248 results on '"Bellouin, Nicolas"'
Search Results
202. Erratum: aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability
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Booth, Ben B.B., Dunstone, Nick J., Halloran, Paul R., Andrews, Timothy, and Bellouin, Nicolas
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Environmental issues ,Science and technology ,Zoology and wildlife conservation - Abstract
Nature 484, 228-232 (2012) The accepted date should read 08 February 2012, rather than 2011. This error has been corrected in the PDF and HTML versions online. [...]
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- 2012
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203. What controls the vertical distribution of aerosol? Relationships between process sensitivity in HadGEM3-UKCA and inter-model variation from AeroCom Phase II.
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Kipling, Zak, Stier, Philip, Johnson, Colin E., Mann, Graham W., Bellouin, Nicolas, Bauer, Susanne E., Bergman, Tommi, Mian Chin, Diehl, Thomas, Ghan, Steven J., Iversen, Trond, Kirkevåg, Alf, Kokkola, Harri, Xiaohong Liu, Gan Luo, van Noije, Twan, Pringle, Kirsty J., von Salzen, Knut, Schulz, Michael, and Seland, Øyvind
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ATMOSPHERIC aerosols ,VERTICAL distribution (Aquatic biology) ,RADIATIVE transfer ,MICROPHYSICS ,BIOMASS burning ,EMISSIONS (Air pollution) - Abstract
The vertical profile of aerosol is important for its radiative effects, but weakly constrained by observations on the global scale, and highly variable among different models. To investigate the controlling factors in one particular model, we investigate the effects of individual processes in HadGEM3-UKCA and compare the resulting diversity of aerosol vertical profiles with the inter-model diversity from the AeroCom Phase II control experiment. In this way we show that (in this model at least) the vertical profile is controlled by a relatively small number of processes, although these vary among aerosol components and particle sizes. We also show that sufficiently coarse variations in these processes can produce a similar diversity to that among different models in terms of the global-mean profile and, to a lesser extent, the zonal-mean vertical position. However, there are features of certain models' profiles that cannot be reproduced, suggesting the influence of further structural differences between models. In HadGEM3-UKCA, convective transport is found to be very important in controlling the vertical profile of all aerosol components by mass. In-cloud scavenging is very important for all except mineral dust. Growth by condensation is important for sulfate and carbonaceous aerosol (along with aqueous oxidation for the former and ageing by soluble material for the latter). The vertical extent of biomass-burning emissions into the free troposphere is also important for the profile of carbonaceous aerosol. Boundary-layer mixing plays a dominant role for sea salt and mineral dust, which are emitted only from the surface. Dry deposition and below-cloud scavenging are important for the profile of mineral dust only. In this model, the microphysical processes of nucleation, condensation and coagulation dominate the vertical profile of the smallest particles by number (e.g. total CN >3 nm), while the profiles of larger particles (e.g. CN>100 nm) are controlled by the same processes as the component mass profiles, plus the size distribution of primary emissions. We also show that the processes that affect the AODnormalised radiative forcing in the model are predominantly those that affect the vertical mass distribution, in particular convective transport, in-cloud scavenging, aqueous oxidation, ageing and the vertical extent of biomass-burning emissions. [ABSTRACT FROM AUTHOR]
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- 2016
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204. Ocean–Atmosphere Interactions of Particles.
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de Leeuw, Gerrit, Guieu, Cécile, Arneth, Almuth, Bellouin, Nicolas, Bopp, Laurent, Boyd, Philip W., van der Gon, Hugo A. C. Denier, Desboeufs, Karine V., Dulac, François, Facchini, M. Cristina, Gantt, Brett, Langmann, Baerbel, Mahowald, Natalie M., Marañón, Emilio, O'Dowd, Colin, Olgun, Nazli, Pulido-Villena, Elvira, Rinaldi, Matteo, Stephanou, Euripides G., and Wagener, Thibaut
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- 2014
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205. Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability
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Booth, Ben B. B., primary, Dunstone, Nick J., additional, Halloran, Paul R., additional, Andrews, Timothy, additional, and Bellouin, Nicolas, additional
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- 2012
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206. Which of satellite- or model-based estimates is closer to reality for aerosol indirect forcing?
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Quaas, Johannes, primary, Boucher, Olivier, additional, Bellouin, Nicolas, additional, and Kinne, Stefan, additional
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- 2011
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207. The roles of aerosol, water vapor and cloud in future global dimming/brightening
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Haywood, Jim M., primary, Bellouin, Nicolas, additional, Jones, Andy, additional, Boucher, Olivier, additional, Wild, Martin, additional, and Shine, Keith P., additional
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- 2011
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208. Observations of the eruption of the Sarychev volcano and simulations using the HadGEM2 climate model
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Haywood, James M., primary, Jones, Andy, additional, Clarisse, Lieven, additional, Bourassa, Adam, additional, Barnes, John, additional, Telford, Paul, additional, Bellouin, Nicolas, additional, Boucher, Olivier, additional, Agnew, Paul, additional, Clerbaux, Cathy, additional, Coheur, Pierre, additional, Degenstein, Doug, additional, and Braesicke, Peter, additional
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- 2010
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209. Precipitation, radiative forcing and global temperature change
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Andrews, Timothy, primary, Forster, Piers M., additional, Boucher, Olivier, additional, Bellouin, Nicolas, additional, and Jones, Andy, additional
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- 2010
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210. Impact of changes in diffuse radiation on the global land carbon sink
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Mercado, Lina M., primary, Bellouin, Nicolas, additional, Sitch, Stephen, additional, Boucher, Olivier, additional, Huntingford, Chris, additional, Wild, Martin, additional, and Cox, Peter M., additional
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- 2009
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211. Updated estimate of aerosol direct radiative forcing from satellite observations and comparison against the Hadley Centre climate model
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Bellouin, Nicolas, primary, Jones, Andy, additional, Haywood, Jim, additional, and Christopher, Sundar A., additional
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- 2008
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212. Satellite-based estimate of the direct and indirect aerosol climate forcing
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Quaas, Johannes, primary, Boucher, Olivier, additional, Bellouin, Nicolas, additional, and Kinne, Stefan, additional
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- 2008
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213. Comparison of the radiative properties and direct radiative effect of aerosols from a global aerosol model and remote sensing data over ocean
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Myhre, Gunnar, primary, Bellouin, Nicolas, additional, Berglen, Tore F., additional, Berntsen, Terje K., additional, Boucher, Olivier, additional, Grini, Alf, additional, Isaksen, Ivar S. A., additional, Johnsrud, Mona, additional, Mishchenko, Michael I., additional, Stordal, Frode, additional, and Tanré, Didier, additional
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- 2007
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214. An “A-Train” Strategy for Quantifying Direct Climate Forcing by Anthropogenic Aerosols
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Anderson, Theodore L., primary, Charlson, Robert J., additional, Bellouin, Nicolas, additional, Boucher, Olivier, additional, Chin, Mian, additional, Christopher, Sundar A., additional, Haywood, Jim, additional, Kaufman, Yoram J., additional, Kinne, Stefan, additional, Ogren, John A., additional, Remer, Lorraine A., additional, Takemura, Toshihiko, additional, Tanré, Didier, additional, Torres, Omar, additional, Trepte, Charles R., additional, Wielicki, Bruce A., additional, Winker, David M., additional, and Yu, Hongbin, additional
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- 2005
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215. Correction to: Evaluation of a new 12 km regional perturbed parameter ensemble over Europe.
