With respect to success of the human species, from human history, and from paleoclimatology, success can be fairly summarized: periods of warmth have been conducive to humanity, taken globally, but frigidness has presented great difficulty. One crucial consideration is the impact of the length of growing seasons on the magnitude, quality, and variety in the food supply. Without doubt, another crucial consideration is the mobility of humans, which is facilitated during warmth, but greatly inhibited during frigid periods. By whatever mechanism, the human species thrives in warmer conditions. Historically, human culture has progressed, by any measure, when abetted by warmth..
An argument is persistently made in The Chilling Stars (deep into the book) that ice-ages are also beneficial to human-kind. Humans, it is argued, evolve better in the freezing cold; or under climatic stress. Karl Marx (and successors) also made an argument which apparently persists today, that humans require more evolution; and some selection, however natural, was in order; as long as he, and they, did the selection. This is an extreme form of social engineering. Please take this opportunity to judge for yourself the fruits of this persistent dogma (don’t forget today’s food riots in Venezuela and elsewhere). The subject is generally avoided in polite discussion, for some reason. If changing humanity for the better requires one innocent human life be sacrificed, we should reject it; if only because we do not, and cannot, know what is better.
I guess we could make the argument that polar-bears would also benefit from some climatic stress.
I would dispute that ice-ages are beneficial to humans. I dispute even more that humans can evolve from our present condition, at any observeable rate. But most of all, I dispute that hypothetical “evolution” of humans can be beneficial; but maybe it can, if we can become independent of a star.
The “history” of Earth is profoundly clear (although more can be learned), with respect to climate: you will not be happy if you are trying to live on a glacier. You may even be dead. I would’ve thought it obvious, but it took me 300 words to get here.
Undoubtedly, species adapt. In terms of human life, and human misery, adapting to cold will be far more costly than adapting to warmth, whether evolution is involved, or not.
In conclusion, denial of Earth’s “history” will not help us avoid its repetition. Carbon dioxide has been higher than today by an order of magnitude and more; and if Earth gets as warm as it has ever been, which is far warmer than today, humans will thrive. On the other hand, if Earth gets as cold as it has been, humans will be decimated, if not become extinct. Studying “history” produces at least one simple result: odds favor a cold future, hands down. Earth today is uncommonly warm; and uncommonly comfortable. Will it get more comfortable, or colder?