Michael Schulz

• Hodnebrog, Øivind; Myhre, Gunnar; Jouan, Caroline; Andrews, Timothy; Forster, Piers M. & Jia, Hailing [Show all 12 contributors for this article] (2024). Recent reductions in aerosol emissions have increased Earth’s energy imbalance. Communications Earth & Environment. ISSN 2662-4435. 5(1). doi: 10.1038/s43247-024-01324-8.
• Fiedler, Stephanie; Naik, Vaishali; O'Connor, Fiona M.; Smith, Christopher J.; Griffiths, Paul & Kramer, Ryan J. [Show all 21 contributors for this article] (2024). Interactions between atmospheric composition and climate change - progress in understanding and future opportunities from AerChemMIP, PDRMIP, and RFMIP. Geoscientific Model Development. ISSN 1991-959X. 17(6), p. 2387–2417. doi: 10.5194/gmd-17-2387-2024.
• Hodzic, Alma; Mahowald, Natalie; Dawson, Matthew; Johnson, Jeffrey; Bernardet, Ligia & Bosler, Peter A. [Show all 13 contributors for this article] (2023). Generalized Aerosol/Chemistry Interface (GIANT): A Community Effort to Advance Collaborative Science across Weather and Climate Models. Bulletin of The American Meteorological Society - (BAMS). ISSN 0003-0007. 104(11), p. E2065–E2080. doi: 10.1175/BAMS-D-23-0013.1.
• Ahsan, Hamza; Wang, Hailong; Wu, Jingbo; Wu, Mingxuan; Smith, Steven J. & Bauer, Susanne [Show all 20 contributors for this article] (2023). The Emissions Model Intercomparison Project (Emissions-MIP): Quantifying model sensitivity to emission characteristics. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 23(23), p. 14779–14799. doi: 10.5194/acp-23-14779-2023. Full text in Research Archive Show summary

  Anthropogenic emissions of aerosols and precursor compounds are known to significantly affect the energy balance of the Earth–atmosphere system, alter the formation of clouds and precipitation, and have a substantial impact on human health and the environment. Global models are an essential tool for examining the impacts of these emissions. In this study, we examine the sensitivity of model results to the assumed height of SO2 injection, seasonality of SO2 and black carbon (BC) particulate emissions, and the assumed fraction of SO2 emissions that is injected into the atmosphere as particulate phase sulfate (SO4) in 11 climate and chemistry models, including both chemical transport models and the atmospheric component of Earth system models. We find large variation in atmospheric lifetime across models for SO2, SO4, and BC, with a particularly large relative variation for SO2, which indicates that fundamental aspects of atmospheric sulfur chemistry remain uncertain. Of the perturbations examined in this study, the assumed height of SO2 injection had the largest overall impacts, particularly on global mean net radiative flux (maximum difference of −0.35 W m−2), SO2 lifetime over Northern Hemisphere land (maximum difference of 0.8 d), surface SO2 concentration (up to 59 % decrease), and surface sulfate concentration (up to 23 % increase). Emitting SO2 at height consistently increased SO2 and SO4 column burdens and shortwave cooling, with varying magnitudes, but had inconsistent effects across models on the sign of the change in implied cloud forcing. The assumed SO4 emission fraction also had a significant impact on net radiative flux and surface sulfate concentration. Because these properties are not standardized across models this is a source of inter-model diversity typically neglected in model intercomparisons. These results imply a need to ensure that anthropogenic emission injection height and SO4 emission fraction are accurately and consistently represented in global models.

• Schmidt, Gavin A.; Andrews, Timothy; Bauer, Susanne E.; Durack, Paul J.; Loeb, Norman G. & Ramaswamy, V. [Show all 22 contributors for this article] (2023). CERESMIP: a climate modeling protocol to investigate recent trends in the Earth's Energy Imbalance. Frontiers in Climate. ISSN 2624-9553. 5, p. 1–10. doi: 10.3389/fclim.2023.1202161.
• Fiedler, Stephanie; van Noije, Twan; Smith, Christopher J.; Boucher, Olivier; Dufresne, Jean-Louis & Kirkevåg, Alf [Show all 11 contributors for this article] (2023). Historical Changes and Reasons for Model Differences in Anthropogenic Aerosol Forcing in CMIP6. Geophysical Research Letters. ISSN 0094-8276. 50(15). doi: 10.1029/2023GL104848.
• Lapere, Rémy; Thomas, Jennie L.; Marelle, Louis; Ekman, Annica M. L.; Frey, Markus M. & Lund, Marianne Tronstad [Show all 14 contributors for this article] (2023). The Representation of Sea Salt Aerosols and Their Role in Polar Climate Within CMIP6. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 128(6). doi: 10.1029/2022JD038235. Full text in Research Archive Show summary

  Natural aerosols and their interactions with clouds remain an important uncertainty within climate models, especially at the poles. Here, we study the behavior of sea salt aerosols (SSaer) in the Arctic and Antarctic within 12 climate models from CMIP6. We investigate the driving factors that control SSaer abundances and show large differences based on the choice of the source function, and the representation of aerosol processes in the atmosphere. Close to the poles, the CMIP6 models do not match observed seasonal cycles of surface concentrations, likely due to the absence of wintertime SSaer sources such as blowing snow. Further away from the poles, simulated concentrations have the correct seasonality, but have a positive mean bias of up to one order of magnitude. SSaer optical depth is derived from the MODIS data and compared to modeled values, revealing good agreement, except for winter months. Better agreement for aerosol optical depth than surface concentration may indicate a need for improving the vertical distribution, the size distribution and/or hygroscopicity of modeled polar SSaer. Source functions used in CMIP6 emit very different numbers of small SSaer, potentially exacerbating cloud-aerosol interaction uncertainties in these remote regions. For future climate scenarios SSP126 and SSP585, we show that SSaer concentrations increase at both poles at the end of the 21st century, with more than two times mid-20th century values in the Arctic. The pre-industrial climate CMIP6 experiments suggest there is a large uncertainty in the polar radiative budget due to SSaer

• Schulz, Michael & McConnell, Joseph R. (2022). Chapter 7 - Historical changes in aerosol. In Carslaw, Ken S. (Eds.), Aerosols and Climate. Elsevier. ISSN 978-0-12-819766-0. p. 249–297. doi: 10.1016/B978-0-12-819766-0.00007-9.
• Leinonen, Ville; Kokkola, Harri; Yli-Juuti, Taina; Mielonen, Tero; Kühn, Thomas & Nieminen, Tuomo [Show all 36 contributors for this article] (2022). Comparison of particle number size distribution trends in ground measurements and climate models. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 22(19), p. 12873–12905. doi: 10.5194/acp-22-12873-2022. Full text in Research Archive Show summary

  Despite a large number of studies, out of all drivers of radiative forcing, the effect of aerosols has the largest uncertainty in global climate model radiative forcing estimates. There have been studies of aerosol optical properties in climate models, but the effects of particle number size distribution need a more thorough inspection. We investigated the trends and seasonality of particle number concentrations in nucleation, Aitken, and accumulation modes at 21 measurement sites in Europe and the Arctic. For 13 of those sites, with longer measurement time series, we compared the field observations with the results from five climate models, namely EC-Earth3, ECHAM-M7, ECHAM-SALSA, NorESM1.2, and UKESM1. This is the first extensive comparison of detailed aerosol size distribution trends between in situ observations from Europe and five earth system models (ESMs). We found that the trends of particle number concentrations were mostly consistent and decreasing in both measurements and models. However, for many sites, climate models showed weaker decreasing trends than the measurements. Seasonal variability in measured number concentrations, quantified by the ratio between maximum and minimum monthly number concentration, was typically stronger at northern measurement sites compared to other locations. Models had large differences in their seasonal representation, and they can be roughly divided into two categories: for EC-Earth and NorESM, the seasonal cycle was relatively similar for all sites, and for other models the pattern of seasonality varied between northern and southern sites. In addition, the variability in concentrations across sites varied between models, some having relatively similar concentrations for all sites, whereas others showed clear differences in concentrations between remote and urban sites. To conclude, although all of the model simulations had identical input data to describe anthropogenic mass emissions, trends in differently sized particles vary among the models due to assumptions in emission sizes and differences in how models treat size-dependent aerosol processes. The inter-model variability was largest in the accumulation mode, i.e. sizes which have implications for aerosol–cloud interactions. Our analysis also indicates that between models there is a large variation in efficiency of long-range transportation of aerosols to remote locations. The differences in model results are most likely due to the more complex effect of different processes instead of one specific feature (e.g. the representation of aerosol or emission size distributions). Hence, a more detailed characterization of microphysical processes and deposition processes affecting the long-range transport is needed to understand the model variability.

