Which doesn't mean that emitting water vapor from a rocket adds to global warming. It just adds to the rain.

True as long as you intend to fly your rocket within the troposphere, the lower ~10 miles of the atmosphere. Above that, water vapor seems to stick around a long time and is currently understood to be quite harmful[1]. This is also an issue with high-flying planes (not that flying low is better, due to the decreased efficiency). However, more research is needed[2].

[1] http://www.grida.no/publications/other/ipcc_sr/?src=/climate... (kind of old, but I think the more recent IPCC reports are in a similar vein)

[2] https://eos.org/research-spotlights/the-forgotten-water-vapo...

Wow, learn something new every day. Thanks!