In other words you don't need much modelling to see that more expensive food will hurt the world's poor here and now, the climate change thing is in the indistinct future (and it might happen the way we prevision it, or it may not).
Poor people already eat less meat. On the other hand, climate change will make basic foods more expensive. I'm from India. I've seen the miseries caused when the price of rice or onions goes up. It becomes a major political issue. But if chicken becomes more expensive, no one blinks, because people don't eat that much of it anyway. Maybe some people in the cities grumble because prices at restaurants went up, but that's about it.
Your argument is like saying "Taxing Ferraris more will make life harder for poor people because it increases average transportation prices".
We might as well do, but what's the alternative? The less-off people, the plebs, eating less meat? How would that be fair?