The sky over Phoenix at dawn, seen from Camelback Mountain. Where did the moisture come from to make these? (Melanie Stetson Freeman/Staff/File)
Researchers study the other greenhouse gas: water vapor
By tracking specific origins of moisture, scientists can better predict regional rain and snowfall.
By Peter N. Spotts | Staff writer of The Christian Science Monitor/ January 29, 2009 edition
Reporter Pete Spotts discusses new research dealing with water vapor effects on global warming.
Reporter Pete Spotts
For years, “follow the water” has been a mantra for exploring one planet in our solar system, Mars. With a slight change, the phrase is also becoming a mantra for exploring Earth’s climate system: Follow the water vapor.
The details of how water behaves after it evaporates, the processes that parcels of moist air undergo as they travel across the planet, and the sources of moisture for several regions around the globe are poorly understood.
Yet that information is key to better forecasts of seasonal changes, such as monsoons, as well as to more reliable projections of global warming’s effects on regional rain and snowfall patterns, researchers say.
“If you look at model projections of rainfall in arid regions – the American Southwest, the Sahel [in Africa], India, China – for 2050 or 2100, half the models say one thing, half the models say another thing,” says Gavin Schmidt, a climate modeler at the National Aeronautics and Space Administration’s Goddard Institute for Space Studies in New York.
Hundreds of millions of people live in these regions, he continues, and they are deeply concerned about the future of their water supplies.
Now scientists are taking advantage of techniques that allow them to more easily read the story of water vapor’s travels and travails. The broad approach involves teasing out the relative abundance of heavier and lighter forms (isotopes) of oxygen and hydrogen atoms that water-vapor samples contains.
This real-world isotope information, which is incorporated into climate simulations, is expected to provide a valuable test for the models as researchers try to sort out which ones do the best job of approximating water vapor’s behavior outside the confines of a computer.
In particular, researchers will be looking to see how well a new generation of models reproduce past events, such as megadroughts that have hit the US Southwest, or the so-called “green Sahara” period some 6,000 years ago. These events are told in isotope records from the affected regions.
Indeed, improving models’ treatment of the hydrological cycle of our planet is one of the key goals set by the Intergovernmental Panel on Climate Change as it looks ahead to its next set of climate reports, currently set for release beginning in June 2013, Dr. Schmidt says.
While water vapor’s largely invisible hand is most obvious in the clouds and precipitation it forms, it’s also the most abundant greenhouse gas in the atmosphere, followed by carbon dioxide and trace amounts of other gases. As CO2 concentrations have risen and warmed the atmosphere, the warming has allowed the atmosphere to hold more water vapor, which in turn further warms the atmosphere.
This effect was most recently documented last October in the journal Geophysical Research Letters, when researchers at Texas A&M University in College Station published the results of a study of the link between global average temperatures and water vapor between 2003 and 2008.
During that period, surface temperatures fell by about 1 degree F., in large part because of a shift from El Niño to La Niña in 2007 and into 2008. (La Niña is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific. El Niño describes the condition when these temperatures are unusually warm.)
Using satellite measurements of water-vapor trends during the warmer and cooler portions of those years, researchers found a strong positive feedback from water vapor. It was similar in strength to what the feedback models estimate. If CO2 emissions continue to grow at a business-as-usual pace during the rest of this century, the positive feedback “is virtually guaranteed to produce warming of several degrees Celsius,” the researchers conclude.
It’s still hard to validate models regarding how this feedback plays out on century-long time scales, notes Andrew Dessler, an atmospheric scientist who led the team. To do so would require a century’s worth of data. Still, he adds, “the models seem to be getting the feedback in response to short-term fluctuations right. So it’s hard to believe they’re not getting the long-term feedback right.”
With or without an increase in water vapor, researchers are increasingly interested in where it comes from and where it goes. The tropical oceans, where the sun’s heat is strongest, is the most obvious source. But for regions interested in their water supplies, the devil is in the details.
At 18,000 feet in an ultralight aircraft
Which is why Mel Strong rousted himself up before dawn on cloudless days for six weeks in the spring of 2005. By sun-up, he was headed toward 18,000 feet in a cross between a propeller-driven go-cart and a parachute. His ultralight aircraft had a tiny weather station that gathered fresh information every 60 seconds. His payload consisted of 10 glass sampling bottles.