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Tucker, Simon O., Kendon, Elizabeth J., Bellouin, Nicolas, Buonomo, Erasmo, Johnson, Ben, and Murphy, James M.
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REFERENCE sources - Abstract
Correction to: Climate Dynamics https://doi.org/10.1007/s00382-021-05941-3 The original html version of the article contained an error in the formatting of Fig. The original article can be found online at https://doi.org/10.1007/s00382-021-05941-3. The caption was swapped and below is the corrected caption. [Extracted from the article]
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- 2022
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216. Estimates of global multicomponent aerosol optical depth and direct radiative perturbation in the Laboratoire de Météorologie Dynamique general circulation model.
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Reddy, M. Shekar, Boucher, Olivier, Bellouin, Nicolas, Schulz, Michael, Balkanski, Yves, Dufresne, Jean-Louis, and Pham, Mai
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- 2005
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217. How to reconstruct aerosol-induced diffuse radiation scenario for simulating GPP in land surface models? An evaluation of reconstruction methods with ORCHIDEE_DFv1.0_DFforc
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Zhang, Yuan, Boucher, Olivier, Ciais, Philippe, Li, Laurent, Bellouin, Nicolas, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), ICOS-ATC (ICOS-ATC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Department of Meteorology [Reading], University of Reading (UOR), European Project: 610028,EC:FP7:ERC,ERC-2013-SyG,IMBALANCE-P(2014), European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
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[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere - Abstract
International audience The impact of diffuse radiation on photosynthesis has been widely documented in field measurements. This impact may have evolved over time during the last century due to changes in cloudiness, increased anthropogenic aerosol loads over polluted regions, and to sporadic volcanic eruptions curtaining the stratosphere with sulfate aerosols. The effects of those changes in diffuse light on large-scale photosynthesis (GPP) are difficult to quantify, and land surface models have been designed to simulate them. Investigating how anthropogenic aerosols have impacted GPP through diffuse light in those models requires carefully designed factorial simulations and a reconstruction of background diffuse light levels during the preindustrial period. Currently, it remains poorly understood how diffuse radiation reconstruction methods can affect GPP estimation and what fraction of GPP changes can be attributed to aerosols. In this study, we investigate different methods to reconstruct spatiotemporal distribution of the fraction of diffuse radiation (Fdf) under preindustrial aerosol emission conditions using a land surface model with a two-stream canopy light transmission scheme that resolves diffuse light effects on photosynthesis in a multi-layered canopy, ORCHIDEE_DF. We show that using a climatologically averaged monthly Fdf, as has been done by earlier studies, can bias the global GPP by up to 13 PgC yr-1 because this reconstruction method dampens the variability of Fdf and produces Fdf that is inconsistent with shortwave incoming surface radiation. In order to correctly simulate preindustrial GPP modulated by diffuse light, we thus recommend that the Fdf forcing field should be calculated consistently with synoptic, monthly, and inter-annual aerosol and cloud variability for preindustrial years. In the absence of aerosol and cloud data, alternative reconstructions need to retain the full variability in Fdf. Our results highlight the importance of keeping consistent Fdf and radiation for land surface models in future experimental designs that seek to investigate the impacts of diffuse radiation on GPP and other carbon fluxes.
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218. Evaluation of a new 12 km regional perturbed parameter ensemble over Europe.
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Tucker, Simon O., Kendon, Elizabeth J., Bellouin, Nicolas, Buonomo, Erasmo, Johnson, Ben, and Murphy, James M.
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COLD (Temperature) , *ATMOSPHERIC models , *DOWNSCALING (Climatology) , *AEROSOLS , *WINTER - Abstract
We evaluate a 12-member perturbed parameter ensemble of regional climate simulations over Europe at 12 km resolution, carried out as part of the UK Climate Projections (UKCP) project. This ensemble is formed by varying uncertain parameters within the model physics, allowing uncertainty in future projections due to climate modelling uncertainty to be explored in a systematic way. We focus on present day performance both compared to observations, and consistency with the driving global ensemble. Daily and seasonal temperature and precipitation are evaluated as two variables commonly used in impacts assessments. For precipitation we find that downscaling, even whilst within the convection-parameterised regime, generally improves daily precipitation, but not everywhere. In summer, the underestimation of dry day frequency is worse in the regional ensemble than in the driving simulations. For temperature we find that the regional ensemble inherits a large wintertime cold bias from the global model, however downscaling reduces this bias. The largest bias reduction is in daily winter cold temperature extremes. In summer the regional ensemble is cooler and wetter than the driving global models, and we examine cloud and radiation diagnostics to understand the causes of the differences. We also use a low-resolution regional simulation to determine whether the differences are a consequence of resolution, or due to other configuration differences, with the predominant configuration difference being the treatment of aerosols. We find that use of the EasyAerosol scheme in the regional model, which aims to approximate the aerosol effects in the driving model, causes reduced temperatures by around 0.5 K over Eastern Europe in Summer, and warming of a similar magnitude over France and Germany in Winter, relative to the impact of interactive aerosol in the global runs. Precipitation is also increased in these regions. Overall, we find that the regional model is consistent with the global model, but with a typically better representation of daily extremes and consequently we have higher confidence in its projections of their future change. [ABSTRACT FROM AUTHOR]
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- 2022
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219. Changes in Clear‐Sky Shortwave Aerosol Direct Radiative Effects Since 2002
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Loeb, Norman G., Su, Wenying, Bellouin, Nicolas, and Ming, Yi
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A new method for determining clear‐sky shortwave aerosol direct radiative effects (ADRE) from the Clouds and the Earth's Radiant Energy System is used to examine changes in ADRE since 2002 alongside changes in aerosol optical depth (AOD) from the Moderate Resolution Spectroradiometer. At global scales, neither ADRE nor AOD show a significant trend. Over the northern hemisphere (NH), ADRE increases by 0.18 ± 0.17 Wm−2per decade (less reflection to space) but shows no significant change over the southern hemisphere. The increase in the NH is primarily due to emission reductions in China, the United States, and Europe. The COVID‐19 shutdown shows no noticeable impact on either global ADRE or AOD, but there is a substantial influence over northeastern China in March 2020. In contrast, February 2020 anomalies in ADRE and AOD are within natural variability even though the impact of the shutdown on industry was more pronounced in February than March. The reason is because February 2020 was exceptionally hot and humid over China, which compensated for reduced emissions. After accounting for meteorology and normalizing by incident solar flux, February ADRE anomalies increase substantially, exceeding the climatological mean ADRE by 23%. February and March 2020 correspond to the only period in which adjusted anomalies exceed the 95% confidence interval for 2 consecutive months. Distinct water‐land differences over northeastern China are observed in ADRE but not in AOD. This is likely due to the influence of surface albedo on ADRE in the presence of absorbing aerosols. Satellite observations show that radiative cooling by aerosols has significantly declined over North America since 2002During the COVID‐19 shutdown, hot and humid conditions over northeastern China masked the influence of reduced aerosol emissionsAfter accounting for meteorology, aerosol radiative cooling over northeastern China is reduced by up to 23% in early 2020 Satellite observations show that radiative cooling by aerosols has significantly declined over North America since 2002 During the COVID‐19 shutdown, hot and humid conditions over northeastern China masked the influence of reduced aerosol emissions After accounting for meteorology, aerosol radiative cooling over northeastern China is reduced by up to 23% in early 2020
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- 2021
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220. Towards a better understanding of the model spread in aerosol forcing.
