Global warming in the Arctic. Computer artwork of a polar bear (Ursus maritimus) on an ice floe in an Arctic affected by global warming. Polar bear numbers have declined during the early years of the 21st century. It thought this is due to the effects of global warming and climate change, such as sea ice melting earlier in the season and glaciers receding. This has reduced the polar bears' territories and altered local food supply patterns. Many polar bears now have to swim hundreds of miles between Arctic islands due to the absence of sea ice cover.