Key Earth System Processes to understand Arctic Climate Warming and Northern Latitude Hydrological Cycle Changes (KeyCLIM)

• 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.
• Heinze, Christoph; Michel, Clio; Torsvik, Tomas; Schwinger, Jörg & Tjiputra, Jerry (2024). More Frequent Abrupt Marine Environmental Changes Expected. Geophysical Research Letters. ISSN 0094-8276. 51(2). doi: 10.1029/2023GL106192.
• Sterl, Miriam F.; Lacasce, Joseph Henry; Groeskamp, Sjoerd; Nummelin, Aleksi Henrynpoika; Isachsen, Pål Erik & Baatsen, Michiel L. J. (2024). Suppression of Mesoscale Eddy Mixing by Topographic PV Gradients. Journal of Physical Oceanography. ISSN 0022-3670. 54(5), p. 1089–1103. doi: 10.1175/JPO-D-23-0142.1.
• Nummelin, Aleksi & Isachsen, Pål Erik (2024). Parameterizing Mesoscale Eddy Buoyancy Transport Over Sloping Topography. Journal of Advances in Modeling Earth Systems. ISSN 1942-2466. 16(3). doi: 10.1029/2023MS003806.
• 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.
• Hanna, Edward; Topal, Daniel; Box, Jason Eric; Buzzard, Sammie; Christie, Frazer D. W. & Hvidberg, Christine [Show all 29 contributors for this article] (2024). Short- and long-term variability of the Antarctic and Greenland ice sheets. Nature Reviews Earth & Environment. ISSN 2662-138X. 5, p. 193–210. doi: 10.1038/s43017-023-00509-7.
• Tjiputra, Jerry; Negrel, Jean & Olsen, Are (2023). Early detection of anthropogenic climate change signals in the ocean interior. Scientific Reports. ISSN 2045-2322. 13:3006, p. 1–14. doi: 10.1038/s41598-023-30159-0.
• Gomez, James; Allen, Robert J.; Turnock, Steven T.; Horowitz, Larry W.; Tsigaridis, Kostas & Bauer, Susanne E. [Show all 9 contributors for this article] (2023). The projected future degradation in air quality is caused by more abundant natural aerosols in a warmer world. Communications Earth & Environment. ISSN 2662-4435. 4(1). doi: 10.1038/s43247-023-00688-7.
• Stjern, Camilla Weum; Forster, Piers M.; Jia, Hailing; Jouan, Caroline; Kasoar, Matthew R. & Myhre, Gunnar [Show all 13 contributors for this article] (2023). The Time Scales of Climate Responses to Carbon Dioxide and Aerosols. Journal of Climate. ISSN 0894-8755. 36(11), p. 3537–3551. doi: 10.1175/JCLI-D-22-0513.1. Full text in Research Archive
• 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.
• 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.
• Shu, Qi; Wang, Qiang; Guo, Chuncheng; Song, Zhenya; Wang, Shizhu & He, Yan [Show all 7 contributors for this article] (2023). Arctic Ocean simulations in the CMIP6 Ocean Model Intercomparison Project (OMIP). Geoscientific Model Development. ISSN 1991-959X. 16(9), p. 2539–2563. doi: 10.5194/gmd-16-2539-2023. Show summary

  Arctic Ocean simulations in 19 global ocean–sea-ice models participating in the Ocean Model Intercomparison Project (OMIP) of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are evaluated in this paper. Our findings show no significant improvements in Arctic Ocean simulations from the previous Coordinated Ocean-ice Reference Experiments phase II (CORE-II) to the current OMIP. Large model biases and inter-model spread exist in the simulated mean state of the halocline and Atlantic Water layer in the OMIP models. Most of the OMIP models suffer from a too thick and deep Atlantic Water layer, a too deep halocline base, and large fresh biases in the halocline. The OMIP models qualitatively agree on the variability and change of the Arctic Ocean freshwater content; sea surface height; stratification; and volume, heat, and freshwater transports through the Arctic Ocean gateways. They can reproduce the changes in the gateway transports observed in the early 21st century, with the exception of the Bering Strait. We also found that the OMIP models employing the NEMO ocean model simulate relatively larger volume and heat transports through the Barents Sea Opening. Overall, the performance of the Arctic Ocean simulations is similar between the CORE2-forced OMIP-1 and JRA55-do-forced OMIP-2 experiments.

• Hofer, Stefan; Hahn, Lily; Shaw, Jonah; McGraw, Zachary; Bruno, Olimpia & Hellmuth, Franziska [Show all 11 contributors for this article] (2023). Realistic representation of mixed-phase clouds increases future climate warming. Research Square. ISSN 2693-5015. doi: 10.21203/rs.3.rs-2981113/v1. Show summary

  Clouds are the main source of uncertainties when projecting climate change. Mixed-phase clouds (MPCs) that contain ice and supercooled-liquid particles are especially hard to constrain, and climate models neither agree on their phase nor their spatial extent. This is problematic, as models that underestimate contemporary supercooled-liquid in MPCs will underestimate future warming. Furthermore, it has recently been shown that supercooled-liquid water in MPCs is not homogeneously-mixed, neither vertically nor horizontally. However, while there have been attempts at observationally constraining MPCs to constrain uncertainties in future warming, all studies only use the phase of the interior of MPCs. Using novel satellite observations, and contrary to current knowledge, we show that MPCs are more liquid at the cloud top globally. We use these observations to constrain, for the first time, the cloud top phase in addition to the interior of MPCs in a global climate model, leading to +1C more 21st century warming in NorESM2 SSP5-8.5 climate projections. We anticipate that the difference between cloud top and interior phase in MPCs is an important new target metric for future climate model development, because similar MPC-related biases in future warming are likely present in many climate models.

