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    Greenhouse Gases And Water Vapor: When 'Positive Feedback' Is A Bad Thing
    By News Staff | September 18th 2007 03:24 PM | 12 comments | Print | E-mail | Track Comments
    Observations and climate model results confirm that human-induced warming of the planet is having a pronounced effect on the atmosphere’s total moisture content.

    “When you heat the planet, you increase the ability of the atmosphere to hold moisture,” said Benjamin Santer, lead author from Lawrence Livermore National Laboratory’s Program for Climate Modeling and Intercomparison. “The atmosphere’s water vapor content has increased by about 0.41 kilograms per cubic meter (kg/m²) per decade since 1988, and natural variability in climate just can’t explain this moisture change. The most plausible explanation is that it’s due to the human-caused increase in greenhouse gases.”

    More water vapor – which is itself a greenhouse gas – amplifies the warming effect of increased atmospheric levels of carbon dioxide. This is what scientists call a “positive feedback.”

    Figure courtesy of Carl Mears and Frank Wentz/
    Remote Sensing Systems.



    Using 22 different computer models of the climate system and measurements from the satellite-based Special Sensor Microwave Imager (SSM/I), atmospheric scientists from LLNL and eight other international research centers have shown that the recent increase in moisture content over the bulk of the world’s oceans is not due to solar forcing or gradual recovery from the 1991 eruption of Mount Pinatubo. The primary driver of this ‘atmospheric moistening’ is the increase in carbon dioxide caused by the burning of fossil fuels.

    “This is the first identification of a human fingerprint on the amount of water vapor in the atmosphere,” Santer said.

    “Fingerprint” studies seek to identify the causes of recent climate change and involve rigorous comparisons of modeled and observed climate change patterns. To date, most fingerprint studies have focused on temperature changes at the Earth’s surface, in the free atmosphere, or in the oceans, or have considered variables whose behavior is directly related to changes in atmospheric temperature.

    The water vapor feedback mechanism works in the following way: as the atmosphere warms due to human-caused increases in carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons, water vapor increases, trapping more heat in the atmosphere, which in turn causes a further increase in water vapor.

    Basic theory, observations and climate model results all show that the increase in water vapor is roughly 6 percent to 7.5 percent per degree Celsius warming of the lower atmosphere.

    The authors note that their findings, when taken together with similar studies of continental-scale river runoff, zonal-mean rainfall, and surface specific humidity, point toward an emerging human-caused signal in the cycling of moisture between the atmosphere, land and ocean.

    “This new work shows that the climate system is telling us a consistent story,” Santer said. “The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally- and physically-consistent way.”

    The Livermore authors included Karl Taylor, Peter Gleckler, Jim Boyle and Stephen Klein.

    Other scientists contributing to this research were Carl Mears and Frank Wentz at Remote Sensing Systems in Santa Rosa, Calif.; Tom Wigley, Jerry Meehl, and Warren Washington at the National Center for Atmospheric Research in Boulder; Tim Barnett and Dave Pierce at Scripps Institution of Oceanography in La Jolla; Wolfgang Brüggemann at the University of Hamburg in Germany;

    Nathan Gillett at the University of East Anglia and Peter Stott at the Hadley Centre for Climate Prediction and Research (both in the U.K.); Toru Nozawa at the National Institute for Environmental Studies in Japan; and Mike Wehner at Lawrence Berkeley National Laboratory.

    Comments

    That is interesting.

    Odd that, water vapor is now proven to be a positive feed back, yet the rate of warming since 1975 to the present day is NO greater than the rate of warming from 1910 to 1945. If water vapor were a positive feed back linked to CO2 you would expect,( with CO2 now being at 388 ppm, that is 168ppm above the so called long term norm of 220ppm) the rate of warming including water vapor from 1975 to be CONSIDERABLY higher than the 1910 to 1945 warming.
    Take away the UHI effect from the 1975 to present warming and this leaves a lower rate of warming in the later part of the 20th century, see link, hence NO water vapor positive feed back and NO AGW CO2 induced warming.

    http://i446.photobucket.com/albums/qq187/bobclive/Lean2004.jpg

    Hank
    Your logic is a little flawed.    No one says water vapor is a contributor to global warming like methane or CO2 or Nitrous Oxide - it is instead a magnifier of warming.    That's simple physics.

