I think this is about the silliest work of science fiction I've ever read: in a near-future world in which Earth is trapped in the twin grips of an ice age and radical environmentalism, two space colonists are forced to make an emergency landing in North Dakota, and it's up to the SF fan underground (yes, really) to get them safely home. For all the humour it's still hard SF, with a distinct Kim Stanley Robinson feel to it, and it's an interesting read, although the authors clearly have an axe or two to grind with the environmental movement.
Unfortunately, the positive portrayal of Scientology in a couple of places left a bad taste in my mouth; I don't think that's really something you can gloss over and get away with. Niven, Pournelle and Flynn really ought to know better.
Available from the Baen Free Library.