Environment

Global warming - What role does water vapor really play?

Scientists say man-made CO2 causes global warming; climate skeptics insist that water vapor is responsible. Here's why both assumptions are true.
Without water vapor average temperatures would be up to 30 degrees Celsius lower/ Credits: Reuters

Here are the perfect ingredients for a conspiracy theory: water vapor is the most important factor influencing the greenhouse effect but doesn’t feature on the UN’s list of greenhouse gases responsible for anthropogenic global warming.

Critics of the idea of man-made global warming love this simple fact and have turned it into one of their most potent arguments to sabotage decisive climate action.

So why doesn’t the UN’s climate body the International Panel on Climate Change (IPCC) list water vapor as a greenhouse gas? It’s because water vapor does not by itself increase temperatures. It amplifies already occurring warming.

Water vapor’s role in the Earth’s climate system is defined by the very short time it remains in the atmosphere and actively traps heat. While additional CO2 from factories or airplanes can remain in the atmosphere for centuries, extra water vapor will only remain a few days before raining down as water.

The concentration of water vapor in the atmosphere is in equilibrium. The atmosphere can only hold more water vapor if overall temperatures increase. So a small warming effect caused by human CO2 emissions will increase the amount of water vapor in the atmosphere.

The added water vapor leads to even more warming, thus amplifying the CO2 warming effect. Water vapor follows temperature changes, it doesn’t cause or, as climatologists say, ‘force’ them. As a feedback effect, water vapor is comparable to a car’s turbo charger that increases a motor’s power.

However, the amount of water vapor in the atmosphere changes regionally. While there is virtually no water vapor above deserts or the Arctic and Antarctic regions, the air above the equator can consist of up to four percent water vapor.

In humid equatorial regions, where there is already a strong natural greenhouse effect, additional CO2 and water vapor have little impact on local climate. The opposite is true in cold, dry places, which is one reason why warming is much more pronounced in Polar regions.

Concentration matters

Regional differences aside, the atmosphere contains on average only 0.4 percent of water vapor and ten times less CO2. This relatively small concentration is another argument often cited to refute the idea of man-made global warming. How can CO2 cause rising temperatures, skeptics demand, if it only accounts for 0.04 percent of the atmosphere?

Again the riddle is solved easily.

Oxygen and nitrogen are the most abundant elements in the Earth’s atmosphere and make up 99 percent of it. But neither of the two gases traps or emits heat.

This is why water vapor is responsible for most of the natural greenhouse effect. Scientists estimate that without water vapor average temperatures would be up to 30 degrees Celsius lower. CO2, on the other hand, is responsible for a much smaller but still substantial amount of the natural warming effect.

If things remain like this, we could continue living on a cozy, warm planet. But too much of a good thing is often bad. CO2 levels have increased from 0.028 percent of the atmosphere to about 0.04 percent since the Industrial Revolution. This has led to a temperature increase of about 0.7 degrees Celsius so far.

About half of this warming could be due to feedback warming from water vapor, estimates the IPCC. But it would not have happened without the added CO2 pumped into the atmosphere. CO2 is the guy robbing the bank, water vapor is just the getaway driver.


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Comments (26)

E-Ray: 05.11.2014, 04:49

My understanding is that 97% of the annual CO2 added to the atmosphere is natural, not man made. So if the CO2 increased since the industrial revolution from 280 ppm to 400 ppm, then the increase is 120 ppm. That means the man made contribution of 3% amounts to about 3.6 ppm added CO2. Are these 3.6 ppm really the cause of the IPCC's prediction of catastrophic global warming if humans don't dramatically reduce CO2 emissions from burning fossil fuels?

H.R.Prakash: 01.10.2014, 04:10

Dry heat is not difficult to bear but the humid climate after the rain is most uncomfortable. The impact of water vapor explains it.

George Carlin: 25.07.2014, 01:07

We’re so self-important. Everybody’s going to save something now. “Save the trees, save the bees, save the whales, save those snails.” And the greatest arrogance of all: save the planet. Save the planet, we don’t even know how to take care of ourselves yet. I’m tired of this rubbish. I’m tired of Earth Day. I’m tired of these self-righteous environmentalists, these white, bourgeois liberals who think the only thing wrong with this country is that there aren’t enough bicycle paths. People trying to make the world safe for Volvos. Besides, environmentalists don’t give a hoot about the planet. Not in the abstract they don’t. You know what they’re interested in? A clean place to live. Their own habitat. They’re worried that some day in the future they might be personally inconvenienced. Narrow, unenlightened self-interest doesn’t impress me.

The planet has been through a lot worse than us. Been through earthquakes, volcanoes, plate tectonics, continental drift, solar flares, sun spots, magnetic storms, the magnetic reversal of the poles … hundreds of thousands of years of bombardment by comets and asteroids and meteors, worldwide floods, tidal waves, worldwide fires, erosion, cosmic rays, recurring ice ages … And we think some plastic bags and some aluminum cans are going to make a difference? The planet isn’t going anywhere. WE are!

We’re going away. Pack your stuff, folks. We’re going away. And we won’t leave much of a trace, either. Maybe a little Styrofoam … The planet’ll be here and we’ll be long gone. Just another failed mutation. Just another closed-end biological mistake. An evolutionary cul-de-sac. The planet’ll shake us off like a bad case of fleas.

