Three bears currently find space in the Nearctic Faunal Region (North America). Their general descriptions appear on the page shown here from my wildlife textbook.
Because modern humans currently emit more greenhouse gases than they sequester and because they currently destroy more carbon sinks (forests, grasslands, fertile soils, etc.) than they conserve or restore, it is more than likely that by 2100 (or before) there will be only two species of bears living free in the Nearctic region.
Climate change (global warming) that reduces the extent of Arctic sea ice (or reduces it altogether) also reduces/eliminates the principal habitat of polar bears and their chief food source-- seals. No sea ice, no ice seals, no ice bears.
See the "Climate Feedback Loop 2" (ice-albedo feedback) post (January 4, 2013), and look for future posts on endangered Arctic wildlife species.