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Fiedler, Stephanie, Bellouin, Nicolas, Kinne, Stefan, van Noije, Twan, Räisänen, Petri, and Stier, Philip
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AEROSOLS , *RADIATIVE forcing , *TIME series analysis , *ATMOSPHERIC models , *OPTICAL properties - Abstract
The radiative forcing of anthropogenic aerosol is important for understanding climate change. However, the uncertainty in anthropogenic aerosol forcing is large, despite decades of research on aerosols and their effect on climate. The reasons for the associated model spread in aerosol forcing are numerous, but their relative importance is largely unclear due to the model complexity. In this presentation, we see how a deliberate reduction of the model complexity aids improving our understanding of the effective radiative forcing of anthropogenic aerosol (ERF). We investigate the impact on ERF from uncertainties that remain when we pretend to know the spatio-temporal distribution of anthropogenic aerosols and their properties. For doing so, we present an ensemble of atmosphere-only experiments of a selection of contemporary climate models (Fiedler et al., 2018a, in review). All five models use the same prescribed anthropogenic aerosol optical properties and an associated effect on clouds from the new observationally informed simple-plumes parameterisation MACv2-SP for use in CMIP6 (Fiedler et al., 2017, Stevens et al., 2017). The highlights of the results are (1) a strong impact of year-to-year variability internal to the models on estimating the ERF, (2) a small change in the global mean ERF between the mid-1970s and the mid-2000s, despite the substantially different spatial distribution of anthropogenic aerosol, and (3) a persistently large model diversity in clouds on the macro- and micro-scale. In the future, MACv2-SP will be used for CMIP6 experiments, e.g., in the radiative forcing model inter-comparison project (RFMIP), and for other scientific endeavours, e.g., decadal climate predictions. These projects will make use of MACv2-SP's time series of anthropogenic aerosol for the past (Stevens et al., 2017) and for the projections into the future, based on CMIP6 emission scenarios (Fiedler et al., 2018b, in review).PublicationsFiedler, et al. (2018a) Anthropogenic aerosol forcing - insights from multi-estimates from aerosol-climate models with reduced complexity, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2018-639, in review.Fiedler, et al. (2018b) First forcing estimates from the future CMIP6 scenarios of anthropogenic aerosol optical properties and an associated Twomey effect, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2018-244, in review.Fiedler, et al. (2017) On the sensitivity of the anthropogenic aerosol forcing to model-internal variability and parameterizing a Twomey effect, J. Adv. Mod. Earth Syst., 9, doi:10.1002/2017MS000932. Stevens, et al. (2017) Simple Plumes: A parameterization of anthropogenic aerosol optical properties and an associated Twomey effect for climate studies, Geosci. Model Dev. 10, 433-452, doi:10.5194/gmd-10-433-2017. [ABSTRACT FROM AUTHOR]
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- 2019
221. Sign and magnitude of the semidirect sffect from elevated smoke layers are sensitive to layer properties and cloud–smoke gap.
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Herbert, Ross, Bellouin, Nicolas, and Highwood, Ellie
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STRATOCUMULUS clouds , *RADIATION absorption , *BOUNDARY layer (Aerodynamics) , *CARBONACEOUS aerosols , *TERRITORIAL waters , *ATMOSPHERIC temperature , *SMOKE , *CIRCADIAN rhythms - Abstract
The absorption of radiation by carbonaceous aerosol can result in mean local heat perturbations of several Kelvin per day. Subsequent rapid-adjustments to the atmosphere lead to changes in radiation fluxes, referred to as semi-direct radiative effects.The SE Atlantic is a region that experiences periodic plumes of strongly absorbing smoke that are transported over extensive semi-permanent marine stratocumulus. Before mixing with the cloud layer the elevated plumes are often separated by smoke-free gaps for extended periods of time.We use the high resolution MetOffice large eddy model to investigate the diurnal cycle of the semi-direct radiative effect from elevated smoke layers above marine stratocumulus cloud. We use a range of experiments to investigate the sensitivity of the semi-direct effect to the gap to layer, thickness of the layer, and smoke aerosol optical depth (AOD). We find a pronounced diurnal cycle driven by changes in cloud-top entrainment that impact daytime coupling to the surface and boundary layer water content. Subsequent changes to the cloud liquid water path drive periods of both positive and negative semi-direct radiative effects, which are sensitive to the amount of time the plume persists over the cloud.Contrary to published literature, the presence of an overlying layer of absorbing aerosol does not systematically exert a negative semi-direct radiative effect. Instead we show that both the sign and magnitude of the daily mean semi-direct radiative effect of above-cloud smoke layers is sensitive to the smoke layer position, thickness, AOD, persistence, and properties of the boundary layer. Thus, rapid adjustments to atmospheric temperature perturbations caused by above-cloud absorbing aerosol both enhance or mitigate the direct radiative effect. [ABSTRACT FROM AUTHOR]
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- 2019
222. Combining ship-borne, airborne and early Southern Hemisphere ground-based lidar measurements with global model predictions to improve early phase dispersion in an improved aerosol extinction datasets for the 1991 Mount Pinatubo aerosol cloud.
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Marrero, Juan Carlos Antuna, Mann, Graham, Winker, David, Young, Stuart, Bellouin, Nicolas, Dhomse, Sandip, and Thomason, Larry
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- 2019
223. The prevalence of meteoric-sulphuric particles within the stratospheric aerosol layer and their influence on how pure sulphuric particles are transported and transformed.
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Mann, Graham, Brooke, James, Sengupta, Kamalika, Marshall, Lauren, Dhomse, Sandip, Feng, Wuhu, Neely, Ryan, Bardeen, Charles, Bellouin, Nicolas, Dalvi, Mohit, Johnson, Colin, Abraham, Luke, Deshler, Terry, Thomason, Larry, and Plane, John
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- 2019
224. Diurnal cycle of the semi–direct effect from a persistent absorbing aerosol layer over marine stratocumulus in large–eddy simulations
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Herbert, Ross, Bellouin, Nicolas, Highwood, Ellie, and Hill, Adrian
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complex mixtures ,Physics::Atmospheric and Oceanic Physics - Abstract
The rapid adjustment, or semi–direct effect, of marine stratocumulus clouds to elevated layers of absorbing aerosols may enhance or dampen the radiative effect of aerosol–radiation interactions. Here we use large eddy simulations to investigate the sensitivity of stratocumulus clouds to the properties of an absorbing aerosol layer located above the inversion layer, with a focus on the location, timing, and strength of the radiative heat perturbation. The sign of the daily mean semi–direct effect depends on the properties and duration of the aerosol layer, the properties of the boundary layer, and the model setup. Our results suggest that the daily mean semi-direct effect is more elusive than previously assessed. We find that the daily mean semi-direct effect is dominated by the distance between the cloud and absorbing aerosol layer. Within the first 24 hours the semi–direct effect is positive but remains under 2 Wm-2 unless the aerosol layer is directly above the cloud. For longer durations, the daily mean semi–direct effect is consistently negative but weakens by 30%, 60%, and 95% when the distance between cloud and aerosol layeris 100m, 250m, and 500m, respectively. Both cloud response and semi–direct effect increase for thinner and denser layers of absorbing aerosol. Considerable diurnal variations in the cloud response mean that an instantaneous semi–direct effect is unrepresentative of the daily mean, and that observational studies may under– or over–estimate semi–direct effects depending on the observed time of day. The cloud response is particularly sensitive to the mixing state of the boundary layer: well-mixed boundary layers generally result in a negative daily mean semi–direct effect, and poorly mixed boundary layers result in a positive daily mean semi–direct effect. Properties of the boundary layer and model setup, particularly the sea surface temperature, precipitation, and properties of the air entrained from the free troposphere, also impact the magnitude of the semi–direct effect and the timescale of adjustment. These results suggest that the semi–direct effect simulated by coarse–resolution models may be erroneous because the cloud response is sensitive to small–scale processes, especially the sources and sinks of buoyancy.
225. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change; Technical Summary
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Arias, Paola, Bellouin, Nicolas, Coppola, Erika, Jones, Richard, Krinner, Gerhard, Marotzke, Jochem, Naik, Vaishali, Palmer, Matthew, Plattner, G.-K., Rogelj, Joeri, Rojas, Maisa, Sillmann, Jana, Storelvmo, Trude, Thorne, Peter, Trewin, Blair, Achutarao, Krishna, Adhikary, Bhupesh, Allan, Richard, Armour, Kyle, Bala, Govindasamy, Barimalala, Rondrotiana, Berger, Sophie, Canadell, Josep G., Cassou, Christophe, Cherchi, Annalisa, Collins, William D., Collins, William J., Connors, Sarah, Corti, Susanna, Cruz, Faye, Dentener, Frank J., Dereczynski, Claudine, Di Luca, Alejandro, Diongue Niang, Aida, Doblas-Reyes, Paco, Dosio, Alessandro, Douville, Hervé, Engelbrecht, Francois, Eyring, Veronika, Fischer, Erich M., Forster, Piers, Fox-Kemper, Baylor, Fuglestvedt, Jan, Fyfe, John, Gillett, Nathan, Goldfarb, Leah, Gorodetskaya, Irina, Gutierrez, Jose Manuel, Hamdi, Rafiq, Hawkins, E., Hewitt, Helene, Hope, Pandora, Islam, Akm Saiful, Jones, Christopher, Kaufmann, Darrell, Kopp, Robert, Kosaka, Yu, Kossin, James, Krakovska, Svitlana, Li, Jian, Lee, June-Yi, Masson-Delmotte, Valérie, Mauritsen, Thorsten, Maycock, Thomas, Meinshausen, Malte, Min, Seung-ki, Ngo Duc, Thanh, Otto, Friederike, Pinto, Izidine, Pirani, Anna, Raghavan, Krishnan, Ranasighe, Roshanka, Ruane, Alexander, Ruiz, Lucas, Sallée, Jean-Baptiste, Samset, Bjorn H., Sathyendranath, Shubha, Monteiro, Pedro Scheel, Seneviratne, Sonia I., Sörensson, Anna Amelia, Szopa, Sophie, Takayabu, Izuru, Treguier, Anne-Marie, van den Hurk, Bart, Vautard, R., Von Schuckmann, Karina, Zaehle, Sönke, Zhang, Xuebin, and Zickfeld, Kirsten
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Climate Change ,Summary for Policymakers ,physical ,chemical and biological processes and components of the climate system
226. Aerosol indirect effects - general circulation model intercomparison and evaluation with satellite data
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Quaas, Johannes, Ming, Y., Menon, Surabi, Takemura, Toshihiko, Wang, M., Penner, Joyce E., Gettelman, Andrew, Lohmann, Ulrike, Bellouin, Nicolas, Boucher, Olivier, Sayer, Andrew M., Thomas, G.E., McComiskey, Allison, Feingold, Graham, Hoose, C., Kristjánsson, Jón E., Liu, X., Balkanski, Yves, Donner, Leo J., Ginoux, Paul A., Stier, Philip, Grandey, Benjamin, Feichter, Johann, Sednev, Igor, Bauer, Susanne E., Koch, Dorothy, Grainger, Roy G., Kirkevåg, Alf, Iversen, Trond, Seland, Øyvind, Easter, Richard, Ghan, Steven J., Rasch, Phil J., Morrison, Hugh, Lamarque, Jean-François, Iacono, Michael J., Kinne, Stefan, and Schulz, M.
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13. Climate action - Abstract
Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterises aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (τa) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at least over the ocean. The relationship between τa and liquid water path is simulated much too strongly by the models. This suggests that the implementation of the second aerosol indirect effect mainly in terms of an autoconversion parameterisation has to be revisited in the GCMs. A positive relationship between total cloud fraction (fcld) and τa as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong fcld–τa relationship, our results indicate that none can be identified as a unique explanation. Relationships similar to the ones found in satellite data between τa and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR–τa relationship show a strong positive correlation between τa and fcld. The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of τa, and parameterisation assumptions such as a lower bound on Nd. Nevertheless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred from the combination of these predictors for the modelled forcings with the satellite-derived statistical relationships yields a global annual mean value of −1.5±0.5 Wm−2. In an alternative approach, the radiative flux perturbation due to anthropogenic aerosols can be broken down into a component over the cloud-free portion of the globe (approximately the aerosol direct effect) and a component over the cloudy portion of the globe (approximately the aerosol indirect effect). An estimate obtained by scaling these simulated clear- and cloudy-sky forcings with estimates of anthropogenic τa and satellite-retrieved Nd–τa regression slopes, respectively, yields a global, annual-mean aerosol direct effect estimate of −0.4±0.2 Wm−2 and a cloudy-sky (aerosol indirect effect) estimate of −0.7±0.5 Wm−2, with a total estimate of −1.2±0.4 Wm−2., Atmospheric Chemistry and Physics, 9 (22), ISSN:1680-7375, ISSN:1680-7367
227. Strong constraints on aerosol-cloud interactions from volcanic eruptions
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Malavelle, Florent F, Haywood, Jim M, Jones, Andy, Gettelman, Andrew, Clarisse, Lieven, Bauduin, Sophie, Allan, Richard P, Karset, Inger Helene H, Kristjánsson, Jón Egill, Oreopoulos, Lazaros, Cho, Nayeong, Lee, Dongmin, Bellouin, Nicolas, Boucher, Olivier, Grosvenor, Daniel P, Carslaw, Ken S, Dhomse, Sandip, Mann, Graham W, Schmidt, Anja, Coe, Hugh, Hartley, Margaret E, Dalvi, Mohit, Hill, Adrian A, Johnson, Ben T, Johnson, Colin E, Knight, Jeff R, O'Connor, Fiona M, Partridge, Daniel G, Stier, Philip, Myhre, Gunnar, Platnick, Steven, Stephens, Graeme L, Takahashi, Hanii, and Thordarson, Thorvaldur
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13. Climate action ,0401 Atmospheric Sciences - Abstract
Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. Here we show that the massive 2014-2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets-consistent with expectations-but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around -0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.
