I recently heard on the news that red wine is good for your teeth. Simply based on the fact that this has been reported, that is some reason to believe it's true, since "more official" methods of coming to a conclusion are more likely to be reported. However, I still don't know much about how the study was done, how many ways there are to go wrong, what is the nature of the people coming to this conclusion, etc, so to me, it only feels about 60% likely to be true so far.
If I looked into the study for maybe a half hour, I would probably get a much better idea of whether the concerns above are actually problems, and I may discover that there are few ways for them to go wrong. I may bump up my opinion to 90% likely. Or I may find that they do have some biases and start to doubt the red wine fact a lot more.
Since I don't feel like looking into the study, I have to stay with my 60% guess. In the case of global warming, the fact that there is a consensus in itself is an indicator, but maybe more like a 70-75% indicator; for me to bump it up to 95%+, I'd probably have to look into the research to make sure there isn't some odd peculiarity about how these scientists reach their conclusions. But, I'm not a policy maker, so I'm ok with not spending the time to do that and remain in some doubt.
Mind you, I do think policy makers have the responsibility to look into the research as I described above. And perhaps they don't, on one side or the other. I can respect one person's believing something and not respect another person believing something, even if they believe in the same thing. I care not just about what they believe, but why they believe it.
"What do you do when you have a medical problem, nineteen doctors tell you you have condition 'A', and one tells you the opposite?"
Again, you're applying this to the global warming issue, while I'm just speaking in general. Say we switched it to ten experts say one thing, ten experts say the opposite. That sort of situation is probably common, by the way.