I think the easiest way to respond to your response is to do it directly to each part, thus keeping the discussion on track. So here we go!
Here is a simple way that science supports it. 1- Carbon in the air retains heat from the sun more than carbon on or in the ground. This is the greenhouse effect, and I propose that it is indisputable. 2 - Humans are doing things that are putting carbon into the air. Again, this is indisputable. Therefore, more heat from the sun is being retained than would be without the intervention of humans, and this therefore is indisputable.
Can we detect the effects of this extra retained heat? That is much more complicated.
Folks flitting around in jets should be irrelevant to the science. There can be many reasons why they do it. I don't think they should unless it's totally necessary, but I can't control them...
Is it all a scam? Again, this is not really about science. I find it very unlikely that so many different people could participate in a 'scam' of this magnitude. There are too many different motivations involved, many of which would naturally lead to exposing the 'scam.' Scientists don't care about being mainstream. In fact, going against the consensus can often lead to the biggest career gains. Scientists love a theory being proved wrong as much as they do seeing it proved right.
Is mankind ultimately responsible for global warming? That is what the whole of science is trying to figure out. Most people are not comfortable with the ambiguity, but scientists are. Scientists are able to say 'maybe, yes, no, it seems to lead in that direction' and continue on sciencing! So we are currently in a state of 'it seems to lead in that direction.' It is the populace and the politics who want the answer to be 'yes, or no.' For the Scientists to all be able to agree on 'yes,' would require more data and more time. And if we were talking about another planet with no life on it, we could just sit around and wait and watch.
To say we do not understand what causes the Earth's periods of warming and cooling at all is a vast exaggeration. We actually understand a lot about it. We don't know every detail that causes it, and the many variables makes it very complicated, but we do have a firm foundation of science about it.
I think it's wrong to group everyone together ('pop-scientists.') That seems like a defense (or offense?) mechanism designed to make it easy to call everyone with a viewpoint not in your favor, wrong. It's probably more accurate to simply listen to and respond to each scientist individually. A scientist's 'agenda' is to find the truth, not to parrot what everyone else is saying. If many scientists are saying the same thing, that more likely indicates a valid line of reasoning, rather than a mass conspiracy. This is a good time to consider the use of Occam's Razor.
I haven't answered him yet, and will likely not have time to do so this week. I'll post my response when I get to it. In the meantime, if anyone has anything they'd like to pass along, feel free to let me know. :D