Here is what NOAA has to say on the subject:
http://www.ncdc.noaa.gov/oa/climate/globalwarming.html
With regards to the way science this complicated works: everything is a theory. None of them are "proven" the way a mathematical theorem is proven. There are just lots and lots of observations that, over time, come to compel a majority of the community to accept the theory as the best working theory and that theory gets tweaked over time.
An example: there is a scientific theory that the US sent men to the moon. There are scientists that argue that the US, in fact, faked it in order to win the Cold War. What do you believe and why?
Another example: when you took science in high school and perhaps even in college, the teacher told you that objects in a vacuum fall at the same rate regardless of their weight. You know, the whole Leaning Tower of Pizza experiment. Would you be surprised to know that that "fact" is not the whole truth? That there are several theories that better explain mass and that thing that we call "gravity"?
Me? I worked on LANDSAT in college. I saw enough raw data then to convince me and nothing to change my mind since.
Regards,