The Big Freeze by Philip Reeve
Buster is not happy. Somebody, or something, is spoiling a perfectly good summer holiday by invading Smogley (again!). Don't they know that Buster has better things to do? He has a full schedule of not-going-to-school, biscuit-eating and Busterball. He doesn't have time to save the world from rampaging ice-freaks-really, they could have asked.