There is a comprehensive post by George Musser on the Blog of the Scientific American about the argument for anthropogenic warming. It lists the different fingerprints of different mechanisms of warming, that is what we would expect to observe if global warming were caused by increased solar radiation, greenhouse gases or other causes. He then lists all the observations and compares them with the predictions, thus making a clear case that it is indeed the greenhouse gases that cause the warming.
Climatologists have maps and time series showing how a boatload of climate variables — mean temperature, temperature ranges, air pressure, precipitation, and so on — vary in time and in space, horizontally across the surface and vertically through the atmosphere. These data sets are a gold mine for resolving ambiguity, because the different forcings leave distinct fingerprints.
It is worth to read the whole post, whether you are skeptic concerning AGW or need arguments when discussing with one.