WC has another post on (I think) climate and economics. As usual, I find his post somewhat inscrutable, but after scruting my best, I think that he's arguing that effects on GDP are the best, or at least a good, way of quantifying the effects of human induced climate change. I have a few problems with this, one of them being that predicting GDP change seems to be a hell of a lot harder than predicting climate change, especially over time periods greater than a decade.
I'm more interested in the prospects for climate catastrophe - climate caused changes severe enough to seriously disrupt civilization. The history of Earth offers us plenty of such catastrophes. The collapse of Bronze Age civilization in approximately 1177 BCE was a good example, albeit one almost certainly far more limited in scope that the kind of global climate change we are now making. The draught that apparently precipitated that collapse saw most major cities destroyed and the hordes of the so-called "Sea Peoples" unleashed on the world. Trade collapsed for hundreds of years and few political entities survived.
A greater climate calamity 70,000 years or so nearly extinguished the human race, and another lesser one played a part in the collapse of the Roman Empire.
The rapid growth of global production in the last two centuries has convinced the gullible (including some economists) that such growth is as natural as the expansion of the universe, but I strongly suspect that is an illusion. Others think it an inevitable side effect of capitalism. What's almost certainly true is that capitalism can only thrive in an era of rapid economic growth and that capitalism is good at exploiting technological change to produce economic growth. What's far from clear is the notion that technology change is an inexhaustible font.
So how could civilization fall apart? I think some tea leafs are already in evidence. The wars in Africa and the Middle East owe something to both population increase and agricultural failure which may be linked to climate change. The migrations they have produced have already helped to destabilize Europe. There is a real threat that climate change could make parts of India and China unlivable - imagine the Sea Peoples reborn with nuclear weapons.
Stick a few major nuclear exchanges into your GDP models and tell me what you get.