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The data used in this study were mainly obtained from the CMIP6 archive. All available ensembles of the 41 CMIP6 coupled models that provide sea ice concentration from both SSP2-4.5 and SSP5-8.5 experiments were used (Table 1). Simulations for the period 1950–2014 were from historical experiments. Future projections were driven by external forcing under the SSP2-4.5 and SSP5-8.5 scenarios, which represent medium and high emission pathways with effective radiative forcings of 4.5 and 8.5 W m–2 in 2100, respectively (O'Neill et al., 2016; Riahi et al., 2017). To investigate the influence of model resolution on sea ice simulation in the Barents Sea, the simulations of eight high-resolution coupled models from the CMIP6 High Resolution Model Intercomparison Project (HighResMIP) (Haarsma et al., 2016) (Table 2) were also used in this study.
No. Model ID Atmospheric
ModelSea-ice Model Ocean Model Ocean Model
Grid Number
(lon×lat×lev)Ensemble 1 ACCESS-CM2 MetUM-HadGEM3-GA7.1 CICE5.1.2 ACCESS-OM2 360×300×50 1–5 2 ACCESS-ESM1-5 HadGAM2 CICE4.1 ACCESS-OM2 360×300×50 1–40 3 AWI-CM-1-1-MR ECHAM6.3.04p1 FESOM 1.4 FESOM 1.4 830305×46 1 4 BCC-CSM2-MR BCC_AGCM3_MR SIS2 MOM4 360×232×40 1 5 CAMS-CSM1-0 ECHAM5_CAMS SIS 1.0 MOM4 360×200×50 1–2 6 CanESM5 CanAM5 LIM2 NEMO3.4.1 361×290×45 1–10 7 CanESM5-CanOE CanAM5 LIM2 NEMO3.4.1 361×290×45 1 8 CAS-ESM2-0 IAP AGCM 5.0 CICE4 LICOM2.0 360×196×30 1,3 9 CESM2 CAM6 CICE5.1 POP2 320×384×60 1,4,10,11 10 CESM2-WACCM CAM6 CICE5.1 POP2 320×384×60 1–5 11 CIESM CIESM-AM1.0 CICE4 CIESM-OM1.0 320×384×60 1 12 CMCC-CM2-SR5 CAM5.3 CICE4.0 NEMO 3.6 362×292×50 1 13 CMCC-ESM2 ECHAM v6.3.02 CICE4.1 NEMO v3.4 362×292×50 1 14 CNRM-CM6-1 Arpege 6.3 Gelato 6.1 NEMO3.6 362×294×75 1 15 CNRM-CM6-1-HR Arpege 6.3 Gelato 6.1 NEMO3.6 1442×1050×75 1 16 CNRM-ESM2-1 Arpege 6.3 Gelato 6.1 NEMO3.6 362×294×75 1 17 EC-Earth3 IFS cy36r4 LIM3 NEMO3.6 362×292×75 1,11,101–149 18 EC-Earth3-CC IFS cy36r4 LIM3 NEMO3.6 362×292×75 1 19 EC-Earth3-Veg IFS cy36r4 LIM3 NEMO3.6 362×292×75 1,2,3,4,6,12 20 EC-Earth3-Veg-LR IFS cy36r4 LIM3 NEMO3.6 362×292×75 1–3 21 FGOALS-f3-L FAMIL2.2 CICE4.0 LICOM3.0 360×218×30 1 22 FGOALS-g3 GAMIL2 CICE4.0 LICOM3.0 360×218×30 1–3 23 FIO-ESM-2-0 CAM4 CICE4.0 POP2-W 320×384×60 1-3 24 GFDL-CM4 GFDL-AM4.1 SIS2 GFDL-MOM6 1440×1080×35 1 25 GFDL-ESM4 GFDL-AM4.1 GFDL-SIM4p5 GFDL-OM4p5 720×576×35 1–3 26 GISS-E2-1-H GISS-E2.1 GISS SI HYCOM Ocean 360×180×33 1–5 27 HadGEM3-GC31-LL MetUM-HadGEM3-GA7.1 CICE-HadGEM3-GSI8 NEMO-HadGEM3-GO6.0 360×330×75 1–4 28 INM-CM4-8 INM-AM4-8 INM-ICE1 INM-OM5 360×180×33 1 29 INM-CM5-0 INM-AM5-0 