Man does affect the climate. But let me just adjust that statement to read "micro-climate". Mankind might have some marginal impact on the climate of the entire planet, but I doubt it is significant. However, we can have a big impact on the micro-climate. That much I know. But it is quite a stretch to say that just because we can affect the micro-climate, we therefore impact on the climate.
My first direct experience of this was when I went in search of one of the locations where An American Werewolf in London was filmed. Don't ask me which scene - the movie came out in 1981, I saw it not long after, and then went hunting for the location in 1991. I do know that the location was Hamstead Heath, and to add to the eerie factor, we went looking for it at night.
Yes, we found the location. It was at the back of a house, which we could see into - just like in the movie. But what struck me was how cold it was out on the Heath. It was summer in London, and quite warm - at least it was warm where the countryside was covered under 10 feet of concrete and tarmac. It was bloody freezing out where there was only grass and trees. The micro-climate of the area surrounding the heath had obviously been affected by the laying down of all that heat absorbing concrete and tar.
It is also why I believe strongly in the idea of the "heat island" effect when it comes to measuring the so-called impact of climate change. I've experienced it first hand - you only had to walk 20 steps out of the Heath, and the temperature went up markedly.
Let me be the first to claim that hunting for a fictitious celluloid werewolf was a large factor in me accepting the sceptical arguments.