228. Anthropogenic aerosol forcing-insights from multiple estimates from aerosol-climate models with reduced complexity
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Fiedler, Stephanie, Kinne, Stefan, Huang, Wan Ting Katty, Räisänen, Petri, O'Donnell, Declan, Bellouin, Nicolas, Stier, Philip, Merikanto, Joonas, Van Noije, Twan, Makkonen, Risto, and Lohmann, Ulrike
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13. Climate action - Abstract
This study assesses the change in anthropogenic aerosol forcing from the mid-1970s to the mid-2000s. Both decades had similar global-mean anthropogenic aerosol optical depths but substantially different global distributions. For both years, we quantify (i) the forcing spread due to model-internal variability and (ii) the forcing spread among models. Our assessment is based on new ensembles of atmosphere-only simulations with five state-of-the-art Earth system models. Four of these models will be used in the sixth Coupled Model Intercomparison Project (CMIP6; Eyring et al., 2016). Here, the complexity of the anthropogenic aerosol has been reduced in the participating models. In all our simulations, we prescribe the same patterns of the anthropogenic aerosol optical properties and associated effects on the cloud droplet number concentration. We calculate the instantaneous radiative forcing (RF) and the effective radiative forcing (ERF). Their difference defines the net contribution from rapid adjustments. Our simulations show a model spread in ERF from −0.4 to −0.9 W m−2. The standard deviation in annual ERF is 0.3 W m−2, based on 180 individual estimates from each participating model. This result implies that identifying the model spread in ERF due to systematic differences requires averaging over a sufficiently large number of years. Moreover, we find almost identical ERFs for the mid-1970s and mid-2000s for individual models, although there are major model differences in natural aerosols and clouds. The model-ensemble mean ERF is −0.54 W m−2 for the pre-industrial era to the mid-1970s and −0.59 W m−2 for the pre-industrial era to the mid-2000s. Our result suggests that comparing ERF changes between two observable periods rather than absolute magnitudes relative to a poorly constrained pre-industrial state might provide a better test for a model's ability to represent transient climate changes., Atmospheric Chemistry and Physics, 19 (10), ISSN:1680-7375, ISSN:1680-7367
229. Bounding Global Aerosol Radiative Forcing of Climate Change
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Bellouin, Nicolas, Quaas, Johannes, Gryspeerdt, Edward, Kinne, Stefan, Stier, Philip, Watson-Parris, Duncan, Boucher, Olivier, Carslaw, Ken, Christensen, Matthew W., Daniau, Anne-Laure, Dufresne, Jean-Louis, Feingold, Graham, Fiedler, Stephanie, Forster, Piers, Gettelman, Andrew, Haywood, Jim M., Lohmann, Ulrike, Malavelle, Florent, Mauritsen, Thorsten, McCoy, Daniel, Myhre, Gunnar, Mülmenstädt, Johannes, Neubauer, David, Possner, Anna, Rugenstein, Maria, Sato, Yousuke, Schulz, Michael, Schwartz, Stephen E., Sourdeval, Odran, Storelvmo, Trude, Toll, Velle, Winker, David, and Stevens, Bjorn
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13. Climate action ,sense organs ,respiratory system ,complex mixtures - Abstract
Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth's radiation budget caused by anthropogenic aerosols, called aerosol radiative forcing, but uncertainties remain large. This review provides a new range of aerosol radiative forcing over the industrial era based on multiple, traceable, and arguable lines of evidence, including modeling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface radiative fluxes constrain the forcing from aerosol‐radiation interactions. A robust theoretical foundation and convincing evidence constrain the forcing caused by aerosol‐driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed‐phase and ice clouds remains poorly constrained. Observed changes in surface temperature and radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective radiative forcing of ‐1.6 to ‐0.6 W m−2, or ‐2.0 to ‐0.4 W m−2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted toward more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial‐era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds., Reviews of Geophysics, 58 (1), ISSN:8755-1209, ISSN:0096-1043, ISSN:1944-9208
230. Influence of horizontal resolution and complexity of aerosol-cloud interactions on marine stratocumulus and stratocumulus-to-cumulus transition in HadGEM3-GC3.1
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Ekman, Annica M. L., Nygren, Eva, Baró Pérez, Alejandro, Schwarz, Matthias, Svensson, Gunilla, Bellouin, Nicolas, Ekman, Annica M. L., Nygren, Eva, Baró Pérez, Alejandro, Schwarz, Matthias, Svensson, Gunilla, and Bellouin, Nicolas
231. Radiative Effect of Two Contrail Cirrus Outbreaks Over Western Europe Estimated Using Geostationary Satellite Observations and Radiative Transfer Calculations.
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Wang, Xinyue, Wolf, Kevin, Boucher, Olivier, and Bellouin, Nicolas
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GEOSTATIONARY satellites , *CONDENSATION trails , *RADIATIVE transfer , *REMOTE-sensing images , *INFRARED imaging , *FORCE & energy - Abstract
Estimation of the perturbation to the Earth's energy budget by contrail outbreaks is required for estimating the climate impact of aviation and verifying the climate benefits of proposed contrail avoidance strategies such as aircraft rerouting. Here we identified two successive large‐scale contrail outbreaks developing in clear‐sky conditions in geostationary and polar‐orbiting satellite infrared images of Western Europe lasting from 22–23 June 2020. Their hourly cloud radiative effect, obtained using geostationary satellite cloud retrievals and radiative transfer calculations, is negative or weakly positive during daytime and positive during nighttime. The cumulative energy forcing of the two outbreaks is 7 PJ and −8.5 PJ, with uncertainties of 3 PJ, stemming each from approximately 15–20 flights over periods of 19 and 7 hr, respectively. This study suggests that an automated quantification of contrail outbreak radiative effect is possible, at least for contrails forming in clear sky conditions. Plain Language Summary: Contrail cirrus is produced by aircraft and perturb the energy budget of the Earth. However, the actual size of the perturbation is uncertain. In this study, we calculate the energy budget perturbation of two successive contrail‐cirrus outbreaks over Western Europe from 22–23 June 2020. An infrared image composite allows the identification and tracking of contrails with a 15 min frequency, which is verified by comparison to satellite images with better horizontal resolution from several polar‐orbiting platforms. Cloud properties of the contrail‐cirrus clusters, estimated from geostationary satellite data, are used in radiative transfer calculations. We find that one contrail cirrus outbreak adds an average power of 2 TW over 20 hr, while the other removes 3.3 TW over 8 hr. This cumulative energy depends on the lifespan and cloud properties of the outbreaks. This case study suggests that geostationary satellite observations allow the estimation of the energy perturbation of a contrail outbreak, with encouraging implications for contrail‐cirrus monitoring and the verification of contrail avoidance strategies. Key Points: The cloud radiative effect (CRE) of two successive contrail‐cirrus outbreaks is estimated from geostationary satellite measurementsThese two outbreaks have different CRE sign and magnitude, which can be explained by their different cloud properties and time evolutionsThe study suggests that automated quantification of contrail‐cirrus CRE for monitoring or verification of contrail avoidance is feasible [ABSTRACT FROM AUTHOR]
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- 2024
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232. Pollution tracks in clouds provide direct observational evidence for weak cloud water response to aerosols.
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Toll, Velle, Bellouin, Nicolas, Christensen, Matthew, Gettelman, Andrew, and Gassó, Santiago
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AEROSOLS , *POLLUTION , *WATER , *EVIDENCE - Published
- 2018
233. Erratum: Strong constraints on aerosol-cloud interactions from volcanic eruptions.
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Malavelle, Florent F., Haywood, Jim M., Jones, Andy, Gettelman, Andrew, Clarisse, Lieven, Bauduin, Sophie, Allan, Richard P., Karset, Inger Helene H., Kristjánsson, Jón Egill, Oreopoulos, Lazaros, Cho, Nayeong, Lee, Dongmin, Bellouin, Nicolas, Boucher, Olivier, Grosvenor, Daniel P., Carslaw, Ken S., Dhomse, Sandip, Mann, Graham W., Schmidt, Anja, and Coe, Hugh
- Abstract
This corrects the article DOI: 10.1038/nature22974 [ABSTRACT FROM AUTHOR]
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- 2017
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234. Climate change: Black carbon and atmospheric feedbacks.