• Julsrud, Ingeborg Rian; Storelvmo, Trude; Schulz, Michael; Moseid, Kine Onsum & Wild, Martin (2022). Disentangling Aerosol and Cloud effects on Dimming and Brightening in Observations and CMIP6. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 127(21). doi: 10.1029/2021JD035476. Full text in Research Archive Show summary

  Periods of dimming and brightening have been recorded in observational datasets of surface solar radiation (SSR) between the mid-20th century and present day. Atmospheric components affect SSR, including aerosols and clouds, though studies disagree somewhat about the relative effect of each component in different regions. Current Earth system models (ESMs) are unable to simulate observed trends in SSR. This study includes an investigation into observed SSR variations between 1961 and 2014 and an evaluation of the effects of cloud cover variations and impacts of aerosol extinction, using timeseries of SSR and cloud cover from in-situ measurements. Historical simulations by 42 ESMs participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) have also been studied and compared to observations. The observational study indicates that cloud cover has had a dampening effect on the variations of SSR and that emissions of aerosol and aerosol precursors are the main cause of the general trends in observed SSR in four regions—China, Japan, Europe and the United States—during 1961-2014. The study of simulated SSR in CMIP6 yields the conclusion that current ESMs remain unable to simulate the magnitude of observed dimming and brightening in China, Japan and the United States, but that the European SSR trends between 1961 and 2014 are fairly well reproduced in the ESMs. A rough quantification of the regional surface radiation extinction efficiency of aerosol and precursor emissions in the simulations is found to agree with observed values in Europe, but not in the other three regions.

• Quaas, Johannes; Jia, Hailing; Smith, Chris; Albright, Anna Lea; Aas, Wenche & Bellouin, Nicolas [Show all 20 contributors for this article] (2022). Robust evidence for reversal of the trend in aerosol effective climate forcing. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 22, p. 12221–12239. doi: 10.5194/acp-22-12221-2022. Full text in Research Archive Show summary

  Anthropogenic aerosols exert a cooling influence that offsets part of the greenhouse gas warming. Due to their short tropospheric lifetime of only several days, the aerosol forcing responds quickly to emissions. Here, we present and discuss the evolution of the aerosol forcing since 2000. There are multiple lines of evidence that allow us to robustly conclude that the anthropogenic aerosol effective radiative forcing (ERF) – both aerosol–radiation interactions (ERFari) and aerosol–cloud interactions (ERFaci) – has become less negative globally, i.e. the trend in aerosol effective radiative forcing changed sign from negative to positive. Bottom-up inventories show that anthropogenic primary aerosol and aerosol precursor emissions declined in most regions of the world; observations related to aerosol burden show declining trends, in particular of the fine-mode particles that make up most of the anthropogenic aerosols; satellite retrievals of cloud droplet numbers show trends in regions with aerosol declines that are consistent with these in sign, as do observations of top-of-atmosphere radiation. Climate model results, including a revised set that is constrained by observations of the ocean heat content evolution show a consistent sign and magnitude for a positive forcing relative to the year 2000 due to reduced aerosol effects. This reduction leads to an acceleration of the forcing of climate change, i.e. an increase in forcing by 0.1 to 0.3 W m−2, up to 12 % of the total climate forcing in 2019 compared to 1750 according to the Intergovernmental Panel on Climate Change (IPCC).

• Moseid, Kine Onsum; Schulz, Michael; Eichler, Anja; Schwikowski, Margit; McConnell, Joseph R. & Oliviè, Dirk Jan Leo [Show all 9 contributors for this article] (2022). Using Ice Cores to Evaluate CMIP6 Aerosol Concentrations Over the Historical Era. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 127(18). doi: 10.1029/2021JD036105. Full text in Research Archive Show summary

  The radiative effect of anthropogenic aerosols is one of the largest uncertainties in Earth's energy budget over the industrial period. This uncertainty is in part due to sparse observations of aerosol concentrations in the pre-satellite era. To address this lack of measurements, ice cores can be used, which contain the aerosol concentration record. To date, these observations have been under-utilized for comparison to aerosol concentrations found in state-of-the-art Earth system models (ESMs). Here we compare long term trends in concentrations of sulfate and black carbon (BC) between 15 ice cores and 11 ESMs over nine regions around the world during the period 1850–2000. We find that for sulfate concentration trends model results generally agree with ice core records, whereas for BC concentration the model trends differ from the records. Absolute concentrations of both investigated species are overestimated by the models, probably in part due to representation errors. However, we assume that biases in relative trends are not altered by these errors. Ice cores in the European Alps and Greenland record a maximum BC concentration before 1950, while most ESMs used in this study agree on a post-1950 maximum. We source this bias to an error in BC emission inventories in Europe. Emission perturbation experiments using NorESM2-LM support the observed finding that BC concentrations in Northern Greenland ice cores are recording European emissions. Errors in BC emission inventories have implications for all future and past studies where Coupled Model Intercomparison Project Phase 6 historical simulations are compared to observations relevant to aerosol forcing.

• Gjermundsen, Ada; Graff, Lise Seland; Bentsen, Mats; Breivik, Lars-Anders; Debernard, Jens Boldingh & Makkonen, Risto [Show all 10 contributors for this article] (2021). How representative is Svalbard for future Arctic climate evolution? An Earth system modelling perspective. SESS report. ISSN 2535-809X. 1(ISBN 978-82-691528-9-0), p. 38–79. doi: 10.5281/zenodo.4034104.
• Sand, Maria; Samset, Bjørn Hallvard; Myhre, Gunnar; Gliss, Jonas; Bauer, Susanne E. & Bian, Huisheng [Show all 25 contributors for this article] (2021). Aerosol absorption in global models from AeroCom phase III. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(20), p. 15929–15947. doi: 10.5194/acp-21-15929-2021. Full text in Research Archive Show summary

  Aerosol-induced absorption of shortwave radiation can modify the climate through local atmospheric heating, which affects lapse rates, precipitation, and cloud formation. Presently, the total amount of aerosol absorption is poorly constrained, and the main absorbing aerosol species (black carbon (BC), organic aerosols (OA), and mineral dust) are diversely quantified in global climate models. As part of the third phase of the Aerosol Comparisons between Observations and Models (AeroCom) intercomparison initiative (AeroCom phase III), we here document the distribution and magnitude of aerosol absorption in current global aerosol models and quantify the sources of intermodel spread, highlighting the difficulties of attributing absorption to different species. In total, 15 models have provided total present-day absorption at 550 nm (using year 2010 emissions), 11 of which have provided absorption per absorbing species. The multi-model global annual mean total absorption aerosol optical depth (AAOD) is 0.0054 (0.0020 to 0.0098; 550 nm), with the range given as the minimum and maximum model values. This is 28 % higher compared to the 0.0042 (0.0021 to 0.0076) multi-model mean in AeroCom phase II (using year 2000 emissions), but the difference is within 1 standard deviation, which, in this study, is 0.0023 (0.0019 in Phase II). Of the summed component AAOD, 60 % (range 36 %–84 %) is estimated to be due to BC, 31 % (12 %–49 %) is due to dust, and 11 % (0 %–24 %) is due to OA; however, the components are not independent in terms of their absorbing efficiency. In models with internal mixtures of absorbing aerosols, a major challenge is the lack of a common and simple method to attribute absorption to the different absorbing species. Therefore, when possible, the models with internally mixed aerosols in the present study have performed simulations using the same method for estimating absorption due to BC, OA, and dust, namely by removing it and comparing runs with and without the absorbing species. We discuss the challenges of attributing absorption to different species; we compare burden, refractive indices, and density; and we contrast models with internal mixing to models with external mixing. The model mean BC mass absorption coefficient (MAC) value is 10.1 (3.1 to 17.7) m2 g−1 (550 nm), and the model mean BC AAOD is 0.0030 (0.0007 to 0.0077). The difference in lifetime (and burden) in the models explains as much of the BC AAOD spread as the difference in BC MAC values. The difference in the spectral dependency between the models is striking. Several models have an absorption Ångstrøm exponent (AAE) close to 1, which likely is too low given current knowledge of spectral aerosol optical properties. Most models do not account for brown carbon and underestimate the spectral dependency for OA.

