Can someone please clarify the importance of water vapour as a greenhouse gas?

Question

Please correct me if I am wrong, but my understanding of the theory of co2 causing temperature increases is that an increase in co2 in the atmosphere will act as an amplification that will trigger more warming. One of the amplifications is that an increase in co2 in the atmosphere will heat up the earth, which will increase water vapour (another greenhouse gas), which will heat up the oceans, releasing more co2, which will cause a further temperature increase, that will increase water vapour, etc.etc.

In another question, a contributor gave the following answer to an answer. "Because excess water vapor falls out of the air as precipitation, it CANNOT cause warming." There seems to be a contradiction there. Any clarification would be appreciated.

Answer 1

Water vapor is the primary greenhouse gas.The theory (positive feedback) is that increase in CO2 will increase the temp. This in turn will cause additional evaporation of water causing more CO2 to be released form the oceans causing more CO2 induced warming. This cycle would continue till everything is gone.

There are some very big problems with this theory though. The first is that an increase in water vapor means additional clouds. An increase in the cloud layer deceases temperatures. Studies have shown that the net effect of increased water vapor will be lower temps because of this effect of clouds.

Also, the original theory says that warmer temps will release additional CO2 from the oceans. This part of the theory is correct. Higher temps allows more CO2 to escape from the oceans. The fallacy comes into play as to the increase in CO2 causing more heating. For every increase in CO2, the heating caused by this increase is reduced. Eventually, no matter how much CO2 is put into the air, there will be no corresponding increase in temp. Think of it this way. If you have a red wall, and you paint a coat of white paint the wall will be more pinkish.  Another coat of paint will make the wall a little more white. Eventually, the wall is white and no matter how many more coats you apply, the wall is still white. CO2 acts the same way. At some point, no matter how much more CO2 is added to the air, there will be zero additional increase in temperature.

Answer 2

First of all global warming is some man made fear like other fears. Second of all since the beginning of time we have had freeze overs and warm overs. So it doesnt matter what mankind does the earth does what it wants to do. The scientists neglect to tell you the closeness to the sun the earth is today then it was  100 yrs ago. The whole universe shifts even though we are in orbit.  Eg: Other planets near earth at certain times etc. Remember matter cannot be created nor destroyed, so the burning of any matter gas, oil , wood, etc goes into the atmosphere and then those molecules then re-shape into other matters like trees, human, animals, etc. My suggestion is to relax enjoy what we have here on earth because humanly we are only here for 80yrs on average.

Answer 3

I answered a similar question already. Please follow the link and it should help clarify things a bit more for you.

Hope this helps!

Answer 4

There are many greenhouse gasses. We produce the most CO2 but water and methane and even refrigerants are bad. Killing off the ozone layer is a big problem and we can solve it.

Today here is what we know:  many of mankind’s advancements cause earth surface to warm, destroy the ozone layer, kill off endanger species, heat cities, and in some way cause more destruction.  Blacktop (roads and parking lots), buildings, air pollution (causes lung and other diseases), deforestation, duststorms (which increase hurricanes and cyclones and cause lung diseases), fires (cause pollution, mud slides, and deforestation), refrigerants (like CFC's), solvents (including benzene destroy the ozone layer raising skin cancer rates) and plastics; cars, airplanes, ships and most electricity production (causes pollution including raised CO2 levels) are human problems we need to fix to keep life on earth sustainable! The federal government needs to adopt a pollution surcharge to balance the field and advance new technologies. We must pay the real price of oil (petrochemicals) including global warming, cleanup and for health effects. But with that we must understand we have never seen what is now happening before. CO2 has never lead to temperature change, but temperature change has led to increases in CO2. The models have to be made as we go along with little evidence! The result is:  change is on the way, we just do not know what changes. But again adding a small amount of CO2 to the atmosphere enlarges the earths sun collection causing warming; increase water in the atmosphere and they form clouds cooling earth but causing flooding. Even natural events are warming earth and causing destruction. The sun has an increased magnetic field causing increases in earthquakes (more destruction), volcanoes (wow, great destruction), and sun spots. Lighting produces ozone near the surface (raising air pollution levels). But humans have destroyed half of the wetlands, cut down nearly half of the rain forest, and advance on the earths grasslands while advancing desertification which increases duststorms. The USA Mayor's have taken a stand and I believe are on the right track, we can have control and can have economic growth. With the peak of oil in the 1970’s, the peak of ocean fishing in the 1980’s, humans must stop procrastinating and make real changes to keep earth sustainable including in the energy debate, finance and regulation. The sun is available to produce energy, bring light to buildings and makes most of human’s fresh water. Composting is the answer to desertification. New dams are the answer to fresh water storage, energy and cooling earth by evaporation, we need many small one all over (California needs 100 by 2012 and has not even started).