• Zhong, Qirui; Schutgens, Nick; van der Werf, Guido R.; Takemura, Toshihiko; van Noije, Twan & Mielonen, Tero [Show all 21 contributors for this article] (2023). Threefold reduction of modeled uncertainty in direct radiative effects over biomass burning regions by constraining absorbing aerosols. Science Advances. ISSN 2375-2548. 9(48), p. 1–13. doi: 10.1126/sciadv.adi3568.
• McGraw, Zachary; Storelvmo, Trude; Polvani, Lorenzo M.; Hofer, Stefan; Shaw, Jonah K. & Gettelman, Andrew (2023). On the Links Between Ice Nucleation, Cloud Phase, and Climate Sensitivity in CESM2. Geophysical Research Letters. ISSN 0094-8276. 50(17). doi: 10.1029/2023GL105053. Full text in Research Archive
• Axelsson, Josefine; Gao, Jing; Eckhardt, Sabine; Cassiani, Massimo; Cheng, Deliang & Zhang, Qiong (2023). A Precipitation Isotopic Response in 2014–2015 to Moisture Transport Changes in the Central Himalayas. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 128(13). doi: 10.1029/2023JD038568. Full text in Research Archive Show summary

  The impact of moisture transport and sources on precipitation stable isotopes (δ18O and d-excess) in the central Himalayas are crucial to understanding the climatic archives. However, this is still unclear due to the lack of in-situ observations. Here we present measurements of stable isotopes in precipitation at two stations (Yadong and Pali) in the central Himalayas during 2014–2015. Combined with simulations from the dispersion model FLEXPART, we investigate effects on precipitation stable isotopes related to changes in moisture sources and convections in the region, and possible influence by El Niño. Our results suggest that the moisture supplies related to evaporation over northeastern India and moisture losses related to convective activities over the Bay of Bengal (BoB) and Bangladesh region play important roles in changes in δ18O and d-excess in precipitation in the Yadong Valley. Outgoing longwave radiation and moisture flux divergence analysis further confirm that the contribution from continental evaporation dominates the moisture supply in the central Himalayas with a lesser contribution from convection over the BoB during the 2015 monsoon season compared with 2014. A change in the altitude effect is observed in 2015, which is more significant than the temperature and precipitation amount effect during the observation period. These findings provide valuable insights into climatic interpretations of paleo-isotopic archives with an isotopic response to changes in moisture transport to the central Himalayas.

• Iversen, Emilie Claussen; Hodnebrog, Øivind; Graff, Lise Seland; Nygaard, Bjørn Egil Kringlebotn & Iversen, Trond (2023). Future Winter Precipitation Decreases Associated With the North Atlantic Warming Hole and Reduced Convection. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 128(12). doi: 10.1029/2022JD038374. Full text in Research Archive
• 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.

• 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

• Madan, Gaurav; Gjermundsen, Ada; Iversen, Silje Christine & Lacasce, Joseph Henry (2023). The weakening AMOC under extreme climate change. Climate Dynamics. ISSN 0930-7575. 62, p. 1291–1309. doi: 10.1007/s00382-023-06957-7. Full text in Research Archive
• 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.

• Berends, Constantijn J.; Goelzer, Heiko; Reerink, Thomas J.; Stap, Lennert & van de Wal, Roderik S.W. (2022). Benchmarking the vertically integrated ice-sheet model IMAU-ICE (version 2.0). Geoscientific Model Development. ISSN 1991-959X. 15(14), p. 5667–5688. doi: 10.5194/gmd-15-5667-2022. Show summary

  Ice-dynamical processes constitute a large uncertainty in future projections of sea-level rise caused by anthropogenic climate change. Improving our understanding of these processes requires ice-sheet models that perform well at simulating both past and future ice-sheet evolution. Here, we present version 2.0 of the ice-sheet model IMAU-ICE, which uses the depth-integrated viscosity approximation (DIVA) to solve the stress balance. We evaluate its performance in a range of benchmark experiments, including simple analytical solutions and both schematic and realistic model intercomparison exercises. IMAU-ICE has adopted recent developments in the numerical treatment of englacial stress and sub-shelf melt near the grounding line, which result in good performance in experiments concerning grounding-line migration (MISMIP, MISMIP+) and buttressing (ABUMIP). This makes it a model that is robust, versatile, and user-friendly, which will provide a firm basis for (palaeo-)glaciological research in the coming years.

• van de Wal, Roderik S.W.; Nicholls, Robert J.; Behar, David; McInnes, K.; Stammer, Detlef & Lowe, Jason A. [Show all 28 contributors for this article] (2022). A high-end estimate of sea-level rise for practitioners. Earth's Future. ISSN 2328-4277. 10(11). doi: 10.1029/2022EF002751. Show summary

  Sea level rise (SLR) is a long-lasting consequence of climate change because global anthropogenic warming takes centuries to millennia to equilibrate for the deep ocean and ice sheets. SLR projections based on climate models support policy analysis, risk assessment and adaptation planning today, despite their large uncertainties. The central range of the SLR distribution is estimated by process-based models. However, risk-averse practitioners often require information about plausible future conditions that lie in the tails of the SLR distribution, which are poorly defined by existing models. Here, a community effort combining scientists and practitioners builds on a framework of discussing physical evidence to quantify high-end global SLR for practitioners. The approach is complementary to the IPCC AR6 report and provides further physically plausible high-end scenarios. High-end estimates for the different SLR components are developed for two climate scenarios at two timescales. For global warming of +2°C in 2100 (RCP2.6/SSP1-2.6) relative to pre-industrial values our high-end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in 2300. Similarly, for a (RCP8.5/SSP5-8.5), we estimate up to 1.6 m in 2100 and up to 10.4 m in 2300. The large and growing differences between the scenarios beyond 2100 emphasize the long-term benefits of mitigation. However, even a modest 2°C warming may cause multi-meter SLR on centennial time scales with profound consequences for coastal areas. Earlier high-end assessments focused on instability mechanisms in Antarctica, while here we emphasize the importance of the timing of ice shelf collapse around Antarctica. This is highly uncertain due to low understanding of the driving processes. Hence both process understanding and emission scenario control high-end SLR.

