There are lots of explanations for climate change. It could be caused by chemical pollution of the air and the air quality has certainly changed for the worse. Perhaps it's simply a natural change that happens every few thousand years. I've read there was a mild ice age during the middle ages.
But I have the true explanation. It's the skateboarders. They jump up and down so much that they've tipped the planet. ;-)
Okay, I'm being silly.
Whatever the real cause, I guess we'll have to figure out how to adapt and cope with it.