At 18,000 feet, he would kill the engine and glide back to earth, capturing air samples in the bottles every 1,000 feet. Back at the University of New Mexico, Albuquerque, where he was working on his PhD, another set-up was gathering roof-top air samples.
Mr. Strong analyzed oxygen- and hydrogen-isotope ratios to try to determine where the moisture in the samples came from. The ocean – even different parts of the ocean – has a distinct set of ratios. As water evaporates, the vapor tends to host more of the lighter isotopes than the heavier ones. When it rains, the heaviest isotopes tend to rain out first, leaving the remaining water vapor and any subsequent precipitation even poorer in heavy isotopes.
By looking at this depletion and working with models that backtrack moving parcels of air, his results point to springtime moisture coming into the state from the Gulf of California and the Gulf of Mexico. The results appeared in the Feb. 17, 2007, issue of Geophysical Research Letters.
On average, half a year’s worth of precipitation in New Mexico comes during the summer monsoons, Mr. Strong says, with three possible sources for moisture: the Gulf of Mexico, the Gulf of California, and the Pacific Ocean. But the monsoons vary in strength each year. They sometimes display false starts. And the region also has undergone decade-scale droughts.
It’s hard to figure out what’s going on “if we don’t know the relative contributions from each” potential moisture source, Strong says.
In the tropics, researchers have been asking a similar “Where does moisture come from?” question, but with a twist. In New Mexico, the contribution of moisture from plants is relatively small. In the humid, fecund tropics, it’s much larger.
John Worden, a researcher at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and his colleagues have looked at isotope data from the Aura satellite, a sister orbiter to the Aqua satellite. He found that water vapor over the Amazon and across tropical Africa has a heavier isotopic content than vapor over the ocean. Some of it is even heavier than ocean water itself.
Rain that evaporates before it lands
Essentially, much of the atmospheric moisture over these continental areas appears to come from rain that evaporates before it reaches the ground (it’s called “virga”), as well as moisture given off by the lush tropical plant life through evapotranspiration.
One approach to getting a better handle on these and other atmospheric moisture issues involves a concerted water-vapor monitoring program, says David Noone, a water-cycle specialist at the University of Colorado, Boulder, and a member of Worden’s team.
Last fall, Dr. Noone and colleagues took off-the-shelf laser-based sensors for an isotope-measuring test drive on the slopes of Mauna Loa, on the big island of Hawaii. The low-budget project aims to see if the sensors could help provide a reality check on satellite measurements as well as act as easy-to-use tools for longer-term monitoring from a range of sites around the world – particularly in the subtropics, which tend to be drier.
“There’s a debate about what really controls the dry regions,” Noone says. One camp holds that cloud processes dominate; the other holds that the drier climate is the result of air masses that mix and, in effect, dehydrate the air in the region.
This may sound like debating how many angels can dance on the head of a pin.
But the outcome can be significant, Noone says. “One of the things that’s evident from the climate models is that you can get the right answer for a variety of wrong reasons,” he explains.
By using isotope measurements to get “the right water vapor for the right reasons, we can improve the way the models are representing the water cycle on the climate system.”
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Comments
2. Skyman | 01.30.09
Try googling “shrinking Mars ice caps” and you’ll see that perhaps the main driver of global warming is variation in output from your friend and mine, the Sun!
3. Erik Anderson | 01.30.09
You should have put the percentages of each gas responsible for the “greenhouse” effect.
Water Vapor = 95%
CO2 = 3.6%
Source: http://www.geocraft.com/WVFossils/greenhouse_data.html
Then ask “How much variation is there in atmospheric water vapor and CO2?” Water Vapor: 400ppm to 10,000ppm.
CO2: 350ppm to 400ppm.
Source: http://pubs.acs.org/subscribe/journals/ci/31/special/may01_viewpoint.html
So, if water vapor accounts for 95% of the greenhouse gas, and it varies by 2400%, how can CO2 be pronounced the culprit if it accounts for only 3.6% of the greenhouse effect and varies 14%?
