Actually, most of the "skeptics" that I've seen online are right on top of this kind of stuff! It's the other side that just wants to hand-wave away far too many things.
> 1) The absorption spectrum of CO2 and other greenhouse gasses: test-able with an aquarium and a UV light
If you want to have some "fun", go track down a full spectrum chart of sunlight and how carbon dioxide and water vapor and such absorb that sunlight. Pay particular attention to the infrared band, which is very large. What do you see?
As to your aquarium example, some years back a "skeptic" once very publicly tried to replicate a similar experiment - one that was claimed to have been done many times and which clearly showed the greenhouse effect of CO2. Only it didn't replicate as described, as I recall, implying that the example itself may very well be bogus. Also, IIRC, another group ran a similar experiment sometime later and claimed a positive result. Except that even a layman like myself could clearly see that their experiment was very poorly controlled, and not nearly as cleanly run as the first one. So while they happily claimed a successful replication, in fact they never actually proved nor disproved anything, as far as I could tell.
> 2) That aggregate 24/7 human industrial activity (ie all: cars, boats, planes, construction, smelting, BTC mining, etc), is somehow increasing greenhouse gasses: this is tested by checking the air, if seeing smog clouds or logic isn't proof enough
This includes water vapor, perhaps the most powerful and important of all the greenhouse gases on Earth. Yet for some reason this is almost completely ignored by the anti-CO2 crowd.
> 3) That Venus exists, our telescopes are not lying, and we don't want to take vacations there
If you want to have some more "fun", go look at the CO2 concentration in the atmosphere of Venus, which is very hot. And while you're at it, go look at the CO2 concentration in the atmosphere of Mars, which is quite cold - cold enough that the CO2 actually freezes out of the air there on a regular basis. Tell me what you find.
> Climate change has been on the end of a 50 year FUD campaign meant to confuse the issue so that laymen only hear the arguing.
So it's 50 years now, is it? Seems a little long to me but whatever. What's important here is that this is another claim of "FUD", no doubt directed at the fossil-fuel industry. But IMO claims that this are often made less to point out "the truth of the matter" (in their opinion) and are instead usually more of a cheap-shot attempt to convince folks not to listen to the points being made by the other side (or to try and justify their own refusal to listen), which often call out glaring weaknesses in the overall argument.