Well, scientifically speaking, there is no real disagreement within the community about whether or not global warming is occurring. It is, and we can prove it. The disagreement is whether or not it is caused by humans or not.
The problem we have, is that we just don't have the information available that we need. The fossil record shows large patterns of movement in the climate of the Earth, yet we don't know if this particular one is natural or man made.
Causality is a woman in climate science, think of it this way. City conceded a goal in the last minute of the derby and we got beat 4-3. Now, whose fault was it? Was it the refs for allowing the extra time, was it Richards for switching off, was it Tevez's for missing a few chances? Any of these could have changed the result, yet there is no one cause and no guarantee that if any of them had been changed that the result would have changed. That's pretty much our problem now.
Climate science relies on our computer models being an accurate reflection of the way the climate works. If these are wrong, then everything we know is wrong.
This is one of those areas that I have a keen interest in, and have read extensively on it, and I wouldn't even hazard a guess at it.
What I do know, is that climate change has become a large money spinner for governments and companies. There are so many people getting paid on this issue that it will never be fully resolved. Also, most of the funding for expeditions comes indirectly from the environmental lobby groups or big energy companies, so it isn't exactly hard to believe that the scientists tend to interpret the data in a way that will keep them in a job. Climate science is currently so far away from real science (due to this introduced bias) that it's a shame.
Michael Crichton wrote an interesting (yet factually flawed) book on this, which name escapes me right now, which is definitely worth a read.