Radiative forcing from the 2020 shipping fuel regulation is large but hard to detect

Communications Earth & Environment, Journal Year: 2025, Volume and Issue: 6(1)

Published: Jan. 13, 2025

Abstract Reduction in aerosol cooling unmasks greenhouse gas warming, exacerbating the rate of future warming. The strict sulfur regulation on shipping fuel implemented 2020 (IMO2020) presents an opportunity to assess potential impacts such emission regulations and detectability deliberate perturbations for climate intervention. Here we employ machine learning capture cloud natural variability estimate a radiative forcing +0.074 ±0.005 W m −2 related IMO2020 associated with changes shortwave effect over three low-cloud regions where routes prevail. We find low this event, attributed strong albedo cover. Regionally, is higher southeastern Atlantic stratocumulus deck. These results raise concerns that reductions emissions will accelerate warming proposed as marine brightening need be substantial order overcome detectability.

Language: Английский

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Buffering of Aerosol‐Cloud Adjustments by Coupling Between Radiative Susceptibility and Precipitation Efficiency

Geophysical Research Letters, Journal Year: 2024, Volume and Issue: 51(11)

Published: June 6, 2024

Abstract Aerosol‐cloud interactions (ACI) in warm clouds are the primary source of uncertainty effective radiative forcing (ERF) during historical period and, by extension, inferred climate sensitivity. The ERF due to ACI (ERFaci) is composed changes cloud microphysics and adjustments microphysics. Here, we examine processes that drive ERFaci using a perturbed parameter ensemble (PPE) hosted CAM6. Observational constraints on PPE result substantial response macrophysics anthropogenic aerosol, but only minimal constraint ERFaci. Examination radiation reveal buffering interaction precipitation efficiency susceptibility.

Language: Английский

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

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(18), P. 10425 - 10440

Published: Sept. 19, 2024

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

Language: Английский

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Exploring Causal Relationships and Adjustment Timescales of Aerosol‐Cloud Interactions in Geostationary Satellite Observations and CAM6 Using Wavelet Phase Coherence Analysis

Geophysical Research Letters, Journal Year: 2025, Volume and Issue: 52(2)

Published: Jan. 23, 2025

Abstract We present for the first time within cloud physics context, application of wavelet phase coherence analysis to disentangle counteracting physical processes associated with lead‐lag difference between cloud‐proxy liquid water path (LWP) and aerosol‐proxy droplet number concentration ( N d ) in an Eulerian framework using satellite‐based observations climate model outputs. This approach allows us identify causality dominant adjustment timescales governing correlation LWP . Satellite indicate a more prevalent positive daytime regardless whether leads or lags The response, precipitation processes, typically occurs 1 hr, while negative response resulting from entrainment drying, usually takes 2–4 hr. CAM6 displays excessively rapid responses along overly strong insufficient leading compared observations.

Language: Английский

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Co-variability drives the inverted-V sensitivity between liquid water path and droplet concentrations

Atmospheric chemistry and physics, Journal Year: 2025, Volume and Issue: 25(6), P. 3413 - 3423

Published: March 21, 2025

Abstract. Climatological data of the liquid water path (LWP) and droplet concentration (Nd) often reveal an inverted-V relationship, where LWP increases then decreases as Nd increases. Our findings show that while this response to increase in aligns with proposed causal mechanisms, such entrainment evaporation feedback precipitation suppression, pattern is primarily driven by co-variability between Nd. This arises from (1) large-scale meteorology, which controls both Nd, causing them vary opposite directions simultaneously, (2) microphysical processes, typically accompanied a decrease Consequently, we suggest sensitivity should not be used evidence for positive radiative forcing through adjustments aerosols it largely explained co-variability. We further demonstrate relationship essentially reflects climatological evolution Stratocumulus clouds (Sc). Therefore, background anthropogenic changes should, principle, reflected redistribution occurrences across inverted V maintaining its shape.

Language: Английский

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Marine Stratocumulus Clouds With More Coarse Sea Spray Aerosols Are Brighter

Geophysical Research Letters, Journal Year: 2025, Volume and Issue: 52(7)

Published: April 1, 2025

Abstract The idea of cooling the Earth by marine cloud brightening is well established. All prior studies considered enhancing albedo only with fine aerosols (FA). Adding coarse sea spray (CSA, radius>1 μm) has been thought to have opposite effect. Using nearly a decade satellite observations and global aerosol reanalysis, we found that maximum radiative effect from stratocumulus occurs when FA around 3 μg m −3 CSA 30 . Under low winds high stability conditions, optimal can enhance −95 W −2 , 60% more than adding alone. This CRE response was consistently observed across various cloud‐controlling factors, thus minimizing probability being caused meteorological co‐variability. These findings improve our understanding how different affect Earth's climate, evaluation achieved through brightening, support its feasibility.