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Booth, Ben and Bellouin, Nicolas
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ATMOSPHERIC research , *SOOT , *CLIMATE change research , *CLOUDS , *CLIMATE research ,ENVIRONMENTAL aspects - Abstract
The article discusses research done on the interactions between particles of black carbon and cloud processes in the atmosphere. It references a study by M. Sand and colleagues published in the 2015 issue of the "Journal of Climate." Topics discussed include the importance of rapid responses in the atmosphere to changes in black carbon and the role of the two-way black carbon-atmosphere interactions in exploring the full climate response.
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- 2015
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235. Aerosols: The colour of smoke.
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Bellouin, Nicolas
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COMBUSTION , *BIOMASS burning & the environment , *SMOKE , *ATMOSPHERIC aerosols , *OXIDATION of soot - Abstract
The article explores the study on the formation of colours from particles of smoke from natural and human made fire, which contributes to the development of global warming. The study examines the biomass-burning aerosols in combustion chamber experiments and reveals the reflectivity of aerosol soot content. The article also discusses the absorption properties of organic aerosols from biomass burning.
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- 2014
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236. Understanding the regional and seasonal influences of the stratospheric contribution to tropospheric ozone
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Williams, Ryan Scott, Hegglin, Michaela, Bellouin, Nicolas, and Kerridge, Brian
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Tropospheric ozone (O3) is the third most important greenhouse gas (GHG) and as an air pollutant, constitutes one of the major contributors to ~7 million premature deaths (WHO, 2019) annually worldwide and also to ecosystem damage. Furthermore, ozone determines hydroxyl (OH) radical levels, which serves to breakdown various pollutants and GHGs. Despite its significance, regional and seasonal variations in tropospheric ozone are poorly understood. Ozone in the troposphere is formed from various precursor species (e.g. CO, NOx and VOCs), which have both natural and anthropogenic sources, as well as transported down from the stratosphere. The relative importance of each influence has been the subject of intense debate in recent decades. Using a combination of in situ (ozonesonde) and satellite (GOME-2A and OMI) observations, in conjunction with state-of-the-art chemistry climate models (EMAC and CMAM), comprehensive quantification of the regional and seasonal variability in tropospheric ozone is here provided, including recent changes and source attribution using the models' stratospheric-tagged ozone tracers. This combined approach is necessary to overcome the shortcomings of individual datasets. The realism of each dataset is first rigorously evaluated and limitations identified. A significant source of retrieval error is identified in the satellite measurements, which will serve to retrospectively improve existing datasets. Using both models, it is quantified that the stratospheric influence is larger than found in previous studies; exceeding 50 % near the surface during winter in the extratropics. Finally, the influence of midwinter Sudden Stratospheric Warmings (SSWs) in relation to upper troposphere/lower stratosphere (UTLS) composition and stratosphere troposphere exchange (STE) of ozone is presented, as a potential source of interannual variability. Approximately half of all SSWs result in significant, prolonged perturbations in UTLS composition, with implications for STE of ozone at lead times of ~50 days. The radiative and air quality implications are subsequently discussed.
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- 2021
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237. Influence of horizontal resolution and complexity of aerosol–cloud interactions on marine stratocumulus and stratocumulus‐to‐cumulus transition in HadGEM3‐GC3.1.
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Ekman, Annica M. L., Nygren, Eva, Pérez, Alejandro Baró, Schwarz, Matthias, Svensson, Gunilla, and Bellouin, Nicolas
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STRATOCUMULUS clouds , *CLOUD droplets , *GENERAL circulation model - Abstract
Stratocumulus (Sc) clouds and stratocumulus‐to‐cumulus transitions (SCTs) are challenging to represent in global models and they contribute to a large spread in modeled subtropical cloud feedbacks. We evaluate the impact of increasing the horizontal model resolution (∼135, 60 and 25 km, respectively) and increasing the complexity of the aerosol–cloud interaction parameterization (interactive versus non‐interactive at medium resolution) on springtime subtropical marine Sc properties and SCTs in the atmosphere‐only version of HadGEM3‐GC3.1. No significant impact on the spatial location of the SCT could be found between the different model versions. Increasing horizontal resolution led to small but significant increases in liquid water content and a stronger (more negative) shortwave (SW) cloud radiative effect (CRE), in particular over the southern‐hemisphere Sc regions. However, for two out of the four studied regions, the stronger SW CRE also brought the model outside the range of satellite‐derived values of the SW CRE. Applying non‐interactive aerosols instead of interactive aerosols also led to significantly higher liquid water content and a stronger SW CRE over the southern‐hemisphere Sc regions, while over the northern‐hemisphere Sc regions, a competition between a substantial increase in the cloud droplet number concentration and small changes in the liquid water content resulted in a weaker SW CRE or non‐significant changes. In general, using interactive instead of non‐interactive aerosol–cloud interactions brought the model closer to satellite‐retrieved mean values of the SW CRE. Our results suggest that increasing the horizontal resolution or the complexity of the aerosol–cloud parameterization has a small but statistically significant effect on the SW CRE of marine Sc, in particular over regions with high liquid water content. For these regions, the effect of introducing non‐interactive versus interactive aerosol–cloud interactions is about as large as increasing the horizontal resolution from medium to high. [ABSTRACT FROM AUTHOR]
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- 2023
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238. Global Climate.
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Dunn, Robert J. H., Aldred, Freya, Gobron, Nadine, Miller, John B., Willett, Kate M., Ades, Melanie, Adler, Robert, Allan, R. P., Anderson, John, Anneville, Orlane, Aono, Yasuyuki, Argüez, Anthony, Arosio, Carlo, Augustine, John A., Azorin-Molina, Cesar, Barichivich, Jonathan, Basu, Aman, Beck, Hylke E., Bellouin, Nicolas, and Benedetti, Angela
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- 2022
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239. Global Carbon Budget 2021.
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Friedlingstein, Pierre, Jones, Matthew W., O'Sullivan, Michael, Andrew, Robbie M., Bakker, Dorothee C. E., Hauck, Judith, Le Quéré, Corinne, Peters, Glen P., Peters, Wouter, Pongratz, Julia, Sitch, Stephen, Canadell, Josep G., Ciais, Philippe, Jackson, Rob B., Alin, Simone R., Anthoni, Peter, Bates, Nicholas R., Becker, Meike, Bellouin, Nicolas, and Bopp, Laurent
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CARBON cycle , *ATMOSPHERIC carbon dioxide , *CARBON emissions , *CARBON dioxide , *GREENHOUSE gases , *CARBON - Abstract
Accurate assessment of anthropogenic carbon dioxide (CO 2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize datasets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO 2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO 2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO 2 sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO 2 sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ± 1 σ. For the first time, an approach is shown to reconcile the difference in our ELUC estimate with the one from national greenhouse gas inventories, supporting the assessment of collective countries' climate progress. For the year 2020, EFOS declined by 5.4 % relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr -1 (9.3 ± 0.5 GtC yr -1 when the cement carbonation sink is included), and ELUC was 0.9 ± 0.7 GtC yr -1 , for a total anthropogenic CO 2 emission of 10.2 ± 0.8 GtC yr -1 (37.4 ± 2.9 GtCO 2). Also, for 2020, GATM was 5.0 ± 0.2 GtC yr -1 (2.4 ± 0.1 ppm yr -1), SOCEAN was 3.0 ± 0.4 GtC yr -1 , and SLAND was 2.9 ± 1 GtC yr -1 , with a BIM of - 0.8 GtC yr -1. The global atmospheric CO 2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021 suggest a rebound in EFOS relative to 2020 of + 4.8 % (4.2 % to 5.4 %) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2020, but discrepancies of up to 1 GtC yr -1 persist for the representation of annual to semi-decadal variability in CO 2 fluxes. Comparison of estimates from multiple approaches and observations shows (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO 2 flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and datasets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this dataset (Friedlingstein et al., 2020, 2019; Le Quéré et al., 2018b, a, 2016, 2015b, a, 2014, 2013). The data presented in this work are available at 10.18160/gcp-2021 (Friedlingstein et al., 2021). [ABSTRACT FROM AUTHOR]
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- 2022
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240. Global Climate.
