Ice ages come and go slowly not quickly like current climate change has.  The Sahara was once a system of lakes, and Antarctica had plant life.  Dinosaurs lived in northern Canada where tropical plant life existed.  These were due to continental drift.  The Sahara was not where it is now and what is now Antarctica was a lot closer to the equator.  People really have no clue to how long this geologic time is considering their short lives and the evidence that they have been on this planet for a mere 100K years or so.  Geologic time is measured in millions and billions of years, not centuries and millennia.
Humans can probably slow or maybe even halt global warming.  The last fifteen or so years have seen a decline in rising temperature, in fact the rise has almost flattened out thanks to greater fuel economy in automobiles, controls on industrial effluent, the Kyoto Protocol, etc.  So there is hope.