• Zhong, Qirui; Schutgens, Nick; van der Werf, Guido R.; van Noije, Twan; Bauer, Susanne E. & Tsigaridis, Kostas [Show all 20 contributors for this article] (2022). Using modelled relationships and satellite observations to attribute modelled aerosol biases over biomass burning regions. Nature Communications. ISSN 2041-1723. 13(1). doi: 10.1038/s41467-022-33680-4.
• Gangadharan, Nidheesh; Goosse, Hugues; Parkes, David C.; Goelzer, Heiko; Maussion, Fabien & Marzeion, Ben (2022). Process-based estimate of global-mean sea-level changes in the Common Era. Earth System Dynamics (ESD). ISSN 2190-4979. 13(4), p. 1417–1435. doi: 10.5194/esd-13-1417-2022. Show summary

  Although the global-mean sea level (GMSL) rose over the twentieth century with a positive contribution from thermosteric and barystatic (ice sheets and glaciers) sources, the driving processes of GMSL changes during the pre-industrial Common Era (PCE; 1–1850 CE) are largely unknown. Here, the contributions of glacier and ice sheet mass variations and ocean thermal expansion to GMSL in the Common Era (1–2000 CE) are estimated based on simulations with different physical models. Although the twentieth century global-mean thermosteric sea level (GMTSL) is mainly associated with temperature variations in the upper 700 m (86 % in reconstruction and 74 ± 8 % in model), GMTSL in the PCE is equally controlled by temperature changes below 700 m. The GMTSL does not vary more than ±2 cm during the PCE. GMSL contributions from the Antarctic and Greenland ice sheets tend to cancel each other out during the PCE owing to the differing response of the two ice sheets to atmospheric conditions. The uncertainties of sea-level contribution from land-ice mass variations are large, especially over the first millennium. Despite underestimating the twentieth century model GMSL, there is a general agreement between the model and proxy-based GMSL reconstructions in the CE. Although the uncertainties remain large over the first millennium, model simulations point to glaciers as the dominant source of GMSL changes during the PCE.

• Shaw, Jonah; McGraw, Zachary; Bruno, O.; Storelvmo, Trude & Hofer, Stefan (2022). Using Satellite Observations to Evaluate Model Microphysical Representation of Arctic Mixed-Phase Clouds. Geophysical Research Letters. ISSN 0094-8276. 49(3). doi: 10.1029/2021GL096191. Full text in Research Archive
• Bourgeois, Timothée; Goris, Nadine; Schwinger, Jörg & Tjiputra, Jerry (2022). Stratification constrains future heat and carbon uptake in the Southern Ocean between 30°S and 55°S. Nature Communications. ISSN 2041-1723. 13. doi: 10.1038/s41467-022-27979-5. Show summary

  The Southern Ocean between 30°S and 55°S is a major sink of excess heat and anthropogenic carbon, but model projections of these sinks remain highly uncertain. Reducing such uncertainties is required to effectively guide the development of climate mitigation policies for meeting the ambitious climate targets of the Paris Agreement. Here, we show that the large spread in the projections of future excess heat uptake efficiency and cumulative anthropogenic carbon uptake in this region are strongly linked to the models’ contemporary stratification. This relationship is robust across two generations of Earth system models and is used to reduce the uncertainty of future estimates of the cumulative anthropogenic carbon uptake by up to 53% and the excess heat uptake efficiency by 28%. Our results highlight that, for this region, an improved representation of stratification in Earth system models is key to constrain future carbon budgets and climate change projections.

• Lauritzen, Peter Hjort; Kevlahan, N.K.-R.; Toniazzo, Thomas; Eldred, Christopher; Dubos, Thomas & Gassmann, Almut [Show all 20 contributors for this article] (2022). Reconciling and Improving Formulations for Thermodynamics and Conservation Principles in Earth System Models (ESMs). Journal of Advances in Modeling Earth Systems. ISSN 1942-2466. 14(9), p. 1–83. doi: 10.1029/2022MS003117.
• 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.
• Meneghello, Gianluca; Marshall, John; Lique, Camille; Isachsen, Pål Erik; Doddridge, Edward & Campin, Jean-Michel [Show all 8 contributors for this article] (2021). Genesis and decay of mesoscale baroclinic eddies in the seasonally ice-covered Arctic Ocean. Journal of Physical Oceanography. ISSN 0022-3670. 51(1), p. 115–129. doi: 10.1175/JPO-D-20-0054.1. Full text in Research Archive
• Lambert, Erwin; Le Bars, Dewi; Goelzer, Heiko & van de Wal, Roderik S.W. (2021). Correlations Between Sea‐Level Components Are Driven by Regional Climate Change. Earth's Future. ISSN 2328-4277. 9. doi: 10.1029/2020EF001825. Show summary

  The accurate quantification of uncertainties in regional sea-level projections is essential for guiding policy makers. As climate models do not currently simulate total sea level, these uncertainties must be quantified through summation of uncertainties in individual sea-level components. This summation depends on the correlation between the components, which has previously been prescribed or derived from each individual component's dependence on global mean surface temperature. In this study, we quantify, for the first time, regional correlations between sea-level components based on regional climate change projections. We compute regional sea-level projections consistent with climate projections from an ensemble of 14 Earth System Models. From the multi-model spread, we estimate the uncertainty in the regional climate's response to greenhouse forcing. To quantify the total uncertainty, we add the uncertainty in the response of sea-level components to this regional climate change. This approach reveals how regional climate processes impose correlations between sea-level components, affecting the total uncertainty. One example is an anti-correlation between North Atlantic sterodynamic change and Antarctic dynamic mass loss, suggesting a teleconnection established by the large-scale ocean circulation. We find that prescribed correlations, applied in the fifth assessment report of the Intergovernmental Panel on Climate Change, lead to a global overestimation in the uncertainty in regional sea-level projections on the order of 20%. Regionally, this overestimation exceeds 100%. We conclude that accurate uncertainty estimates of regional sea-level change must be based on projections of regional climate change and cannot be derived from global indicators such as global mean surface temperature.

• 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 ...