• Su, Wenying; Liang, Lusheng; Myhre, Gunnar; Thorsen, Tyler J.; Loeb, Norman G. & Schuster, Gregory L. [Show all 16 contributors for this article] (2021). Understanding Top-of-Atmosphere Flux Bias in the AeroCom Phase III Models: A Clear-Sky Perspective. Journal of Advances in Modeling Earth Systems. ISSN 1942-2466. 13(9). doi: 10.1029/2021MS002584. Full text in Research Archive Show summary

  Biases in aerosol optical depths (AOD) and land surface albedos in the AeroCom models are manifested in the top-of-atmosphere (TOA) clear-sky reflected shortwave (SW) fluxes. Biases in the SW fluxes from AeroCom models are quantitatively related to biases in AOD and land surface albedo by using their radiative kernels. Over ocean, AOD contributes about 25% to the urn:x-wiley:19422466:media:jame21429:jame21429-math-0001S–urn:x-wiley:19422466:media:jame21429:jame21429-math-0002N mean SW flux bias for the multi-model mean (MMM) result. Over land, AOD and land surface albedo contribute about 40% and 30%, respectively, to the urn:x-wiley:19422466:media:jame21429:jame21429-math-0003S–urn:x-wiley:19422466:media:jame21429:jame21429-math-0004N mean SW flux bias for the MMM result. Furthermore, the spatial patterns of the SW flux biases derived from the radiative kernels are very similar to those between models and CERES observation, with the correlation coefficient of 0.6 over ocean and 0.76 over land for MMM using data of 2010. Satellite data used in this evaluation are derived independently from each other, consistencies in their bias patterns when compared with model simulations suggest that these patterns are robust. This highlights the importance of evaluating related variables in a synergistic manner to provide an unambiguous assessment of the models, as results from single parameter assessments are often confounded by measurement uncertainty. Model biases in land surface albedos can and must be corrected to accurately calculate TOA flux. We also compare the AOD trend from three models with the observation-based counterpart. These models reproduce all notable trends in AOD except the decreasing trend over eastern China and the adjacent oceanic regions due to limitations in the emission data set.

• Gjermundsen, Ada; Nummelin, Aleksi; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2021). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming. Nature Geoscience. ISSN 1752-0894. 14, p. 724–731. doi: 10.1038/s41561-021-00825-x. Show summary

  The effective climate sensitivity estimates the equilibrium response of near-surface temperature to doubling atmospheric carbon dioxide concentration and is a widely used metric to characterize potential global warming. Earth system models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) exhibit considerable spread in effective climate sensitivity estimates. Cloud feedbacks are thought to be the cause of this, with marine boundary layer clouds over the Southern Ocean playing an important role. Here, we show that Southern Ocean deep convection is a major contributor to the CMIP6 intermodel spread in effective climate sensitivity. By comparing two Earth system models with very different sensitivities, we find that greater storage of heat at depth can delay the Southern Ocean surface warming and associated cloud response, thereby delaying global surface warming by centuries. The link between Southern Ocean convection and effective climate sensitivity is seen across 41 CMIP6 models, with low-sensitivity models exhibiting substantial deep ocean warming. Our results reveal the influence of Southern Ocean convection on potential long-term climate warming.

• Schutgens, Nick; Dubovik, Oleg; Hasekamp, Otto; Torres, Omar; Jethva, Hiren & Leonard, Peter J. T. [Show all 14 contributors for this article] (2021). AEROCOM and AEROSAT AAOD and SSA study - Part 1: Evaluation and intercomparison of satellite measurements. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(9), p. 6895–6917. doi: 10.5194/acp-21-6895-2021.
• Checa-Garcia, Ramiro; Balkanski, Yves; Albani, Samuel; Bergman, Tommi; Carslaw, Ken & Cozic, Anne [Show all 17 contributors for this article] (2021). Evaluation of natural aerosols in CRESCENDO Earth system models (ESMs): mineral dust. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(13), p. 10295–10335. doi: 10.5194/acp-21-10295-2021.
• Smith, Christopher J.; Harris, Glen R.; Palmer, Matthew D.; Bellouin, Nicolas; Collins, William J. & Myhre, Gunnar [Show all 11 contributors for this article] (2021). Energy Budget Constraints on the Time History of Aerosol Forcing and Climate Sensitivity. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 126(13). doi: 10.1029/2020JD033622. Full text in Research Archive Show summary

  An observationally constrained time series of historical aerosol effective radiative forcing (ERF) from 1750 to 2019 is developed in this study. We find that the time history of aerosol ERFs diagnosed in CMIP6 models exhibits considerable variation and explore how the time history of aerosol forcing influences the probability distributions of present-day aerosol forcing and emergent metrics such as climate sensitivity. Using a simple energy balance model, trained on CMIP6 climate models and constrained by observed near-surface warming and ocean heat uptake, we derive estimates for the historical aerosol forcing. We find 2005–2014 mean aerosol ERF to be −1.1 (−1.8 to −0.5) W m−2 relative to 1750. Assuming recently published historical emissions from fossil fuel and industrial sectors and biomass burning emissions from SSP2-4.5, aerosol ERF in 2019 is −0.9 (−1.5 to −0.4) W m−2. There is a modest recovery in aerosol forcing (+0.025 W m−2 decade−1) between 1980 and 2014. This analysis also gives a 5%–95% range of equilibrium climate sensitivity of 1.8°C –5.1°C (best estimate 3.1°C) with a transient climate response of 1.2°C –2.6°C (best estimate 1.8°C).

• Thornhill, Gillian; Collins, William J.; Oliviè, Dirk Jan Leo; Skeie, Ragnhild Bieltvedt; Archibald, Alexander T. & Bauer, Susanne E. [Show all 26 contributors for this article] (2021). Climate-driven chemistry and aerosol feedbacks in CMIP6 Earth system models. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(2), p. 1105–1126. doi: 10.5194/acp-21-1105-2021. Full text in Research Archive Show summary

  Feedbacks play a fundamental role in determining the magnitude of the response of the climate system to external forcing, such as from anthropogenic emissions. The latest generation of Earth system models includes aerosol and chemistry components that interact with each other and with the biosphere. These interactions introduce a complex web of feedbacks that is important to understand and quantify. This paper addresses multiple pathways for aerosol and chemical feedbacks in Earth system models. These focus on changes in natural emissions (dust, sea salt, dimethyl sulfide, biogenic volatile organic compounds (BVOCs) and lightning) and changes in reaction rates for methane and ozone chemistry. The feedback terms are then given by the sensitivity of a pathway to climate change multiplied by the radiative effect of the change. We find that the overall climate feedback through chemistry and aerosols is negative in the sixth Coupled Model Intercomparison Project (CMIP6) Earth system models due to increased negative forcing from aerosols in a climate with warmer surface temperatures following a quadrupling of CO2 concentrations. This is principally due to increased emissions of sea salt and BVOCs which are sensitive to climate change and cause strong negative radiative forcings. Increased chemical loss of ozone and methane also contributes to a negative feedback. However, overall methane lifetime is expected to increase in a warmer climate due to increased BVOCs. Increased emissions of methane from wetlands would also offset some of the negative feedbacks. The CMIP6 experimental design did not allow the methane lifetime or methane emission changes to affect climate, so we found a robust negative contribution from interactive aerosols and chemistry to climate sensitivity in CMIP6 Earth system models.

• Thornhill, Gillian D.; Collins, William J.; Kramer, Ryan J.; Oliviè, Dirk Jan Leo; Skeie, Ragnhild Bieltvedt & O'Connor, Fiona M. [Show all 30 contributors for this article] (2021). Effective radiative forcing from emissions of reactive gases and aerosols-A multi-model comparison. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21(2), p. 853–874. doi: 10.5194/acp-21-853-2021. Show summary

  This paper quantifies the pre-industrial (1850) to present-day (2014) effective radiative forcing (ERF) of anthropogenic emissions of NOX, volatile organic compounds (VOCs; including CO), SO2, NH3, black carbon, organic carbon, and concentrations of methane, N2O and ozone-depleting halocarbons, using CMIP6 models. Concentration and emission changes of reactive species can cause multiple changes in the composition of radiatively active species: tropospheric ozone, stratospheric ozone, stratospheric water vapour, secondary inorganic and organic aerosol, and methane. Where possible we break down the ERFs from each emitted species into the contributions from the composition changes. The ERFs are calculated for each of the models that participated in the AerChemMIP experiments as part of the CMIP6 project, where the relevant model output was available. The 1850 to 2014 multi-model mean ERFs (± standard deviations) are −1.03 ± 0.37 W m−2 for SO2 emissions, −0.25 ± 0.09 W m−2 for organic carbon (OC), 0.15 ± 0.17 W m−2 for black carbon (BC) and −0.07 ± 0.01 W m−2 for NH3. For the combined aerosols (in the piClim-aer experiment) it is −1.01 ± 0.25 W m−2. The multi-model means for the reactive well-mixed greenhouse gases (including any effects on ozone and aerosol chemistry) are 0.67 ± 0.17 W m−2 for methane (CH4), 0.26 ± 0.07 W m−2 for nitrous oxide (N2O) and 0.12 ± 0.2 W m−2 for ozone-depleting halocarbons (HC). Emissions of the ozone precursors nitrogen oxides (NOx), volatile organic compounds and both together (O3) lead to ERFs of 0.14 ± 0.13, 0.09 ± 0.14 and 0.20 ± 0.07 W m−2 respectively. The differences in ERFs calculated for the different models reflect differences in the complexity of their aerosol and chemistry schemes, especially in the case of methane where tropospheric chemistry captures increased forcing from ozone production.

