It'd be either during the Medieval Warm Period (AD 900 to 1300) or Roman Warm Period (time of Christ), both of which were warmer than we are now, with the Medieval Warm Period not getting as warm as the Roman Warm Period, just like the Roman Warm Period didn't get as warm as the prior Minoan Warm Period (time of Moses). But the crop yields during those times were amazingly good, just like they are now during our Modern Warm Period (since AD 1800's) but without modern farming techniques.
History shows that our current temps aren't closed to being as warm as our climate optimum. And if the trend continues, our Modern Warm Period won't reach that point before temps turn down again for another centuries long cooling period before the next warm period begins. A few centuries from now when the cooling period makes crop yields go down, rain patterns harder to predict, and deaths by plague go way up (as they always do during cooling periods), people will look back at our time and laugh at our hysteria over global warming when we should be happy to be in a relatively nice climate.
I’d define the “correct” temperature range for the planet as when our planet had the highest crop yields
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You do understand there is NO correct temperature? There are only better or worse growing seasons in ever changing areas of the Earth.
The Sahara and all of North Africa was once fertile and supported millions of people in the Mediterranean region with the crops and animals raised there.
You cannot go back, you can only go forward. No matter what any one does the Earth’s climate will continue to change all on its own. Then, there are comet strikes like 10,800 BC which altered the climate worldwide overnight, killing off most the mega fauna and ushering in the Younger Dryas event.
You cannot halt of alter this progression; you can only adapt and survive.
Quotable and true.
In terms of life, the best times were the hothouse days of the dinosaurs!