Milder winters are also resulting in snow dens collapsing and killing bears and their cubs in some cases.
From the paper above:
While travelling along the coastline of the Northwest Territories (N.W.T.) and Yukon (Fig. l) on 18 June 1989, Co-author D. Irish saw the head of a dead polar bear sticking out of the snow...Den collapse may have been induced by the following climatic events. Warm temperature(+ 2C) on 17 December 1988 may have weakened the snow structure above the den chamber. On 12 January 1989 high winds (28 knots) would have caused heavy drifting on the coast. The area experienced a major snow storm during 26-28 January 1989. In Inuvik winds were 24-25 knots, with falling snow, and the weather on the coast would have been worse (Watts, pers. comm. 1990). The added weight of newly accumulated snow and the possible weaker snow structure over the den may have caused the collapse...The snow level where bears were lying was approximately 5 m lower than the ridge tops on either side of the drainage. It is quite possible that the snow line was level with the ridge tops before spring melt, as the drainage was still mostly full of snow late in June. If this were the case, there would have been a great weight of snow over the roof of the den chamber...Although den collapse can and does occur,the impact of this type of natural mortality on bear populations is probably minimal.