• Brown, Hunter; Liu, Xiaohong; Pokhrel, Rudra; Murphy, Shane; Lu, Zheng & Saleh, Rawad [Show all 21 contributors for this article] (2021). Biomass burning aerosols in most climate models are too absorbing. Nature Communications. ISSN 2041-1723. 12:277, p. 1–15. doi: 10.1038/s41467-020-20482-9. Show summary

  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.

• Gliss, Jonas; Mortier, Augustin; Schulz, Michael; Andrews, Elisabeth; Balkanski, Yves & Bauer, Susanne E. [Show all 31 contributors for this article] (2021). AeroCom phase III multi-model evaluation of the aerosol life cycle and optical properties using ground- and space-based remote sensing as well as surface in situ observations. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 21, p. 87–128. doi: 10.5194/acp-21-87-2021. Full text in Research Archive Show summary

  Within the framework of the AeroCom (Aerosol Comparisons between Observations and Models) initiative, the state-of-the-art modelling of aerosol optical properties is assessed from 14 global models participating in the phase III control experiment (AP3). The models are similar to CMIP6/AerChemMIP Earth System Models (ESMs) and provide a robust multi-model ensemble. Inter-model spread of aerosol species lifetimes and emissions appears to be similar to that of mass extinction coefficients (MECs), suggesting that aerosol optical depth (AOD) uncertainties are associated with a broad spectrum of parameterised aerosol processes. Total AOD is approximately the same as in AeroCom phase I (AP1) simulations. However, we find a 50 % decrease in the optical depth (OD) of black carbon (BC), attributable to a combination of decreased emissions and lifetimes. Relative contributions from sea salt (SS) and dust (DU) have shifted from being approximately equal in AP1 to SS contributing about 2∕3 of the natural AOD in AP3. This shift is linked with a decrease in DU mass burden, a lower DU MEC, and a slight decrease in DU lifetime, suggesting coarser DU particle sizes in AP3 compared to AP1. Relative to observations, the AP3 ensemble median and most of the participating models underestimate all aerosol optical properties investigated, that is, total AOD as well as fine and coarse AOD (AODf, AODc), Ångström exponent (AE), dry surface scattering (SCdry), and absorption (ACdry) coefficients. Compared to AERONET, the models underestimate total AOD by ca. 21 % ± 20 % (as inferred from the ensemble median and interquartile range). Against satellite data, the ensemble AOD biases range from −37 % (MODIS-Terra) to −16 % (MERGED-FMI, a multi-satellite AOD product), which we explain by differences between individual satellites and AERONET measurements themselves. Correlation coefficients (R) between model and observation AOD records are generally high (R>0.75), suggesting that the models are capable of capturing spatio-temporal variations in AOD. We find a much larger underestimate in coarse AODc (∼ −45 % ± 25 %) than in fine AODf (∼ −15 % ± 25 %) with slightly increased inter-model spread compared to total AOD. These results indicate problems in the modelling of DU and SS. The AODc bias is likely due to missing DU over continental land masses (particularly over the United States, SE Asia, and S. America), while marine AERONET sites and the AATSR SU satellite data suggest more moderate oceanic biases in AODc. Column AEs are underestimated by about 10 % ± 16 %. For situations in which measurements show AE > 2, models underestimate AERONET AE by ca. 35 %. In contrast, all models (but one) exhibit large overestimates in AE when coarse aerosol dominates (bias ca. +140 % if observed AE < 0.5). Simulated AE does not span the observed AE variability. These results indicate that models overestimate particle size (or underestimate the fine-mode fraction) for fine-dominated aerosol and underestimate size (or overestimate the fine-mode fraction) for coarse-dominated aerosol. This must have implications for lifetime, water uptake, scattering enhancement, and the aerosol radiative effect, which we can not quantify at this moment. Comparison against Global Atmosphere Watch (GAW) in situ data results in mean bias and inter-model variations of −35 % ± 25 % and −20 % ± 18 % for SCdry and ACdry, respectively. The larger underestimate of SCdry than ACdry suggests the models will simulate an aerosol single scattering albedo that is too low. The larger underestimate of SCdry than ambient air AOD is consistent with recent findings that models overestimate scattering enhancement due to hygroscopic growth. The broadly consistent negative bias in AOD and surface scattering suggests an underestimate of aerosol radiative effects in current global aerosol models. Considerable ...

• Schutgens, Nick; Sayer, Andrew M.; Heckel, Andreas; Hsu, Christina; Jethva, Hiren & De Leeuw, Gerrit [Show all 21 contributors for this article] (2020). An AeroCom-AeroSat study: Intercomparison of satellite AOD datasets for aerosol model evaluation. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(21), p. 12431–12457. doi: 10.5194/acp-20-12431-2020.
• Turnock, Steven T.; Allen, Robert J.; Andrews, Martin; Bauer, Susanne E.; Deushi, Makoto & Emmons, Louisa [Show all 24 contributors for this article] (2020). Historical and future changes in air pollutants from CMIP6 models. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(23), p. 14547–14579. doi: 10.5194/acp-20-14547-2020.
• Moseid, Kine Onsum; Schulz, Michael; Storelvmo, Trude; Julsrud, Ingeborg Rian; Oliviè, Dirk Jan Leo & Nabat, Pierre [Show all 12 contributors for this article] (2020). Bias in CMIP6 models as compared to observed regional dimming and brightening. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(24), p. 16023–16040. doi: 10.5194/acp-20-16023-2020. Full text in Research Archive
• Seland, Øyvind; Bentsen, Mats; Oliviè, Dirk Jan Leo; Toniazzo, Thomas; Gjermundsen, Ada & Graff, Lise Seland [Show all 30 contributors for this article] (2020). Overview of the Norwegian Earth System Model (NorESM2) and key climate response of CMIP6 DECK, historical, and scenario simulations. Geoscientific Model Development. ISSN 1991-959X. 13(12), p. 6165–6200. doi: 10.5194/gmd-13-6165-2020. Full text in Research Archive
• Mortier, Augustin; Gliss, Jonas; Schulz, Michael; Aas, Wenche; Andrews, Elisabeth & Bian, Huisheng [Show all 22 contributors for this article] (2020). Evaluation of climate model aerosol trends with ground-based observations over the last 2 decades – an AeroCom and CMIP6 analysis. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 13355–13378. doi: 10.5194/acp-20-13355-2020. Full text in Research Archive Show summary

  This study presents a multiparameter analysis of aerosol trends over the last 2 decades at regional and global scales. Regional time series have been computed for a set of nine optical, chemical-composition and mass aerosol properties by using the observations from several ground-based networks. From these regional time series the aerosol trends have been derived for the different regions of the world. Most of the properties related to aerosol loading exhibit negative trends, both at the surface and in the total atmospheric column. Significant decreases in aerosol optical depth (AOD) are found in Europe, North America, South America, North Africa and Asia, ranging from −1.2 % yr−1 to −3.1 % yr−1. An error and representativity analysis of the spatially and temporally limited observational data has been performed using model data subsets in order to investigate how much the observed trends represent the actual trends happening in the regions over the full study period from 2000 to 2014. This analysis reveals that significant uncertainty is associated with some of the regional trends due to time and space sampling deficiencies. The set of observed regional trends has then been used for the evaluation of 10 models (6 AeroCom phase III models and 4 CMIP6 models) and the CAMS reanalysis dataset and of their skills in reproducing the aerosol trends. Model performance is found to vary depending on the parameters and the regions of the world. The models tend to capture trends in AOD, the column Ångström exponent, sulfate and particulate matter well (except in North Africa), but they show larger discrepancies for coarse-mode AOD. The rather good agreement of the trends, across different aerosol parameters between models and observations, when co-locating them in time and space, implies that global model trends, including those in poorly monitored regions, are likely correct. The models can help to provide a global picture of the aerosol trends by filling the gaps in regions not covered by observations. The calculation of aerosol trends at a global scale reveals a different picture from that depicted by solely relying on ground-based observations. Using a model with complete diagnostics (NorESM2), we find a global increase in AOD of about 0.2 % yr−1 between 2000 and 2014, primarily caused by an increase in the loads of organic aerosols, sulfate and black carbon.

