I am thoroughly unimpressed with the belief that global warming scientists have been engaging in some kind of massive conspiracy to conceal the truth. First, because we seem to be able to observe things like polar ice sheets melting, which point to warming. And second, because, well, why the hell would they? I can imagine a sort of selection bias in the grant process. I cannot imagine hundreds of scientists thinking, well, I put ten years into getting my PhD--time to spend the rest of my life faking data in order to get some grant money! One, yes. All of them, no.
To me, the worry is the subtler kind of bias that we indisputably know has led to scientific errors in the past. Richard Feynman has the most elegant exposition I've ever read:
We have learned a lot from experience about how to handle some of the ways we fool ourselves. One example: Millikan measured the charge on an electron by an experiment with falling oil drops, and got an answer which we now know not to be quite right. It's a little bit off, because he had the incorrect value for the viscosity of air. It's interesting to look at the history of measurements of the charge of the electron, after Millikan. If you plot them as a function of time, you find that one is a little bigger than Millikan's, and the next one's a little bit bigger than that, and the next one's a little bit bigger than that, until finally they settle down to a number which is higher.
Why didn't they discover that the new number was higher right away? It's a thing that scientists are ashamed of--this history--because it's apparent that people did things like this: When they got a number that was too high above Millikan's, they thought something must be wrong--and they would look for and find a reason why something might be wrong. When they got a number closer to Millikan's value they didn't look so hard. And so they eliminated the numbers that were too far off, and did other things like that.
We've learned those tricks nowadays, and now we don't have that kind of a disease. But this long history of learning how not to fool ourselves--of having utter scientific integrity--is, I'm sorry to say, something that we haven't specifically included in any particular course that I know of. We just hope you've caught on by osmosis.
The first principle is that you must not fool yourself--and you are the easiest person to fool. So you have to be very careful about that. After you've not fooled yourself, it's easy not to fool other scientists. You just have to be honest in a conventional way after that.
That is the actual worrying question about CRU, and GISS, and the other scientists working on paleoclimate reconstruction: that they may all be calibrating their findings to each other. That when you get a number that looks like CRU, you don't look so hard to figure out whether it's incorrect as you do when you get a number that doesn't look like CRU--and maybe you adjust the numbers you have to look more like the other "known" datasets. There is always a way to find what you're expecting to find if you look hard enough.