If all cars were run with hydrogen and spewing water vapour---?

Question

how much green house gas (water vapour) would be entering our atmosphere and causing climate change and would this vapour be worse, or not, than CO2.

Answer 1

There would be no change. The hydrogen would have been generated from water in the first place. Burning hydrogen would simply return water to the atmosphere. Nature balances the amount of water in the air .. if it's too saturated, it rains.

Answer 2

If the hydrogen vehicles emitted the same amount of pollution as gas powered vehicles then it would be about 6 billion tons a year of water vapour that was released into the atmosphere each year.

There's already 14 trillion tons of water vapour in the atmosphere so adding another 6 billion tons would make almost no difference. To put it into perspective, each year there's about one quadrillion tons of water vapour enters the atmosphere through natural evapouration, fortunately the same amount falls as rain.

Water vapour is a very weak greenhouse gas, by far the weakest of all the greenhouse gases.

Most importantly, the amount of water vapour in the atmosphere is limited by it's physical properties. If you add water vapour to the atmosphere then it falls as rain a few days later, add more water vapour and it rains that little bit sooner. No matter how much water vapour we produce we'd never increase the amount in the atmosphere so the contribution that water vapour makes to global warming will remain constant.

Answer 3

Water is important if you're thirsty or want to go swimming on a hot day, but...
Whenever three or more contrarians are gathered together, one will inevitably claim that water vapour is being unjustly neglected by 'IPCC' scientists. "Why isn't water vapour acknowledged as a greenhouse gas?", "Why does anyone even care about the other greenhouse gases since water vapour is 98% of the effect?", "Why isn't water vapour included in climate models?", "Why isn't included on the forcings bar charts?" etc. Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing. From personal experience, I am aware that these distinctions are not clear to many, and so here is a more in-depth response

http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/

Answer 4

Actually, H2O (in vapor form) IS a greenhouse gas, but the question is, whether H2O in the atmosphere is as bad of a greenhouse gas as CO2? I don't know the answer to this. I think I read CO2 is worse, but can't confirm it. In fact, there are worse greenhouse gases than CO2, like methane. But, even if H2O is a greenhouse gas, this earth is fitted with the water cycle, which is constantly recycling water into different forms. Would the effect of H2O emissions result is more rain? I don't know, but I believe switching to a hydrogen based fuel system would be a step in the right direction.

Answer 5

John Walkup said:
"[water vapor] is included in all climate models, but it is a feedback and not a forcing."

This is such BS, I have to laugh every time I hear it.

The concepts of "feedback" and "forcing" are entirely artificial constructs created so that computer modelers can make sense of global climate. The whole notion operates under the invalid assumption that there is some "zero" point - a climate "equilibrium", which might be true if the Earth has an entirely homogeneous surface and troposphere. It most obviously doesn't. Climate depends upon these none too subtle differences.

The GW crowd loves to hoist out the argument that water can't be a forcing because it cannot exceed this imaginary "equilibrium" - ie, it "rains out". This might be true if water vapor uniformly diffused. Anyone with even a modest knowledge of meteorology knows this to be ridiculous. The chaotic movements of water vapor are what makes predicting the weather so difficult in the first place, which is likely why climate modelers prefer to average this chaos over an arbitrary unit of time - again making an invalid assumption that, over time, one can expect a uniform variation of water vapor cycling into and out of the atmosphere.

Modelers like to claim that water vapor only stays in the atmosphere for "days", while CO2 stays for "centuries" and use this as a justification for relegating water to the role of "feedback" instead of "forcing". They seem to totally gloss over the fact that CO2 has a strong feedback signal relative to water, entering and exiting the atmosphere dependent on temperature - and additionally, hitching a ride back to the Earth's surface every time it rains.

But there is an even more glaring omission that modelers appear to gloss over: While water vapor DOES remain in the atmosphere a relatively short time, its cumulative thermal energy DOESN'T. The energy price that water vapor "pays" in order to precipitate out to eventually reach the surface is its latent heat. That heat remains in the atmosphere, more often than not absorbed by neighboring water vapor and droplets. The formation of thunderheads and hurricanes are testament to the incredible amounts of energy this represents. For what it's worth, CO2 molecules do NOT pay this same price when they reenter the cycle at the Earth's surface - they take their energy with them.

They also gloss over the fact that water vapor entering the atmosphere is not simply a temperature dependent phenomenon. This includes water vapor from hydrogen-fueled cars (humorously enough, the most likely large-scale source of this hydrogen will be derived from hydrocarbons, ie, fossil fuels). More importantly, this also includes every fossil fueled vehicle out there, spewing an equal amount of "ancient" water vapor to go along with its "ancient" carbon dioxide. All totally independent of temperature.

And let's not even get into increased transpiration and respiration of the Earth's biota - part of the natural reaction to the return of all this fossil carbon back into the carbon cycle. This, too, represents a significant increase of water vapor into the atmosphere independent of temperature.

Answer 6

The effect on climate would be zero. Water stays in the air for a few days before precipitating out. CO2 stays in the air for centuries.

That means that, while a world of H2 powered vehicles might make small changes in the weather, it would not change climate at all.

Answer 7

Virtually none. Excess water vapor will simply precipitate out of the atmosphere.

Answer 8

Well, it would not be CO2. It would be H2O and that is not a green house gas. I suppose even that could be a bad thing. maybe if we made enough water to raise sea level. But I'l bet it would take a lot of cars and trucks to do that.

H2O is a green house gas? Looks like I spoke without thinking. Is there a sort-of sliding scale here? some worse than others? I hope so....gotta salvage some pride.