INM-ICE1 INM-OM5 360×180×33 1 30 IPSL-CM6A-LR LMDZ NEMO-LIM3 NEMO-OPA 362×332×75 1-4,6,14 31 KIOST-ESM CCSR AGCM COCO4.9 COCO4.9 360×256×63 1 32 MIROC6 CCSR AGCM COCO4.9 COCO4.9 360×256×63 1–50 33 MIROC-ES2L CCSR AGCM COCO4.9 COCO4.9 360×180×63 1–10 34 MPI-ESM1-2-HR ECHAM6.3 sea ice in MPIOM MPIOM1.63 802×404×40 1–2 35 MPI-ESM1-2-LR ECHAM6.3 sea ice in MPIOM MPIOM1.63 256×220×40 1-30 36 MRI-ESM2-0 MRI-AGCM3.5 MRI.COM4.4 MRI.COM4.4 360×362×61 1 37 NESM3 ECHAM v6.3.02 CICE4.1 NEMO v3.4 362×292×46 1-2 38 NorESM2-LM CAM-OSLO CICE MICOM 360×385×70 1 39 NorESM2-MM CAM-OSLO CICE MICOM 360×385×70 1 40 TaiESM1 TaiAM1 CICE4 POP2 320×384×60 1 41 UKESM1-0-LL MetUM-HadGEM3-GA7.1 CICE-HadGEM3-GSI8 NEMO-HadGEM3-GO6.0 360×330×75 1–4,8 Table 1. Details of the 41 CMIP6 climate models used in this study.
No. Model ID Atmospheric
ModelSea-ice Model Ocean Model Ocean Model Grid Number
(lon×lat×lev)Ensemble 1 CESM1-CAM5-SE-HR CAM5.2 CICE4 POP2 3600×2400×62 1 2 CMCC-CM2-HR4 CAM4 CICE4.0 NEMO3.6 1442×1051×50 1 3 CMCC-CM2-VHR4 CAM4 CICE4.0 NEMO3.6 1442×1051×50 1 4 CNRM-CM6-1-HR Arpege 6.3 Gelato 6.1 NEMO3.6 1442×1050×75 1 5 EC-Earth3P-HR IFS cy36r4 LIM3 NEMO3.6 1442×1921×75 1–3 6 ECMWF-IFS-HR IFS CY43R1 LIM2 NEMO3.4 1442×1021×75 1–6 7 ECMWF-IFS-MR IFS CY43R1 LIM2 NEMO3.4 1442×1021×75 1–3 8 GFDL-CM4C192 GFDL-AM4C192 GFDL-SIM4p25 GFDL-OM4p25 1440×1080×75 1 Table 2. Details of the eight HighResMIP CMIP6 models used in this study.
To assess and quantify the variability and trends of sea ice in the Barents Sea during winter, the satellite-derived SIC from 1980 to 2020 was used, which was produced from brightness temperature data processed at the NASA Goddard Space Flight Center and the National Snow and Ice Data Center (Cavalieri et al., 1996; Meier et al., 2013). The Goddard Institute for Space Studies surface air temperature (SAT) dataset (Hansen et al., 2010; Lenssen et al., 2019) was also used in this study to investigate the sensitivity of sea ice to global warming.
We mainly focused on winter (November–April) sea ice simulations and projections in the Barents Sea (area defined by the blue box in Fig. 1a) because the Barents Sea is nearly ice-free in summer. The SIE in the Barents Sea, which is mainly used to evaluate the models and project future sea ice changes, was calculated as the cumulative area of all grid cells that had a monthly average SIC >15% (Onarheim and Årthun, 2017). To project when the Barents Sea might become close to being ice-free in winter, we defined the ice-free condition as 10% of the 1980–1982 average winter SIE (0.08 × 106 km2) referencing the method of Onarheim and Årthun (2017).
