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Paper on the sensitivity of winter Arctic amplification in NorESM2-MM published in Earth System Dynamics

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One of the great achievements of the KeyCLIM project was the completion of a coordinated set of fully coupled experiments carried out in WP6, facilitating testing model developments from other work packages in a consistent way in the fully coupled model. These experiments were based on the CMIP6 historical and ssp585 experiments, but with modifications to mixed-phase clouds, eddy processes in the upper ocean, Greenland ice-sheet coupling, snow on sea ice processes, and ozone chemistry implemented separately. The result is a coordinated set of five historical-based and five ssp585-based experiments, known as the NorESM2 Ensemble Exploring Model Sensitivity (NEEMS; see Table 1). 

Table 1 (from Graff et al. 2025): Overview of the NEEMS experiments and other experiments considered in Graff et al.. See Table 1 in Graff et al. (2025) for further details.

The NEEMS experiments are now documented in a new paper in Earth System Dynamics: Sensitivity of winter Arctic amplification in NorESM2. The paper explores how winter Arctic warming is affected by the model updates. Results show that all experiments are associated with enhanced Arctic warming and that this warming varies substantially between the experiments. By the end of the 21st century, the range between the NEEMS experiment with the strongest and weakest warming is about 9 K. The warming is linked to changes in ocean heat flux and sea ice area and is strongest in the sea-ice retreat regions, with the strongest variability found in the retreat regions on the Atlantic side. 

The paper was a joint NorESM effort, led by Lise Seland Graff and Jerry Tjiputra, with contributions from 20 scientists that are part of the NorESM development community.

Figure 1 (from Graff et al. 2025): time evolution of winter Arctic surface temperature shown for the NEEMS mean (solid red line), NEEMS range (red shading), CMIP6 ScenarioMIP mean (solid black line), and CMIP6 ScenarioMIP range (grey shading). See Figure 1 in Graff et al. (2025) for further details.