The future is likely subject to a huge addition in greenhouse forcing, whereas the past was in a relatively stable configuration. (planet3.org)
It, like Greenland, is in a far more stable configuration now than it was then. (realclimate.org)
To do this, the cells are driven to a region of instability — like climbers on a mountain ridge line — and they are then left to evolve freely towards one of the two possible stable configurations. (sciencedaily.com)