A pointed question

What is the perfect temperature of Earth?
This is an important question. I think he meant “what would be the perfect average temperature of the planet earth”? A related question is “what should be the level of CO2 in the atmosphere”?
I think that the earth needs to warm at least 10C and that CO2 should increase to about 1500 ppm. “For most crops the saturation point will be reached at about 1,000–1,300 ppm under ideal circumstances.” (from greenhouse experts on what level to have in your greenhouse)
“There were crocodiles above the Arctic Circle and palm trees in Alaska.” Studies show that the earth has been much, much warmer than present. So being at least 10C warmer than present is a good start.
I don’t think humans have any say in this matter; and CO2 plays at best a minor, trace role in the average temperature of the planet. So; it will warm, not warm, or get colder depending on what nature gives us.

@azleader

The temperature achieved when 100% of global GDP/year is spent to slow CO2 rise.

That’s not nearly enough. We’ll have to borrow a lot more, increasing public debt further.

Temperature is always one standard deviation away from perfection.

Excellent answer, what was the question?

Most of the commenters here are thinking empirically, in terms of thermometer ranges. But that is not how this question came about. To use the popular alarmist terminology, I’ll “reframe” the question.
What temperature is “acceptable” or “unacceptable” to the alarmist camp?
For many of them, the answer is not defined by effect, but by cause. For many of them, any global temperature influenced by man is not acceptable. That is not a scientific viewpoint. It is a philosophical or religious one. Our actions have “upset” the “balance of nature”. We have “violated” Mother Earth.
So the “perfect temperature”, for them, is one with no “discernible” human influence. If it’s man-made (even in part) it is automatically bad. That is, I think, why they are not interested in doing a cost-benefit analysis of any particular change in climate.
Global warming/climate change/whatever, (i.e. the social phenomenon) will change with the weather, but it will never go away.

The answer from us Michiganders is, at least 20 degrees F warmer than it is right now!

Mike P says: 42
Good one!
Seriously though, although I understand that it would not be a popular move here, a look at the Manufacturer’s Handbook gives the answer straight away, i.e:
“While the Earth remains,
Seedtime and harvest,
Cold and heat,
Winter and summer,
And day and night
Shall not cease.” (Genesis 8 v 22)
But that DOES raise the question of why YHWH said this “in His heart” and why He saw fit to have His musings recorded for our benefit. The only rational explanation I can think of is that these were all unprecedented in Noah’s experience (and, yes, I did see the recent debate on the word ‘unprecedented’). Need some justification? Let’s start at the end and work back, with some help from the scribe who wrote down the book. (My apologies in advance to Moses if I have put anything into his mouth that should not be there.)
“Moses, in Chapter 8 verse 3a of your book ‘Genesis’ you wrote “And the waters receded continually from the earth.”
“Correct.”
“But hang on Moses, you had just written “And the waters prevailed exceedingly on the earth, and all the high hills under the whole heaven were covered (Gen7 v 19)” Even I know that water flows downhill, so if ALL the hills were covered, how could the waters recede?”
“The hills rose up and the seas got deeper.”
“Huh?”
“I had also just written “In the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month, on that day all the fountains of the great deep were broken up and the windows of heaven were opened”. What do you think caused that?”
“A meteor strike?”
“Bigger. Much bigger.”
“How big?”
“Big enough to knock the Earth out of its orbit close to the Sun into the orbit it has now. Big enough to collapse the water mantle that protected the Earth’s surface when it was closer to the Sun (“the waters which were above the firmament”) and to cause the first rains, which lasted worldwide for 40 days and 40 nights. Big enough to slow down the velocity of the Earth around the Sun. Big enough to leave a ‘ring of fire’ around its impact crater, which you call the Pacific Ocean. Big enough to tilt the Earth’s axis of rotation and thereby create conditions of cold and heat, winter and summer, and day and night, none of which had previously been experienced on the dry land at the poles before. Big enough to provide the energy to shatter the continents that then existed into jigsaw puzzle pieces. Big enough to penetrate the mantle and cold enough to create the convection currents that sent the pieces scudding around the Earth’s surface. Big enough to keep the cracks widening and molten for long enough for the jigsaw puzzle pieces to relocate to their new positions. Big enough to give those pieces the momentum to cause the impact crumple zones that you know as mountain ranges, when they collided with each other. Big enough to significantly increase the mass of the Earth. That big.”
“Cataclysmic seems too mild a description!”
“Absolutely. Your movie-makers haven’t even come close, by many orders of magnitude.”
“So before The Flood there were no mountains?”
“The ‘mountains’ then were only 15 cubits higher than the ‘high hills’ – read Verses 19 and 20 of Chapter 7 of my first book. Originally, the waters covered the Earth, but were “gathered together into one place” which let “dry land appear”, just as I was instructed to write in Genesis 1 v 9. No mention of mountains is there? And if the waters were in one place, how many places do you think the dry land occupied?”
“One, or at most two. And it, or they, must have been at the poles.”
“Right. You call them Pangea, or Gondwanaland and Eurasia.”
“Which was it?”
“Put the jigsaw back together and consider each piece’s movement and its impact with others, then you’ll know.”
“OK. So if the Earth is now travelling slower and its orbit is longer that explains why the antediluvians lived longer?”
“Right – they didn’t. Methusela’s 960-odd years and my 120 years were much the same in absolute time. His year was about 45 days long. But it didn’t happen overnight, or even during the Flood period. Check the ages of the post-Flood people – they reduced from 960 years to 480 years, to 240 years and ended up at 120 years, just as YHWH determined beforehand and told me to record it in Genesis 6 v 3.”
“And that makes nonsense of trying to extrapolate any timeline for current events back through the Flood event?”
“Correct. Totally pointless, and bound to lead to incorrect ideas. Evolution is a religion, not science, and of the three things YHWH abhors most religion is probably top of the list. The others are politics and economics.”
“So what is the ideal temperature for the Earth?”
“Conditions were ideal before the Flood. Good enough to support the growth of vegetation that was turned into gigatonnes of coal. The water mantle ensured that conditions were uniformly warm over the whole surface of the Earth. But those conditions can never be recreated, just as those conditions could never support the formation of a rainbow.”
“And the burning question of this hour – what was the carbon dioxide level then?”
“Burn ALL of the coal, ALL of the wood in your furniture and houses; cremate ALL of the 7 billion bodies in excess of eight; empty ALL of the CO2 fire extinguishers, and release any other sequestered atmospheric carbon and you will have a good idea of what ideal conditions were like, and how much carbon dioxide affected them. As Smokey used to say before he spontaneously combusted and came back as his alter ego “The only effect that can be definitively connected with the increase in CO2 is rising agricultural production.” That is why there are gigatonnes of coal”.

Well once you come to the proper temp, I see the bigger question to be….. What is the perfect CO2 level that we have to maintain to keep it there? We will have build a world wide system of carbon pollution collectors, and then transport the evil carbon to other areas for release through our new carbon injection system. I am sure they are programing the model now to keep the planet in harmony. With the science of CO2 we will now be able to heat or cool any area to fit the need of the people. Control must be maintained by our leaders at the UN, to keep evil people from using CO2 as a WMD.