The implication of the meme is that the people talking about how stupid the protests are are actually blind to the very real climate change happening. They might know about it, but they don't really comprehend that defacing the Stonehenge is nothing compared to it being completely underwater, alongside the whole area.

Whether the comic is right or wrong is another thing, and the other guy arguing in bad faith is a cunt, but I strongly believe that's what the comic is meant to portray.