What are two main environmental factors of polar bears that limit their species distribution?

This question is worded a bit oddly.  It's unclear if the question is meaning to ask about polar bear adaptations that limit its spread to other habitats, or if the question is asking about environmental factors that hold the polar bears back.  To some extent, the difference isn't that big of a deal because adaptations are closely tied to environmental factors.  For polar bears, one major environmental factor that limits polar bear spread to other areas is their food source.  Polar bears feed almost exclusively on ringed seals and bearded seals.  This food source really limits the habitat area that the bears can occupy.  The bears are confined to Arctic regions near the edges of pack ice where currents and wind interact and form a continually melting and refreezing area of ice patches and open spaces in the ocean water. This is where polar bears can find the greatest number of seals.  Another environmental factor that limits bear movement southward is the temperature.  Polar bears are adapted to the cold weather.  They have a thick layer of blubber and white fur to protect against the cold.  Additionally, polar bears are huge.  What this does is give them a small surface area to volume ratio, and their body heat loss is minimal.  Moving to warmer climates would be difficult because their bodies would struggle to stay cool enough to live well.  
https://arcticwwf.org/species/polar-bear/threats/

https://defenders.org/wildlife/polar-bear

https://www.bbc.co.uk/bitesize/guides/zydbqhv/revision/1