Look. I know that (a) this was meant as a metaphor, and (b) climate change is no laughing matter. But, at the same time, (a) the metaphor doesn’t really work, and (b) HA, HA, HA, HA, HA!
I guess the point is that climate change will lead to rising sea levels and so, with the passing of epochs, the human race (which for some reason will resolutely refuse to move inland) will evolve to look like fish. From the neck up.
To truly get the metaphor, you’ll just have to suspend your belief in the incremental nature of evolution by natural selection. I mean, it would take tens of millions of years for human beings to grow fish-heads. And if you’re worried about what the human race will look like in tens of millions of years time, then you should, well…calm down. It will certainly look different. Let’s leave it at that.
Also, that shirt is just all wrong.
But I guess the real point is that climate change will lead to rising sea levels.
(I do like his shirt, though.)