Yes, we've never actually experimented to observe the results over 50 years of artificially adding a large amount of carbon dioxide to the atmosphere. But we know from physics that it's a greenhouse gas. It's not a privileged hypothesis we're pulling out of nowhere. It's not like saying "You can't prove there's no invisible pink unicorn in my garage!" [Anthropological Global Warming] is, ceteris paribus, what we should expect to happen if the other things we believe are true. We don't have any experimental results on what will happen 50 years from now, and so you can't grant the proposition the special, super-strong status of something that has been scientifically confirmed by a replicable experiment. But as I point out in "Scientific Evidence, Legal Evidence, Rational Evidence", if science couldn't say anything about that which has not already been observed, we couldn't ever make scientific predictions by which the theories could be confirmed. Extrapolating from the science we do know, global warming should be occurring; you would need specific experimental evidence to contradict that.
We are, I think, dealing with that old problem of motivated cognition. As Gilovich says: "Conclusions a person does not want to believe are held to a higher standard than conclusions a person wants to believe. In the former case, the person asks if the evidence compels one to accept the conclusion, whereas in the latter case, the person asks instead if the evidence allows one to accept the conclusion." People map the domain of belief onto the social domain of authority, with a qualitative difference between absolute and nonabsolute demands: If a teacher tells you certain things, and you have to believe them, and you have to recite them back on the test. But when a student makes a suggestion in class, you don't have to go along with it - you're free to agree or disagree (it seems) and no one will punish you.
Polarity conventions are arbitrary. "Greenhouse gas" is an analogy, one that is deliberately deceptive in order to provoke a maladaptive political response.
Yes, we've never actually experimented to observe the results over 50 years of artificially adding a large amount of carbon dioxide to the atmosphere. But we know from physics that it's a greenhouse gas. It's not a privileged hypothesis we're pulling out of nowhere. It's not like saying "You can't prove there's no invisible pink unicorn in my garage!" [Anthropological Global Warming] is, ceteris paribus, what we should expect to happen if the other things we believe are true. We don't have any experimental results on what will happen 50 years from now, and so you can't grant the proposition the special, super-strong status of something that has been scientifically confirmed by a replicable experiment. But as I point out in "Scientific Evidence, Legal Evidence, Rational Evidence", if science couldn't say anything about that which has not already been observed, we couldn't ever make scientific predictions by which the theories could be confirmed. Extrapolating from the science we do know, global warming should be occurring; you would need specific experimental evidence to contradict that.
We are, I think, dealing with that old problem of motivated cognition. As Gilovich says: "Conclusions a person does not want to believe are held to a higher standard than conclusions a person wants to believe. In the former case, the person asks if the evidence compels one to accept the conclusion, whereas in the latter case, the person asks instead if the evidence allows one to accept the conclusion." People map the domain of belief onto the social domain of authority, with a qualitative difference between absolute and nonabsolute demands: If a teacher tells you certain things, and you have to believe them, and you have to recite them back on the test. But when a student makes a suggestion in class, you don't have to go along with it - you're free to agree or disagree (it seems) and no one will punish you.