(Net) reducer/increaser make sense, yes. I haven’t seen “carbon positive” a lot: in reality, we assume most of our activity frees CO2 (or whatever else), so it’s almost redundant to point out. When it doesn’t, or actually causes a net reduction in whatever pollutant, that’s a Big Deal and we needed a term for it. There’s not much practical room for confusion: same as how a “positive” medical finding might be really bad news, it’s all context.