Arena of the Ice Queen: Book 1 of The Restoration

Five hundred years have passed since the evil Lord Gar was banished into the Void. The world is plunging into an age of ice, and not even the caretakers--Master Klaybear, Master Thalamar, Sir Blakstar, and Lady Kovaine--understand why. As the ice flows mercilessly from the north, the seas withdraw, leaving all the ports high and dry. Crops begin to fail, and many people have begun to migrate south to escape the ice.
A new generation of heroes, guided by the caretakers, must rise up to face this new challenge, first discovering why their world has turned cold, and who is responsible for this change.