Ta for that (the nylon thing's a mad one), but nope, it doesn't answer the question. That remains: what is the feedstock?

Heat that ammonium nitrate to make nitrous oxide, fine, but what's the ammonium nitrate made of?

Wikipedia says ammonia gas and concentrated nitric acid. Fine, but what's that made from?

My big question is; is this stuff adding new greenhouse gases to the atmosphere (a la burning coal), or is it coming from source that doesn't add any (a la burning wood)?

Yes Jim, it's not as big an issue as whether one uses aeroplanes or whatever, but it's just something I'm curious about and the answer doesn't come readily to hand. And, though it be a small choice, if a few minutes feeling fuzzy has such a big greenhouse impact, certainly there are people who would like to choose to lay off it.

(The next question would be what's the comparitive climate impacts of a balloon of nitrous and, say, a can of beer with all its aluminium and stuff - smelters dish out greenhouse gases tens of thousands of times more potent than CO2)