Do you have a clear concept of a viable solution? (Hint: Killing the ecosystem that sustains humans is not it.)
Nuclear. Solar farms take 450 times more land than nuclear to produce the same amount of energy (source: https://www.forbes.com/sites/michaelshellenberger/2018/05/08...)
Also, I don't see how you could build sufficient nuclear capacity in time to sufficiently reduce carbon emissions without compromising safety (after all, nuclear energy is inherently extremely dangerous--the fact that we so far have been able to operate it very safely does not mean that that is an inherent property of the technology that we could maintain if we tried building hundreds of gigawatts in a decade). Nuclear (fission) energy might have been a sensible route in the past, but it doesn't seem so right now.
After all, "solving climate change" is technologically a solved problem. Humanity has all the technological knowledge to switch to carbon-free energy production. The problem are the costs of that switch based on current technology. But if we can't reduce the costs further, that still does not invalidate the demand of protesters who don't want to be stuck with paying the massive price of having to deal with a broken ecosystem later. It's still a perfectly justified demand that current generations pay in order to avoid costs for future generations.
You do the same. You claim it is "technically a solved problem". It really isn't. You are just naive about "renewable energy".
> They believe everything could just be switched over to renewables at no cost,
> in fact, they think it would be cheaper to do so.
So, how do you know that is not the case? (And no, pretending that climate change won't cause any costs is not how this works. If your stance is that climate change won't have any costs, that's on you to demonstrate.)
> You do the same. You claim it is "technically a solved problem". It really isn't.
So, which part of it is not technically solved?