Andreas T,
Thank you for providing these very illustrative diagrams. They led med to think about an old illustration, I came across many years ago.
Basically, it was a “raw” average of observed cloud cover from exactly the area shown in your diagram, It was based on monthly time series from around 80 climatological surface stations over the period 1890 through 2000.
In summary, it was evident that cloud cover in the Nordic Seas region had historically been on average between 60 % (Summer) and 75 % (Winter). It was also clear that the general warming, which took place in this area between around 1920 and the 1930ies, added appr. 5 % points to the average cloud cover back then.
Assuming this most recent warming period has also added another 5-10 % to the cloud cover (actually it is sky cover seen from the ground), then it is highly likely, that infrared radiation reflected back to the ground from the bottom of the clouds is a stronger positive feedback, which more than compensates the increase in shortwave radiation being reflected back to space due to the increase in cloud cover.
So, in some ways, we might assume that loss of sea ice (with high albedo) leads to an increase in clouds locally (with similar high albedo as seen from the sky), so the main difference will be the increase in longwave back radiation (as seen from the surface).
In my view, the warming, the loss of sea ice and the increase in cloud cover all go together, so trying to separate things and let one be the driver of others could be a futile exercise.