# Hydrogen economy -> dead Earth?

In a “hydrogen economy”, where we will crack water for hydrogen to burn or use in fuel cells, some of the hydrogen we produce will escape into the atmosphere and eventually into space. Will this eventually deplete Earth of water?

Here’s my “Drake Equation”:
(1) The surface of Earth contains M moles of water.
(2) In a hydrogen economy we will crack C moles of water each year.
(3) Most of the hydrogen we get will be recombined with O2 to make water but, inevitably, a fraction, E, will escape into the atmosphere.
(4) Earth does not have enough mass to hold on to molecular hydrogen; hydrogen that does not recombine with oxygen in the atmosphere will eventually be lost to space. The fraction of atmospheric hydrogen that gets lost into space is L.

The number of years we can sustain a hydrogen economy until all our water is gone is M/(CEL). M could be looked up. For C we could assume that all the energy used by all the vehicles currently on Earth would come from hydrogen fuel cells. E we could guess at 0.01 to 0.05. I have no idea what L is. Do we have millions of years? Billions? Trillions?

I think we would not need to worry so much about the loss of water as we would the excess O2 causing raging fires as the H floated off into space. Assuming that one O was released to the atmosphere for every H, and only the H floated away, the increased concentration of O would lead to increased combustion of our forests. The extra CO2 from the fires would lead to increased global warming and pollution. I think we would burn the place to the ground and overheat the planet before we ran out of water.

Diatomic hydrogen (H[sub]2[/sub]) is quite reactive and will recombine with a oxidizing species quickly; if no place else it will do so in the stratosphere and above where it will react with free positive ions generated by UV radiation. By the time we have to worry about hydrogen loss we’ll have much bigger problems to deal with, like figuring out how the “three sea shells” work on our interstellar spacecraft, and how to get that fetching young yeoman out of a spandex uniform that has no zipper. (This is where the Finite Improbability Generator comes in handy.)

There are some significant problems with the hypothetical hydrogen economy, but this isn’t one of them.

Stranger

We would have to worry about the escaping hydrogen. In the current Scientific American is an article analyzing the loss of gasses off the top of planetary atmospheres, and IIRC it says that hydrogen is light enough to disappear from Earth.

We may only be able to sustain a hydrogen economy for a few hundred million years.

Dammit!

Until electricity is much, much cheaper than it is now, we will not be commercially producing hydrogen from the hydrolysis of water any time soon. Nearly all the commercially produced hydrogen today comes from steam reforming of natural gas. So long as that is cheaper than hydrolysis, hydrogen will remain a fossil fuel.

Don’t we still get periodically bombarded by water bearing astronomical bodies? Like every few million years or so?

That’s good news. So maybe a hydrogen molecule would be, say, 100 times more likely to to return as water than to escape the planet.

I hadn’t thought about that. Maybe it would be enough to offset hydrogen lost from (future) human action.

Won’t the Sun start to expand and cause Earth to be uninhabitable anyway in the same time in that timeframe?

Personally I don’t think there ever will be a hydrogen economy. I think that once fossil fuel is gone our current energy binge (and civilization) will be over, never to recover.

But you can hypothesize a rosy future in which solar, wind, and nuclear energy pick up the fossil fuel slack and civilization continues to chug along. If we still have cars and trucks then we would need to manufacture a high-energy-density, off-the-grid fuel to power them. Hydrogen doesn’t pollute the air, so maybe we’ll be cracking water in this fantasy future.

And paying considerably more per mile than hydrogen from natural gas, which we have hundreds of years worth. Just because green energy is a good idea is not going to overcome the economic obstacle of relatively cheap fossil fuel. At least not without artificial incentives, like onerous taxes on fossil fuels. Green electricity to crack water into hydrogen is just too expensive.

Can you put a ball-park figure on the time frame you speculate with respect to fossil fuel exhaustion? No cites needed since you were just extrapoating on what you think.

We had fairly respectable civilization before extensive fossil fuel use. We’ll have to scale back consumption to an almost incomprehensible, to us, degree. But I disagree that civilization will be over. Then again, maybe we have different definitions of civilization.

I think the Sun expansion problem would take maybe tenfold longer to ruin us than the hydrogen problem would, but it’s really hard to say, especially without working on it. They don’t even create the same kinds of difficulties for us.

So, hold off making any decisions that depend on it.

Everything I’ve read (example) says that life as we know it on Earth has less than 500 Million years and probably only half of that, due to Solar warming, and CO2 depletion.

I don’t believe so. This happened in the very early days of the solar system. The vast majority of those bodies were perturbed out of orbit billions of years ago. I can’t remember reading about any large amounts of water in the major hits that have caused major extinctions since.

It would require bodies that have sat in the Oort clouds for 4 billion years, and therefore not been circling the sun as a comet so that the water wouldn’t be boiled off, being suddenly knocked down to earth. Highly unlikely, to say the least.

But splitting water through hydrolsis into H2 is a good way of storing and transporting solar power. It solves the problem of lead batteries, and allows to use deserts, like the Sahara, to produce lots of electrictiy and then transport it across the country to where it’s needed without using long power lines.

I don’t exactly know what your plan to use deserts for solar energy production entails but you seem to have little experience in dealing with equipment in arid desert environments. Aeolien deserts like the norther Sahara are very erosive environments with large thermal swings, wind-blown grit that contaminates any unsealed lubricated joints, periodic monsoons that will swamp anything electrical, and very delicate microcosms that take years or decades to recover from damage. Next to littoral marine environments this is probably the most aggressive terrestrial environmental conditions for equipment to survive. The idea of covering the Sahara in photovoltaic panels is fraught with difficulty.

As for the viability of using H[sub]2[/sub] as an energy storage and conveyance medium, the problem is that in any uncombined liquid state diatomic hydrogen is cryogenic and will quickly bleed off or build up pressure from environmental heating. Current research into matrix storage systems (in which the hydrogen is stored in some kind of carbon, silicon, or organic-metal substrate offers some possibilities for near-room temperature storage at energy densities that are within the same order of magnitude as petrofuels, but none are ready for prime time. Long term (weeks) storage of liquid hydrogen is only economical and efficient on large scales with a a large volume to surface area ratio to limit heat transfer; small containment vessels end up bleeding off a lot of fuel in order to remain within pressure limits. Also, unlike electrical distribution grids, there is the physical work involved in moving hydrogen from one place to another. So liquid or slurry hydrogen is far from the ideal means to store and transport energy, especially compared to high voltage DC transmission and fixed energy storage systems like large water or pressurized reservoirs that achieve efficiency by scale.

Stranger

Sure. It was a respectable civilization, as long as you don’t mind losing 80% of your fellow humans, probably to hunger. Or don’t have any problems that would require you to move very far or very quickly. Or any one of the niceties that fossil fuels have given us. I don’t think we have a very good picture of what civilization was really like for the average person in the pre-fossil fuel days. For most people, it was hard work for your personal survival. There were certainly those who had it pretty good, and whose stories paint a very pastoral picture, but I most definitely would not want to go back to those times.

I think we need to wean ourselves off fossil fuels, or at least find ways to capture the CO2 they generate, but I also think they’ve done far more good than harm. It’s just time to move on.

Relative to a hydrogen economy, I’ve read a paper that suggests that excess H2 would rise into the stratosphere and participate in ozone-depleting reactions. Which would act much more quickly than any “boiling off” of H2 and depletion of terrestrial water. Unfortunately, I can’t find the cite, but it was published in a reputable journal in the past few years.