ALBERT

Description: The surface of the world’s oceans has been warming since the beginning of industrialization. In addition to this, multidecadal sea surface temperature (SST) variations of internal origin exist. Evidence suggests that the North Atlantic Ocean exhibits the strongest multidecadal SST variations and that these variations are connected to the overturning circulation. This work investigates the extent to which these internal multidecadal variations have contributed to enhancing or diminishing the trend induced by the external radiative forcing, globally and in the North Atlantic. A model study is carried out wherein the analyses of a long control simulation with constant radiative forcing at preindustrial level and of an ensemble of simulations with historical forcing from 1850 until 2005 are combined. First, it is noted that global SST trends calculated from the different historical simulations are similar, while there is a large disagreement between the North Atlantic SST trends. Then the control simulation is analyzed, where a relationship between SST anomalies and anomalies in the Atlantic meridional overturning circulation (AMOC) for multidecadal and longer time scales is identified. This relationship enables the extraction of the AMOC-related SST variability from each individual member of the ensemble of historical simulations and then the calculation of the SST trends with the AMOC-related variability excluded. For the global SST trends this causes only a little difference while SST trends with AMOC-related variability excluded for the North Atlantic show closer agreement than with the AMOC-related variability included. From this it is concluded that AMOC variability has contributed significantly to North Atlantic SST trends since the mid nineteenth century.

Description: Surface mass balance (SMB) is the builder of the Greenland ice sheet and the driver of ice dynamics. Quantifying the past, present and future state of SMB is important to understand the drivers and climatic processes that control SMB, and to both initialize and run ice sheet models which will help clarify sea level rise, and how likely changes in ice sheet extent feedback within the climate system. Regional climate models (RCMs) and climate reanalysis are used to quantify SMB estimates. Although different models have different spatial and temporal biases and may include different processes giving significant uncertainty in both SMB and the ice sheet dynamic response to it, all RCMs show a recent declining trend in SMB from the Greenland ice sheet, driven primarily by enhanced melt rates. Here, we present new simulations of the Greenland ice sheet SMB at 5 km resolution from the RCM HIRHAM5. The RCM is driven by the ERA-Interim reanalysis and the global climate model (GCM) EC-Earth v2.3 to make future projections for climate scenarios RCP8.5 and RCP4.5. Future estimates of SMB are affected by biases in driving global climate models, and feedbacks between the ice sheet surface and the global and regional climate system are neglected, likely resulting in significant underestimates of melt and precipitation over the ice sheet. These challenges will need to be met to better estimate the role climate change will have in modulating the surface mass balance of the Greenland ice sheet.

Description: International Workshop on Polar-lower Latitude Linkages in Weather and Climate Prediction What: Eighty experts from twenty different countries met to assess recent progress in, and new directions for, our understanding of the mechanisms governing polar-lower latitude linkages and their role in weather and climate prediction including services. When: 10–12 December 2014 Where: Barcelona, Spain

Description: We analyze simulated sea ice changes in eight different Earth System Models that have conducted experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP). The simulated response of balancing abrupt quadrupling of CO2 (abrupt4xCO2) with reduced shortwave radiation successfully moderates annually averaged Arctic temperature rise to about 1°C, with modest changes in seasonal sea ice cycle compared with the preindustrial control simulations (piControl). Changes in summer and autumn sea ice extent are spatially correlated with temperature patterns but much less in winter and spring seasons. However, there are changes of ±20% in sea ice concentration in all seasons, and these will induce changes in atmospheric circulation patterns. In summer and autumn, the models consistently simulate less sea ice relative to preindustrial simulations in the Beaufort, Chukchi, East Siberian, and Laptev Seas, and some models show increased sea ice in the Barents/Kara Seas region. Sea ice extent increases in the Greenland Sea, particularly in winter and spring and is to some extent associated with changed sea ice drift. Decreased sea ice cover in winter and spring in the Barents Sea is associated with increased cyclonic activity entering this area under G1. In comparison, the abrupt4xCO2 experiment shows almost total sea ice loss in September and strong correlation with regional temperatures in all seasons consistent with open ocean conditions. The tropospheric circulation displays a Pacific North America pattern-like anomaly with negative phase in G1-piControl and positive phase under abrupt4xCO2-piControl.

Description: The methods to quantify equilibrium climate sensitivity are still debated. We collect millennial-length simulations of coupled climate models and show that the global mean equilibrium warming is higher than those obtained using extrapolation methods from shorter simulations. Specifically, 27 simulations with 15 climate models forced with a range of CO2 concentrations show a median 17% larger equilibrium warming than estimated from the first 150 years of the simulations. The spatial patterns of radiative feedbacks change continuously, in most regions reducing their tendency to stabilizing the climate. In the equatorial Pacific, however, feedbacks become more stabilizing with time. The global feedback evolution is initially dominated by the tropics, with eventual substantial contributions from the mid-latitudes. Time-dependent feedbacks underscore the need of a measure of climate sensitivity that accounts for the degree of equilibration, so that models, observations, and paleo proxies can be adequately compared and aggregated to estimate future warming.

