How would climate change bring about the collapse of human civilization?
All of these things put together will put severe strains on unstable parts of the world first, but if the trends are not abated and we end up in 'Hothouse Earth' territory, modern civilization will not be sustainable.
The worst stuff comes when we're talking 3, 4, 5 degrees C of average warming. But the tricky thing is that we don't have a full understanding of all the planetary feedback loops and tipping points.
I hear this a lot from people online. But how realistic is this really? Say we enter 4 degrees of warming. I assume that we will experience food losses in both agriculture and fishing. The expectation seems to be that we will make no adjustments to our supply chains, no adaptations, no restrictions on food waste (currently over 50% in the developed world) or any other attempt to mitigate these factors.
Heatwaves/wet bulb stuff is worrying, and so are hurricanes. I don't want to diminish the problem. But it seems that this argument really rests on an understanding that we don't understand feedback loops, and that they are much worse than we anticipate, and that they lock us in to a Hothouse Earth scenario that pushes us into much higher levels of warming that we anticipate, and etc.
Maybe that's true, maybe it isn't. But I haven't seen any evidence for it, despite how often people parrot it from other Reddit comments or whatever.
It's hard to put in context the scale of the problem, but you have to understand that certain forces of nature are far beyond our ability to adapt to in a way that avoids widescale misery and death.
The plants and animals alive today have evolved over many millions of years to live in a climate that operates in a certain range, on a certain schedule (seasons). Shifting climate across the planet by 4 degrees C means millions of species will be put into a climate they are not adapted for, and along with other pressures of pollution, and habitat loss, these species will go extinct.
As far as fisheries go, higher seat temperatures will cause hypoxic zones with mass fish die-offs and at a certain level of acidity, phytoplankton can't form their shells and that whole food chain collapses. It also means coral not only will die off, but it will dissolve the reefs.
For terrestrial crops, we have some ability to engineer crops that are more drought resistant and can stand some level of heat waves. Not only that, but the pollinators that many crops depend on will be severely impacted. When droughts wild fires, floods, sudden cold snaps, and the like are frequent and severe, it is very unlikely human kind will be able to sustain agricultural yields in a way that won't result in famines, particularly in the developing world.
There are already parts of the world that are unstable and have difficulty supplying resources to their populaces. Add these stressors and it is all but certain that basic order will break down in those parts of the world on a scale that is hard to fathom.
> I assume that we will experience food losses in both agriculture and fishing.
You're underestimating the scale of losses and assuming that whatever we do (other than preventing it in the first place) will actually have any significant effects on this, which there is no evidence for.
Think about fresh water losses, irrigation, and then try growing all your food inside and you'll understand.