• Jonson, Jan Eiof; Gauss, Michael; Schulz, Michael; Jalkanen, Jukka-Pekka & Fagerli, Hilde (2020). Effects of global ship emissions on European air pollution levels. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. doi: 10.5194/acp-20-11399-2020.
• Myhre, Gunnar; Samset, Bjørn Hallvard; Mohr, Christian Wilhelm; Alterskjær, Kari; Balkanski, Yves & Bellouin, Nicolas [Show all 19 contributors for this article] (2020). Cloudy-sky contributions to the direct aerosol effect . Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 8855–8865. doi: 10.5194/acp-20-8855-2020. Full text in Research Archive Show summary

  The radiative forcing of the aerosol–radiation interaction can be decomposed into clear-sky and cloudy-sky portions. Two sets of multi-model simulations within Aerosol Comparisons between Observations and Models (AeroCom), combined with observational methods, and the time evolution of aerosol emissions over the industrial era show that the contribution from cloudy-sky regions is likely weak. A mean of the simulations considered is 0.01±0.1 W m−2. Multivariate data analysis of results from AeroCom Phase II shows that many factors influence the strength of the cloudy-sky contribution to the forcing of the aerosol–radiation interaction. Overall, single-scattering albedo of anthropogenic aerosols and the interaction of aerosols with the short-wave cloud radiative effects are found to be important factors. A more dedicated focus on the contribution from the cloud-free and cloud-covered sky fraction, respectively, to the aerosol–radiation interaction will benefit the quantification of the radiative forcing and its uncertainty range.

• Zanis, Prodromos; Akritidis, Dimitris; Georgoulias, Aristeidis K.; Allen, Robert J.; Bauer, Susanne E. & Boucher, Olivier [Show all 18 contributors for this article] (2020). Fast responses on pre-industrial climate from present-day aerosols in a CMIP6 multi-model study . Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 8381–8404. doi: 10.5194/acp-20-8381-2020.
• Burgos, María A.; Andrews, Elisabeth; Titos, Gloria; Benedetti, Angela; Bian, Huisheng & Buchard, Virginie [Show all 26 contributors for this article] (2020). A global model–measurement evaluation of particle light scattering coefficients at elevated relative humidity, Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 10231–10258. doi: 10.5194/acp-20-10231-2020. Full text in Research Archive Show summary

  The uptake of water by atmospheric aerosols has a pronounced effect on particle light scattering properties, which in turn are strongly dependent on the ambient relative humidity (RH). Earth system models need to account for the aerosol water uptake and its influence on light scattering in order to properly capture the overall radiative effects of aerosols. Here we present a comprehensive model–measurement evaluation of the particle light scattering enhancement factor f(RH), defined as the particle light scattering coefficient at elevated RH (here set to 85 %) divided by its dry value. The comparison uses simulations from 10 Earth system models and a global dataset of surface-based in situ measurements. In general, we find a large diversity in the magnitude of predicted f(RH) amongst the different models, which can not be explained by the site types. Based on our evaluation of sea salt scattering enhancement and simulated organic mass fraction, there is a strong indication that differences in the model parameterizations of hygroscopicity and model chemistry are driving at least some of the observed diversity in simulated f(RH). Additionally, a key point is that defining dry conditions is difficult from an observational point of view and, depending on the aerosol, may influence the measured f(RH). The definition of dry also impacts our model evaluation, because several models exhibit significant water uptake between RH = 0 % and 40 %. The multisite average ratio between model outputs and measurements is 1.64 when RH = 0 % is assumed as the model dry RH and 1.16 when RH = 40 % is the model dry RH value. The overestimation by the models is believed to originate from the hygroscopicity parameterizations at the lower RH range which may not implement all phenomena taking place (i.e., not fully dried particles and hysteresis effects). This will be particularly relevant when a location is dominated by a deliquescent aerosol such as sea salt. Our results emphasize the need to consider the measurement conditions in such comparisons and recognize that measurements referred to as dry may not be dry in model terms. Recommendations for future model–measurement evaluation and model improvements are provided.

• Allen, Robert J.; Turnock, Steven T; Nabat, Pierre; Neubauer, David; Lohmann, Ulrike & Oliviè, Dirk Jan Leo [Show all 34 contributors for this article] (2020). Climate and air quality impacts due to mitigation of non-methane near-term climate forcers. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20, p. 9641–9663. doi: 10.5194/acp-20-9641-2020.
• Pommier, Matthieu; Fagerli, Hilde; Schulz, Michael; Valdebenito, Alvaro; Kranenburg, Richard & Schaap, Martijn (2020). Prediction of source contributions to urban background PM10 concentrations in European cities: A case study for an episode in December 2016 using EMEP/MSC-W rv4.15 and LOTOS-EUROS v2.0 - Part 1: The country contributions. Geoscientific Model Development. ISSN 1991-959X. 13(4), p. 1787–1807. doi: 10.5194/gmd-13-1787-2020.
• Tjiputra, Jerry; Schwinger, Jörg; Bentsen, Mats; Morée, Anne; Gao, Shuang & Bethke, Ingo [Show all 13 contributors for this article] (2020). Ocean biogeochemistry in the Norwegian Earth System Model version 2 (NorESM2). Geoscientific Model Development. ISSN 1991-959X. 13(5), p. 2393–2431. doi: 10.5194/gmd-13-2393-2020. Full text in Research Archive Show summary

  The ocean carbon cycle is a key player in the climate system through its role in regulating the atmospheric carbon dioxide concentration and other processes that alter the Earth's radiative balance. In the second version of the Norwegian Earth System Model (NorESM2), the oceanic carbon cycle component has gone through numerous updates that include, amongst others, improved process representations, increased interactions with the atmosphere, and additional new tracers. Oceanic dimethyl sulfide (DMS) is now prognostically simulated and its fluxes are directly coupled with the atmospheric component, leading to a direct feedback to the climate. Atmospheric nitrogen deposition and additional riverine inputs of other biogeochemical tracers have recently been included in the model. The implementation of new tracers such as “preformed” and “natural” tracers enables a separation of physical from biogeochemical drivers as well as of internal from external forcings and hence a better diagnostic of the simulated biogeochemical variability. Carbon isotope tracers have been implemented and will be relevant for studying long-term past climate changes. Here, we describe these new model implementations and present an evaluation of the model's performance in simulating the observed climatological states of water-column biogeochemistry and in simulating transient evolution over the historical period. Compared to its predecessor NorESM1, the new model's performance has improved considerably in many aspects. In the interior, the observed spatial patterns of nutrients, oxygen, and carbon chemistry are better reproduced, reducing the overall model biases. A new set of ecosystem parameters and improved mixed layer dynamics improve the representation of upper-ocean processes (biological production and air–sea CO2 fluxes) at seasonal timescale. Transient warming and air–sea CO2 fluxes over the historical period are also in good agreement with observation-based estimates. NorESM2 participates in the Coupled Model Intercomparison Project phase 6 (CMIP6) through DECK (Diagnostic, Evaluation and Characterization of Klima) and several endorsed MIP simulations.

• Bellouin, Nicolas; Quaas, Johannes; Gryspeerdt, Edward; Kinne, Stephan A.; Stier, Philip & Watson-Parris, Duncan [Show all 33 contributors for this article] (2020). Bounding global aerosol radiative forcing of climate change. Reviews of Geophysics. ISSN 8755-1209. 58. doi: 10.1029/2019RG000660. Full text in Research Archive Show summary

  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.

