According to George Kukla, respected former professor of paleoclimatology at Columbia University and researcher at the Lamont-Doherty Earth Observatory, forget global warming and prepare for the new ice age.
As he points out correctly, geological record shows that earth's history has been dominated by ice ages (mini or prolonged ones), with occasional, brief warming periods. The article is worth reading.
My favorite quote of his: "The only thing to worry about global warming is the damage that can be done by worrying. Why are some scientists worried? Perhaps because they feel that to stop worrying may mean to stop being paid."