Aerosol-cloud-climate cooling overestimated by ship-track data

Science, Journal Year: 2021, Volume and Issue: 371(6528), P. 485 - 489

Published: Jan. 28, 2021

Making tracks The magnitude of the effect anthropogenic aerosols on formation clouds is an important unknown about how humans are affecting climate. Studies stratocumulus cloud that formed by ship exhaust have been used to estimate radiative impact this process, but Glassmeier et al. now show approach overestimates cooling aerosol addition up 200%. These findings underscore need quantify responses understand climate system. Science , issue p. 485

Language: Английский

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The CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) measurement campaign

Atmospheric chemistry and physics, Journal Year: 2021, Volume and Issue: 21(2), P. 1049 - 1084

Published: Jan. 27, 2021

Abstract. The representations of clouds, aerosols, and cloud–aerosol–radiation impacts remain some the largest uncertainties in climate change, limiting our ability to accurately reconstruct past predict future climate. south-east Atlantic is a region where high atmospheric aerosol loadings semi-permanent stratocumulus clouds are co-located, providing an optimum for studying full range aerosol–radiation aerosol–cloud interactions their perturbations Earth's radiation budget. While satellite measurements have provided useful insights into over region, these observations do not spatial temporal resolution, nor required level precision allow process-level assessment. Detailed from resolution airborne very sparse, use assessing performance modelling numerical weather prediction models. CLARIFY-2017 was major consortium programme consisting five principal UK universities with project partners Met Office European- USA-based research centres involved complementary ORACLES, LASIC, AEROCLO-sA projects. aims were fourfold: (1) improve representation reduce uncertainty model estimates direct, semi-direct, indirect radiative effect absorbing biomass burning aerosols; (2) knowledge processes determining cloud microphysical properties transition cumulus regimes; (3) challenge, validate, retrievals impacts; (4) aerosols This paper describes measurement strategies central deployment FAAM BAe146 instrumented aircraft campaign, summarizes flight objectives patterns, highlights key results initial analyses.

Language: Английский

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Opportunistic experiments to constrain aerosol effective radiative forcing

Atmospheric chemistry and physics, Journal Year: 2022, Volume and Issue: 22(1), P. 641 - 674

Published: Jan. 17, 2022

Aerosol-cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due human activities. The nonlinearity cloud-state changes aerosol perturbations make it challenging attribute causality in observed relationships forcing. Using correlations infer can when meteorological variability also drives both and cloud independently. Natural anthropogenic from well-defined sources provide "opportunistic experiments" (also known as natural experiments) investigate ACI cases where may more confidently inferred. These cover a wide range locations spatiotemporal scales, including point such volcanic eruptions or industrial sources, plumes biomass burning forest fires, tracks individual ships shipping corridors. We review different experimental conditions conduct synthesis available satellite datasets field campaigns place these opportunistic experiments on common footing, facilitating new insights clearer understanding key uncertainties Cloud albedo strongly sensitive background conditions. Strong liquid water path increases largely ruled out by averaging across experiments. Opportunistic have significantly improved process-level ACI, but remains unclear how reliably found scaled global level, thus demonstrating need for deeper investigation order improve assessments climate change.

Language: Английский

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Machine learning reveals climate forcing from aerosols is dominated by increased cloud cover

Nature Geoscience, Journal Year: 2022, Volume and Issue: 15(8), P. 609 - 614

Published: Aug. 1, 2022

Language: Английский

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

Science Advances, Journal Year: 2024, Volume and Issue: 10(12)

Published: March 20, 2024

Marine cloud brightening (MCB) is the deliberate injection of aerosol particles into shallow marine clouds to increase their reflection solar radiation and reduce amount energy absorbed by climate system. From physical science perspective, consensus a broad international group scientists that viability MCB will ultimately depend on whether observations models can robustly assess scale-up local-to-global in today's identify strategies ensure an equitable geographical distribution benefits risks associated with projected regional changes temperature precipitation. To address knowledge gaps required societal implications MCB, we propose substantial targeted program research-field laboratory experiments, monitoring, numerical modeling across range scales.

Language: Английский

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Invisible ship tracks show large cloud sensitivity to aerosol

Nature, Journal Year: 2022, Volume and Issue: 610(7930), P. 101 - 106

Published: Oct. 5, 2022

Abstract Cloud reflectivity is sensitive to atmospheric aerosol concentrations because aerosols provide the condensation nuclei on which water condenses 1 . Increased due human activity affect droplet number concentration, liquid and cloud fraction 2 , but these changes are subject large uncertainties 3 Ship tracks, long lines of polluted clouds that visible in satellite images, one main tools for quantifying aerosol–cloud interactions 4 However, only a small by shipping show ship tracks 5,6 Here we even when no emissions change properties substantially. We develop new method quantify effect all clouds, showing increase more positive response there tracks. directly detect shipping-induced property trade cumulus regions Atlantic, known display almost Our results indicate previous studies were suffering from selection biases focusing imagery. The strong path find translates larger cooling climate, potentially masking higher climate sensitivity than observed temperature trends would otherwise suggest.

