I'm sorry to be blunt, but this just doesn't fly. Ruddiman's hypothesis is neither here nor there with regard to the cause of recent warming. If anything, it's logically inconsistent to argue that a small change in GHG in pre-industrial time did affect climate and yet a large change in GHG in the present day isn't affecting climate. And snowball earth was > 500 MYa, which is way outside any relevant time frame for current global warming (the continents were in completely different places, for a start).  Finally, Ruddiman himself would likely take exception to being thrown in with the "scientists objecting..." camp  the fact that his latest book is "Plows, Plagues, and Petroleum: How Humans Took Control of Climate" gives a hint as to his stance on recent warming.