President Bush has made a choice of energy (ethanol) over food and feeding the starving people around the world; this is a choice China has rejected.

Answer 5

Water accounts for 60% of green house gases.  The miniscule increase in CO2 is "chicken little" hysteria.  If the theory was true:  the hotter it gets the more water vapor there is, which makes it hotter, which makes more water vapor.......We all melt.  Therefore logically it's B.S.  Notice:  I use NASA sources, not hearsay, self gratification ones.

Answer 6

mcorr55's link to NASA is a good link that gives the basics of water vapor, but what he failed to tell you is how important CO2 is. I show the link regarding CO2 from the same NASA website. Here is an excerpt...

"Carbon dioxide (CO2) traps heat in Earth's atmosphere like a warm blanket. CO2 is the most important greenhouse gas that is increasing in concentration due to human activities. This is because carbon dioxide accounts for 75% of the "increased" greenhouse effect caused by nonnatural sources (i.e. man). The burning of fossil fuels has increased the levels of CO2 from 280 ppm in pre-industrial times to over 380 ppm today. The annual total amount of carbon dioxide that enters the atmosphere from fossil fuel burning is 6 to 7 Gigatons, more in the northern hemisphere than southern hemisphere. It is estimated that it would take several hundred years for the CO2 to return to normal levels if all non-natural emissions stopped today."

Regarding Water vapor and the greenhouse effect...

"Although water in its vapor form will usually enhance the greenhouse effect, clouds can sometimes act like a greenhouse gas and sometimes can weaken it. Some types of clouds trap infrared heat rays, and some types of clouds reflect sunlight back to space very efficiently and prevent this energy from contributing to the heating process.

Clouds that are low in the atmosphere are warm and thus radiate heat back to space at a greater rate than high altitude clouds which are colder. High cold clouds are usually reflective, typically because they consist of very small droplets of small to large ice crystals."

Answer 7

The contributor was wrong. Water vapor is a very strong greenhouse gas (by virtue of its sheer volume in the atmosphere), and is responsible for approximately 36-66% of the overall greenhouse effect (66-85% when you include clouds). So it definitely helps warm the planet. However, water vapor is not a climate *forcing* because the amount of it it in the air varies as a function of temperature. This is because air at a given temperature can only hold a certain amount of H2O before it condenses and precipitates out.

So you were right in thinking that water vapor can *exacerbate* warming caused by increased CO2, it just can't initiate warming on its own. Put simply, water vapor acts as a feedback, not a forcing (interestingly, CO2 acts as both. See the link to the IPCC report for more info).

Answer 8

When temperature rises, for whatever reason, the first effect is to reduce cloud formation with a given level of water vapour. We then see less reflectivity until the water vapour concentration rises to the extent that clouds again form. However, with reduced cloud formation and water vapour (not cloud) acting as a GHG, we do get both increased solar incidence (less reflectivity) and increased retention of long wave light.

Water vapour changes did not directly start the process. But anything else that causes an increase in temperature will make the GHG effect of  water vapour more potent, not primarily by increasing the amount of water going into the air (though that happens too), byt by raising the amount of water vapour that must be present to induce cloud formation.

It is the lack of cloud formation that leaves excess water vapour in the air, and which bathes the land and oceans with extra sunlight.

When a volcano gives us a sudden increase in reflectivity, we get an increase in cloud cover because we get a lower temperature.

That increased cloud cover comes with a drop in water vapour as a GHG. Once it condenses into a cloud it stops being water vapour, acts to reflect daylight sun. This is to say that water vapour responds to other factors that raise or lower temperature... such as other GHGs, but also such as snow on the ground, volcanic dust.

CO2 then may have greater secondary effect as a result of increasing temperature, thereby reducing cloud cover  with greater water vapour.

Answer 9

Water is by far the most important greenhouse gas.  

But, because an excess falls out as precipitation, it cannot by itself initiate an INCREASE in temperature.

But, once warming is initiated by CO2, increased temperature of the air can cause it to hold more water and so water vapor can amplify a warming which is mostly caused by CO2.

"in the jargon of climate science, water vapour is a feedback, but not a forcing."

More details about the issue here:

http://environment.newscientist.com/chan...

http://www.realclimate.org/index.php?p=1...

Bottom line, water vapor is important, cannot initiate global warming, but can make global warming worse.

I hope that (or what's in the links) is clear.  Very reasonable question on your part.

"Studies have shown that the net effect of increased water vapor will be lower temps because of this effect of clouds."

CrazyConservative - please cite such a study.  I know of none with any data, only speculation on the issue.