Global warming isn't "to blame" for this situation, but it is a factor: the infrequency of ice bridges between the mainland and the island has grown because of it. The real "blame" is more general human interference.
The summary is misleading in suggesting that new wolves have come to Isle Royale fairly often. They haven't (I think there were only two documented migrations) which is why this ongoing study has been so scientifically useful: the island has been a (mostly) closed system for decades, allowing scientists such as Rolf Peterson to track the system without too many external variables. Before the wolves arrived over the ice, Isle Royale was being deforested by its moose population (which can swim to the island). Prior to that, the apex predators on the island were humans, during the island's period as a mining, logging, and resort area. After the island was made a national park, humans left that role, which created a boom in the moose population, which led to overgrazing, which led to starvation of the moose, etc. The wolves have stabilized that system.
Before humans became a major influence on the island, it had a different predator/prey system, based on coyotes and caribou. But both of those populations have died out, and humans almost certainly played a part in that. Isle Royale is being preserved today as a wilderness, but it isn't an "untainted" one, and hasn't been for a couple hundred years. It is what it is because of human activities. Humans didn't introduce the wolves to Isle Royale, but in a very real sense, we made them necessary. Which is why I support the idea of restocking the island's wolf population, in much the same way that we restocked many of the rivers of the Great Lakes region after destroying their fish populations.