• Bock, Josué; Michou, Martine; Nabat, Pierre; Abe, Manabu; Mulcahy, Jane P. & Oliviè, Dirk Jan Leo [Show all 13 contributors for this article] (2021). Evaluation of ocean dimethylsulfide concentration and emission in CMIP6 models. Biogeosciences. ISSN 1726-4170. 18(12), p. 3823–3860. doi: 10.5194/bg-18-3823-2021.
• Berends, Constantijn J.; Goelzer, Heiko & van de Wal, Roderik S.W. (2021). The Utrecht Finite Volume Ice-Sheet Model: UFEMISM (version 1.0). Geoscientific Model Development. ISSN 1991-959X. 14, p. 2443–2470. doi: 10.5194/gmd-14-2443-2021. Show summary

  Improving our confidence in future projections of sea-level rise requires models that can simulate ice-sheet evolution both in the future and in the geological past. A physically accurate treatment of large changes in ice-sheet geometry requires a proper treatment of processes near the margin, like grounding line dynamics, which in turn requires a high spatial resolution in that specific region, so that small-scale topographical features are resolved. This leads to a demand for computationally efficient models, where such a high resolution can be feasibly applied in simulations of 105–107 years in duration. Here, we present and evaluate a new ice-sheet model that solves the hybrid SIA–SSA approximation of the stress balance, including a heuristic rule for the grounding-line flux. This is done on a dynamic adaptive mesh which is adapted to the modelled ice-sheet geometry during a simulation. Mesh resolution can be configured to be fine only at specified areas, such as the calving front or the grounding line, as well as specified point locations such as ice-core drill sites. This strongly reduces the number of grid points where the equations need to be solved, increasing the computational efficiency. A high resolution allows the model to resolve small geometrical features, such as outlet glaciers and sub-shelf pinning points, which can significantly affect large-scale ice-sheet dynamics. We show that the model reproduces the analytical solutions or model intercomparison benchmarks for a number of schematic ice-sheet configurations, indicating that the numerical approach is valid. Because of the unstructured triangular mesh, the number of vertices increases less rapidly with resolution than in a square-grid model, greatly reducing the required computation time for high resolutions. A simulation of all four continental ice sheets during an entire 120 kyr glacial cycle, with a 4 km resolution near the grounding line, is expected to take 100–200 wall clock hours on a 16-core system (1600–3200 core hours), implying that this model can be feasibly used for high-resolution palaeo-ice-sheet simulations.

• Mulder, Thomas E.; Goelzer, Heiko; Wubs, Fred W. & Dijkstra, Henk A. (2021). Snowball Earth Bifurcations in a Fully-Implicit Earth System Model. International Journal of Bifurcation and Chaos in Applied Sciences and Engineering. ISSN 0218-1274. 31. doi: 10.1142/S0218127421300172. Show summary

  There is now much geological evidence that the Earth was fully glaciated during several periods in the geological past (about 700Myr ago) and attained a so-called Snowball Earth (SBE) state. Additional support for this idea has come from climate models of varying complexity that show transitions to SBE states and undergo hysteresis under changes in solar radiation. In this paper, we apply large-scale bifurcation analyses to a novel, fully-implicit Earth System Model of Intermediate Complexity (I-EMIC) to study SBE transitions. The I-EMIC contains a primitive equation ocean model, a model for atmospheric heat and moisture transport, a sea ice component and formulations for the adjustment of albedo over snow and ice. With the I-EMIC, high-dimensional branches of the SBE bifurcation diagram are obtained through parameter continuation. We are able to identify stable and unstable equilibria and uncover an intricate bifurcation structure associated with the ice-albedo feedback. Moreover, large-scale linear stability analyses are performed near major bifurcations, revealing the spatial nature of destabilizing perturbations.

• Edwards, Tamsin L.; Nowicki, Sophie; Marzeion, Ben; Hock, Regine; Goelzer, Heiko & Seroussi, Helene [Show all 84 contributors for this article] (2021). Projected land ice contributions to 21st century sea level rise. Nature. ISSN 0028-0836. 593, p. 74–82. doi: 10.1038/s41586-021-03302-y. Show summary

  The land ice contribution to global mean sea level rise has not yet been predicted1 using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models, but primarily used previous-generation scenarios and climate models, and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.

• 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.

• 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.

• Jones, Chris D.; Hickman, Jonathan; Rumbold, Steven T; Walton, Jeremy; Lamboll, Robin & Skeie, Ragnhild Bieltvedt [Show all 49 contributors for this article] (2021). The Climate Response to Emissions Reductions Due to COVID-19: Initial Results From CovidMIP. Geophysical Research Letters. ISSN 0094-8276. 48(8). doi: 10.1029/2020GL091883. Full text in Research Archive Show summary

  Many nations responded to the corona virus disease-2019 (COVID-19) pandemic by restricting travel and other activities during 2020, resulting in temporarily reduced emissions of CO2, other greenhouse gases and ozone and aerosol precursors. We present the initial results from a coordinated Intercomparison, CovidMIP, of Earth system model simulations which assess the impact on climate of these emissions reductions. 12 models performed multiple initial-condition ensembles to produce over 300 simulations spanning both initial condition and model structural uncertainty. We find model consensus on reduced aerosol amounts (particularly over southern and eastern Asia) and associated increases in surface shortwave radiation levels. However, any impact on near-surface temperature or rainfall during 2020–2024 is extremely small and is not detectable in this initial analysis. Regional analyses on a finer scale, and closer attention to extremes (especially linked to changes in atmospheric composition and air quality) are required to test the impact of COVID-19-related emission reductions on near-term climate.

• Liddicoat, Spencer; Wiltshire, Andy; Jones, Chris D.; Arora, Vivek K; Brovkin, Victor & Cadule, Patricia [Show all 13 contributors for this article] (2021). Compatible fossil fuel CO2 emissions in the CMIP6 Earth system models’ historical and shared socioeconomic pathway experiments of the twenty-first century. Journal of Climate. ISSN 0894-8755. doi: 10.1175/JCLI-D-19-0991.1. Show summary

  We present the compatible CO2 emissions from fossil fuel (FF) burning and industry, calculated from the historical and Shared Socioeconomic Pathway (SSP) experiments of nine Earth system models (ESMs) participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6). The multimodel mean FF emissions match the historical record well and are close to the data-based estimate of cumulative emissions (394 ± 59 GtC vs 400 ± 20 GtC, respectively). Only two models fall inside the observed uncertainty range; while two exceed the upper bound, five fall slightly below the lower bound, due primarily to the plateau in CO2 concentration in the 1940s. The ESMs’ diagnosed FF emission rates are consistent with those generated by the integrated assessment models (IAMs) from which the SSPs’ CO2 concentration pathways were constructed; the simpler IAMs’ emissions lie within the ESMs’ spread for seven of the eight SSP experiments, the other being only marginally lower, providing confidence in the relationship between the IAMs’ FF emission rates and concentration pathways. The ESMs require fossil fuel emissions to reduce to zero and subsequently become negative in SSP1-1.9, SSP1-2.6, SSP4-3.4, and SSP5-3.4over. We also present the ocean and land carbon cycle responses of the ESMs in the historical and SSP scenarios. The models’ ocean carbon cycle responses are in close agreement, but there is considerable spread in their land carbon cycle responses. Land-use and land-cover change emissions have a strong influence over the magnitude of diagnosed fossil fuel emissions, with the suggestion of an inverse relationship between the two.

