The abiotic change that may decrease a polar bear's ability to hunt for ringed seals is "increased temperatures."
Increased temperatures lead to the melting of sea ice, which is essential for polar bears as it provides a platform for them to hunt seals. If the ice melts earlier in the spring or freezes later in the fall, polar bears may have reduced access to their hunting grounds, making it more difficult for them to find food. Conversely, increased ice cover would likely provide more hunting opportunities, while increased competition and population density would not be abiotic factors.