Warning non-scientist question..

[Zac Naloen]

Okay. Somethings been bugging me, and i've never really seen it address Re : Global Warming and Hydrogen Fuel Cells.


My understanding is that h2o is a Greenhouse Gas, significantly more effective than co2 is.

So.. the replacement for co2 is to use Hydrogen fuel cells which give off h2o in a gaseous form straight into the atmosphere.

Presumably this hydrogen is going to be obtained from the oceans.

So, the net result from using this will be more h2o in the atmosphere (as entropy means most of it will want to stay in the atmosphere and not be precipitated down).

Therefore there will be a significant increase in the greenhouse effect caused this time by h2o making things worse?

Is my understanding of this completely incorrect?

[drachefly]

When you put water in the atmosphere, it can quickly fall back out, on its own, as rain. The level of water in the atmosphere is determined pretty much by the actual temperature, not so much by dumping water into it.

When you put CO2 in the atmosphere, it doesn't have as many places to go. in particular, it can't rain or snow down on us, nor even dew up.

[Zac Naloen]

When you put water in the atmosphere, it can quickly fall back out, on its own, as rain. The level of water in the atmosphere is determined pretty much by the actual temperature, not so much by dumping water into it.

When you put CO2 in the atmosphere, it doesn't have as many places to go. in particular, it can't rain or snow down on us, nor even dew up.

So it's a 100% efficient system?

[Zac Naloen]

That is to say, everything that goes up, inevitably comes down.

[Ted C]

I don't know if water vapor is a more effective heat trap than CO2, but unlike CO2, water does tend to precipitate out of the atmosphere.

The more obvious problem I see with hydrogen fuel cells is the source of hydrogen. Free hydrogen isn't found on Earth in any significant quantity; it's to reactive. The only way to get it is to make it from water or methane, either of which will require an energy source. If you use electricity from coal-fired power plants to make your hydrogen, you're putting as much CO2 (or more) into the atmosphere as a gasoline engine.

[Zac Naloen]

I don't know if water vapor is a more effective heat trap than CO2, but unlike CO2, water does tend to precipitate out of the atmosphere.

The more obvious problem I see with hydrogen fuel cells is the source of hydrogen. Free hydrogen isn't found on Earth in any significant quantity; it's to reactive. The only way to get it is to make it from water or methane, either of which will require an energy source. If you use electricity from coal-fired power plants to make your hydrogen, you're putting as much CO2 (or more) into the atmosphere as a gasoline engine.

H20 being a major heat trap came from the girlfriend, who's a chemistry student. She only did one term on it though so her knowledge is incomplete. Still much better than my knowledge though.

[General Zod]

When you put water in the atmosphere, it can quickly fall back out, on its own, as rain. The level of water in the atmosphere is determined pretty much by the actual temperature, not so much by dumping water into it.

When you put CO2 in the atmosphere, it doesn't have as many places to go. in particular, it can't rain or snow down on us, nor even dew up.

So it's a 100% efficient system?

Wouldn't that depend on what you were measuring efficiency against?

[Ted C]

When you put water in the atmosphere, it can quickly fall back out, on its own, as rain. The level of water in the atmosphere is determined pretty much by the actual temperature, not so much by dumping water into it.

When you put CO2 in the atmosphere, it doesn't have as many places to go. in particular, it can't rain or snow down on us, nor even dew up.

So it's a 100% efficient system?

No such thing, but energy coming from the sun is more than adequate to maintain the water cycle.

[Ted C]

H20 being a major heat trap came from the girlfriend, who's a chemistry student. She only did one term on it though so her knowledge is incomplete. Still much better than my knowledge though.

To my knowledge, the atmosphere should be maintaining a fairly steady overall content of water vapor, although the vapor content could increase as global average temperatures go up. On the whole, though, it should be maintaining an equilibrium state, with evaporation adding water and precipitation removing water.

Observation shows that global temperature fluctuations follow CO2 concentrations pretty closely, and water temperature concentrations would tend to follow due to warmer air's ability to hold more water.

[Zac Naloen]

When you put water in the atmosphere, it can quickly fall back out, on its own, as rain. The level of water in the atmosphere is determined pretty much by the actual temperature, not so much by dumping water into it.

When you put CO2 in the atmosphere, it doesn't have as many places to go. in particular, it can't rain or snow down on us, nor even dew up.

So it's a 100% efficient system?

Wouldn't that depend on what you were measuring efficiency against?

Efficiency was probably the wrong word to use.