• Brenna, Hans; Kutterolf, Steffen; Mills, Michael; Niemeier, Ulrike; Timmreck, Claudia & Krüger, Kirstin (2021). Decadal Disruption of the QBO by Tropical Volcanic Supereruptions. Geophysical Research Letters. ISSN 0094-8276. 48(5), p. 1–13. doi: 10.1029/2020GL089687. Show summary

  The Los Chocoyos (14.6°N, 91.2°W) supereruption happened ∼75,000 years ago in Guatemala and was one of the largest eruptions of the past 100,000 years. It emitted enormous amounts of sulfur, chlorine, and bromine, with multi‐decadal consequences for the global climate and environment. Here, we simulate the impact of a Los Chocoyos‐like eruption on the quasi‐biennial oscillation (QBO), an oscillation of zonal winds in the tropical stratosphere, with a comprehensive aerosol chemistry Earth System Model. We find a ∼10‐year disruption of the QBO starting 4 months post eruption, with anomalous easterly winds lasting ∼5 years, followed by westerlies, before returning to QBO conditions with a slightly prolonged periodicity. Volcanic aerosol heating and ozone depletion cooling leads to the QBO disruption and anomalous wind regimes through radiative changes and wave‐mean flow interactions. Different model ensembles, volcanic forcing scenarios and results of a second model back up the robustness of our results.

• Keen, Ann; Blockley, Ed; Bailey, David A.; Debernard, Jens Boldingh; Bushuk, Mitchell & Delhaye, Steve [Show all 18 contributors for this article] (2021). An inter-comparison of the mass budget of the Arctic sea ice in CMIP6 models. The Cryosphere. ISSN 1994-0416. 15, p. 951–982. doi: 10.5194/tc-15-951-2021.
• 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.

• Payne, Antony; Nowicki, Sophie; Abe-Ouchi, Ayako; Agosta, Cécilie; Alexander, Patrick & Albrecht, Torsten [Show all 63 contributors for this article] (2021). Future sea level change under coupled model intercomparison project phase 5 and phase 6 scenarios from the Greenland and Antarctic ice sheets. Geophysical Research Letters. ISSN 0094-8276. 48(16). doi: 10.1029/2020GL091741. Show summary

  Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming.

• Michel, Clio; Sorteberg, Asgeir; Eckhardt, Sabine; Weijenborg, Christian; Stohl, Andreas & Cassiani, Massimo (2021). Characterization of the atmospheric environment during extreme precipitation events associated with atmospheric rivers in Norway - Seasonal and regional aspects. Weather and Climate Extremes. ISSN 2212-0947. 34. doi: 10.1016/j.wace.2021.100370. Full text in Research Archive Show summary

  Extreme precipitation events in Norway in all seasons are often linked to atmospheric rivers (AR). We show that during the period 1979–2018 78.5% of the daily extreme precipitation events in Southwestern Norway are linked to ARs, this percentage decreasing to 59% in the more northern coastal regions and ~40% in the inland regions. The association of extreme precipitation with AR occurs most often in fall for the coastal areas and in summer inland. All Norwegian regions experience stronger winds and 1–2°C increase of the temperature at 850 hPa during AR events compared to the climatology, the extreme precipitation largely contributing to the wet climatology (only considering rainy days) in Norway but also in Denmark and Sweden when the rest of Europe is dry. A cyclone is found nearby the AR landfall point in 70% of the cases. When the cyclone is located over the British Isles, as it is typically the case when ARs reach Southeastern Norway, it is associated with cyclonic Rossby wave breaking whereas when the ARs reach more northern regions, anticyclonic wave breaking occurs over Northern Europe. Cyclone-centered composites show that the mean sea level pressure is not significantly different between the eight Norwegian regions, that baroclinic interaction can still take place although the cyclone is close to its decay phase and that the maximum precipitation occurs ahead of the AR. Lagrangian air parcel tracking shows that moisture uptake mainly occurs over the North Atlantic for the coastal regions with an additional source over Europe for the more eastern and inland regions.

• Hagen, Jenny Sjåstad; Leblois, Etienne; Lawrence, Deborah; Solomatine, Dimitri & Sorteberg, Asgeir (2021). Identifying major drivers of daily streamflow from large-scale atmospheric circulation with machine learning. Journal of Hydrology. ISSN 0022-1694. 596. doi: 10.1016/j.jhydrol.2021.126086.
• 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.

• Van Breedam, Jonas; Goelzer, Heiko & Huybrechts, Philippe (2020). Semi-equilibrated global sea-level change projections for the next 10 000 years. Earth System Dynamics (ESD). ISSN 2190-4979. 11(4), p. 953–976. doi: 10.5194/esd-11-953-2020.
• 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
• J. Smith, Christopher; J. Kramer, Ryan; Myhre, Gunnar; Alterskjær, Kari; Collins, William J. & Sima, Adriana [Show all 29 contributors for this article] (2020). Effective radiative forcing and adjustments in CMIP6 models. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(16), p. 9591–9618. doi: 10.5194/acp-20-9591-2020. Show summary

  The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.

• McGraw, Zachary; Storelvmo, Trude; Samset, Bjørn Hallvard & Stjern, Camilla Weum (2020). Global radiative impacts of black carbon acting as ice nucleating particles. Geophysical Research Letters. ISSN 0094-8276. 47(20), p. 1–9. doi: 10.1029/2020GL089056. Full text in Research Archive Show summary

  Black carbon (BC) aerosols from incomplete combustion generally warm the climate, but the magnitudes of their various interactions with climate are still uncertain. A key knowledge gap is their role as ice nucleating particles (INPs), enabling ice formation in clouds. Here we assess the global radiative impacts of BC acting as INPs, using simulations with the Community Earth System Model 2 climate model updated to include new laboratory‐based ice nucleation parameterizations. Overall, we find a moderate cooling through changes to stratiform cirrus clouds, counteracting the well‐known net warming from BC's direct scattering and absorption of radiation. Our best estimates indicate that BC INPs generally thin cirrus by indirectly inhibiting the freezing of solution aerosol, with a global net radiative impact of −0.13 ± 0.07 W/m2. Sensitivity tests of BC amounts and ice nucleating efficiencies, and uncertainties in the environment where ice crystals form, show a potential range of impacts from −0.30 to +0.02 W/m2.