Language: Английский

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Using Machine Learning to Generate a GISS ModelE Calibrated Physics Ensemble (CPE)

Journal of Advances in Modeling Earth Systems, Journal Year: 2025, Volume and Issue: 17(4)

Published: April 1, 2025

Abstract A neural network (NN) surrogate of the NASA GISS ModelE atmosphere (version E3) is trained on a perturbed parameter ensemble (PPE) spanning 45 physics parameters and 36 outputs. The NN leveraged in Markov Chain Monte Carlo (MCMC) Bayesian inference framework to generate second posterior constrained coined “calibrated ensemble,” or CPE. CPE members are characterized by diverse combinations are, definition, close top‐of‐atmosphere radiative balance, must broadly agree with numerous hydrologic, energy cycle forcing metrics simultaneously. Global observations cloud, environment, radiation properties (provided global satellite products) crucial for generation. explicitly accounts discrepancies (or biases) products during We demonstrate that product strongly impact calibration important model settings (e.g., convective plume entrainment rates; fall speed cloud ice). Structural improvements new E3 retained across stratocumulus simulation). Notably, improved simulation shallow cumulus Amazon rainfall while not degrading fields, an upgrade neither default nor Latin Hypercube searching achieved. Analyses initial PPE suggested several were unimportant output variation. However, many “unimportant” needed generation, result brings forefront how importance should be determined PPEs. From CPE, two 45‐dimensional configurations radiatively‐balanced, auto‐tuned atmospheres used submissions CMIP6.

Language: Английский

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Constraining aerosol–cloud adjustments by uniting surface observations with a perturbed parameter ensemble

Atmospheric chemistry and physics, Journal Year: 2025, Volume and Issue: 25(8), P. 4547 - 4570

Published: April 25, 2025

Abstract. Aerosol–cloud interactions (ACIs) are the largest source of uncertainty in inferring magnitude future warming consistent with observational record. The effective radiative forcing due to ACI (ERFaci) is dominated by liquid clouds and composed two terms: change cloud albedo redistributing over a larger number droplets (Nd) macrophysical properties changes microphysics. These terms are, respectively, referred as (RFaci) aerosol–cloud adjustments. While RFaci uncertain, its sign confidently negative results cooling historical In contrast, adjustment water path (LWP) enhanced Nd associated uncertain sign. Increased LWP response increased precipitation suppression, while decreased evaporation from top. Observational constraints these processes poor part because causal ambiguity relationship between LWP. To better understand this relationship, (P), Nd, surface observations Eastern North Atlantic (ENA) atmospheric observatory combined output perturbed parameter ensemble (PPE) hosted Community Atmosphere Model version 6 (CAM6). This allows for interpretation observed covariability. Observations ENA constrain range possible adjustments relative prior PPE 15 %, resulting global value that positive (a cooling) ranging 2.1 6.9 g m−2. It found covariability coalescence scavenging not strongly related

Language: Английский

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Model analysis of biases in the satellite-diagnosed aerosol effect on the cloud liquid water path

Atmospheric chemistry and physics, Journal Year: 2025, Volume and Issue: 25(3), P. 1533 - 1543

Published: Feb. 4, 2025

Abstract. The response in cloud water content to changes condensation nuclei remains one of the major uncertainties determining how aerosols can perturb properties. In this study, we used an ensemble large eddy simulations marine stratocumulus clouds investigate correlation between liquid path (LWP) and amount nuclei. We compare directly from model derived using equations which are retrieve satellite observations. Our comparison shows that spatial variability properties instrumental noise retrievals optical depth effective radii results bias satellite-derived path. In-depth investigation high-resolution data part a cloud, assumption adiabaticity does not hold, similar LWP–CDNC (cloud droplet number concentration) relationship as seen data. addition, our analysis significant positive 18 % 40 concentration. However, for individual members, mean was very methods. This suggests if cases carefully chosen meteorological conditions it is ensured concentrations well-defined, be confidently determined

Language: Английский

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Can general circulation models (GCMs) represent cloud liquid water path adjustments to aerosol–cloud interactions?

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(23), P. 13633 - 13652

Published: Dec. 11, 2024

Abstract. General circulation models (GCMs), unlike other lines of evidence, indicate that anthropogenic aerosols cause a global-mean increase in cloud liquid water path (ℒ) and thus negative adjustment to radiative forcing the climate by aerosol–cloud interactions. In part 1 this series papers, we showed is true even reproduce correlation observed present-day internal variability ℒ droplet number concentration (Nd). We studied several possible confounding mechanisms could explain noncausal cloud–aerosol correlations GCMs possibly contaminate observational estimates adjustments. Here, perform single-column full-atmosphere GCM experiments investigate causal model-physics underlying model estimate. find both interaction thought be operating real clouds – precipitation suppression entrainment evaporation enhancement are active behave qualitatively agreement with physical process understanding. However, modeled has negligible effect. This raises question whether estimate incorrect due parametric or base-state representation errors understanding gleaned from limited set canonical cases insufficiently representative diversity climate. Regardless, at resolution, physics appears able parameterize small-scale microphysics–turbulence interplay responsible for mechanism. suggest ways resolve tension between current future (storm-resolving) global modeling systems evidence synthesis projections.

Language: Английский

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