Does the IPCC conclusively prove with 100% certainty that the fraction of the 0.04% of CO2 comprising Earth's atmosphere humans contribute is the main thing which affects the Earth's climate(s)?
In 01988 Jacques Benveniste did some experiments which seemed to show some sort of chemical alteration of water in the presence of antibodies, though it didn't show up with the usual spectroscopic techniques: https://en.wikipedia.org/wiki/Water_memory which were published in Nature. Replication attempts were made by several teams. They failed, so Benveniste was wrong.
So I wouldn't say it's "settled science" that water is H2O. When contrary evidence pops up, chemists investigate it and find out what's wrong with it; they don't just dismiss it. That would be unscientific.
We could also quibble about the meaning of "H2O", though perhaps this is less interesting. For example, although it's only about 0.1 ppm, a part of any sample of water exists in the form of free hydronium (H3O+) and hydroxyl (OH-) ions, not H2O. Because this is an equilibrium, you can't just remove the ions to get pure H2O; they come right back. This self-ionization is responsible for significant aspects of water's behavior, including the formation of streamers that limit the storage time of water-dielectric capacitors, and the particular way acid-base chemistry works in water.
Natural water also contains about 155 ppm DOH and D2O, though this can be removed, and it's arguable that this is within the meaning of "H2O" anyway.
And the water molecules in liquid water or ice form a continuous hydrogen-bonded network, though this was not known until 01920; to some extent it's just a matter of convention rather than objective fact that we consider those bonds to be "intermolecular", making water H2O rather than an (H2O)n polymer; we consider the weaker hydrogen bonds between DNA strands to make DNA a single molecule rather than two intertwined molecules. (The polywater affair, however, posited the formation of a covalent water polymer.)
The list of things "conclusively prove[n] with 100% certainty" is vanishingly small and not a burden of proof that anyone applies to something unless they are looking for literally any reason to dismiss it out of hand. Other folks have already mentioned the difference between "carbon" in climate science parlance and "CO2" which you appear to have ignored in subsequent comments.
Assuming your question is indeed in good faith (I don't believe it is, but others may have the same question with a little more honesty) - anthropogenic climate change is a scientific theory that is the best answer to the evidence we currently have. No other theories taken seriously by the scientific community come close, and new data fits ACC models with more and more accuracy. So "no, but close enough."
Yes. Though that sounds like weasel words, the word change is missing.
It was 100% proven that human contribution is the main and most important culprit of (the current) climate change. Also that human released CO2 is the most important mechanism.
Literally the only thing the IPCC is virtually certain of is that the upper oceans warmed since 1970.
If you are pointing at studies that haven't been incorporated by the IPCC, then they are definitely subject to doubt. This isn't some deterministic problem you can repeat in a lab and science the shit out of. This is heuristics, fudges, and elbow grease type science where we do our best and then compare against the same type of work of others.