My theory of the seasons has to do with The Others (the White-walkers).
When they stir, or a few "wake up," there is a winter.
But, when several awaken, then a brutal winter comes. GRRM has alluded to this since the very first chapter of the series. With the Winter comes The Others. This brings about significant changes to, well...everything. And, if you've kept up with the books, there are things moving into place that both forshadow this occurence and potentially oppose it (the Red Comet, the Red Priest, etc.)
When they stir, or a few "wake up," there is a winter.
But, when several awaken, then a brutal winter comes. GRRM has alluded to this since the very first chapter of the series. With the Winter comes The Others. This brings about significant changes to, well...everything. And, if you've kept up with the books, there are things moving into place that both forshadow this occurence and potentially oppose it (the Red Comet, the Red Priest, etc.)