I am told that water vapour is a potent greenhouse gas. Aren't hydrogen fuel-cells therefore eco-unfriendly?

Question

Water vapour is present only in small amounts in the atmosphere, but contributes significantly to the greenhouse effect. Many say that the solution to global warming lies in the use, especially in vehicles, of hydrogen fuel cells, which emit only water vapour. If this water vapour is not forcibly condensed, at the expense of more energy, before being emitted, is it not likely that, in the long run, say 50 years later, be in itself a cause of climate change. Even if the water vapour condenses in the atmosphere and falls as rain, would it not increase global rainfall? Also, what is the truth about suggestions that hydrogen fuel cells emit dangerous levels of hydrogen peroxide, and if so, how may this affect global climate and/or human health?

Answer 1

Unlike CO2, excess water vapor leaves the air as precipitation.

No problem.

Answer 2

This will depend on where the hydrogen comes from.  At present, commercial production of hydrogen is done via steam reforming of hydrocarbons, primarily methane (natural gas).  This is also the process used by Honda in its hydrogen refueling systems.  Approximately half of the hydrogen produced in this method comes from the hydrocarbon molecule (the other half comes from water).  When this hydrogen is burned in the fuel cell, it comes out as water.  Thus, fuel cells operating on hydrogen produced from steam methane reforming, actually increase the quantity of water present in the world.  This additional water will be emitted into the atmosphere, increasing the overall humidity.  Since water is a green house gas,  it could have the effect of increasing global temperatures.  It may also increase the level of rainfall and thus flooding in certain areas, or increase cloud cover reducing global temperatures..  It all depends on how the atmosphere adjusts to the increased water content.  The only thing that is certain is that the quantity of water will increase.

Answer 3

I go into great depth in this q at CoolingEarth.org see wetlands. Water in vapor form is a greenhouse gas, clouds on the other hand reflect sun energy and is much more powerful.

Answer 4

Then so are the oceans and the rain forest!

Answer 5

Hydrogen fuel cells are enormously expensive and don't last long.  This is a far bigger problem than their effluent.

Water vapor is the biggest greenhouse gas (on average) by weight, but only accounts for about half the total greenhouse effect (mostly in the tropics, very little at the poles - this is why AGW warms the poles much more than the rest of the earth).  Also, water vapor only lasts about 9 days in the atmosphere before it precipitates out as rain or snow.  Adding or subtracting water vapor has a very small influence on climate; the movers and shakers are the things which drive the amount of water which stays, how much forms high clouds vs. low clouds vs. vapor, etc.

Answer 6

Each day brings us a little closer to the day when we can kick OPEC off the planet. Hfc's problems are being worked out in Labs all over the world.

Heres some up and coming research.

http://www.sciencedaily.com/releases/200...

The last time I checked water vapor was good thing, but I hadn't considered the points you bring up very good question.

Answer 7

the same suv driving person who told you this probably scoffs at global warming as junk science because it snowed in maine this winter, while thinking that creationism is sound science that should be taught in schools.  Maybe there is a little one sided truth in what you heard, but id rather be breathing water vapor than petrol exhaust, not to mention the fact that we buy that petrol at high prices from countries that want nothing more than to destroy us.

Answer 8

You are correct, water vapor is the most abundant and important greenhouse gas.

The surface area of the oceans are such (70% of the earth), that evaporation from natural sources would make any contribution from fuel cells negligible.

There are fuel cells based on hydrogen peroxide as a reactant, but hydrogen fuel cells produce water and do not emit hydrogen peroxide (H2O2).  Hydrogen peroxide is unstable and very reactive, and has been used as a rocket fuel.

Hydrogen fuel cells emit no pollutants (like internal combustion engines), and have no influence one way or another on global warming.

Keep in mind that hydrogen is not a primary energy source like coal, oil, hydroelectric, and nuclear.  Hydrogen must be MADE on earth, there are no hydrogen wells or reservoirs to tap.  You still need a primary source, that might emit a lot of CO2 (like coal), or none at all (like nuclear or hydroelectric) to make hydrogen fuel.

Answer 9

WikiPedia Greenhouse gas entry has a section on water vapor

http://en.wikipedia.org/wiki/Greenhouse_...

I *suspect* that the lifetime of water vapor is shorter than that for carbon dioxide.

Answer 10

Gasoline burning engines emit water vapor as well. Given how efficient fuel cells are they may emit even less water vapor than a petrol fueled vehicle.

Answer 11

u r right bro....bt h2o can b used to produced h2 again so it is less effective than fossil fuel which produced methane,co2,nitrates