• Xie, Xiaoning; Myhre, Gunnar; Liu, Xiaodong; Li, Xinzhou; Shi, Zhengguo & Wang, Hongli [Show all 11 contributors for this article] (2020). Distinct responses of Asian summer monsoon to black carbon aerosols and greenhouse gases. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(20), p. 11823–11839. doi: 10.5194/acp-20-11823-2020. Full text in Research Archive Show summary

  Black carbon (BC) aerosols emitted from natural and anthropogenic sources induce positive radiative forcing and global warming, which in turn significantly affect the Asian summer monsoon (ASM). However, many aspects of the BC effect on the ASM remain elusive and largely inconsistent among previous studies, which is strongly dependent on different low-level thermal feedbacks over the Asian continent and the surrounding ocean. This study examines the response of the ASM to BC forcing in comparison with the effect of doubled greenhouse gases (GHGs) by analyzing the Precipitation Driver Response Model Intercomparison Project (PDRMIP) simulations under an extremely high BC level (10 times modern global BC emissions or concentrations, labeled BC×10) from nine global climate models (GCMs). The results show that although BC and GHGs both enhance the ASM precipitation minus evaporation (P−E; a 13.6 % increase for BC forcing and 12.1 % for GHGs from the nine-model ensemble, respectively), there exists a much larger uncertainty in changes in ASM P−E induced by BC than by GHGs. The summer P−E is increased by 7.7 % to 15.3 % due to these two forcings over three subregions, including East Asian, South Asian and western North Pacific monsoon regions. Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P−E induced by BC and GHGs. The change in ASM P−E by BC is dominated by the dynamic effect due to the enhanced large-scale monsoon circulation, whereas the GHG-induced change is dominated by the thermodynamic effect through increasing atmospheric water vapor. Radiative forcing of BC significantly increases the upper-level atmospheric temperature over the Asian region to enhance the upper-level meridional land–sea thermal gradient (MLOTG), resulting in a northward shift of the upper-level subtropical westerly jet and an enhancement of the low-level monsoon circulation, whereas radiative forcing of GHGs significantly increases the tropical upper-level temperature, which reduces the upper-level MLOTG and suppresses the low-level monsoonal circulation. Hence, our results indicate a different mechanism of BC climate effects under the extremely high BC level: that BC forcing significantly enhances the upper-level atmospheric temperature over the Asian region, determining ASM changes, instead of low-level thermal feedbacks as indicated by previous studies.

• 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.

• Hopkins, Frances E.; Suntharalingam, Parvadha; Gehlen, Marion; Andrews, Oliver D.; Archer, Stephen D. & Bopp, Laurent [Show all 23 contributors for this article] (2020). The impacts of ocean acidification on marine trace gases and the implications for atmospheric chemistry and climate. Proceedings of the Royal Society. Mathematical, Physical and Engineering Sciences. ISSN 1364-5021. 476(2237). doi: 10.1098/rspa.2019.0769.
• 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.

• Davy, Richard & Outten, Stephen (2020). The Arctic Surface Climate in CMIP6: Status and Developments since CMIP5. Journal of Climate. ISSN 0894-8755. 33(18), p. 8047–8068. doi: 10.1175/JCLI-D-19-0990.1.
• MacDougall, Andrew; Frölicher, Thomas L.; Jones, Chris D.; Rogelj, Joeri; Damon Matthews, H. & Zickfeld, Kirsten [Show all 29 contributors for this article] (2020). Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2. Biogeosciences. ISSN 1726-4170. doi: 10.5194/bg-17-2987-2020.
• Brenna, Hans; Kutterolf, Steffen; Mills, Michael J. & Krüger, Kirstin (2020). The potential impacts of a sulfur- And halogen-rich supereruption such as Los Chocoyos on the atmosphere and climate. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 20(11), p. 6521–6539. doi: 10.5194/acp-20-6521-2020. Full text in Research Archive
• Rückamp, Martin; Goelzer, Heiko & Humbert, Angelika (2020). Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the Alfred Wegener Institute (AWI) contribution to ISMIP6 Greenland using the Ice-sheet and Sea-level System Model (ISSM). The Cryosphere. ISSN 1994-0416. doi: 10.5194/tc-14-3309-2020.
• Goelzer, Heiko; Nowicki, Sophie; Payne, Anthony J.; Larour, Eric; Seroussi, Hélène & Lipscomb, William H. [Show all 42 contributors for this article] (2020). The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6. The Cryosphere. ISSN 1994-0416. doi: 10.5194/tc-14-3071-2020.

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• Bourgeois, Timothée; Goris, Nadine; Schwinger, Jörg & Tjiputra, Jerry (2024). Emergent constraint on future anthropogenic carbon and excess heat uptake in the Southern Ocean. Show summary