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Dunn, Robert J. H., Aldred, F., Gobron, Nadine, Miller, John B., Willett, Kate M., Ades, M., Adler, Robert, Allan, Richard, P., Allan, Rob, Anderson, J., Argüez, Anthony, Arosio, C., Augustine, John A., Azorin-Molina, C., Barichivich, J., Beck, H. E., Becker, Andreas, Bellouin, Nicolas, Benedetti, Angela, and Berry, David I.
- Published
- 2021
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241. How to reconstruct aerosol-induced diffuse radiation scenario for simulating GPP in land surface models? An evaluation of reconstruction methods with ORCHIDEE_DFv1.0_DFforc.
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Zhang, Yuan, Boucher, Olivier, Ciais, Philippe, Li, Laurent, and Bellouin, Nicolas
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- *
SULFATE aerosols , *RADIATION , *EVALUATION methodology , *VOLCANIC eruptions , *LIGHT transmission , *AEROSOLS - Abstract
The impact of diffuse radiation on photosynthesis has been widely documented in field measurements. This impact may have evolved over time during the last century due to changes in cloudiness, increased anthropogenic aerosol loads over polluted regions, and to sporadic volcanic eruptions curtaining the stratosphere with sulfate aerosols. The effects of those changes in diffuse light on large-scale photosynthesis (GPP) are difficult to quantify, and land surface models have been designed to simulate them. Investigating how anthropogenic aerosols have impacted GPP through diffuse light in those models requires carefully designed factorial simulations and a reconstruction of background diffuse light levels during the preindustrial period. Currently, it remains poorly understood how diffuse radiation reconstruction methods can affect GPP estimation and what fraction of GPP changes can be attributed to aerosols. In this study, we investigate different methods to reconstruct spatiotemporal distribution of the fraction of diffuse radiation (Fdf) under preindustrial aerosol emission conditions using a land surface model with a two-stream canopy light transmission scheme that resolves diffuse light effects on photosynthesis in a multi-layered canopy, ORCHIDEE_DF. We show that using a climatologically averaged monthly Fdf, as has been done by earlier studies, can bias the global GPP by up to 13 PgC yr -1 because this reconstruction method dampens the variability of Fdf and produces Fdf that is inconsistent with shortwave incoming surface radiation. In order to correctly simulate preindustrial GPP modulated by diffuse light, we thus recommend that the Fdf forcing field should be calculated consistently with synoptic, monthly, and inter-annual aerosol and cloud variability for preindustrial years. In the absence of aerosol and cloud data, alternative reconstructions need to retain the full variability in Fdf. Our results highlight the importance of keeping consistent Fdf and radiation for land surface models in future experimental designs that seek to investigate the impacts of diffuse radiation on GPP and other carbon fluxes. [ABSTRACT FROM AUTHOR]
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- 2021
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242. Application of remotely-sensed cloud properties for climate studies
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Giulia Saponaro, University of Helsinki, Faculty of Science, Doctoral Programme in Atmospheric Sciences, Finnish Meteorological Institute, Helsingin yliopisto, matemaattis-luonnontieteellinen tiedekunta, Ilmakehätieteiden tohtoriohjelma, Helsingfors universitet, matematisk-naturvetenskapliga fakulteten, Doktorandprogrammet i atmosfärvetenskap, Bellouin, Nicolas, de Leeuw, Gerrit, and Kolmonen, Pekka
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Astrophysics::Galaxy Astrophysics ,Physics::Atmospheric and Oceanic Physics ,Atmospheric Sciences - Abstract
Clouds play a vital role in Earth's energy balance by modulating atmospheric processes, thus it is crucial to have accurate information on their spatial and temporal variability. Furthermore, clouds are relevant in those processes involved in aerosol-cloud-radiation interactions. The work conducted and presented herein concentrates on the retrievals of cloud properties, as well as their application for climate studies. While remote sensing observation systems have been used to analyze the atmosphere and observe its changes for the last decades, climate models predict how climate will change in the future. Altogether, these sources of observations are needed to better understand cloud processes and their impact on climate. In this thesis aerosol and cloud properties from the three above mentioned sources are applied to evaluate their potential in representing cloud properties and applicability in climate studies on local, regional and global scales. One aim of this thesis focuses on evaluating cloud parameters from ground-based remote-sensing sensors and from climate models using the MODerate Imaging Spectroradiometer (MODIS) data as a reference dataset. It is found that ground-based measurements of liquid clouds are in good agreement with MODIS cloud droplet size while poor correlation is found in the amount of cloud liquid water due to the management of drizzle. The comparison of the cloud diagnostic from three climate models with MODIS data, enabled through the application of a satellite simulator, helped to understand discrepancies among models as well as discover deficiencies in their simulation processes. These findings are important to further improve the parametrization of atmospheric constituents in climate models, therefore enhancing the accuracy of climate projections. In this thesis it is also assessed the impact of aerosol particles on clouds. Satellite data can be used to derive climatically crucial quantities that are otherwise not directly retrieved (such as aerosol index and cloud droplet number concentration) which can be used to infer the sensitivity of clouds to aerosols changes. Results on the local and regional scales show that contrasting aerosol backgrounds indicate a higher sensitivity of clouds to aerosol changes in cleaner ambient air and a lower sensitivity in polluted areas, further corroborating the notion that anthropogenic emission modify clouds. On the global scale, the estimates of the aerosol-cloud interactions present, overall, a good agreement between the satellite- and model-based values which are in line with the results from other models. Abstract available only in English.
243. Aerosol effects on clouds are concealed by natural cloud heterogeneity and satellite retrieval errors.
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Arola A, Lipponen A, Kolmonen P, Virtanen TH, Bellouin N, Grosvenor DP, Gryspeerdt E, Quaas J, and Kokkola H
- Abstract
One major source of uncertainty in the cloud-mediated aerosol forcing arises from the magnitude of the cloud liquid water path (LWP) adjustment to aerosol-cloud interactions, which is poorly constrained by observations. Many of the recent satellite-based studies have observed a decreasing LWP as a function of cloud droplet number concentration (CDNC) as the dominating behavior. Estimating the LWP response to the CDNC changes is a complex task since various confounding factors need to be isolated. However, an important aspect has not been sufficiently considered: the propagation of natural spatial variability and errors in satellite retrievals of cloud optical depth and cloud effective radius to estimates of CDNC and LWP. Here we use satellite and simulated measurements to demonstrate that, because of this propagation, even a positive LWP adjustment is likely to be misinterpreted as negative. This biasing effect therefore leads to an underestimate of the aerosol-cloud-climate cooling and must be properly considered in future studies., (© 2022. The Author(s).)
