The real nightmare scenario is when all these changes begin to rein- force one another. The Arctic loses its summer sea ice, causing Greenland's ice to melt and encouraging the boreal forests to change as well. The freshwater runoff changes the thermohaline dynamics and affects the jet stream. The El Niño–Southern Oscillation and the Amazon interact in such a way as to reinforce one another, perhaps affecting the monsoon in India and Africa. "It wouldn't be such a silly thing to say that if you meddle with one, you might affect the other," says Lenton. "Which direction the causality would go is not always obvious. We know it's connected, we know it's nonlinear, we know they somehow couple together. When you see one change, you see changes in the other."
"Then we start talking about domino dynamics," says Lenton. "The worse case would be that kind of scenario in which you tip one thing and that encourages the tipping of another. You get these cascading effects."
It would take a perfect storm of climate flips to get us to this particular worst-case scenario. If it does come to pass, however, at least it will happen quickly.
For more, see Scientific American