  The Southern Ocean is a major sink of anthropogenic carbon and excess heat. In this region, the Earth system model projections of these sinks provided by the CMIP5 and CMIP6 scenario experiments show a large model spread. This contributes significantly to the large uncertainties in the overall climate sensitivity and remaining carbon budgets for ambitious climate targets. Hence, a reduction in the uncertainty of the future Southern Ocean carbon and heat sinks is urgently needed. Globally, Bronselaer and Zanna (2020) identified an emergent coupling between anthropogenic carbon and excess heat uptake, highlighting that the passive-tracer behavior of these two quantities is dominant under high-emissions scenarios. This coupling indicates that the use of a single observational constraint might be sufficient to reduce projection uncertainties in both anthropogenic carbon and excess heat uptake. Here, we use this approach for the northern limb of the Southern Ocean (30°S-55°S) where the subduction of intermediate and mode water is known to drive carbon and heat uptake. We found that, in this region, the variations in the models’ contemporary water-column stability over the first 2000 m is highly correlated to both their future anthropogenic carbon uptake and excess heat uptake efficiency. Using observational data of water-column stability, we reduce the uncertainty of future estimates of (1) the cumulative anthropogenic carbon uptake by up to 53% and (2) the excess heat uptake efficiency by 28%. Independent studies have found similar constraints in the Southern Ocean and globally, strengthening our findings (Liu et al., 2023; Newsom et al., 2023; Terhaar et al., 2021, 2022), and pinpointing that a better representation of water-column stratification in Earth system models is essential to improve future anthropogenic climate change projections. Bourgeois, T., Goris, N., Schwinger, J., and Tjiputra, J. F.: Stratification constrains future heat and carbon uptake in the Southern Ocean between 30°S and 55°S, Nat Commun, 13, 340, https://doi.org/10.1038/s41467-022-27979-5, 2022. Bronselaer, B. and Zanna, L.: Heat and carbon coupling reveals ocean warming due to circulation changes, Nature, 584, 227–233, https://doi.org/10.1038/s41586-020-2573-5, 2020. Liu, M., Soden, B. J., Vecchi, G. A., and Wang, C.: The Spread of Ocean Heat Uptake Efficiency Traced to Ocean Salinity, Geophys. Res. Lett., 50, e2022GL100171, https://doi.org/10.1029/2022GL100171, 2023. Newsom, E., Zanna, L., and Gregory, J.: Background Pycnocline Depth Constrains Future Ocean Heat Uptake Efficiency, Geophys. Res. Lett., 50, e2023GL105673, https://doi.org/10.1029/2023GL105673, 2023. Terhaar, J., Frölicher, T. L., and Joos, F.: Southern Ocean anthropogenic carbon sink constrained by sea surface salinity, Sci. Adv., 7, eabd5964, https://doi.org/10.1126/sciadv.abd5964, 2021. Terhaar, J., Frölicher, T. L., and Joos, F.: Observation-constrained estimates of the global ocean carbon sink from Earth system models, Biogeosciences, 19, 4431–4457, https://doi.org/10.5194/bg-19-4431-2022, 2022.

• He, Yanchun; Torsvik, Tomas & Gupta, Alok Kumar (2023). ESMValTool Workshop 2023.
• Booge, Dennis; Tjiputra, Jerry; Olivie, Dirk Jan Leo; Birgit, Quack & Krüger, Kirstin (2023). Global and regional marine bromoform emissions in a fully coupled ocean-atmosphere-model. Show summary

  Bromoform (CHBr3) is one of the most important precursors of atmospheric reactive bromine with an atmospheric lifetime of ~20 days. Natural production, being the main source of oceanic CHBr3, is high at the coasts and in open ocean upwelling regions due to production by macroalgae and phytoplankton. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and their emissions are still poorly constrained in observations and are mostly neglected in Earth System Model (ESM) climate projections. Here, we show first model results of fully coupled ocean-atmosphere bromoform interactions in the Norwegian ESM (NorESM) with the ocean model BLOM and the ocean biogeochemistry component iHAMOCC for the CMIP6 historical period from 1850 to 2014. Our results are validated using oceanic and atmospheric measurements listed in the HalOcAt (Halocarbons in the Ocean and Atmosphere) data base and show an overall good agreement with those observations in open ocean regions. The NorESM open ocean emissions of CHBr3 are higher than previously published emission estimates from bottom-up approaches. Moreover, the emissions are mainly positive (sea-to-air fluxes) driven by the oceanic production, sea surface temperature and wind speed, dependent on season and location. However, during low-productive winter seasons, model results also show local negative fluxes (air-to-sea fluxes) in high latitudes, suggesting some oceanic regions to be a sink of atmospheric bromoform. Driving factors will be shown for different case studies, e.g. the tropical West Pacific, which is a hot spot for oceanic bromine delivery to the stratosphere. How to cite: Booge, D., Tjiputra, J., Olivié, D., Quack, B., Schulz, M., and Krüger, K.: Global and regional marine bromoform emissions in a fully coupled ocean-atmosphere-model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12225, https://doi.org/10.5194/egusphere-egu23-12225, 2023.

• 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. .
• Goelzer, Heiko (2023). Ice sheets, sea-level and climate change.
• Goelzer, Heiko; Langebroek, Petra Margaretha; Born, Andreas; Haubner, Konstanze; Hofer, Stefan & Storelvmo, Trude (2023). Coupled Greenland ice sheet-climate simulations with the Norwegian Earth System Model (NorESM2).
• Goelzer, Heiko (2023). Lecture on ice sheets.
• Eckhardt, Sabine; Svendby, Tove Marit; Steensen, Birthe Marie Rødssæteren; Myhre, Gunnar; Gjermundsen, Ada & Oliviè, Dirk Jan Leo (2023). Moisture transport into the Arctic in a past and future climate.
• Goelzer, Heiko; Langebroek, Petra Margaretha; Born, Andreas; Haubner, Konstanze; Hofer, Stefan & Storelvmo, Trude (2023). Coupled Greenland ice sheet-climate simulations with the Norwegian Earth System Model (NorESM2).
• Gjermundsen, Ada; Bentsen, Mats; Oliviè, Dirk Jan Leo; Nummelin, Aleksi Henrynpoika; Seland, Øyvind & Schulz, Michael (2023). The Norwegian Earth System Model.
• Graff, Lise Seland; Parding, Kajsa & Landgren, Oskar Andreas (2023). Evaluating CMIP6 models with a simple climatology score.
• Oliviè, Dirk Jan Leo; Seland, Øyvind; Tjiputra, Jerry & Schwinger, Jörg (2023). Lessons from COVID-19 emission reduction simulations with NorESM2 .
• Oliviè, Dirk Jan Leo; Seland, Øyvind; Krüger, Kirstin & Schulz, Michael (2023). Analysis of NorESM2 full-chemistry simulation of the historical period (1850–2014).
• Tjiputra, Jerry; Negrel, Jean & Olsen, Are (2023). Detecting anthropogenic climate change signals of marine stressors in the interior.
• Tjiputra, Jerry (2023). Detection timescales of environmental stressors in the interior ocean.
• Tjiputra, Jerry; Goris, Nadine; Schwinger, Jörg; Bourgeois, Timothée; Ayar, Pradeebane Vaittinada & Johannsen, Klaus (2023). Constraining ocean carbon sink projections in CMIP6 models.
• Guo, Chuncheng; Bentsen, Mats; Ilicak, Mehmet & Nummelin, Aleksi Henrynpoika (2022). CMIP6/OMIP simulations of the Arctic Ocean and Resolution effects.
• Tjiputra, Jerry; Booge, Dennis; Oliviè, Dirk Jan Leo; Quack, Birgit & Krüger, Kirstin (2022). Modeling bromoform in Norwegian Earth system model.
• Heinze, Christoph (2022). Triple threats to our ocean - the triple blow and how one can try to address it:ocean warming, acidification, and deoxygenation .
• 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.
• Heinze, Christoph (2022). Ocean tipping points - an overview.
• Krüger, Kirstin; Booge, Dennis; Quack, Birgit; Tjiputra, Jerry & Olivie, Dirk (2022). Future stratospheric halogen loading and ozone cycle: Modelling biogenic halocarbons in the ocean and their impact on the atmosphere. Show summary