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- 2022
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244. Disentangling the Impacts of Anthropogenic Aerosols on Terrestrial Carbon Cycle During 1850-2014.
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Zhang Y, Ciais P, Boucher O, Maignan F, Bastos A, Goll D, Lurton T, Viovy N, Bellouin N, and Li L
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Aerosols have a dimming and cooling effect and change hydrological regimes, thus affecting carbon fluxes, which are sensitive to climate. Aerosols also scatter sunlight, which increases the fraction of diffuse radiation, increasing photosynthesis. There remains no clear conclusion whether the impact of aerosols on land carbon fluxes is larger through diffuse radiation change than through changes in other climate variables. In this study, we quantified the overall physical impacts of anthropogenic aerosols on land C fluxes and explored the contribution from each factor using a set of factorial simulations driven by climate and aerosol data from the IPSL-CM6A-LR experiments during 1850-2014. A newly developed land surface model which distinguishes diffuse and direct radiation in canopy radiation transmission, ORCHIDEE_DF, was used. Specifically, a subgrid scheme was developed to distinguish the cloudy and clear sky conditions. We found that anthropogenic aerosol emissions since 1850 cumulatively enhanced the land C sink by 22.6 PgC. Seventy-eight percent of this C sink enhancement is contributed by aerosol-induced increase in the diffuse radiation fraction, much larger than the effect of the aerosol-induced dimming. The cooling of anthropogenic aerosols has different impacts in different latitudes but overall increases the global land C sink. The dominant role of diffuse radiation changes found in this study implies that future aerosol emissions may have a much stronger impacts on the C cycle through changing radiation quality than through changing climate alone. Earth system models need to consider the diffuse radiation fertilization effect to better evaluate the impacts of climate change mitigation scenarios., (© 2021. The Authors.)
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- 2021
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245. Biomass burning aerosols in most climate models are too absorbing.
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Brown H, Liu X, Pokhrel R, Murphy S, Lu Z, Saleh R, Mielonen T, Kokkola H, Bergman T, Myhre G, Skeie RB, Watson-Paris D, Stier P, Johnson B, Bellouin N, Schulz M, Vakkari V, Beukes JP, van Zyl PG, Liu S, and Chand D
- Abstract
Uncertainty in the representation of biomass burning (BB) aerosol composition and optical properties in climate models contributes to a range in modeled aerosol effects on incoming solar radiation. Depending on the model, the top-of-the-atmosphere BB aerosol effect can range from cooling to warming. By relating aerosol absorption relative to extinction and carbonaceous aerosol composition from 12 observational datasets to nine state-of-the-art Earth system models/chemical transport models, we identify varying degrees of overestimation in BB aerosol absorptivity by these models. Modifications to BB aerosol refractive index, size, and mixing state improve the Community Atmosphere Model version 5 (CAM5) agreement with observations, leading to a global change in BB direct radiative effect of -0.07 W m
-2 , and regional changes of -2 W m-2 (Africa) and -0.5 W m-2 (South America/Temperate). Our findings suggest that current modeled BB contributes less to warming than previously thought, largely due to treatments of aerosol mixing state.- Published
- 2021
- Full Text
- View/download PDF
246. Author Correction: Weak average liquid-cloud-water response to anthropogenic aerosols.
- Author
-
Toll V, Christensen M, Quaas J, and Bellouin N
- Abstract
An Amendment to this paper has been published and can be accessed via a link at the top of the paper.
- Published
- 2020
- Full Text
- View/download PDF
247. Weak average liquid-cloud-water response to anthropogenic aerosols.
- Author
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Toll V, Christensen M, Quaas J, and Bellouin N
- Subjects
- Air Pollution analysis, Greenhouse Effect prevention & control, Greenhouse Effect statistics & numerical data, Rain, Uncertainty, Aerosols analysis, Aerosols chemistry, Climate Change statistics & numerical data, Human Activities, Models, Theoretical, Temperature, Water analysis, Water chemistry
- Abstract
The cooling of the Earth's climate through the effects of anthropogenic aerosols on clouds offsets an unknown fraction of greenhouse gas warming. An increase in the amount of water inside liquid-phase clouds induced by aerosols, through the suppression of rain formation, has been postulated to lead to substantial cooling, which would imply that the Earth's surface temperature is highly sensitive to anthropogenic forcing. Here we provide direct observational evidence that, instead of a strong increase, aerosols cause a relatively weak average decrease in the amount of water in liquid-phase clouds compared with unpolluted clouds. Measurements of polluted clouds downwind of various anthropogenic sources-such as oil refineries, smelters, coal-fired power plants, cities, wildfires and ships-reveal that aerosol-induced cloud-water increases, caused by suppressed rain formation, and decreases, caused by enhanced evaporation of cloud water, partially cancel each other out. We estimate that the observed decrease in cloud water offsets 23% of the global climate-cooling effect caused by aerosol-induced increases in the concentration of cloud droplets. These findings invalidate the hypothesis that increases in cloud water cause a substantial climate cooling effect and translate into reduced uncertainty in projections of future climate.
- Published
- 2019
- Full Text
- View/download PDF
248. Evaluation of the aerosol vertical distribution in global aerosol models through comparison against CALIOP measurements: AeroCom phase II results.
- Author
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Koffi B, Schulz M, Bréon FM, Dentener F, Steensen BM, Griesfeller J, Winker D, Balkanski Y, Bauer SE, Bellouin N, Berntsen T, Bian H, Chin M, Diehl T, Easter R, Ghan S, Hauglustaine DA, Iversen T, Kirkevåg A, Liu X, Lohmann U, Myhre G, Rasch P, Seland Ø, Skeie RB, Steenrod SD, Stier P, Tackett J, Takemura T, Tsigaridis K, Vuolo MR, Yoon J, and Zhang K
- Abstract
The ability of 11 models in simulating the aerosol vertical distribution from regional to global scales, as part of the second phase of the AeroCom model intercomparison initiative (AeroCom II), is assessed and compared to results of the first phase. The evaluation is performed using a global monthly gridded data set of aerosol extinction profiles built for this purpose from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Layer Product 3.01. Results over 12 subcontinental regions show that five models improved, whereas three degraded in reproducing the interregional variability in Z
α 0-6 km , the mean extinction height diagnostic, as computed from the CALIOP aerosol profiles over the 0-6 km altitude range for each studied region and season. While the models' performance remains highly variable, the simulation of the timing of the Zα 0-6 km peak season has also improved for all but two models from AeroCom Phase I to Phase II. The biases in Zα 0-6 km are smaller in all regions except Central Atlantic, East Asia, and North and South Africa. Most of the models now underestimate Zα 0-6 km over land, notably in the dust and biomass burning regions in Asia and Africa. At global scale, the AeroCom II models better reproduce the Zα 0-6 km latitudinal variability over ocean than over land. Hypotheses for the performance and evolution of the individual models and for the intermodel diversity are discussed. We also provide an analysis of the CALIOP limitations and uncertainties contributing to the differences between the simulations and observations.- Published
- 2016
- Full Text
- View/download PDF
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