[cbacba]

First off,

With any linear negative feedback system, there are an infinite number of stability states. It's a linear rather than digital situation. There's absolutely no reason to think there are only a few plateaus of stability around or that there are places which are any more 'stable' than any other. The universe pretty much operates in a linear fashion despite its discrete foundations until you reach them at the quantum level.

Earth's temperature is a function of the parameters that go into causing it to be what it is. All of them within this tiny range are linear variables. their changes are linear. Not even such absolute points such as h2o freezing or boiling points are actually linear as the earth is an orb, not a flat pizza pan so those temperatures would not be reached instantaneously at all spots - making it linear NOT digital.

Freezing water is 273K. Boiling water is 373K (1 atm press.) Thats a range of 100K. 100K forms a range over temperature of 100/323 = 30%. A 1 degree variation corresponds to a change of 1/323 = 0.3% . Those points are major rails that when reached, the major factors affecting our climate will change (assuming uniform temperature) and new sets of parameters will become the dominant factors.

When you're talking about the earth's temperature change from GHGs, you're basically talking about a tiny amount, a tiny fraction of the overall temperature. Even a well designed feedback control system using PID doesn't keep things perfectly at a setting. As input parameters change, control parameters act or counteract because of a slightly different condition that changes their value.

As for ocean currents, they are a result of differential heat causing heat flow transfer. They're somewhat like rising bubbles in a pot of boiling water. If the conditions are such that there's not enough energy to cause them to happen, they stop. If there's enough energy coming in to create the differential heat, they'll start. If you built a wall across and through the ocean to stop them, they'd eventually find a suitable efficient alternative. It seems some of the mainland europeans were wanting to or trying to build power stations that exploited this current to generate electrical power. I think perhaps they believed it to be a form of 'green' power with no fuel consumption, not even nuclear. I wonder if they have given up or cancelled their plans on that now.