[Why] Winter is Coming

Many of you are probably familiar with the show Game of Thrones on HBO based on the A Song of Ice and Fire novels by George R. R. Martin. To me, one of the most interesting aspects of the world that Martin creates is the seasonal cycle. For those of you unfamiliar, basically seasons can last many years at a time before changing. I have not been able to find exact numbers referenced, but it is implied that a season typically lasts around ten years. However, in the mythology of the world, some winters last much longer than that, though that only happens every thousand years or so. I found these cycles interesting and wanted to know if such cycles might have a scientific basis. Read on to find out what kind of explanation I came up with.