scales larger than ship track or shipping lane speaks to the substantial challenge in validating the viability of MCB at regional-to-global scales 34,35 .…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, significant IMO2020 perturbations can be masked by overwhelmingly large natural variability in cloud properties, leading to a "missed detection". Both these scenarios underscore an important confounding effect of natural variability on the detectability of natural or deliberate perturbations to the aerosol field, with the latter being a critical "checkpoint" for the viability of marine cloud brightening 34,35 .…”

Section: Natural Variability Masks Detectability Of the Imo2020-pertu...mentioning

confidence: 99%

Large radiative forcing from the 2020 shipping fuel regulation is hard to detect

Zhang,

Chen,

Gryspeerdt

et al. 2024

Preprint

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A key uncertainty in projecting the rate of future warming derives from regulations on aerosol emissions that involve socioeconomic decisions. Given that a reduction in aerosol cooling unmasks greenhouse gas warming, the 2020 implementation of strict regulations on the sulfur content of ship fuels (IMO2020) presents a natural experiment that can be used to assess the potential impacts of future emission regulations and the detectability of deliberate aerosol perturbations for climate intervention. Using an ensemble of neural networks trained to capture the natural variability in cloud driven by variations in meteorological conditions, we estimate a substantial global radiative forcing of +0.084 ±0.006 W m-2 from IMO2020-related changes in low-cloud radiative effect. We find a strong masking effect of natural variability on the detectability of this radiative perturbation, manifested as high chances of missed detection and false detection. After removing the masking effect, the true detection-fraction of IMO2020’s radiative perturbation is at most 6%, while cloud microphysical changes have a higher chance of being detected. These results raise concerns that future reductions in aerosol emissions will accelerate warming and that proposed deliberate aerosol perturbations such as marine cloud brightening will need to be substantial in order to overcome the low detectability.

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“…Lastly, despite the insights gained from nocturnal simulations, the daytime behavior of marine stratocumulus population needs to be explored to understand the shortwave radiative effects of these clouds, which are more relevant to aerosol-cloud climate forcing and issues like marine cloud brightening (Latham, 1990;Feingold et al, 2024).…”

Section: Introductionmentioning

confidence: 99%

Diurnal evolution of non-precipitating marine stratocumuli in an LES ensemble

Chen,

Zhang,

Hoffmann

et al. 2024

Preprint

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Abstract. We explore the impacts of the diurnal cycle, free-tropospheric (FT) humidity values, and interactive surface fluxes on the cloud system evolution of non-precipitating marine stratocumuli based on a large ensemble of large-eddy simulations. Cases are separated into three categories based on their degree of decoupling and cloud liquid water path (LWPc). A new budget analysis method is proposed to analyze the evolution of LWPc under both coupled and decoupled conditions. More coupled clouds start with relatively low LWPc and cloud fraction (fc) but experience the least decrease in LWPc and fc during the daytime. More decoupled clouds undergo greater daytime reduction in LWPc and fc, especially those with higher LWPc at sunrise because they suffer from faster weakening of a net radiative cooling. During the nighttime, a positive correlation between FT humidity and LWPc emerges, consistent with higher FT humidity reducing both radiative cooling and the humidity jump, both of which reduce entrainment and increase LWPc. The time rate of change in the LWPc is more likely to be negative for higher LWPc and greater inversion base height (zi), conditions under which entrainment dominates as turbulence develops. In the morning, the rate of the LWPc reduction depends on the LWPc at sunrise, zi, and the degree of decoupling, with distinct contributions from subsidence and radiation. Under well-mixed conditions, it takes about 10 h for the surface fluxes to offset 15 % of the changes in entrainment warming and drying, assuming no changes in transfer coefficients or surface wind speed.

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Physical science research needed to evaluate the viability and risks of marine cloud brightening

Cited by 5 publications

References 129 publications

Cloud water adjustments to aerosol perturbations are buffered by solar heating in non-precipitating marine stratocumuli

Cloud water adjustments to aerosol perturbations are buffered by solar heating in non-precipitating marine stratocumuli

Large radiative forcing from the 2020 shipping fuel regulation is hard to detect

Diurnal evolution of non-precipitating marine stratocumuli in an LES ensemble

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