Figure 1. Spatial distribution of winter sea ice concentration (SIC) and sea ice extent (SIE) in the Barents Sea during 1980−2014. (a) Climatological SIC in the Barents Sea in winter based on observations and (b) the ratio of CMIP6 models with SIC above 15% of the climatological mean SIC. (c) Winter climatological SIE in the Barents Sea. (d) One standard deviation (STD) of winter detrended SIE in the Barents Sea. The area within the blue line in (a) is the region of the Barents Sea defined in this study to calculate SIE in the Barents Sea. The red line in (a) represents the section of the Barents Sea Opening. Solid black lines in (a) and (b) represent the observed sea ice edge during 1980−2014, indicating SIC of 15%.
The ocean heat transport (OHT) through the Barents Sea Opening (BSO; red section in Fig. 1a) was used to investigate the reason for the bias of simulated sea ice in the Barents Sea. It was calculated using monthly seawater potential temperature and ocean velocity (Shu et al., 2022):
where
${\rho }_{\rm{o}}$ is the density of seawater,$ {c}_{\mathrm{p}} $ is the specific heat capacity of seawater,$ \boldsymbol{v} $ is the velocity of the ocean perpendicular to the section of the BSO,$ T $ is the potential temperature in the BSO section,$ {T}_{\mathrm{r}\mathrm{e}\mathrm{f}} $ is a reference temperature (here, set to 0°C),$ H $ is water depth, and$ \lambda $ is the distance along the gateway transect.Correlation analysis was used to study the relationship between OHT through the BSO and sea ice extent in the Barents Sea and the relationship between the initial state of sea ice and its future changes. The correlation coefficient used in this paper is Spearman’s rho, and the p-value is computed using large-sample approximations. If the p-value is less than 0.05, the correlation is considered significant.
No. | Model ID | Atmospheric Model | Sea-ice Model | Ocean Model | Ocean Model Grid Number (lon×lat×lev) | Ensemble |
1 | ACCESS-CM2 | MetUM-HadGEM3-GA7.1 | CICE5.1.2 | ACCESS-OM2 | 360×300×50 | 1–5 |
2 | ACCESS-ESM1-5 | HadGAM2 | CICE4.1 | ACCESS-OM2 | 360×300×50 | 1–40 |
3 | AWI-CM-1-1-MR | ECHAM6.3.04p1 | FESOM 1.4 | FESOM 1.4 | 830305×46 | 1 |
4 | BCC-CSM2-MR | BCC_AGCM3_MR | SIS2 | MOM4 | 360×232×40 | 1 |
5 | CAMS-CSM1-0 | ECHAM5_CAMS | SIS 1.0 | MOM4 | 360×200×50 | 1–2 |
6 | CanESM5 | CanAM5 | LIM2 | NEMO3.4.1 | 361×290×45 | 1–10 |
7 | CanESM5-CanOE | CanAM5 | LIM2 | NEMO3.4.1 | 361×290×45 | 1 |
