Well without seeking any arguments (as I don't use SP to swap opinions on this kind of thing) the general consensus (regardless of whether it's a valid one) is that if you account (read: modelled using physics, chemistry and super-computers) for all the known natural contributions (solar variation, El Nino, volcanoes, orbital variations, albedo, feedback effects etc.) that there's still some long term warming going on. This warming can be largely accounted for (by most) by modelling anthropogenic contributions such as carbon dioxide, methane etc. Obviously there are lots of error bars, misunderstandings, counter-evidence and things we don't know about (just yesterday I read about a PhD proposal on the contribution of meteorites burning up in the atmosphere). The more people look at it the better handle they'll have on it, whatever's happening, or not happening. If you can make a giant hole in the ozone layer you can do other things too.