Polar bears live in the north pole, and they rely heavily on the large slabs of ice for many aspects of their lives.
For example, they often hunt for animals in the ocean, and these chunks of ice serve as resting points for the bears when they tire of swimming.
If these ice blocks are melting, the polar bears will have to swim farther distances. Many become tired and don't make it, dying in the process. Therefore, the change in climate negatively affects polar bears.