From what I've seen taking Hydrogen from water is the easiest way to get it, if this is the case then extra H2O will be getting put into the atmosphere (in much the same way extra CO2 is getting put into the atmosphere, that was previously trapped). Would all of this get precipitated, or would there be a slight net increase resulting in extra H2O?

Is the use of Hydrogen Fuel cells simply going to mean it will rain more often (like we need more rain in england) or will some stay in the atmosphere throwing off the balance of whats up there?

On the other hand, if there are more clouds reflecting sunlight, does this mean that it will get colder on average?

As you may be able to tell I haven't got a clue and I haven't found anywhere that really addresses this particular subject which is why I'm asking.

[Ted C]

So it's a 100% efficient system?

Wouldn't that depend on what you were measuring efficiency against?

Efficiency was probably the wrong word to use.

From what I've seen taking Hydrogen from water is the easiest way to get it, if this is the case then extra H2O will be getting put into the atmosphere (in much the same way extra CO2 is getting put into the atmosphere, that was previously trapped). Would all of this get precipitated, or would there be a slight net increase resulting in extra H2O?

I doubt that water from hydrogen fuel cells would significantly affect total atmospheric water vapor. The amount of water vapor coming off the oceans should dwarf anything we can put into it.

[Zac Naloen]

I doubt that water from hydrogen fuel cells would significantly affect total atmospheric water vapor. The amount of water vapor coming off the oceans should dwarf anything we can put into it.

I'm sure similar was said about CO2 at one point too

[Ted C]

I doubt that water from hydrogen fuel cells would significantly affect total atmospheric water vapor. The amount of water vapor coming off the oceans should dwarf anything we can put into it.

I'm sure similar was said about CO2 at one point too

The CO2 cycle doesn't work the same way. It won't literally fall out of the air without assistance; plants have to scrub it out via photosynthesis.

Industrial societies really do produce a significant amount of CO2 compared to the Earth's animal life, and human activity has also substantially reduced the size of some of the world's biggest CO2 sinks, tropical rainforests.

Remember that if we're using the oceans as our source of hydrogen, then we're removing as much H20 from the system to make hydrogen as we're putting back in with fuel cells.

[Zac Naloen]

Remember that if we're using the oceans as our source of hydrogen, then we're removing as much H20 from the system to make hydrogen as we're putting back in with fuel cells.

But that H2O is trapped in the oceans, not the atmosphere.


If there is a natural cycle, and we are removing H2O to form Hydrogen on top of that cycle for our own needs. If that hydrogen is then bonded with oxygen to form H2O. Then extra H2O will be going into the atmosphere compared to if we weren't using hydrogen fuel cells.

I understand that the final amount of H2O will be less than that which was taken out originally but this is still adding H2O into the atmosphere that wouldn't otherwise have been there. Right?

But I do accept my knowledge is very much incomplete, and although it makes sense to me it's probably absoluting baffling that I could think this to someone with a view of the bigger picture.

I can't get my head round it.

[Lord Zentei]

I don't know if water vapor is a more effective heat trap than CO2, but unlike CO2, water does tend to precipitate out of the atmosphere.

The more obvious problem I see with hydrogen fuel cells is the source of hydrogen. Free hydrogen isn't found on Earth in any significant quantity; it's to reactive. The only way to get it is to make it from water or methane, either of which will require an energy source. If you use electricity from coal-fired power plants to make your hydrogen, you're putting as much CO2 (or more) into the atmosphere as a gasoline engine.

Though of course, with fuel cells you have the option to use nuclear, amongst onther things.

And wouldn't a gas or coal plant be more efficient than a fleet of car engines, since it always runs at the optimal RPM, with no idling at the intersection, accellerating, braking, etc?

[Ted C]

Remember that if we're using the oceans as our source of hydrogen, then we're removing as much H20 from the system to make hydrogen as we're putting back in with fuel cells.

But that H2O is trapped in the oceans, not the atmosphere.

The forces that move water out of the atmosphere don't care how it got there. There's nothing different about the water dripping from the exhaust pipe of a fuel-cell than water evaporated of the ocean.

[Ted C]

Though of course, with fuel cells you have the option to use nuclear, amongst onther things.

True enough, but they make up a small fraction of the existing electric power supply.

And wouldn't a gas or coal plant be more efficient than a fleet of car engines, since it always runs at the optimal RPM, with no idling at the intersection, accellerating, braking, etc?

I haven't the resources to guess at the relative efficiencies. I believe the energy density of gasoline and diesel are already higher than the energy density of coal, which may be a factor. A lot would depend on the efficiency of the coal plant, the transmission lines to the fuel factory, the efficiency of the fuel-making process, etc.

