Personally, I find the renovation of the polar bear exhibit quite problematic. A Californian dry hot almost desert / xerophytic environment for an Arctic species ....? I would almost feel it is a cynical jibe at trying to highlight climate change ....! Well, just my 5 cents of rationale
Downtown San Diego (where the zoo is located) actually has a very mild microclimate for California; even in peak summer it starts in the mid-60s F (18-21 C) in the mornings and usually stays below 80 F (~26 C) in the afternoons. I'd estimate the zoo's summer temps are cooler than 90% of other major zoos in the country, actually - including many much further north that also have polar bears.
The AZA care manual for polar bears doesn't have scientific maximums and minimums for either temperature or humidity, and says that they "are mostly tolerant of fluctuating temperatures". The temperature and humidity section focus mainly on controllable aspects of their enclosure - shade, misters, fans, chilled water, ice piles, and access to climate-controlled indoor spaces (which I believe the bears at SDZ use, since they were nowhere to be seen the last time I tried to visit them in the afternoon).