This is the part where the argument goes into pure speculation. In order to prove that humans are contributing to climate change, one would have to to separate out all natural factors and be able to show exactly what climate change is being caused naturally and what is likely human caused. As far as I know, nobody has even come close to doing that. The entire AGW theory appears to be based on a Post Hoc Ergo Propter Hoc argument, hardly a viable standard for make scientific conclusions. And even under that weak argument, they have had to manipulate the data.
Indeed.
One of the arguments I use to shut down the the eco-Nazis runs along these lines:
Me: So you say there is GW.
Them: Yes.
M: And that GW is caused by Man’s activity?
T: Yes.
M: Do you think GW is caused 100% by Man’s activity, or do you believe there may be some natural causes, such as sun cycles, atmospheric processing of moisture, wind patterns, ocean currents?
T: Well, I suppose there may be ‘some’ natural causes to GW, but it is mainly caused by Man’s activity.
M: If that’s the case, what percentage of GW would you ascribe to Man’s activity and what percentage to natural causes?
T: I don’t know.
M: Then how do you know how much of Man’s activity we need to curb in order to reverse GW if we do not know what percentage of GW is due to Man’s activity?
T: DENIER! DENIER! Here’s one of those deniers that thinks the earth is flat and who hates anyone and everyone and wants to destroy the earth and is a greedy pig who doesn’t mind killing cute little furry animals and cutting down old trees all for his selfish greed!!!! (Insert picture of red, screaming face here.)
The point being, if we acknowledge that some of the GW (if there is any) is caused by natural causes, we don’t know what percentage. And if we don’t know that, it is silly to talk about curbing activity in order to effect some unknown percentage of change we are seeking.