You should also mention that the EPA doesn’t include water vapor when citing the percentage that CO2 contributes to the greenhouse effect. Of course, they tell the reader this, but they don’t tell “how much” the water vapor has an effect. I’d say 95% is just slightly bigger than 3.6%. We should all know these facts to put things in perspective, and as a staff writer, you have the power to do it.
4. Guy Thompto | 01.30.09
We need to stop water vapor now! Humans should stop using water to save the planet. No more beer, soda, or bottled water. No more ice rinks, car washes, window washers or showers. You greedy, evil humans! Yes, the way to save the planet is for us to die. We must not wait!
5. Daly bred | 01.30.09
Good to see that the IPCC has set a goal to focus on the hydrological cycle in the next round of reports - not before time! How about new discoveries about the sun, like the plasma conveyor belt and the changes in its speed which are believed to affect the sunspot cycle (Cycle 24 is taking longer than expected to get started); and the effect of magnetic portals connecting the sun to the earth every 8 minutes with “tons of high-energy particles [flowing] through the opening before it closes again” (flux transfer events) reported by NASA (October 30 2008)? Leaving these factors out of computer models can only result in dodgy climate forecasts.
Reducing pollution, conserving finite energy resources, reducing waste and better stewardship of the planet are all positive outcomes from the current climate change debate. But if the doom-laden forecasts of some climate change ‘experts’ (and particularly their acolytes) are based on very incomplete data the real danger is that extreme prescriptions for combating global warming could plunge us back into the dark ages where all sense of responsible stewardship is lost for generations and sincere scientific enquiry that questions dogma is condemned as heresy in the new ‘religion’.
Judging by the graphs plotted from the Vostock ice-core samples over 600,000 years or more, we are nearing or at the top of a normal 125,000-year (approx) global warming cycle - previously without human intervention! So it would also be a good idea for the IPCC to focus on what could have triggered the global cooling that followed all the other peaks - in case it’s just around the cosmic corner!
6. nawalfleet | 01.30.09
my dear
I think that religion is conected with science&the world arouund us.but we should have a broad mind&immagination for this ¬ take the version as it is but as what is underneath,I think that water was the beging of everything or it was a great great womb for humunity who was grwn inside it &then God blow in them from his spirit,this was very early in the begining,but now lot of people&lot water vapour which make the disturbance in the climate by making hot weather in some places ,ice meling.increase of humidity,,but we can make use of this water vapour by condensation&changing it to rains in places of droug weather like africa,&change desert int green lands,but also water vapour is accomanid with carbon dioxide,which we can make use of it as for ex;mingling it with another gas&making them fuel insted of petrol.we should make use of everthing in nature to help feeding the poor nations who suffers famine.so we achieve the willing of God by science what do you think do you agree with me or you think lot of people difficlt to be able helped.
7. Moira Egan | 01.30.09
As soon as I read,…”more reliable projections of global warming’s effects”, I concluded that this is shoddy science and shoddy science reporting. “Reliable” is an adjective that cannot modify any existing climate projections. Perhaps some day it will be able to do so. Right now, “global warming” is a only a theory based on computer models that in themselves are far from reliable. I say, put the research money into something useful and let this study be considered water under the bridge.
8. Don Snethen | 01.30.09
Water vapor is also a combustion product. Take combusion of methane which consists of 4 atoms of hydrogen and 1 atom of carbon. When methane is burned it consumes 2 molecules of oxygen and produces one molecule of carbon dixoide and 2 molecules of water. Given that fossel fuel combustion is a major source of carbon dioxide, combusition as a source of water vapor should not be overlooked.
10. Jim Redden | 01.31.09
In prior comments, there seems to be some misunderstanding in the comments about the relationship of water vapor and CO2, and the basic physics at hand.
In order for water to reside in the Earth’s atmosphere, energy is required to power the hydrologic process that results in rain, ice formation, melting, sublimation, condensation, and so on and so forth. Calculations using basic physics indicate that without the Sun, most all of the water vapor would be out of the Atmosphere in about a week.
Carbon dioxide, on the other hand, is a well mixed resident gas that serves to retain energy and open the energy throttle on the atmosphere. The increased energy retention of carbon dioxide engenders greater hydrologic activity that tends to increased water vapor.
Water vapor is akin to currency of an economic system; hence, worthy of study to deconstruct its movement, flux, and sources.
