Much is made of our current hydrocarbon-based energy and industry economy and the resulting pumping of carbon dioxide—CO2—into the atmosphere, with the supposedly bad planetary warming associated with that pumping.

Hydrogen production is being seriously looked at as a substitute source of energy, along with solar and wind energy production (although the extreme costs and environmental pollutions of the latter two are being ignored). Hydrogen, though, is supposed to be utterly clean: its only product from use, after all, is water.

Air Liquide, one of the three truly major producers of hydrogen for energy production use, for instance, believes that hydrogen will be

powering buses and smaller commercial vehicles by 2025 and big-rig trucks, trains, and cars by 2030. Ships and airplanes will take longer still. The market will need support for years but seems likely to get it.

And there’s hydrogen-based energy to power industrial production. But what about that water that results from hydrogen use? What about, in particular, the vast amounts of water that would get produced (reproduced, since the hydrogen will come primarily from splitting water molecules) were hydrogen to become as ubiquitous for energy production as hydrocarbons are today? Where would all that water go?

Much of it would, to be sure, be used as liquid—drinking, food production, even aquifer replenishment in the few places where that would be practical. Much of that water, though, would be evaporated into the atmosphere. And there’s the rub, maybe.

Today’s Earth is two-thirds covered by clouds, on average (with wide variations by region, season, whether over land or sea, but we’re talking about the planet as a whole here). Clouds have three contradictory effects on planetary temperature. One is that they’re fine infrared reflectors, so as the earth radiates its heat (from lots of sources, one of which is industrial activity, another is loss of heat absorption at the surface due, among other things, to human clearing of land for urbanized use), clouds reflect that heat back to the surface—if not contributing directly to global warming, contributing to global not-cooling.

Another cloud effect is blocking sunlight, which prevents solar heat from getting to the surface in the first place. The third effect is from clouds’ albedo: they actively reflect sunlight back into space. This is related to, but separate from, the simple blocking effect.

What are the relative weights of the three effects? Today, that two-thirds coverage is in relative balance for today’s planetary temperature.

What happens, though, if a planet-wide hydrogen energy economy pumps significant amounts of water vapor into the atmosphere to become an increased level of cloud cover? We worry about increasing atmospheric CO2, yet the lifetime of CO2 in the atmosphere is measurable in a very few decades; it has constantly to be replenished to have any warming effect. Individual clouds might last a few hours to a very few days, but the aggregated cloud cover is permanent relative to human lifetimes.

Just a thought.