[Zac Naloen]

The forces that move water out of the atmosphere don't care how it got there. There's nothing different about the water dripping from the exhaust pipe of a fuel-cell than water evaporated of the ocean.

So if we take water and use it to power fuel cells in cars, the atmosphere will then take up less water from the ocean than it would have done otherwise, to balance it out keeping the atmospheric H2O levels the same?

[aerius]

And wouldn't a gas or coal plant be more efficient than a fleet of car engines, since it always runs at the optimal RPM, with no idling at the intersection, accellerating, braking, etc?

The funny part is no, it wouldn't, it would actually end up doubling our energy consumption. I worked out the numbers here and it wasn't pretty. In short, there are massive losses in making & storing hydrogen.

[Feil]

You can't use water to fuel a car. You use hydrogen to fuel a car, and you get water.

Amusingly, when you burn a fossil fuel, all you're really doing is reacting the hydrogen stored in the hydrocarbon with oxygen to get energy and water. Carbon dioxide is just an inconvenient byproduct. I'd imagine you'd get almost exactly the same amount of water vapor per joule by burning fossil fuels as by burning hydrogen, though I'd have to look at the numbers before I would be comfortable making an assertion.

Unfortunately, unless you use nuclear power plants to create the hydrogen for your power cells, you've just moved the problem somewhere else.

[Ariphaos]

According to the Atmospheric Science department at my University, water is 120 times as efficient at trapping heat as CO2 is (per molecule, I think).

Of course, it precipitates, more often during cooler temperatures (ie at night), meaning water vapor tends, overall, to reflect more heat than it absorbs. CO2 traps all day long, however.

[Sikon]

Average annual precipitation is on the order of 1 meter, over the world's 500 million square kilometer or 500 trillion square meter area. Such corresponds to on the order of 500 trillion cubic meters or 500 trillion tons of water annually. (Water is 1000 kg/m^3, which is 1 metric ton per cubic meter). The preceding figure is very approximate, with average annual precipitation possibly different by up to tens of percent, but it just needs to be the right order of magnitude.

In contrast, human fuel consumption is a few billion tons annually, a very small fraction of a trillion tons per year, releasing a similarly limited amount of water vapor in combustion, so there is a difference of a number of orders of magnitude between human emissions of water vapor versus natural evaporation from the oceans and land. And the water vapor from vehicles doesn't stay in the atmosphere for more than days on average, with the water cycle of condensation and rain. There is no long-term continuous buildup, also unlike the situation with CO2.

In general, human emissions of water vapor from combustion are from the equivalent of a few terawatts of average power usage, while natural evaporation of water from the oceans and elsewhere comes from some portion of the 170,000 terawatts of sunlight intersecting earth. The effect of water vapor emissions from vehicles is vastly less than the effect of their CO2 emissions.

With carbon dioxide, the situation is much different, as human emissions have increased total levels in the atmosphere by 30% to 40% already.

[Ted C]

Amusingly, when you burn a fossil fuel, all you're really doing is reacting the hydrogen stored in the hydrocarbon with oxygen to get energy and water. Carbon dioxide is just an inconvenient byproduct. I'd imagine you'd get almost exactly the same amount of water vapor per joule by burning fossil fuels as by burning hydrogen, though I'd have to look at the numbers before I would be comfortable making an assertion.

Although I'll dispute the wording a bit -- burning hydrocarbons naturally produces energ, CO2, and H2O: the CO2 isn't a byproduct, as such -- Feil certainly has a point. Burning gasoline is doing more to introduce water to the atmosphere than fuel cell cars would.

[Winston Blake]

One point that hasn't been mentioned is one that I heard recently - having all the CO2 production that results from the energy needed to make hydrogen means you can sequester the CO2 much more easily. I have no idea if this somehow offsets the lower efficiency of making hydrogen using fossil energy.

The wikipedia article is surprisingly bare, but AFAIK the idea is to use various methods for removing CO2 from the atmosphere. I assume it's simply a man-made improvement on the job plants do. Anyway, having all the fossil fuel burnt at the power station means you just need to attach sequestration plants to fix the concentrated CO2 there, instead of letting all the cars release CO2 into the air first and then trying to collect it all.

[Darth Servo]

The forces that move water out of the atmosphere don't care how it got there. There's nothing different about the water dripping from the exhaust pipe of a fuel-cell than water evaporated of the ocean.

So if we take water and use it to power fuel cells in cars, the atmosphere will then take up less water from the ocean than it would have done otherwise, to balance it out keeping the atmospheric H2O levels the same?

No. Probably more rain will fall to balance the atmospheric H2O levels.