  Halogenated very short-lived substances (VSLSs) contribute to the tropospheric and stratospheric halogen burden, take part in ozone depletion, and, thus, impact climate. The contribution of oceanic VSLSs is estimated to be 10–40 % of the current total stratospheric bromine. Among them, is bromoform (CHBr3) one the most important precursor of atmospheric reactive bromine with a lifetime of ~20 days in the atmosphere. Oceanic sources of bromoform are highest at the coasts and in the open ocean in upwelling regions due to macroalgae and phytoplankton production. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global bromoform production in the ocean and their emissions are still poorly constrained in observations and are mostly neglected in chemistry climate and Earth System Models (ESMs). Here, we show first model results following Stemmler et al (2015) but adding the full coupling of the oceanic bromoform production with the atmosphere through air-sea gas exchange and atmospheric chemistry in the Norwegian ESM (NorESM) with the ocean model BLOM and the biogeochemistry component iHAMOCC. We run NorESM for the CMIP6 historic scenario from 1850 to 2014. Our results reveal higher global bromoform emissions to the atmosphere than previously reported from bottom up approaches. Comparing our modelled bromoform results with HalOcAt observations reveal an overall good agreement for the open ocean and the seasonal cycle. Case studies for the tropical Indian Ocean and Pacific will be shown, which are hot spots in the ocean and for the stratospheric bromine delivery.

• Krüger, Kirstin; Brenna, Hans; Fuglestvedt, Herman; Zhuo, Zhihong; Mills, Mike & Niemeier, Ulrike [Show all 7 contributors for this article] (2022). How large has a volcanic eruption to be to disrupt the QBO? Show summary

  The dominating circulation phenomenon in the tropical stratosphere is the quasi-biennial oscillation (QBO), an approximately 28 months oscillation of alternating easterly or westerly winds centered at the equator. Volcanic aerosols may have an impact on the QBO phase as was observed for the Pinatubo eruption, which showed a “remarkably” prolonged Easterly wind regime. In contrast, geo-engineering studies model a prolonged Westerly phase or a shut-down of the QBO due to the artificial injection of sulfate aerosols. Extremely large volcanic eruptions which inject several 10s to 100s Tg SO2 might therefore have the potential to disturb the QBO. In addition, recent observations revealed two anomalous disruptions of the QBO in the 2010s with anomalous westerly winds probably due to Rossby wave propagating from the extratropics. We use an Earth System Model taking volcanic aerosol chemistry climate interactions into account to study the QBO response to violent volcanic eruptions. Simulating a tropical supereruption with 1000 Tg SO2 and halogens injection into the stratosphere reveals a disruption of the QBO for up to 10 years first with anomalous Easterlies followed by anomalous Westerlies before returning to a QBO regime with slightly longer period. Volcanic aerosol heating and ozone depletion cooling lead to the QBO disruption and anomalous wind regimes through radiation and wave-mean flow interactions. Here, we present a new set of sulfur- and halogen-rich volcanic eruptions experiments with 17 and 200 Tg SO2 injections into the tropical and Northern Hemisphere extratropics during January and July season to answer the above raised question.

• 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.
• Oliviè, Dirk Jan Leo (2022). The ESM2025 project and interactive methane modelling .
• Oliviè, Dirk Jan Leo; Seland, Øyvind; Krüger, Kirstin & Schulz, Michael (2022). Implementation of gas-phase chemistry in NorESM2.
• 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 .
• 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.
• Heinze, Christoph (2021). EU H2020 Project COMFORT.
• 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. .
• 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.
• 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.
• 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.
• Auganæs, Sigrid Marie & Krüger, Kirstin (2023). Ozone Above the Tropical Atlantic Ocean. Universitetet i Oslo. Show summary

  Ozone (O3) plays a crucial role in the Earth’s atmosphere, both in the stratosphere and the troposphere. This thesis investigates tropospheric ozone above the tropical Atlantic Ocean using observations, trajectories and the Norwegian Earth system model (NorESM). The research questions addressed include the presence of a minimum in tropospheric ozone over the tropical Atlantic, the comparison of ozone profiles between ship campaigns and land-based stations, the variability of ozone above the Atlantic compared to other ocean basins, and the performance of NorESM in representing observed ozone features. Observations from the SO287 CONNECT ship campaign crossing the tropical Atlantic Ocean reveal no ozone minimum similar to that previously observed in the tropical West Pacific. Ozone concentrations over the tropical Atlantic ranged from 25 to 80 parts per billion (ppb), with an average of 45 ppb throughout the troposphere. The sampled air masses exhibited characteristics from different regions, indicating biomass burning and stratospheric influences. Comparisons with nearby SHADOZ stations confirmed the successful sampling of the same air mass by the ship campaign and the Paramaribo SHADOZ station. Furthermore, the ozone concentrations from ship campaigns in different tropical ocean basins, revealed higher ozone concentrations above the tropical Atlantic compared to other tropical ocean basins. The NorESM model, newly including the MOZART-TS1 chemistry scheme, captures the expected patterns of surface ozone and wave-one distributions, with some deviations. However, the model simulates the abrupt increase to stratospheric ozone at lower altitudes than observed, likely due to coarse resolution in the upper troposphere and stratosphere.

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