Description: Recent observations have indicated rapidly increasing mass loss from the Greenland Ice Sheet. To explore the interactions and feedbacks of the ice sheets in the climate system, it is important to develop coupled climate-ice sheet models. The integration of an ice sheet model in a global model is challenging, and, currently, relatively few climate models include a two-way coupling to a dynamical ice sheet model. In this work package, we have continued developing the coupled ice sheet-climate model system comprising the global climate model EC-Earth and the Parallel Ice Sheet Model (PISM) for Greenland. The new model system, EC-Earth3-GrIS, is upgraded to include the recent model versions, EC-Earth3 and PISM version 1.2. In addition, a new module has been developed to handle the exchange of information between the ice sheet model and EC-Earth using the OASIS3- MCT software interface. The new module reads output from the ice sheet model and exchanges the fields with the relevant EC-Earth components. The ice sheet mask and topography are provided to the atmosphere and land surface components. The heat and freshwater fluxes from basal melt and ice discharge are provided to the ocean module via the runoff-mapper that routes surface runoff into the ocean. The new module also prepares the forcing fields for the ice sheet model, i.e., subsurface temperature and surface mass balance. These fields are calculated in EC- Earth3 using a land ice surface parameterization, developed explicitly for the Greenland ice sheet. The parameterization contains a responsive snow and ice albedo scheme and includes land ice characteristics in the calculation of heat and energy transfer at the surface. Experiments with and without the land ice surface parameterization have been carried out for preindustrial and present-day conditions to assess the influence of the surface parameterization on the calculated surface mass balance. The results show that the ice sheet responds stronger and more realistically to forcing changes when the new surface parameterization is used. Besides the model development, the results from experiments with the first model version, EC- Earth-PISM, have been analyzed. These results stress that a decent surface scheme with a responsive snow albedo scheme is necessary for investigating mass balance changes of the Greenland Ice Sheet. Overall, our results indicate that the feedbacks induced by the interactive ice sheet have a significant influence on Arctic climate change under warming conditions. In warm scenarios where the CO2 level is raised to four times the preindustrial level, the coupled model has a colder Arctic surface, a fresher ocean, and more sea-ice in winter.

Description: Assessment of the projected future climate change relies on experiments using complex climate models (i.e., Earth System Models) that can realistically represent the Earth climate system. In this work package we made great efforts to enhance our capability in climate modelling using the family of the EC-Earth3 Earth System Model, and to increase our contribution to the international Coupled Model Intercomparison Project phase 6 (CMIP6). The contributions include performing another set of climate change simulations for the historical period (https://www.dmi.dk/fileadmin/Rapporter/2021/DMI_Report_21-33.pdf1850-2014) followed by four future scenarios (i.e., SSP5-8.5, SSP3-7.0, SSP2-4.5, SSp1-2.6, respectively) using the Earth System Model EC- Earth3-Veg; Extending the climate change simulation under the high-end emission scenario SSP5- 8.5 to year 2300; and performing the new CMIP6-endorsed CovidMIP aiming at assessing the climate impact of the emission reduction due to COVID19 pandemic. Archiving the CMIP6 experiment data following the CMIP6 standards and compliance on the Earth System Federation Grid (ESGF) data nodes is important to ensure the contribution to CMIP6 is available for scientists worldwide to access the data for a variety of applications from assessment and understanding of climate change, to studies of climate impacts and mitigation. We have worked a great deal to prepare the above mentioned and other CMIP6 simulation data for publishing on the DMI's ESGF data node. The processes involve in reformatting the simulation data into the CMIP standard and quality control the reformatted data to ensure their correctness. With our efforts and contributions to CMIP6, we have joined several multi-model multi-member ensemble analyses using the CMIP6 experiment ensembles. We have quantified the future climate changes under variety of future scenarios, and analyzed climate response to the COVID19 related emission reduction. We have also participated in the documentation of the EC-Earth3 model development and performance. These studies have led to a number of scientific papers. We foresee our contributed simulation ensembles, as subsets in the CMIP6 experiment ensembles, have contributed and will continue to contribute to many climate change assessments and studies for many years ahead. www.dmi.dk

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Suo, L., Gastineau, G., Gao, Y., Liang, Y.-C., Ghosh, R., Tian, T., Zhang, Y., Kwon, Y.-O., Otterå, O., Yang, S., & Matei, D. Simulated contribution of the interdecadal Pacific oscillation to the west Eurasia cooling in 1998–2013. Environmental Research Letters, 17(9), (2022): 094021, https://doi.org/10.1088/1748-9326/ac88e5.

Description: Large ensemble simulations with six atmospheric general circulation models involved are utilized to verify the interdecadal Pacific oscillation (IPO) impacts on the trend of Eurasian winter surface air temperatures (SAT) during 1998–2013, a period characterized by the prominent Eurasia cooling (EC). In our simulations, IPO brings a cooling trend over west-central Eurasia in 1998–2013, about a quarter of the observed EC in that area. The cooling is associated with the phase transition of the IPO to a strong negative. However, the standard deviation of the area-averaged SAT trends in the west EC region among ensembles, driven by internal variability intrinsic due to the atmosphere and land, is more than three times the isolated IPO impacts, which can shadow the modulation of the IPO on the west Eurasia winter climate.

Description: This work is funded by the JPI Climate-Oceans ROADMAP and the Blue‐Action Project (European Union's Horizon 2020 research and innovation program, 727852). The CAM6-Nor simulations were performed on resources provided by UNINETT Sigma2—the National Infrastructure for High Performance Computing and Data Storage in Norway (nn2343k, NS9015K). The simulations of IAP4.1 were supported by National Key R&D Program of China 2017YFE0111800.