Here are a couple of scientific articles from two of the more well respected science organizations in the world. There are a plethora more, though it's hard to wade through the opinion pieces, which are far more numerous. The general consensus among the experts is human activity does have something to do with global warming. And there is a ton of direct evidence. In my mind (I'm not a climate scientist, but as a biologist I have been exposed to a lot of the research over the last 15 years or so), the question isn't so much are we contributing to global warming as it is how much we're contributing to global warming.

Like it or not politically, the way science works within a scientific community on issues like this is driven by the consensus of the expert community, which is informed by the data. Granted, it's easier to get published in a peer reviewed journal with an article that supports global warming than one that tries to debunk it, but in a scientific forum the data will eventually stand up on its own. If someone uncovers a preponderance of empirical data that contradicts human contribution to global warming, it will stand up to scientific scrutiny. The best example of a paradigm changing finding of this sort that I can think of in modern science is punctuated equilibrium. A lot of the evolutionary biology community screamed bloody murder at first, but the data were just too compelling to ignore. Unfortunately, on global warming the data all point in the opposite direction right now, i.e. global warming is happening and we as humans are contributing to it.

http://royalsociety.org/uploadedFiles/Royal_Society_Content/...

http://www.sciencemag.org/cgi/content/full/306/5702/1686