    There's a whole contingent of people out there who are no different than irrational environmentalists insisting American cars cause CO2 but Chinese cars are exempt - you instead believe more people, more methane, more greenhouse gases instead cause no effect at all, so let's just pollute and not think about smarter energy.   Bookmarked pseudo-facts with no knowledge at all of the underlying science plus cutesy acronyms like AGW CO2 are a dead giveaway.
    I have to disagree with you there. Water vapour is the single biggest contributor to the greenhouse effect. Therefore, an increase in water vapour ought to lead to a global warming effect, yet we do not see acceleration of the warming rate - and this is in spite of all Hansen & Co.'s "corrections" to the temp records to increase the slope.
    Also, if a system has positive feedback it should always be in saturation (like a Schmitt Trigger), so how can a small increase in CO2 produce a small increase in temps - shouldn't small changes have no effect unless and until the 'tipping point' is reached at which point temps would rise at tens of Kelvin per year and then none of us would be denying AGW. Can't have it both ways: either CO2 has caused temps to rise gradually OR there is positive feedback in the system (or neither, of course). Not both.
    However, I am not a scientist and may be making considerable errors in the foregoing. If so, corrections are welcome.

    Of course we should think about smarter energy. Conservation of scarce resources is not the same thing as carbon emissions panic. What we need is Fast Breeder Reactors (fission) in the short to medium term, fusion in the long term (don't worry, we've got 3000 years to perfect it before the uranium runs out), and a hydrogen infrastructure to enable nuclear energy to be used in applications like transport. But not because of CO2! Rather, we should do this because the fossil fuels are running out (50yrs oil, 80yrs gas, 300yrs coal iirc) - which is not the same issue!

    Hank
    I think our disagreement is one of language.  I wrote:
      No one says water vapor is a contributor to global warming like methane or CO2 or Nitrous Oxide - it is instead a magnifier of warming.  
    but the effect is likely what you are talking about.   If you have a headache, and laying down makes it worse, laying down did not cause your headache, it just magnified it.
    But if a warming trend is measured, then that part of it, which is due to the 'magnification' rather than directly caused by the added GHG forcing, is due to the water vapour. (By the way, English quibble: I don't like the spelling "vapor")
    Could you please answer my other points? Your feedback (!) would be much appreciated.

    Hank
    You need to get rid of the headache.   Obviously doing things that make it worse is a good idea but getting rid of the source is the best idea.    There is a debate on the specific causes of global warming and that's healthy - it caused the term to be mostly disregarded in favor of 'climate change'.    If records are being shattered for cold temperatures and people with political agendas who disagree with CO2 as a cause of climate change are happy, it's going to be a pyrrhic victory.    Wilder fluctuations in weather cannot take us to a good place so being 'right' about CO2 is a pretty minor win.

    The disagreement on CO2 levels historically can happen because of the nature of measurement and statistical analysis.   If you take 10 million years and pick 500 data points and do a numerical model, where and how you pick the data points is key.   Someone who claims CO2 levels are the highest now in history is clearly cherry picking data - so is anyone claiming they were 10X higher in the past without effect on human life.   

    1.4 billion years ago CO2 was maybe 200 times higher than today.  That doesn't mean you want to live here when that happens so let's ignore pollution and be happy France was wrong about CO2 and the degree of global warming.

    If you're not an expert in statistics (don't feel bad - most climate scientists are not either, nor are most scientists, nor am I) you aren't going to interpret ice core data in any meaningful way.   If you're just bookmarking the conclusions of someone who has an agenda you like and throwing them around on the internet, then you have an agenda too.
    However, one of the most credible theories regarding the causes of global warming - inasmuch as it is occurring at all, which is heavily uncertain given the meddling practised upon temp records - is that of solar forcing. Put simply, Maunder Minimum causes LIA. Sun gets back on track. Temps rise gradually back to "normal" level. At this point we look at temp records that started shortly after LIA, and of course we see a warming trend. However, this isn't anthropogenic and in fact it's not even harmful since this is the kind of temp human civilisation lived in for a few millennia. (aside: don't trust temp proxy reconstructions such as MBH98, Mann08. Their methodology is flawed; I don't need to be an expert in statistics to see that; an A-Level in maths and fifteen minutes with a BASIC compiler is enough to demonstrate the flaws in their system. Btw I am a sixth-form student applying to various unis to study mathematics. I already have a 1 in STEP II so I may not be an expert but I'm not an analphabet either)
    Next stage: SC24 fails to get started, or at the very least occurs late. Result: a period of cooler temps. You might notice that the temp anomaly has gone quite sharply downwards recently. This looks like it could have something to do with the prolonged post-SC23 minimum. If the Sun really has 'crashed', and SC24 is not going to happen, we're looking at another Little Ice Age - and there's nothing we can do about it except adapt.
    I don't like being accused of "bookmarking". I concluded independently that Anthropogenic Global Warming was ludicrous conceit. It shouldn't count against my views that others on the internet share them!
    As for your "pretty minor win" comments, I should point out that valuable science is that which is right*, not that which we want to be right.
    *i.e. that which conforms to and accurately predicts the results of observatoins and experiments.