• Kim, Dongchul; Chin, Mian; Yu, Hongbin; Pan, Xiaohua; Bian, Huisheng & Tan, Qian [Show all 13 contributors for this article] (2019). Asian and trans-Pacific dust: A multimodel and multiremote sensing observation analysis. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 124(23), p. 13534–13559. doi: 10.1029/2019JD030822.
• Myhre, Gunnar; Alterskjær, Kari; Stjern, Camilla Weum; Hodnebrog, Øivind; Marelle, Louis & Samset, Bjørn Hallvard [Show all 11 contributors for this article] (2019). Frequency of extreme precipitation increases extensively with event rareness under global warming. Scientific Reports. ISSN 2045-2322. 9(16063). doi: 10.1038/s41598-019-52277-4. Full text in Research Archive Show summary

  The intensity of the heaviest extreme precipitation events is known to increase with global warming. How often such events occur in a warmer world is however less well established, and the combined effect of changes in frequency and intensity on the total amount of rain falling as extreme precipitation is much less explored, in spite of potentially large societal impacts. Here, we employ observations and climate model simulations to document strong increases in the frequencies of extreme precipitation events occurring on decadal timescales. Based on observations we find that the total precipitation from these intense events almost doubles per degree of warming, mainly due to changes in frequency, while the intensity changes are relatively weak, in accordance to previous studies. This shift towards stronger total precipitation from extreme events is seen in observations and climate models, and increases with the strength – and hence the rareness – of the event. Based on these results, we project that if historical trends continue, the most intense precipitation events observed today are likely to almost double in occurrence for each degree of further global warming. Changes to extreme precipitation of this magnitude are dramatically stronger than the more widely communicated changes to global mean precipitation.

• McClintock, MA; McDowell, William H; Gonzalez, Grizelle; Schulz, Michael & Pett-Ridge, Julie C (2019). African dust deposition in Puerto Rico: Analysis of a 20-year rainfall chemistry record and comparison with models. Atmospheric Environment. ISSN 1352-2310. 216, p. 1–11. doi: 10.1016/j.atmosenv.2019.116907.
• Heinze, Christoph; Eyring, Veronika; Friedlingstein, Pierre; Jones, Colin; Balkanski, Yves & Collins, William [Show all 20 contributors for this article] (2019). ESD Reviews: Climate feedbacks in the Earth system and prospects for their evaluation. Earth System Dynamics (ESD). ISSN 2190-4979. 10(3), p. 379–452. doi: 10.5194/esd-10-379-2019. Full text in Research Archive
• Inness, Antje; Ades, Melanie; Agustí-Panareda, Anna; Barré, Jérôme; Benedictow, Anna Maria Katarina & Blechschmidt, Anne-Marlene [Show all 20 contributors for this article] (2019). The CAMS reanalysis of atmospheric composition. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 19(6), p. 3515–3556. doi: 10.5194/acp-19-3515-2019.
• Aas, Wenche; Mortier, Augustin; Bowersox, Van C.; Cherian, Ribu; Faluvegi, Greg & Fagerli, Hilde [Show all 24 contributors for this article] (2019). Global and regional trends of atmospheric sulfur. Scientific Reports. ISSN 2045-2322. 9:953, p. 1–11. doi: 10.1038/s41598-018-37304-0. Full text in Research Archive Show summary

  The profound changes in global SO2 emissions over the last decades have affected atmospheric composition on a regional and global scale with large impact on air quality, atmospheric deposition and the radiative forcing of sulfate aerosols. Reproduction of historical atmospheric pollution levels based on global aerosol models and emission changes is crucial to prove that such models are able to predict future scenarios. Here, we analyze consistency of trends in observations of sulfur components in air and precipitation from major regional networks and estimates from six different global aerosol models from 1990 until 2015. There are large interregional differences in the sulfur trends consistently captured by the models and observations, especially for North America and Europe. Europe had the largest reductions in sulfur emissions in the first part of the period while the highest reduction came later in North America and East Asia. The uncertainties in both the emissions and the representativity of the observations are larger in Asia. However, emissions from East Asia clearly increased from 2000 to 2005 followed by a decrease, while in India a steady increase over the whole period has been observed and modelled. The agreement between a bottom-up approach, which uses emissions and process-based chemical transport models, with independent observations gives an improved confidence in the understanding of the atmospheric sulfur budget.

• Dong, Xinyi; Fu, Joshua; Zhu, Qingzhao; Sun, Jian; Tan, Jiani & Keating, Terry [Show all 19 contributors for this article] (2018). Long-range transport impacts on surface aerosol concentrations and the contributions to haze events in China: an HTAP2 multi-model study. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 18(21), p. 15581–15600. doi: 10.5194/acp-18-15581-2018.
• Lund, Marianne Tronstad; Myhre, Gunnar; Haslerud, Amund Søvde; Skeie, Ragnhild Bieltvedt; Griesfeller, Jan & Platt, Stephen Matthew [Show all 9 contributors for this article] (2018). Concentrations and radiative forcing of anthropogenic aerosols from 1750 to 2014 simulated with the Oslo CTM3 and CEDS emission inventory. Geoscientific Model Development. ISSN 1991-959X. 11(12), p. 4909–4931. doi: 10.5194/gmd-11-4909-2018. Full text in Research Archive Show summary

  We document the ability of the new-generation Oslo chemistry-transport model, Oslo CTM3, to accurately simulate present-day aerosol distributions. The model is then used with the new Community Emission Data System (CEDS) historical emission inventory to provide updated time series of anthropogenic aerosol concentrations and consequent direct radiative forcing (RFari) from 1750 to 2014. Overall, Oslo CTM3 performs well compared with measurements of surface concentrations and remotely sensed aerosol optical depth. Concentrations are underestimated in Asia, but the higher emissions in CEDS than previous inventories result in improvements compared to observations. The treatment of black carbon (BC) scavenging in Oslo CTM3 gives better agreement with observed vertical BC profiles relative to the predecessor Oslo CTM2. However, Arctic wintertime BC concentrations remain underestimated, and a range of sensitivity tests indicate that better physical understanding of processes associated with atmospheric BC processing is required to simultaneously reproduce both the observed features. Uncertainties in model input data, resolution, and scavenging affect the distribution of all aerosols species, especially at high latitudes and altitudes. However, we find no evidence of consistently better model performance across all observables and regions in the sensitivity tests than in the baseline configuration. Using CEDS, we estimate a net RFari in 2014 relative to 1750 of −0.17 W m−2, significantly weaker than the IPCC AR5 2011–1750 estimate. Differences are attributable to several factors, including stronger absorption by organic aerosol, updated parameterization of BC absorption, and reduced sulfate cooling. The trend towards a weaker RFari over recent years is more pronounced than in the IPCC AR5, illustrating the importance of capturing recent regional emission changes.

• Jonson, Jan Eiof; Schulz, Michael; Emmons, Louisa; Flemming, Johannes; Henze, Daven & Sudo, Kengo [Show all 14 contributors for this article] (2018). The effects of intercontinental emission sources on European air pollution levels. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 18(18), p. 13655–13672. doi: 10.5194/acp-18-13655-2018.
• Kirkevåg, Alf; Grini, Alf; Oliviè, Dirk Jan Leo; Seland, Øyvind; Alterskjær, Kari & Hummel, Matthias [Show all 14 contributors for this article] (2018). A production-tagged aerosol module for earth system models, OsloAero5.3-extensions and updates for CAM5.3-Oslo. Geoscientific Model Development. ISSN 1991-959X. 11(10), p. 3945–3982. doi: 10.5194/gmd-11-3945-2018. Full text in Research Archive
• Samset, Bjørn Hallvard; Stjern, Camilla Weum; Andrews, Elisabeth; Kahn, Ralph A.; Myhre, Gunnar & Schulz, Michael [Show all 7 contributors for this article] (2018). Aerosol Absorption: Progress Towards Global and Regional Constraints. Current Climate Change Reports. ISSN 2198-6061. 4(2), p. 65–83. doi: 10.1007/s40641-018-0091-4.
• Karset, Inger Helene H.; Berntsen, Terje Koren; Storelvmo, Trude; Alterskjær, Kari; Grini, Alf & Oliviè, Dirk Jan Leo [Show all 10 contributors for this article] (2018). Strong impacts on aerosol indirect effects from historical oxidant changes. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 18(10), p. 7669–7690. doi: 10.5194/acp-18-7669-2018. Full text in Research Archive
• Wang, Rong; Andrews, Elisabeth; Balkanski, Yves; Boucher, Olivier; Myhre, Gunnar & Samset, Bjørn Hallvard [Show all 10 contributors for this article] (2018). Spatial Representativeness Error in the Ground-Level Observation Networks for Black Carbon Radiation Absorption. Geophysical Research Letters. ISSN 0094-8276. 45(4), p. 2106–2114. doi: 10.1002/2017GL076817.
• Muri, Helene; Tjiputra, Jerry; Otterå, Odd Helge; Adakudlu, Muralidhar; Lauvset, Siv Kari & Grini, Alf [Show all 9 contributors for this article] (2018). Climate response to aerosol geoengineering: a multi-method comparison. Journal of Climate. ISSN 0894-8755. 31(16), p. 6319–6340. doi: 10.1175/JCLI-D-17-0620.1. Full text in Research Archive
• Schutgens, Nick A. J.; Tsyro, Svetlana G.; Gryspeerdt, Edward; Goto, Daisuke; Weigum, Natalie & Schulz, Michael [Show all 7 contributors for this article] (2017). On the spatio-temporal representativeness of observations. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(16), p. 9761–9780. doi: 10.5194/acp-17-9761-2017.
• Bian, Huisheng; Chin, Mian; Hauglustaine, Didier A.; Schulz, Michael; Myhre, Gunnar & Bauer, Susanne E. [Show all 17 contributors for this article] (2017). Investigation of global particulate nitrate from the AeroCom phase III experiment. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(21), p. 12911–12940. doi: 10.5194/acp-17-12911-2017.
• Steensen, Birthe Marie Rødssæteren; Schulz, Michael; Wind, Peter Ariaan; Valdebenito Bustamante, Alvaro Moises & Fagerli, Hilde (2017). The operational eEMEP model version 10.4 for volcanic SO2 and ash forecasting. Geoscientific Model Development. ISSN 1991-959X. 10(5), p. 1927–1943. doi: 10.5194/gmd-10-1927-2017.
• Sand, Maria; Samset, Bjørn Hallvard; Balkanski, Yves; Bauer, Susanne; Bellouin, Nicolas & Berntsen, Terje Koren [Show all 29 contributors for this article] (2017). Aerosols at the poles: an AeroCom Phase II multi-model evaluation. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(19), p. 12197–12218. doi: 10.5194/acp-17-12197-2017. Full text in Research Archive
• Steensen, Birthe Marie Rødssæteren; Kylling, Arve; Kristiansen, Nina Iren & Schulz, Michael (2017). Uncertainty assessment and applicability of an inversion method for volcanic ash forecasting. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(14), p. 9205–9222. doi: 10.5194/acp-17-9205-2017. Full text in Research Archive
• Galmarini, Stefano; Koffi, Brigitte; Solazzo, Efisio; Keating, Terry J.; Hogrefe, Christian & Schulz, Michael [Show all 12 contributors for this article] (2017). Technical note: Coordination and harmonization of the multi-scale, multi-model activities HTAP2, AQMEII3, and MICS-Asia3: Simulations, emission inventories, boundary conditions, and model output formats. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(2), p. 1543–1555. doi: 10.5194/acp-17-1543-2017.
• Myhre, Gunnar; Aas, Wenche; Cherian, Ribu; Collins, W; Faluvegi, Greg & Flanner, M. [Show all 22 contributors for this article] (2017). Multi-model simulations of aerosol and ozone radiative forcing due to anthropogenic emission changes during the period 1990-2015. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 17(4), p. 2709–2720. doi: 10.5194/acp-17-2709-2017. Full text in Research Archive Show summary

