<P> Steven Amstrup and other U.S. Geological Survey scientists have predicted two - thirds of the world's polar bears may disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by climate change, though the validity of this study has been debated . The bears could disappear from Europe, Asia, and Alaska, and be depleted from the Canadian Arctic Archipelago and areas off the northern Greenland coast . By 2080, they could disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic Archipelago . However, in the short term, some polar bear populations in historically colder regions of the Arctic may temporarily benefit from a milder climate, as multiyear ice that is too thick for seals to create breathing holes is replaced by thinner annual ice . </P> <P> Polar bears diverged from brown bears 400,000--600,000 years ago and have survived past periods of climate fluctuation . It has been claimed that polar bears will be able to adapt to terrestrial food sources as the sea ice they use to hunt seals disappears . However, most polar bear biologists think that polar bears will be unable to completely offset the loss of calorie - rich seal blubber with terrestrial foods, and that they will be outcompeted by brown bears in this terrestrial niche, ultimately leading to a population decline . </P> <P> Warnings about the future of the polar bear are often contrasted with the fact that worldwide population estimates have increased over the past 50 years and are relatively stable today . Some estimates of the global population are around 5,000 to 10,000 in the early 1970s; other estimates were 20,000 to 40,000 during the 1980s . Current estimates put the global population at between 20,000 and 25,000 or 22,000 and 31,000 . </P> <P> There are several reasons for the apparent discordance between past and projected population trends: estimates from the 1950s and 1960s were based on stories from explorers and hunters rather than on scientific surveys . Second, controls of harvesting were introduced that allowed this previously overhunted species to recover . Third, the recent effects of climate change have affected sea ice abundance in different areas to varying degrees . </P>

Where does the name polar bear come from