    However, clouds are supposedly one of the main 'minimizer' of warming, i.e. they reflect rays from the sun. So .... if we follow this logic then we would get more warming, more water vapor, more clouds, more cooling, less water vapor, ... You cannot ignore the effects of clouds in your calculations but it seems that you are doing so. Perhaps that is why the last few years have seen no warming and in fact a bit of cooling.

    I think there is some big mistake in the numbers. How can the water vapour content have increased by 0.82 Kg per cubic meter since 1988? The density of air AFAIK is about 1Kg per cubic meter so if that figure is right there is today almost as much water as air in the atmosphere.

    Was it meant to be perhaps 0.41 grams per cubic meter per decade ?

    Keeping in mind that windmills are hazardous to birds, be wary of the unintended consequences of believing and contributing to the all-knowing environmental lobby groups.
    Climate and economy are being linked. Yes there has been warming since the Pleistocene. Climate is a multiple input, multiple loop, multiple output, complex system. The facts and the hypotheses do not support CO2 as a serious 'pollutant'. In fact it is plant fertilizer and seriously important to all life on the planet. It is the red herring used by the left to unwind our economy. That issue makes the science relevant.
    Water vapour (0.4% overall by volume in air, but 1 – 4 % near the surface) is the most effective green house gas followed by methane (0.0001745%). The third ranking greenhouse gas is CO2 (0.0383%), and it does not correlate well with global warming or cooling either; in fact, CO2 in the atmosphere trails warming which is clear natural evidence for its well-studied inverse solubility in water: CO2 dissolves in cold water and bubbles out of warm water. The equilibrium in seawater is very high; making seawater a great 'sink'; CO2 is 34 times more soluble in water than air is soluble in water.
    CO2 has been rising and Earth has been warming. However, the correlation trails. Correlation, moreover, is not causation. The causation is being studied, however, and while the radiation from the sun varies only in the fourth decimal place, the magnetism is awesome.
    “Using a box of air in a Copenhagen lab, physicists traced the growth of clusters of molecules of the kind that build cloud condensation nuclei. These are specks of sulphuric acid on which cloud droplets form. High-energy particles driven through the laboratory ceiling by exploded stars far away in the Galaxy - the cosmic rays - liberate electrons in the air, which help the molecular clusters to form much faster than climate scientists have modeled in the atmosphere. That may explain the link between cosmic rays, cloudiness and climate change.”
    As I understand it, the hypothesis of the Danish National Space Center goes as follows:
    Quiet sun → reduced magnetic and thermal flux = reduced solar wind → geomagnetic shield drops → galactic cosmic ray flux → more low-level clouds and more snow → more albedo effect (more heat reflected) → colder climate
    Active sun → enhanced magnetic and thermal flux = solar wind → geomagnetic shield response → less low-level clouds → less albedo (less heat reflected) → warmer climate
    That is how the bulk of climate change might work, coupled with (modulated by) sunspot peak frequency there are cycles of global warming and cooling like waves in the ocean. When the waves are closely spaced, the planets warm; when the waves are spaced farther apart, the planets cool.
    The ultimate cause of the solar magnetic cycle may be cyclicity in the Sun-Jupiter centre of gravity. We await more on that.
    Although the post 60s warming period appears to be over, it has allowed the principal green house gas, water vapour, to kick in with more humidity, clouds, rain and snow depending on where you live to provide the negative feedback that scientists use to explain the existence of complex life on Earth for 550 million years. Ancient sedimentary rocks and paleontological evidence indicate the planet has had abundant liquid water over the entire span. The planet heats and cools naturally and our gasses are the thermostat.
    Check the web site of the Danish National Space Center.
    http://www.space.dtu.dk/English/Research/Research_divisions/Sun_Climate/...

    rholley
    Why do people insist on an either-or argument in regard to natural vs anthropogenic global warming.  If our planet is getting warmer naturally due to a sun-cycle or similar, that puts a greater onus on us to keep down the amount of thermokepiogenic (Greek θερμοκηπίο) pollutants we ourselves produce.
    Robert H. Olley / Quondam Physics Department / University of Reading / England