Thanks. That article refers to paper doi:10.1016/j.atmosenv.2009.04.044 https://elib.dlr.de/68051/1/fugl-2010-4648.pdf https://elib.dlr.de/68051/1/fugl-2010-46

Thanks. That article refers to paper doi:10.1016/j.atmosenv.2009.04.044 https://elib.dlr.de/68051/1/fugl-2010-4648.pdf https://elib.dlr.de/68051/1/fugl-2010-4648.pdf which says > At pressures greater than 500 hPa (i.e. below roughly 6 km), the forcing [of water vapor] is assumed to be negligible So flying below 6km would help a lot for impact of water vapor. However, given this was not yet acted upon, IPCC is probably right that > the effect of water vapour emissions is likely to be a significant, or even the dominant, contributor to their climate forcing. This is even worse given the projections of aviation expansion. Right now the water does not seem to be a big problem and it could stay that way - water lifetimes even in stratosphere is counted in years, as opposed to centuries for CO2 - but if aviation expands, then it becomes more serious than CO2.