Explain how polar bears can't adapt to climate change?

lets say that they did adapt to the ice from years ago, but then something known as global warming starts to melt the ice or the bears shelters which is in the pole where a few large glaciers are turning to water, then the bears wouldnt adapt to anything else 'cause theyre used to cold and not heated areas or climates, which is similar to a tortoise for example with a hot dry desert then it would last with the species.