I've been reading up on JK's website quite a bit over the last week and I am intrigued. He certainly has studied biochemistry and physiology very well. But I also agree with others on this site that he seems a bit monomanic. Anyway, I am looking forward to his book which I certainly will read as soon as it is available. I think, he is on to something, but he has not fully worked it out yet.
Australian aboriginal people come to mind, who clearly would be warm adapted for the major part of the year. Maybe during the dry season (June to August), they might get slightly cooler temps. They certainly used to live a relatively low-carb lifestyle - maybe not zero-carb like Inuits, but certainly nowhere near the levels of carbs they ingest nowadays - with the obvious consequences, a horrific amount of "civilisatory diseases" at very young age (cardiovascular disease, renal failure, type 2 diabetes, obesity, cancer etc.). The guys still living on the outstations however are skinny like anything, just muscles and tendons, grow old healthy and fit. So I think that evolution has given us enough time to adapt our bodies to warm climates. But maybe that adaptation is not as prefect as the cold adaptation and we still keep that program hidden in our metabolism for a rainy day ...
At this stage I don't plan to cold adapt, because I live in the tropics most of the year and it's just too hard to do here. However I regularly move to colder (as in very cold climates) on a regular basis - and next time I do this I certainly will try it. Maybe I will precondition myself a bit shortly before I leave, just to ease the transition.
Cold baths? Don't think I would have too much trouble to do that, just not sure if that alone would be sufficient. A whole-body cryo chamber is nowhere near where I live, so that falls by the wayside too.
Even though I live in the tropics, I don't plan at this stage to give up my paleo diet either - it has worked fabulously well for me on many levels - last but not least on a mental level. Gone are the mood-swings (according to my wife, who attributes it to something else ...), I feel much more energized and tolerant to problems (and MAN, have I had a rotten 12 months just passed!).
Other than that for the time being I will sit tight and wait for the next ice age - can't wait for the temperatures in my part of the world to come down a tad (although I read somewhere that temps in the southern hemisphere during the last ice age weren't very much different from today).