Recent fossil founds indicate that Polar bears seem to be both older as a species and more able to adopt to climate changes than some might assume.
The Oldest Polar Bear Fossil: 130,000 Years Old! - From Svalbard - Softpedia
There are other, less popular species of Arctic Wildlife that could be more severly impacted.
The majority of the current zoo exhibits displaying ursidae could indeed be improved-no doubt about that. However, this doesn't consequently mean that polar bears or other ursidae disqualify for zoo husbandry in general; zoos just have to improve their current husbandry according to their bearish needs. Various horses, dogs and other domestic animals/pets display stereotypical behaviour; this doesn't have to mean that these animals are not suited for husbandry in general, but that the particular husbandry they are currently in needs improvement.
A general aspect could be, and that is already put into practise by some zoos, to keep the species best suited to the native environment of the zoo. Why have Polar Bears in San Diego or Sloth Bears in Moscow?
One should also be aware of the availableness of the particular species. In terms of sloth bears, mentioned here as "apt inner city zoo bears", the situation and future of the species in zoos is rather bleak: the European zoo population (in 6 zoos) is tiny and closely related, wheras the American one is not really prolific and also includes several subspecies hybrids. India doesn't allow the export of sloth bears, so that Sri Lanka remains as the sole possible "source" (except maybe Pakistan, Bhutan or Nepal-but try to get animals from there...)-however, that's a different subspecies than the one kept in European zoos..."Phasing out" other species with a more promising zoo population doesn't seem to be the way to go. Additionally, given the life span of most bears, that would take a while...
Andean/Spectacled Bears, on the other hand, are now quite common in zoos-to the extent that some zoos have problems to find suitable places for their offspring. Moon Bears are also impacted by the TCM trade-yet neglected in favour of other bear species...
A rather "novel" idea in ursidae husbandry is the idea of mixing them with different species, may it be primates, canidae, mustelidae, procynidae or even ungulates. It's a nice idea, but can backfire in both ways.
Why should the "Siberian" tiger be called Amur Tiger instead? From a zoogeographical viewpoint, the term "Amur" (or Manchurian/Ussuri tiger) would be more appropriate. However, if the recent results about tiger subspecies are true, we might have to find a new common term for both Pantera tigris altaica and virgata...
And @Dan, even if you don't want to respond to my post: please don't try to act like the innocent victim that you surely aren't...