Global warming is a problem for the bears because it slowly melts ice that they depend on to survive in. Their main source of food, seals live in the cold weather. A polar bear's body is made to handle cold conditions.
Oil is common in the arctic so spills are common. However polar bears are not aware of this. The oil is killing their food source causing them to starve. Oil is also hard to get off their fur and that effects their hygiene and they can not do anything about it.