How do I tackle this?

Sorry for vertical pics, can't show the whole thing in landscape.

UPDATE: We decided not go. Thanks for the tips! I left the engine and defroster on since when I posted this and nothing's happened. Only the mirrors and rear window are now free of ice. Also, our driveway is pitched downwards towards the house. Even if I cleared the ice, we would've slid into the house or the garage or the deck support columns.