We've also seen the lowest sea - ice thickness, and we've seen the greatest amount of water vapor in the atmosphere. (scientificamerican.com)
Another process knows as a «runaway greenhouse» occurs due to the increased greenhouse effect of water vapor in the lower atmosphere, which further drives evaporation and more warming. (haqqmisra.net)
Outside of an increase in temperature, I don't see any particular reason to expect hydrogen - based fuels to do anything to increase the concentration of water vapor in the air. (realclimate.org)