On water vapor and climate change

26 Apr 2006

Got questions about the environment? Ask Umbra.

Dear Umbra,

Coming from a scientific background, I was under the assumption that water vapor was the worst -- or you could say the best -- at causing global warming. Do you believe this to be false, and if not, why is no one talking about it?

Erik Nash

Ask Umbra continues below

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Dearest Erik,

I've decided to use your letter as a continuation of B's from earlier this week.

Spouting off on global warming.

Photo: iStockphoto.

Water vapor is a powerful greenhouse gas. It is the dominant greenhouse gas in the atmosphere by mass and volume, but scientists don't seem to agree on a quantification. It provides maybe 35 to 70 percent of the natural greenhouse effect, 80 percent of the greenhouse gases by mass. But these numbers can be misleading, because the way gases combine is an important component of the greenhouse effect; if water vapor accounts for, say, 55 percent of the effect, that doesn't mean the rest of the gases make up 45 percent. If you are interested in more exactitude, check out this post on the RealClimate blog.

From my understanding of others' understanding, the reason "no one talks about it" -- i.e., the reason we focus on carbon dioxide -- is that we are not directly creating water vapor. We are loading the atmosphere with carbon, resulting in the many metaphors -- adding an extra blanket to the atmosphere, overheating the well-managed greenhouse -- and the techno-speak, "direct forcing." We release the carbon by burning it, the carbon goes into the atmosphere, the atmosphere retains more of the sun's radiation. That is a direct impact we have and should stop having.

Water vapor does offer us "climate feedback." On the simplest level: as the atmosphere warms, it is able to, and will, hold more moisture. Moisture in the form of water vapor, which will be retained and itself make the atmosphere warmer, leading to higher water retention in the atmosphere, and on and on. Comprehending the properties of water vapor in the atmosphere begins to tire my little climate-obsessed head, because it is quite technical. If you (coming from a scientific background) wish to understand theories of how long this moisture feedback will continue, the scary factors by which it will increase projected global temperatures, and more, try that RealClimate link and the Intergovernmental Panel on Climate Change's water vapor feedback page as starting points.

Basically, our "take-home learning" (hee hee, I love these horrible corporate gerunds) is that increased water vapor will amplify anthropogenic carbon emissions. Water vapor is not "the best" at causing global warming, because it has a short life in the atmosphere. Also, we are causing global warming and we have found the easiest, best way to do so is to burn fossil fuels and deforest. No, we don't need to worry about lids on pasta pots. We should, however, feel very sober about the avalanche of climate changes we are bringing upon ourselves.

Unsmilingly,
Umbra

Yours is to wonder why, hers is to answer (or try). Please send Umbra any nagging question pertaining to the environment -- but first check out her FAQs!

The claims made in this column may not reflect the views of this magazine. Neither the magazine nor the author guarantees that any advice contained in this column is wise or safe. Please use this column at your own risk.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

Comments: (6 comments)

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steamed up

While no one really needs to worry about the pasta pot, water vapor as a global warmer merits some consideration from advocates of a hydrogen economy who foresee widespread use of fuel cells in place of today's carbon burners. The "emission" from a fuel cell is water vapor.

by organic boater at 5:24 PM on 26 Apr 2006

No combustion can much affect atmospheric [H2O(g)]

The water just falls out again, quickly.

Also, the hydrogen economy will never exist for other reasons, but if one could be conjured into being, we would find that the cars produced a little more water vapour than today's -- hydrocarbon are compounds of carbon and hydrogen, and when they burn, the hydrogen becomes water -- but still not enough to make a heavily hydrogen-motoring city that doesn't water its lawns a patch, water vapour emissions-wise, on a bicycle-using one that does.

--- G.R.L. Cowan, former hydrogen fan
B: internal combustion, nuclear cachet

by GRLCowan at 6:47 PM on 26 Apr 2006

hydrogen fan, hydrogen apostate

Sorry, GRL, that was not crystal clear. But in fact I am interested in what you and Boater are saying, and was already on the point of asking you to explain "hydrogen economy," in really baby terms.

