Yeah. But that isn't that unusual in the human experience. In fact, that was the default state of play for pretty much the period from 1900 (conditions become ripe for world wars) -> 1990 (end of the pressing nuclear threat of the cold war). The start date can be dragged back in time if you include the risk of being overrun by Europeans which was a substantial global concern and from which there was no escaping.
We already have some local food shortages here and there caused by climate change which are somewhat smoothed out by global trade for now but that's only the beginning right now so I don't know how long it's going to last.
These risks exist independently of climate change and, frankly, the link the climate people make between crop pressure and these wars is tenuous. There'll be some bad years as farmers adapt. If the scientists are worth the money we spend on them that might be averted.
> When you have economic decline...
I don't think there is any strong reason to suspect that climate change will cause economic conditions to decline. Glancing at Wikipedia, there are figures suggesting that global GDP will be down 30% from baseline by 2100, which assuming 1% real growth rates globally would still leave us better off than we are now.
Even though that sort of model is notoriously delicate.
The current change is absolutely disastrous already and the climate lag will push us even further into chaos no matter what happens.
I really hope we do invent some miraculous tech because that's the only thing I can see being a mattress on the fall down. I'd be in a position of power now, I'd push every last resource I could into this last hope.