Language: Английский

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Albedo susceptibility of northeastern Pacific stratocumulus: the role of covarying meteorological conditions

Atmospheric chemistry and physics, Journal Year: 2022, Volume and Issue: 22(2), P. 861 - 880

Published: Jan. 19, 2022

Abstract. Quantification of the radiative adjustment marine low clouds to aerosol perturbations, regionally and globally, remains largest source uncertainty in assessing current future climate. One important steps towards quantifying role modifying cloud properties is quantify susceptibility albedo liquid water path (LWP) perturbations droplet number concentration (Nd). We use 10 years spaceborne observations from polar-orbiting Aqua satellite Nd over northeast (NE) Pacific stratocumulus (Sc) region. Mutual information analysis reveals a dominating control state (e.g., LWP Nd) on low-cloud susceptibility, relative meteorological states that drive these states. Through LWP–Nd space decomposition susceptibilities, we show clear separation among regimes (brightening or darkening), consistent with previously established mechanisms through which modulates properties. These include (i) thin non-precipitating (LWP < 55 g m−2) exhibit brightening (occurring 37 % time), corresponding Twomey effect; (ii) thicker clouds, entrainment-driven negative adjustments manifest as darkening regime (36 time); (iii) another (22 time) consisting mostly precipitating precipitation-suppression positive adjustments. Overall, find an annual-mean regional potential 20.8±2.68 W m−2 ln(Nd)−1, despite overall for stratocumulus, owing high occurrence Twomey–brightening regime. Over NE Pacific, seasonal covariabilities factors related large-scale circulation are found play grouping conditions favorable each When considering covarying conditions, our results indicate northeastern strongest occur most frequently within shallow boundary layers cool ocean surface stable atmosphere dry free troposphere above. Clouds associated deep atmospheric instability not strong warm enough produce frequent precipitation. Cloud warm-rain suppression preferably either under unstable humid free-tropospheric co-occur surface.

Language: Английский

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General circulation models simulate negative liquid water path–droplet number correlations, but anthropogenic aerosols still increase simulated liquid water path

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(12), P. 7331 - 7345

Published: June 27, 2024

Abstract. General circulation models' (GCMs) estimates of the liquid water path adjustment to anthropogenic aerosol emissions differ in sign from other lines evidence. This reduces confidence effective radiative forcing climate by aerosol–cloud interactions (ERFaci). The discrepancy is thought stem part GCMs' inability represent turbulence–microphysics cloud-top entrainment, a mechanism that leads reduction response an increase aerosols. In real atmosphere, enhanced entrainment be dominant for path, weakening overall ERFaci. We show latest generation GCMs includes models produce negative correlation between present-day cloud droplet number and key piece observational evidence supporting aerosols one earlier-generation could not reproduce. However, even with this correlation, preindustrial values still simulated due parameterized precipitation suppression mechanism. adds correlations are necessarily causal. investigate sources confounding explain noncausal number. These results reminder assessments parameters based on multiple must carefully consider complementary strengths different when disagree.

Language: Английский

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Diurnal Patterns in the Observed Cloud Liquid Water Path Response to Droplet Number Perturbations

Geophysical Research Letters, Journal Year: 2024, Volume and Issue: 51(4)

Published: Feb. 10, 2024

Abstract A key uncertainty in Aerosol‐cloud interactions is the cloud liquid water path (LWP) response to increased aerosols ( λ ). LWP can either increase due precipitation suppression or decrease entrainment‐drying. Previous research suggests that dominates thick clouds, while entrainment‐drying prevails thin clouds. The time scales of two competing effects are vastly different, requiring temporally resolved observations. We analyze 3‐day Lagrangian trajectories stratocumulus clouds over southeast Pacific using 2019–2021 geostationary data. find with a exceeding 200 g m −2 exhibit positive response, lower show negative response. observe significant diurnal cycle , indicating more strongly daytime adjustment driven by In contrast, at night, occasionally fully counteract mechanism. Overall, appears weaker than previously suggested studies do not account for cycle.

Language: Английский

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Assessing the potential efficacy of marine cloud brightening for cooling Earth using a simple heuristic model

Atmospheric chemistry and physics, Journal Year: 2021, Volume and Issue: 21(19), P. 14507 - 14533

Published: Oct. 1, 2021

Abstract. A simple heuristic model is described to assess the potential for increasing solar reflection by augmenting aerosol population below marine low clouds, which nominally leads increased cloud droplet concentration and albedo. The estimates collective impact of many point source particle sprayers, each generates a plume injected particles that affects clouds over limited area. look-up table derived from simulations an explicit activation scheme used derive as function sub-cloud size distribution updraft speed, modified version Twomey's formulation estimate radiative forcing. Plume overlap accounted using Poisson distribution, assuming idealized elongated cuboid plumes have length driven lifetime wind width consistent with satellite observations ship track broadening, depth equal assumed boundary layer depth. found perform favorably against brightening large eddy simulation studies explicitly responses injections range conditions. Although does not account condensate or coverage adjustments aerosol, in most realistic ambient remote conditions these tend augment Twomey effect simulations, result being modest underprediction model. evaluate global forcing quantity, size, salt per sprayer number sprayers deployed. Radiative sensitive both background into are speed. Given representative values literature, sufficient offset doubling carbon dioxide ΔF2×CO2 possible but would require spraying 50 % more ocean This likely at least 104 avoid major losses due near-sprayer coagulation. optimal dry diameter particles, given mass injection rate, 30–60 nm. consequence total emission rate (50–70 Tg yr−1) required factor five lower than emissions rates generate significant previous climate models, mostly diameters excess 200 With emissions, loading dominated natural only contributing ∼ 10 %. When sizes optimized brightening, direct shown make minimal contribution overall

Language: Английский

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