You've unwittingly stumbled into an interesting lesson in motivated reasoning.
Why did the Medieval scholastics attempt to prove there was a God? Well, the Medieval church depended on the acceptance of revealed truth. With most of the population uneducated and illiterate, they were dependent on authority figures to tell them what as true. This provided tremendous power to church leaders. However, there were a class of educated clergy that were learned by the standards of the day and had read the ancient Greeks and Romans enough to know there was a lot more to truth than what the elders said. But they knew they were in no position to challenge the authority of the church. But proving the existence of God? Well, the church elders could hardly argue with that as an academic pursuit- notwithstanding that it was an exercise in independent reason. It was also relatively safe because only the clergy and a few noblemen could read what they wrote anyways.
Fast forward to Copernicus. Likewise, he exercised independent reason and pursuit of knowledge outside the Church, but he wasn't clergy. Now, a much wider swath of the population could read given the expanding merchant class, and his ideas could potentially get traction in the broader population. Why did the church care though? There's not much in Christian theology that has anything to do with planetary movements. It wasn't so much what he said as the fact that he exercised independent reason from the Church on a matter that was not in service to the church. Thus, his investigations were forbidden. The Church, in a fit of motivated reasoning, called his ideas blasphemous- but it was only because the method of his ideas challenged the authority of the clergy.
As an aside, the Medieval Scholastics laid the foundation for the modern scientific method. Descartes heavily relied on Medieval philosophers like St Ansalem. Prior to writing the Cogito ("I think therefore I am") he started with a similar argument to the scholastics, and went beyond with powerful statement of self identity. But there was a problem: Descartes relied on what was later called "pure reason." He did not perform any observations to perform his conclusions and believed knowledge could be rationally derived. Scholars like Hume across the English Channel pointed out some of the significant limitations to rationalism and advocated empiricism (only knowledge based on observation). Kant effectively merged rationalism and empiricism and laid the foundation for the modern scientific method, which evolved in fits and starts over the 19th century (Kant wrote in the late 18th century). Without the scientific method, the internal combustion engine would have never been invented, and we'd be stuck at the level of discourse about climate change exhibited in this thread.
Now on today. In a vacuum, the fact that the earth is warming should be free of any value judgment. It's a fairly simple fact. But to accept AGW is a threat to certain power structures and political convictions- and that cannot stand. Thus, AGW deniers must invent reasons why it cannot be true. To be clear, it is good and healthy to challenge AGW, but it must be done with science, not with politics.
To answer your point above. The fact that the earth's climate has change over geologic time is well known to scientists and fully accounted for in climate change studies. It's important to understand, however, that the rate of change far exceeds any prior natural change absent those caused by calamity like meteor strikes. A great illustration (supported by published scientific studies) can be found here:
Additionally, what you've done is answer science with anecdote and conjecture. Your idea of oceans absorbing C02 according to temperature might be an interesting hypothesis, but you need to present evidence that the hypothesis has been successfully tested to be persuasive.