  Over the past few decades, the geographical distribution of emissions of substances that alter the atmospheric energy balance has changed due to economic growth and air pollution regulations. Here, we show the resulting changes to aerosol and ozone abundances and their radiative forcing using recently updated emission data for the period 1990–2015, as simulated by seven global atmospheric composition models. The models broadly reproduce large-scale changes in surface aerosol and ozone based on observations (e.g. −1 to −3 % yr−1 in aerosols over the USA and Europe). The global mean radiative forcing due to ozone and aerosol changes over the 1990–2015 period increased by +0.17 ± 0.08 W m−2, with approximately one-third due to ozone. This increase is more strongly positive than that reported in IPCC AR5. The main reasons for the increased positive radiative forcing of aerosols over this period are the substantial reduction of global mean SO2 emissions, which is stronger in the new emission inventory compared to that used in the IPCC analysis, and higher black carbon emissions.

• Collins, William J.; Lamarque, Jean-Francois; Schulz, Michael; Boucher, Olivier; Eyring, Veronika & Hegglin, Michaela I. [Show all 11 contributors for this article] (2017). AerChemMIP: Quantifying the effects of chemistry and aerosols in CMIP6. Geoscientific Model Development. ISSN 1991-959X. 10(2), p. 585–607. doi: 10.5194/gmd-10-585-2017. Show summary

  The Aerosol Chemistry Model Intercomparison Project (AerChemMIP) is endorsed by the Coupled-Model Intercomparison Project 6 (CMIP6) and is designed to quantify the climate and air quality impacts of aerosols and chemically reactive gases. These are specifically near-term climate forcers (NTCFs: methane, tropospheric ozone and aerosols, and their precursors), nitrous oxide and ozone-depleting halocarbons. The aim of AerChemMIP is to answer four scientific questions. 1. How have anthropogenic emissions contributed to global radiative forcing and affected regional climate over the historical period? 2. How might future policies (on climate, air quality and land use) affect the abundances of NTCFs and their climate impacts? 3.How do uncertainties in historical NTCF emissions affect radiative forcing estimates? 4. How important are climate feedbacks to natural NTCF emissions, atmospheric composition, and radiative effects? These questions will be addressed through targeted simulations with CMIP6 climate models that include an interactive representation of tropospheric aerosols and atmospheric chemistry. These simulations build on the CMIP6 Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, the CMIP6 historical simulations, and future projections performed elsewhere in CMIP6, allowing the contributions from aerosols and/or chemistry to be quantified. Specific diagnostics are requested as part of the CMIP6 data request to highlight the chemical composition of the atmosphere, to evaluate the performance of the models, and to understand differences in behaviour between them.

• Steensen, Birthe Marie Rødssæteren; Schulz, Michael; Theys, N. & Fagerli, Hilde (2016). A model study of the pollution effects of the first three months of the Holuhraun volcanic fissure. Atmospheric Chemistry and Physics Discussions (ACPD). ISSN 1680-7367. 2016. doi: 10.5194/acp-2015-907.
• Forster, Piers M.; Richardson, Thomas; Maycock, Amanda C.; Smith, Christopher J.; Samset, Bjørn Hallvard & Myhre, Gunnar [Show all 9 contributors for this article] (2016). Recommendations for diagnosing effective radiative forcing from climate models for CMIP6. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 121, p. 12,460–12,475. doi: 10.1002/2016JD025320.
• Schutgens, Nick A.J.; Gryspeerdt, Edward; Weigum, Natalie; Tsyro, Svetlana; Goto, Daisuke & Schulz, Michael [Show all 7 contributors for this article] (2016). Will a perfect model agree with perfect observations? the impact of spatial sampling. Atmospheric Chemistry and Physics Discussions (ACPD). ISSN 1680-7367. 2016. doi: 10.5194/acp-2015-973.

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• Gjermundsen, Ada; Bentsen, Mats; Oliviè, Dirk Jan Leo; Nummelin, Aleksi Henrynpoika; Seland, Øyvind & Schulz, Michael (2023). The Norwegian Earth System Model.
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2023). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming. .
• Schmidt, Gavin A.; Andrews, Timothy; Bauer, Susanne E.; Durack, Paul J.; Loeb, Norman G. & Ramaswamy, V. [Show all 22 contributors for this article] (2023). Corrigendum: CERESMIP: a climate modeling protocol to investigate recent trends in the Earth's Energy Imbalance (Frontiers in Climate, (2023), 5, (1202161), 10.3389/fclim.2023.1202161). Frontiers in Climate. ISSN 2624-9553. 5. doi: 10.3389/fclim.2023.1298599.
• Oliviè, Dirk Jan Leo; Seland, Øyvind; Krüger, Kirstin & Schulz, Michael (2023). Analysis of NorESM2 full-chemistry simulation of the historical period (1850–2014).
• Gjermundsen, Ada; Buraas, Marte Sofie; Oliviè, Dirk Jan Leo; Debernard, Jens Boldingh; Graff, Lise Seland & Nummelin, Aleksi Henrynpoika [Show all 9 contributors for this article] (2022). Assessing Arctic climate change with the Norwegian Earth System Model.
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2022). Assessing the oceanic control on ECS in CMIP6.
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2022). NorESM2 and Climate Sensitivity.
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2022). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming. .
• Oliviè, Dirk Jan Leo; Balkanski, Yves; Bergman, Tommi; Carslaw, Ken; Checa-Garcia, Ramiro & O'Connor, Fiona M [Show all 17 contributors for this article] (2022). Impact of natural aerosol uncertainty on anthropogenic aerosol forcing .
• Oliviè, Dirk Jan Leo; Seland, Øyvind; Krüger, Kirstin & Schulz, Michael (2022). Implementation of gas-phase chemistry in NorESM2.
• Haugvaldstad, Ove Westermoen; Oliviè, Dirk Jan Leo; Schulz, Michael & Storelvmo, Trude (2022). Decomposing the direct and indirect radiative effects by mineral dust aerosols in CMIP6.
• Fanny, Peers; Haywood, Jim; Allan, Richard; Peters, Francis J.; Johnson, Ben & Myhre, Gunnar [Show all 7 contributors for this article] (2022). Observation of the direct effect of aerosols in the South-East Atlantic at high temporal resolution from MSG/SEVIRI.
• Moseid, Kine Onsum; Hofer, Stefan & Schulz, Michael (2022). What Might the Future Climate Look Like? Frontiers for Young Minds. ISSN 2296-6846. doi: 10.3389/frym.2022.715603.
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2022). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming.
• Gjermundsen, Ada; Graff, Lise Seland; Bentsen, Mats; Breivik, Lars-Anders; Debernard, Jens Boldingh & Makkonen, Risto [Show all 10 contributors for this article] (2021). How representative is Svalbard for future Arctic climate evolution? An Earth system modelling perspective.
• Gjermundsen, Ada; Graff, Lise Seland; Bentsen, Mats; Breivik, Lars-Anders; Debernard, Jens Boldingh & Makkonen, Risto [Show all 10 contributors for this article] (2021). How representative is Svalbard for future Arctic climate evolution? An Earth system modelling perspective. .
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2021). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming. .
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2021). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming. .
• Oliviè, Dirk Jan Leo; Fagerli, Hilde & Schulz, Michael (2021). METs work on methane in ESM2025 (Earth System Modelling) and for DG-ENV (air quality).
• Oliviè, Dirk Jan Leo; Gjermundsen, Ada; Kirkevåg, Alf; Moseid, Kine Onsum; Schulz, Michael & Seland, Øyvind (2021). Comparing the climate impact of CMIP5 versus CMIP6 aerosol (precursor) emissions in NorESM2.
• Gjermundsen, Ada; Nummelin, Aleksi Henrynpoika; Oliviè, Dirk Jan Leo; Bentsen, Mats; Seland, Øyvind & Schulz, Michael (2021). Shutdown of Southern Ocean convection controls long-term greenhouse gas-induced warming.
• He, Yanchun; Gupta, Alok Kumar; Bentsen, Mats; Schulz, Michael; Torsvik, Tomas & Gjermundsen, Ada [Show all 9 contributors for this article] (2021). The 3rd iNES NorESM User Workshop. Show summary

