Proofs don't exist in sciences concerned with the physical world. For proofs to work in the real world, you'd need certainty that you have recognised and correctly measured every variable that could affect the outcome of an observation/experiment.
The last philosophy of science that allowed proofs was positivism. For the natural sciences, it has been replaced by critical rationalism (https://en.wikipedia.org/wiki/Critical_rationalism). CR gave a solution to the proof problem: While positive proofs like in your quote don't work, you can still falsify a theory. By continuously falsifying theory after theory about an observed outcome, something resembling truth remains. Truth, but never certainty. Hence the talk about likelihood and probability.
> I'm curious. Gravity has not been proven to attract two masses, for instance?
Correct. That's why it's called the theory of gravity :) You would need Laplace's demon (https://en.wikipedia.org/wiki/Laplace's_demon) for a proof. "Proof" means absolute certainty. You only find that in math, not in the physical world.
As he already said, science doesn't do proofs; proof is something for Math, science does evidence, nothing is ever proven. Asking a scientist for proof merely shows you don't know what science is and thus aren't capable of using it to make decisions.
> Is there any evidence that two masses don't attract ?
The answer to that question does not in any way proof the existence of gravity.
I don't mean to offend, but if you honestly ask these types of questions, I doubt you are able to evaluate the quality of original papers dealing with climate research.
Proofs don't exist in sciences concerned with the physical world. For proofs to work in the real world, you'd need certainty that you have recognised and correctly measured every variable that could affect the outcome of an observation/experiment.
The last philosophy of science that allowed proofs was positivism. For the natural sciences, it has been replaced by critical rationalism (https://en.wikipedia.org/wiki/Critical_rationalism). CR gave a solution to the proof problem: While positive proofs like in your quote don't work, you can still falsify a theory. By continuously falsifying theory after theory about an observed outcome, something resembling truth remains. Truth, but never certainty. Hence the talk about likelihood and probability.