For an informed detailed scientific discussion, see
http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/
Or for a more elaborate explanation for those who prefer a relatively easy to understand text, Elementary Climate Physics by F.W. Taylor.
While water vapor is indeed a very important greenhouse gas, it varies in response to physics, and with diligence, these relationships are understood better and better.
With a detailed understanding of the processes at hand, you will find lumping water vapor, that adjusts to forcings, and CO2, a resident gas, which does not, is a rather large mistake of fact.
Moreover, this rather gross simplification results in flawed thinking, attribution error, and dangerous judgments and conclusions.
11. Big Ed | 02.02.09
As to the Goracle and why he is the CO2 man… read this.
http://www.kusi.com/weather/colemanscorner/38574742.html
12. Hans Kramer | 02.03.09
It’s not possible to change the amount of water vapor but there is a way to lower CO2. Use less fossil fuel. Use energy efficiently and use green energy.
It’s been found that higher atmospheric temperatures produce more water vapor (increasing the greenhouse effect) and less cloud cover (decreasing the heat reflected to space.)
Failing to control CO2 because water vapor may be worse is a losing strategy.
13. Hans Kramer | 02.03.09
To be complete, I will add the reference for the information in my previous comment. It was an article in Science, 15 Feb 2008, pg 889.
If you want to discuss scientific issues, read the real science literature.
14. eric s taggart | 02.03.09
Over the last 200 years the atmospheric content of CO2 has increased from about 280 parts per million to about 380 parts per million of this only 3% is man made from all sources. Thus reducing CO2 emissions by 10% will have a negligible effect on global warming. The changes in CO2 content and atmospheric warming are corelated but one is not effect and the other cause. CO2 is not a greenhouse gas it is perfectly transparent in visible and the 8 to 12 micron spectral region which correspònds to the 300K average emission (re-radiation) temperature of the earth. The real source of atmospheric heating is water vapor and particulate emissions, especially from volcanos. The earth is not warming overall but there is a major redistribution of the global weather patterns which will continue after a rather quiescent period over the last 10,000 years. These changes will occur far faster than any atmospheric emmission models will predict because the CO2 content of the atmosphere as a whole is very small. The good thing about this whole debate is that it has made us more concious of our global environment. Lets have some real numbers instead of confusing cause and effect
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18. Bill Woods | 06.25.09
Tax and Trade
Real science is in agreement that global warming is caused mostly by water vapor and to a much lesser extent by carbon dioxide. Only political science still claims that carbon dioxide is the problem.
The rising sea levels are also caused mostly by water. Many areas of the world have drilled wells in reservoirs where the water has been for hundreds of years. The many billions of gallons of depleted water have lowered the level of these reservoirs. This water is used mostly for agriculture, quickly evaporates, and within a month or so ends up in the ocean, raising the level.
All agriculture irrigation water, even if it comes from rivers, is the major cause of global warming. The many millions of irrigated acres greatly increase worldwide evaporation, increasing the greenhouse effect. Even though this water eventually precipitates out of the air, it is constantly being replaced by man-made irrigation. The result is a permanent increase over “normal levels” of water vapor in the air and a hotter climate on the earth.
The percent of water vapor in the air varies from fractional to over four percent. It averages about two and a half percent which in scientific terms is written as 25,000 parts per million. Comparing this number with the 360 parts per million of carbon dioxide in the air and you easily see that there is no comparison. Basic theory, observations and climate models all show that an increase in water vapor of around 3 to 4% will cause one degree Fahrenheit warming of the lower atmosphere.
Clouds should also be included in the water vapor numbers. Clouds cause much of the green house effect, and the higher the water vapor level, the more clouds. In fact, when you add the effect of the water vapor with the cloud effect, they combine to cause about 95 percent of the earth’s greenhouse effect. The remaining 5 percent is due to carbon dioxide, methane, ozone, nitrous oxide and CFCs.
So what is this cap and trade thing the political scientists are pushing. It is really a tax on everyone that ends up in the pockets of these politicians as bribes, pork barrel and just plain corruption. It won’t do anything for the environment but is just another grab for power and money at the expense of normal people.
1. AGW doubter | 01.29.09
Oooo, the Goracle is gonna banish you from his world for suggesting that *anything* other than CO2 produced by human activity is responsible for “climate change!”