Final answer:
About 50% of the world's polar bears could face extinction due to habitat loss caused by global warming, which results in the melting of their sea ice hunting grounds.
Step-by-step explanation:
What percentage of the world's polar bears could face extinction due to habitat loss is a significant question when considering the effects of climate change on biodiversity. Polar bears are threatened primarily because of global warming, which causes the sea ice they rely on for hunting grounds to melt. A key aspect of their hunting technique is to walk on sea ice and wait at breathing holes for seals to surface. With the loss of sea ice, polar bears are forced to embark on longer and more dangerous journeys to find suitable hunting areas, disrupting their traditional feeding patterns.
Looking at the broader picture of biodiversity loss, the 2007 IUCN Red List shows that between 0% and 30% of species from several groups are listed as critically endangered, endangered, or vulnerable. Specifically addressing the question, scientific estimates based on habitat loss and species-area relationships suggest that with about 90 percent of habitat loss, an expected 50 percent of species would become extinct. Therefore, the most accurate answer to the question is 3) 50% of the world's polar bears could face extinction due to habitat loss.