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I have not a climate expert but I can give the abstract math answer to what is a boundary. A dynamic system can have several stable states. There can exist for

I have not a climate expert but I can give the abstract math answer to what is a boundary. A dynamic system can have several stable states. There can exist forcing functions F_param, which can push the system towards different directions. Due to the interaction of the these pushes, the system can settle into a single stable state. Now, start changing one param, which only linearly changes one of the forcing function's direction. But eventually, the forcing function param will cross a value so that instead of the system accelerating towards the first stable state, the system starts accelerating towards another stable state. That crossover point for param is the boundary. In other words a linear small change in param can create a highly non-linear and large change in the state of the system. That is the intuition about keeping warming below 2C, for example. Once Delta T goes beyond 2C, the system starts rapidly accelerating towards a new stable state which is very bad for humans.

retrac 3y ago
There are examples at a smaller scale. Nutrient pollution (nitrogen, phosphorous fertilizer in water) can build up for quite a while in a lake with no apparent effect. For reasons not well understood, sometimes after quite a long time (many years) of rising nitrogen/phosphorous levels, run-away growth of algae occurs suddenly and rapidly, depleting the lake of oxygen and killing off most animals and plants. Lakes and ocean regions which have undergone this process thoroughly become stable in their own way, with anaerobic bacteria and algae, but no plants or fish: https://en.wikipedia.org/wiki/Dead_zone_(ecology) https://en.wikipedia.org/wiki/Dead_zone_(ecology)
nostrademons 3y ago
That's very helpful, thanks. It sounds like the implication is that the earth has already left the stable equilibrium of the holocene and has now entered chaotic-behavior territory. This squares with a lot of the other climate science I've read (eg. 1.5C being the boundary and us going past it, my wife's climate-change focused employer shifting the focus from mitigation to resilience, or just private chats with climate scientists where they admit that yes, we're past the point of no return) and geologists now saying we're in the anthropocene era. I'm not entirely sure I'd classify this as being "very bad for humans" though. It does mean that our assumptions about very basic things like "Can humans live in this part of earth?" may not be valid. But humanity (and life) in general has proven to be very resilient. It's probably bad news for a significant number of specific humans, and very bad news for the social systems that currently bind us, but it seems likely that some form of descendant from humanity will survive.

retrac 3y ago

There are examples at a smaller scale. Nutrient pollution (nitrogen, phosphorous fertilizer in water) can build up for quite a while in a lake with no apparent effect. For reasons not well understood, sometimes after quite a long time (many years) of rising nitrogen/phosphorous levels, run-away growth of algae occurs suddenly and rapidly, depleting the lake of oxygen and killing off most animals and plants. Lakes and ocean regions which have undergone this process thoroughly become stable in their own way, with anaerobic bacteria and algae, but no plants or fish: https://en.wikipedia.org/wiki/Dead_zone_(ecology) https://en.wikipedia.org/wiki/Dead_zone_(ecology)

nostrademons 3y ago

That's very helpful, thanks. It sounds like the implication is that the earth has already left the stable equilibrium of the holocene and has now entered chaotic-behavior territory. This squares with a lot of the other climate science I've read (eg. 1.5C being the boundary and us going past it, my wife's climate-change focused employer shifting the focus from mitigation to resilience, or just private chats with climate scientists where they admit that yes, we're past the point of no return) and geologists now saying we're in the anthropocene era. I'm not entirely sure I'd classify this as being "very bad for humans" though. It does mean that our assumptions about very basic things like "Can humans live in this part of earth?" may not be valid. But humanity (and life) in general has proven to be very resilient. It's probably bad news for a significant number of specific humans, and very bad news for the social systems that currently bind us, but it seems likely that some form of descendant from humanity will survive.