  About 15 participants actively involved in the meeting, both physically and virtually on line. There are presentations and hands-on sessions for different topics. The agenda of the workshop is found at the workshop webpage: https://noresmhub.github.io/NorESM_Workshop_2021/

• Brown, Hunter; Liu, Xiaohong; Pokhrel, Rudra; Murphy, Shane; Lu, Zheng & Saleh, Rawad [Show all 21 contributors for this article] (2021). Summary of research paper published in Nature Communications titled: Biomass burning aerosols in most climate models are too absorbing. Clean Air Journal. ISSN 1017-1703. 31(1), p. 1–1. doi: 10.17159/caj/2021/31/1.11221.
• Gjermundsen, Ada; Bentsen, Mats; Oliviè, Dirk Jan Leo; Seland, Øyvind & Schulz, Michael (2020). Earth System Models.
• Schulz, Michael; Zieger, Paul & Kong, Yuen Man (2020). Fourth Nordic course on eScience Tools in Climate Science: Linking Observations with Modelling.
• He, Yanchun; Gupta, Alok Kumar; Bentsen, Mats; Schulz, Michael; Oliviè, Dirk Jan Leo & Torsvik, Tomas [Show all 9 contributors for this article] (2020). NorESM User Workshop 2020.
• Laj, Paolo; Rose, Clemence; Bigi, Alessandro; Coen, Martine Collaud; Andrews, Elisabeth & Myhre, Cathrine Lund [Show all 21 contributors for this article] (2020). A global analysis of climate-relevant aerosol properties retrieved from the network of GAW near-surface observatories.
• Bigi, Alessandro; Coen, Martine Collaud; Andrews, Elisabeth J.; Rose, Clemence; Myhre, Cathrine Lund & Fiebig, Markus [Show all 20 contributors for this article] (2020). Global variability of aerosol optical properties retrieved from the network of GAW near-surface observatories.
• Aas, Wenche; Mortier, Augustin; Bowersox, Van; Cherian, Ribu; Faluvegi, Greg & Fagerli, Hilde [Show all 24 contributors for this article] (2020). Author Correction: Global and regional trends of atmospheric sulfur. Scientific Reports. ISSN 2045-2322. 10. doi: 10.1038/s41598-020-62441-w. Full text in Research Archive Show summary

  Correction to: Scientific Reports https://doi.org/10.1038/s41598-018-37304-0, published online 30 January 2019

• Schulz, Michael & Zieger, Paul (2018). Report from the second Nordic course on e-science tools for climate research.
• Fagerli, Hilde; Klein, Heiko; Nyiri, Agnes; Steensen, Birthe Marie Rødssæteren; Schulz, Michael & Mortier, Augustin [Show all 13 contributors for this article] (2018). The operational system for forecasting of volcanic ash in Norwegian air space.
• Aas, Wenche; Mortier, Augustin; Cherian, Ribu; Oliviè, Dirk Jan Leo; Faluvegi, Greg & Hand, Jenny [Show all 15 contributors for this article] (2018). Evaluation of global models abilities to assess the regional and global sulfate aerosol trends, 1990-2015.
• Muri, Helene; Tjiputra, Jerry; Otterå, Odd Helge; Lauvset, Siv Kari; Schulz, Michael & Ekici, Altug [Show all 8 contributors for this article] (2017). Exploring the Potential and Side-effects of Aerosol-based Geoengineering.
• Muri, Helene; Tjiputra, Jerry; Otterå, Odd Helge; Lauvset, Siv Kari; Adakudlu, Muralidhar & Schulz, Michael [Show all 8 contributors for this article] (2017). An introduction to aerosol injection climate engineering.
• Adakudlu, Muralidhar; Otterå, Odd Helge; Tjiputra, Jerry; Muri, Helene; Grini, Alf & Schulz, Michael (2017). Impacts of radiation management techniques on the North Atlantic Oscillation. Show summary

  The effectiveness of various climate engineering techniques in limiting the global warming signal to reasonable levels has been the topic of state-of-the-art research on climate change. Using an Earth system model, we show that these techniques have the potential to bring down the high CO2 concentration climate in RCP8.5 to a moderate climate similar to RCP4.5 in terms of global temperature. Nevertheless, their influence on the regional aspects of atmospheric circulation is not clear. The regional circulation patterns in the atmosphere are largely characterized by the natural variability modes, such as the North Atlantic Oscillation (NAO). In this study, we assess the impacts of three radiation managment techniques, namely, Stratospheric Aerosol Injection (SAI), Marine Sky Brightening (MSB) and Cirrus Cloud Thinning (CCT), on the structure and features of the NAO. The results indicate an east-northeastward shift as well as intensification of the NAO spatial pattern in the global warming scenarios of RCP4.5 and RCP8.5, with the signal being most intense in the latter. The climate engineering forcings when applied to the RCP8.5 case tend to reduce the strength of the NAO with little impact on its position. The CCT case appears to have the maximum effect on the NAO signal. The patterns of cloud radiative forcing, expressed as the difference between net radiative forcing at TOA under average conditions and clear sky conditions, reveal a northeastward shift of the radiative heating in the north Atlantic region. This implies a possible link between the changes in the NAO signal and the cloud radiative forcing.

• Muri, Helene; Tjiputra, Jerry; Grini, Alf; Otterå, Odd Helge; Lauvset, Siv Kari & Schulz, Michael [Show all 8 contributors for this article] (2017). Exploring the potential and side effects of radiation management climate engineering.
• Muri, Helene; Tjiputra, Jerry; Grini, Alf; Otterå, Odd Helge; Lauvset, Siv Kari & Schulz, Michael [Show all 7 contributors for this article] (2017). Comparative climate response of using three different aerosol geoengineering techniques to transfer from RCP8.5 to RCP4.5.
• Fagerli, Hilde; Tsyro, Svetlana; Jonson, Jan Eiof; Nyiri, Agnes; Gauss, Michael & Simpson, David [Show all 33 contributors for this article] (2018). Transboundary particulate matter, photo-oxidants, acidifying and eutrophying components. Norwegian Meteorological Institute. ISSN 1504-6109.
• Fagerli, Hilde; Tsyro, Svetlana; Denby, Bruce; Nyiri, Agnes; Gauss, Michael & Simpson, David [Show all 40 contributors for this article] (2017). Transboundary particulate matter, photo-oxidants, acidifying and eutrophying components. Meteorologisk Institutt. ISSN 1504-6109.

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