OI don't think 'they' know any more than has already been published. I don't think anyone is keeping a secret.
If you look at the progression of man and the ecosphere that gave us the present distribution of Mankind, it wouldn't have happened on a close reading of modern text books. We would still be swinging from trees on the African savanna.
The Ice Ages Happened, Elephants graised on the Barents Sea, you can buy mastidon meat in San Francisco, roasted or for Kabobs. If you look at the distribution of Ice in the Northern hemisphere there could be no Ice Free zone to let the horses out, they would be frozen in Northern Sibera.
Why was Sibera so warm, flowers in the mouth of flash frozen Mastidon and Mass under a couple of hundred feet of Ice?