it is true. the last major ice age was triggered by global warming. It has to do with the Gulf stream "switch" or "conveyor"
the gulf stream begins south of the equator and as it flows along the gulf of Mexico it absorbs heat from the tropics. It continues on past the coast of Britain. When it gets up in to the northern regions of the Atlantic, cooled and make denser and it sinks in to the deep sea and goes back the other way.
This sinking is caused by salt in the water. When the salty water cools near Greenland it becomes so dense that it plummets to the bottom of the ocean. The water then heads back south to where the gulf stream began, and the whole process begins again. It’s a continuously circulating belt of water and heat, that’s why it’s called the conveyor.
when global warming melts polar ice caps, it dilutes the salinity of the warm, thereby shutting down the gulf stream switch. and it is this that triggers an ice age.
If you are up for some rather disturbing reading, here is a website. It talks more in depth about the shutting off of the switch, and how it causes an ice age to come on very quickly (2 - 3 years) as opposed to the previously held theory that it came on gradually.
www.commondreams.org/cgi-bin/print.cgi? ... 130-11.htm
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And these changes came suddenly.
For early humans living in Europe 30,000 years ago - when the cave paintings in France were produced - the weather would be pretty much like it is today for well over a thousand years, giving people a chance to build culture to the point where they could produce art and reach across large territories.
And then a particularly hard winter would hit.
The spring would come late, and summer would never seem to really arrive, with the winter snows appearing as early as September. The next winter would be brutally cold, and the next spring didn't happen at all, with above-freezing temperatures only being reached for a few days during August and the snow never completely melting. After that, the summer never returned: for 1500 years the snow simply accumulated and accumulated, deeper and deeper, as the continent came to be covered with glaciers and humans either fled or died out. (Neanderthals, who dominated Europe until the end of these cycles, appear to have been better adapted to cold weather than Homo sapiens.)