Factors that may play a part that I can think of include:
At what stage will it be warm enough for what you suggest to be significant?
How long will it take for Polar Bears to adjust their strategies to take warmer conditions into account. For example I understand that mothers hibernate in snow enclaves that they build for the gestation and birth of their young.
To me the worrying aspect is the ability of Polar Bears that evolved for the polar conditions to adjust when these conditions change so rapidly.