The planet will be here for a long, long, LONG time after we’re gone, and it will heal itself, it will cleanse itself, ’cause that’s what it does. It’s a self-correcting system. The air and the water will recover, the earth will be renewed. And if it’s true that plastic is not degradable, well, the planet will simply incorporate plastic into a new paradigm: the earth plus plastic. The earth doesn’t share our prejudice toward plastic. Plastic came out of the earth. The earth probably sees plastic as just another one of its children. Could be the only reason the earth allowed us to be spawned from it in the first place. It wanted plastic for itself. Didn’t know how to make it. Needed us. Could be the answer to our age-old egocentric philosophical question, “Why are we here?”

Plastic...

K. N. Owledge: 02.12.2013, 10:32

Hilarious! This "article" is so full of political baloney that you could feed Italy for years.

Water vapor absorbs infrared. Even the most basic of scientists understand this simple fact. When water vapor absorbs heat, the air around it is warmed, allowing it to absorb more water vapor, increasing the heat in the atmosphere. That's a certain positive feedback cycle.

It's amazing how the IPCC (Idiots Promoting Climate Catastrophe) will do back flips to link it all to CO2.

The reason they do this is simple . . . try and tax water vapor.

Eugen Kumicic: 02.07.2013, 21:55

if we all start driving hydrogen fuel cell cars won't that create massive amounts of extra vapor in the atmosphere and how do we deal with that? i don't think we can do anything if global warming is real.

Gadepalli Subrahmanyam: 29.05.2013, 15:11

For excess humidity in the atmosphere, I hope Man is not blamed. As I am fond of repeating, Sun is relentlessly heating the earth with so much energy (6000 times the per capita consumption of energy) that it has got to evaporate the water on earth or at least heat the atmosphere. There have been cycles of deluge and drought on earth, much before Man intervened in changing nature.

Nature has its own ways of dealing with these aberrations. If some species (Again creation of nature) cannot survive, then there is the theory of survival of the fittest to fall back upon. Let us not blame Man for every thing bad happening.

earthhead: 03.01.2013, 19:32

We need to release the water that is retained/stored outside of earth's natural cycle. Please read....Human's (7+ billion) contain on avg 12 gallons of water, cattle (1.3+ billion) contain on average 150 gal of H2O, pigs, sheep, chickens, etc..each contain their respective avg amounts of water. Look at all of the houses, apartments, hotels, motels, businesses, etc that have plumbing, hot water heaters, etc storing water. Automobiles, trucks, planes, etc. store water in their respective coolant systems. How about all of the bottling plants for beer, soda, water, etc. as well as all of the distribution points along the supply chain including each personal refrigerator or cupboard. There are probably many other areas that could be identified as a container's of water not mentioned above.

Have you ever stood next to a water fall...the mist keeps you cool. Water in the atmosphere or the lack thereof is the reason for the warming trend. The items listed above have been growing exponentially since 1850 when the world's population was estimated at 1 billion. It only takes a small percentage of water removal for the earth to begin to correct itself to an appropriate ratio of water in the atmosphere.

GADEPALLI SUBRAHMANYAM: 16.09.2011, 16:45

IF WE SEE HISTORY, YOU WILL FIND THAT THE EARTH SUFFERED FROM SURFEIT OR SHORTAGE OF RAINS OVER EONS AND AT LEAST IN iNDIA, WE ARE COGNISANT OF RECURRING FAMINES, ESPECIALLY IN BENGAL. IF INDIA IS SELF SUFFICIENT IN FOOD GRAIN PRODUCTION, DESPITE THE HUGE INCREASE IN POPULATION THANKS ARE DUE TO 'HUMAN' INTERVENTION LOKE BUILDING DAMS OVER MAHANADI, INDUS, KRISHNA. AND QUITE A FEW OTHER RIVERS. THANKS ARE ALSO DUE TO DR. SWAMINATHAN OF IARI.

SIMPLY BLAMING MAN FOR ALL THE ILLS OR CHANGES IN NATURE PERHAPS IS NOT EXACTLY RIGHT. WHETHER THERE IS INCREASE IN WATER VAPOUR OR CARBON DIOXIDE IN THE ATMOSPHERE IS A PART OF NATURAL PROCESS/

GADEPALLI SUBRAHMANYAM

dev dongol: 15.09.2011, 09:23

NO! It is not possible at our will but we can maintain the nature’s way. There are many examples that man has disturbed the nature’s ways, e.g. pollution of air, water, soil etc. We have changed the faces of the earth so we must confront the nature’s reactions/effects.
Similarly, we have disrupted rain cycle by obstructing the evaporation from the earth’s surface through millions of settlements by constructing houses, roads etc. If we minimize the covering of land areas as used to be in old days, older the situation the better, we will have more and more regular rain cycle like in those days. Regular rain means solution to all the problems related to climate change.
For details please visit my blog: devbahadurdongol.blogspot.com
Email: dev.dangol@yahoo.co.uk
Regards,
Dr. Dev

gadepalli subrahmanyam: 15.09.2011, 04:24

Are humans capable of changing weather ? Dod they have the power to bring rain/cyclones/snowfall at will ?
Let us not abscribe too much to human power. That will be ego.

Gadepalli Subrahmanyam



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