Does anybody know if such a collapse would happen instantaneous or more gradual? With the massive amount of water in motion it feels like it would take a long time to stop, or are fluids behaving differently?
When I used to run simulations, a current of the size of the Gulf Stream could be turned on (with winds and Earth’s rotation), from nothing, in around 400 years (see p. 68). Then it maintained steadily. But turning off or changing in important ways can happen much faster. I’d like to know as well. There should be open-access articles in that journal about this.
My understanding (and I’m not a scientist, I just have read a lot about this), is that there are two flow states of the AMOC. There is a fast state, and a slower state (which we are in now). It seems like it could just stop, but they don’t know for certain that it will ever completely stop. It will more likely just slow to a point where it is functionally dead. The current has already started to slow, so lots of people are trying to make predictive models about just how slowly it can go or when it will “collapse”.
It’s not an on / off situation. It will gradually decline until it finally stops or reaches a critical threshold where it’s movement no longer significantly alters weather patterns. None of these climate change thresholds are as black and white as they are made out to be which is one of the argument tactics deniers use to argue against it. The reality is a slow decline until the affects are unrecoverable from.
There is a fast state, and a slower state (which we are in now).
I think you wrote that backwards.
Actually no. There is a much faster state than what we’re in now, but there is a lot of variability in the flow states. Since we’re approaching the point of a collapse, we’re solidly in the slow state, but not yet at the slowest point. https://www.nature.com/articles/s41586-018-0007-4
But which are the stable states? I was under the impression if a wizard made climate change stop now it would go back to the fast state, since we probably haven’t hit the tipping point yet.
I don’t think there really is a “stable” state that we can point to, just because it is always changing based on the climate conditions, and we have very imperfect data for talking about what it was like even a century ago. I’m also not certain that we haven’t hit a tipping point, from what I’ve read we’ve started to enter positive feedback loops climate wise, so the Earth would keep warming a bit and then stabilize to a warmer-than-it-should-be level even if we stopped polluting now. That would definitely continue to impact the currents.