At our house, when He Who Must Be Obeyed pours the pasta from the pot into the collender, Little Dog and I know much better than to be too concerned at that moment with the effect of water vapor on global warming.

Really, though, what are the plusses and minuses about using hydrogen as a fuel source, especially in transportation, as George W. Bush seemed to think was worthwhile a couple of years ago. (I lose track of time so easily: State of the Union address, 2005? 2004?) It would be terrific to have a decent summary.

And I do not dare ask Umbra Fisk herself. She has never forgiven me for suggesting that she, or definitely someone with her name, might be teaching Magical Meteorological Phenomena at Hogwarts.

Chickens deserve our true friendship! So do fish! So do other sentient beings! Let us learn to be kind.

by caniscandida at 3:14 AM on 27 Apr 2006

Sorry, [H2O(g)] is shorthand for ...

water vapour concentration. Burning gasoline adds water vapour to the air, a process also known as raising humidity. So, to a much greater degree, does watering lawns and gardens, washing cars, filling swimming-pools. None of this affects the climate the way CO2 does.

As for defining the hydrogen economy in baby terms ... why don't you show the best you've got, first. It may well turn out to be good enough.

--- G.R.L. Cowan, former hydrogen fan
B: internal combustion, nuclear cachet

by GRLCowan at 7:02 AM on 27 Apr 2006

hydrogen fuel cells?

OK Graham, thanks, I think I know where you are going with that boron paper, but don't be surprised if I stay home sick the day you give the quiz. Really, what an admirable, tough-love coach you are, encouraging me to leap over such high hurdles!

Let me clarify that I am not so much interested in the emission of water vapor (or vapour, comme vous l'ecrivez la au nord) resulting from hydrogen combustion. I am more interested in the energy required -- how much, and what kind of expenditure is it -- in the production of the hydrogen fuel cells. After our beloved American president made his announcement about promoting the development of hydrogen fuel, and a reformed vehicle industry that would utilize it, and once we all stopped joyously dancing in the streets, some of you environmentalists with a firmer grasp of chemistry than what I can claim (ha!) suggested it was not really worth it. It was in either Audubon or Sierra that I read something to the effect that the production of those fuel cells is just as costly in greenhouse-gas emissions.

I do not know if in Canada you are seeing a new line of TV commercials from the coal industry, being shown in the US. In each of around four of them, there is a darling brilliant ten-to-twelvish-year-old kid, sitting at a computer, announcing how wonderful coal is, and how it will solve all our problems. In one of them, the happy child chirps cheerily that we use coal to make hydrogen fuel cells. And since, as we all know (!!!), hydrogen fuel cells are good, then coal must be manna from Heaven.

Chickens deserve our true friendship! So do fish! So do other sentient beings! Let us learn to be kind.

by caniscandida at 4:20 PM on 27 Apr 2006

When Bush announced the H2 future had arrived,

I said something like, "Well, at least he didn't say fuel ce-- ", and then something like "Oh".

(Internal combustion has a very long future; for many years I thought it would be combustion of hydrogen generated and liquefied at nuclear power stations, shipped in ordinary cryotankers like those on the highway today, just more of them, and poured into insulated tanks in cars.

Then I learned the weight of those tanks -- they're big -- and realized heavier fuels could end up lighter in total, even if their ashes weren't dumped, because their tanks, even with space reserved for ash, would be much smaller, not insulated, not requiring heroic anti-leak design. Duh. Sorry it took me so long, surely everyone else had already got caught up before me?)

--- G.R.L. Cowan, former hydrogen fan
Internal B combustion: real-car range, nuclear cachet
http://tinyurl.com/4xt8g

by GRLCowan at 5:10 PM on 27 Apr 2006

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The Vapor Chase

On water vapor and climate change