8 | CAS-ESM2-0 | IAP AGCM 5.0 | CICE4 | LICOM2.0 | 360×196×30 | 1,3 |
9 | CESM2 | CAM6 | CICE5.1 | POP2 | 320×384×60 | 1,4,10,11 |
10 | CESM2-WACCM | CAM6 | CICE5.1 | POP2 | 320×384×60 | 1–5 |
11 | CIESM | CIESM-AM1.0 | CICE4 | CIESM-OM1.0 | 320×384×60 | 1 |
12 | CMCC-CM2-SR5 | CAM5.3 | CICE4.0 | NEMO 3.6 | 362×292×50 | 1 |
13 | CMCC-ESM2 | ECHAM v6.3.02 | CICE4.1 | NEMO v3.4 | 362×292×50 | 1 |
14 | CNRM-CM6-1 | Arpege 6.3 | Gelato 6.1 | NEMO3.6 | 362×294×75 | 1 |
15 | CNRM-CM6-1-HR | Arpege 6.3 | Gelato 6.1 | NEMO3.6 | 1442×1050×75 | 1 |
16 | CNRM-ESM2-1 | Arpege 6.3 | Gelato 6.1 | NEMO3.6 | 362×294×75 | 1 |
17 | EC-Earth3 | IFS cy36r4 | LIM3 | NEMO3.6 | 362×292×75 | 1,11,101–149 |
18 | EC-Earth3-CC | IFS cy36r4 | LIM3 | NEMO3.6 | 362×292×75 | 1 |
19 | EC-Earth3-Veg | IFS cy36r4 | LIM3 | NEMO3.6 | 362×292×75 | 1,2,3,4,6,12 |
20 | EC-Earth3-Veg-LR | IFS cy36r4 | LIM3 | NEMO3.6 | 362×292×75 | 1–3 |
21 | FGOALS-f3-L | FAMIL2.2 | CICE4.0 | LICOM3.0 | 360×218×30 | 1 |
22 | FGOALS-g3 | GAMIL2 | CICE4.0 | LICOM3.0 | 360×218×30 | 1–3 |
23 | FIO-ESM-2-0 | CAM4 | CICE4.0 | POP2-W | 320×384×60 | 1-3 |
24 | GFDL-CM4 | GFDL-AM4.1 | SIS2 | GFDL-MOM6 | 1440×1080×35 | 1 |
25 | GFDL-ESM4 | GFDL-AM4.1 | GFDL-SIM4p5 | GFDL-OM4p5 | 720×576×35 | 1–3 |
26 | GISS-E2-1-H | GISS-E2.1 | GISS SI | HYCOM Ocean | 360×180×33 | 1–5 |
27 | HadGEM3-GC31-LL | MetUM-HadGEM3-GA7.1 | CICE-HadGEM3-GSI8 | NEMO-HadGEM3-GO6.0 | 360×330×75 | 1–4 |
28 | INM-CM4-8 | INM-AM4-8 | INM-ICE1 | INM-OM5 | 360×180×33 | 1 |
29 | INM-CM5-0 | INM-AM5-0 | INM-ICE1 | INM-OM5 | 360×180×33 | 1 |
30 | IPSL-CM6A-LR | LMDZ | NEMO-LIM3 | NEMO-OPA | 362×332×75 | 1-4,6,14 |
31 | KIOST-ESM | CCSR AGCM | COCO4.9 | COCO4.9 | 360×256×63 | 1 |
32 | MIROC6 | CCSR AGCM | COCO4.9 | COCO4.9 | 360×256×63 | 1–50 |
33 | MIROC-ES2L | CCSR AGCM | COCO4.9 | COCO4.9 | 360×180×63 | 1–10 |
34 | MPI-ESM1-2-HR | ECHAM6.3 | sea ice in MPIOM | MPIOM1.63 | 802×404×40 | 1–2 |
35 | MPI-ESM1-2-LR | ECHAM6.3 | sea ice in MPIOM | MPIOM1.63 | 256×220×40 | 1-30 |
36 | MRI-ESM2-0 | MRI-AGCM3.5 | MRI.COM4.4 | MRI.COM4.4 | 360×362×61 | 1 |
37 | NESM3 | ECHAM v6.3.02 | CICE4.1 | NEMO v3.4 | 362×292×46 | 1-2 |
38 | NorESM2-LM | CAM-OSLO | CICE | MICOM | 360×385×70 | 1 |
39 | NorESM2-MM | CAM-OSLO | CICE | MICOM | 360×385×70 | 1 |
40 | TaiESM1 | TaiAM1 | CICE4 | POP2 | 320×384×60 | 1 |
41 | UKESM1-0-LL | MetUM-HadGEM3-GA7.1 | CICE-HadGEM3-GSI8 | NEMO-HadGEM3-GO6.0 | 360×330×75 | 1–4,8 |