The reverse of global warming you may be referring to is the threat of the shutdown of the Gulf stream and the deep salt water conveyer (from Iceland to mid Pacific).
It is proposed that this occured when fresh water flooded the Greenland/Icelandic area, reducing the salinity (a major climatic trigger - bigger than el nino/la nina).
I am not sure that the climate theorist have taken into account the large dose of pollution (added salinity?) in comparing their models to the prehistoric record.
There is another state of oceanic equalibrium found in the paleontological record and that is one of the ocean settling into two or more layered zones. If I recall properly, this record correspondes to periods of high temps and high seas.
Another potential missing part of the climatic model is the impact of human activity to thwart the coming of an ice age. All our traffic, night lights, air conditioners, heaters, power plants, autos, and so on create a large heat footprint that was not in effect the last time the Gulf Stream flipped "off".
The most likely result of the Gulf Stream stopping would be an Ice Age, but another steady state has dominated the planet and its lifeforms in the past.
Those who think human activity has no influence on the planet and its atmosphere must think we as a species are insignificant in comparison to cyno-bacteria and lichens - the first settlers and builders of the world we have inherited.
"polars flipping again", a reference to the Magnetic Poles - the shifting of which is long overdue. This would have some impact on the climate because the ionosphere and the earth's magnetic fields would flux, possibly a decrease in ozone. Which is a whole different set of problems.
