Water vapor and global warming


With Copenhagen on the horizon, is it time to check over the physics and chemistry behind the climate change debate? SciScoop has spoken to several scientists recently who would say so, some of whom consider the climate change debate nothing more than a hell-on-earth scenario to give governments a taxation stick with which to beat us. The main point of contention seems to be that water vapor is a much more predominant player in global warming than the trace amounts of carbon dioxide, methane and other greenhouse gases.

But, before we jumped on the denialist bandwagon, we did a reality check with a climate scientist who put the record straight and pointed out that most of the arguments put forward ignored important issues such as the fact that the greenhouse effect is an entirely natural phenomenon. Rather, it’s the human-produced or anthropic “enhanced” effect, caused by our burning fossil fuels, raising beef cattle etc that is the anthropic component we should be very concerned about.

Climate change now?

Carbon dioxide accounts for only one in every 4000 molecules in the air; water vapor accounts for one in every 20. Carbon dioxide absorbs only a quarter as much energy from sunlight as water vapor, molecule for molecule; suggesting that water vapor is responsible for the majority of atmospheric heating.

Indeed, the IPCC (International Panel on Climate Change) essentially agrees:

Water vapour is the most abundant and important greenhouse gas in the atmosphere. However, human activities have only a small direct influence on the amount of atmospheric water vapour. Indirectly, humans have the potential to affect water vapour substantially by changing climate. For example, a warmer atmosphere contains more water vapour. Human activities also influence water vapour through methane emissions, because methane undergoes chemical destruction in the stratosphere, producing a small amount of water vapour.

So, where does carbon come into the equation, if at all? Even late nineteenth century chemist Svante Arrhenius famously outlined a mathematical argument proving that raising atmospheric carbon dioxide levels could not be used to heat Sweden so it could again grow bananas as it had in antiquity.

Scientists have been analyzing these energies since 1857 and British physicist John Tyndall who wrote, “Water vapor is the principle gas heating the atmosphere.” He too made absolutely no reference to carbon dioxide because he considered it insignificant.

Well, superficially it would seem that carbon is trivial. The atmosphere is 78% nitrogen, 18% oxygen, around 1-2% water vapor, 1% trace gases not relevant to atmospheric physics and a mere 0.038% carbon dioxide and 0.00017% methane.

Atmospheric heating is done by infrared, IR, heat energy from sunlight, with wavelengths between 1 and 16 micrometers, which is invisible but we feel as heat on our skin. Nitrogen and oxygen absorb no IR from sunlight; they are transparent to it.

But, climate change is happening, global average temperatures are rising and ice sheets are melting. Burning fossil fuels releases carbon dioxide into the atmosphere and belching beef cattle release methane.

The greenhouse effect is, as we said, an entirely natural phenomenon. If we didn’t have the natural greenhouse effect, the earth’s average temperature would be about -25 Celsius, instead of a relatively mild almost 15 Celsius. There would not be life on earth as we know it, and the earth would most likely be a frozen ball of ice. The greenhouse effect is caused by naturally occurring levels of greenhouse gases in the atmosphere, including water vapor, carbon dioxide, methane, nitrous oxide, and several others in trace amounts.

The actual amounts of these various gases in the atmosphere does not complete the picture in terms of the greenhouse effect and the climate debate. What is important is how powerful the gases are, not their absolute concentrations.

Back in the 1700s and 1800s, scientists did think that water vapor accounted for all of the greenhouse effect. It is such an effective absorber, and occurs in relatively high concentrations near the earth’s surface, that how could it not be? But then they began to realize, on the basis of high-altitude balloon measurements, that water vapor levels drop off very quickly with height; whereas carbon dioxide, methane, and other gases remain well-mixed throughout the lower atmosphere. Not only that, but greenhouse gases are much more effective higher up in the atmosphere where it’s colder, as opposed to near the warm surface of the earth.

Since water vapor is such a comprehensive absorber, many of the [spectroscopic] absorption lines of these gases do overlap with it, so it’s difficult to pin an exact number on how much any individual gas contributes to the natural greenhouse effect. However, with radiative transfer models it is possible to calculate the strength of the greenhouse effect if we just had other greenhouse gases, without water vapor or clouds. When we do so, we get about 35% of the total. We can also calculate the strength if we just had water vapor, but no other gases. When we do this, we get about 85%. So the truth is that water vapor and clouds are responsible for somewhere between 65 and 85% of the natural greenhouse effect. This is not the 99.9% effect claimed by skeptics.

The current problem has arisen because we are artificially “enhancing” this natural balanced phenomenon through our carbon emissions from vehicles, industry and power generation using fossil fuels. Indeed, we’ve been upsetting this balance significantly since the middle of the twentieth century and some would argue since the dawn of the industrial revolution in the nineteenth.

By massively increasing the amount of non-water vapor greenhouse gases in the atmosphere, we are increasing the amount of heat trapped by the atmosphere. Not only that, but warmer temperatures are causing more water to evaporate into the atmosphere. A British scientist proved this in 2007 (see footnote reference). So not only are humans artificially enhancing the non-water part of the greenhouse effect, we are also increasing levels of water vapor as well. And that has to be a lose-lose situation.

Research Blogging IconWillett, K., Gillett, N., Jones, P., & Thorne, P. (2007). Attribution of observed surface humidity changes to human influence Nature, 449 (7163), 710-712 DOI: 10.1038/nature06207


14 thoughts on “Water vapor and global warming

  1. If humans’ burning of oil is causing the warming during the last century, why did half of the warming happen before we started burning oil in 1940? If carbon dioxide is so powerful, why didn’t this start in the 19th century rather than have a cold spell then?

  2. EdwardT,
    You can’t have it both ways. Did we start producing significant amounts of carbon dioxide in the 19th century, or in 1940?

  3. In answer to treeves. This article is a sound answer as I have the graphics that show that this is a harmonic cycle that has been going on for centuries, in fact this cycle can be identified and traced back to as far as 400,000 years ago. This present climate cycle is natural cycle and has little to do with Carbon Dioxide, that is a trace element
    Totally our Earth is a global emitter of CO2 of 3.62%. Of this the Human added proportion is 3.62% and if you are prepared, our commitment to this is 3.4%, so the effect of our CO2 emissions is extremely small. Just one volcano emits between 3,000 to 8,000 tonnes of CO2 PER DAY and this one of five others within a 75km radius of the IPCC record laboratory is situated on this Island of Hawaii.
    I have concluded that it is the Sun’s influence is undergoing one of its eleven year cyclic Heliosphere reversals and is determining this climate change and if everyone on Earth stopped breathing out, now, it would not change the current climate we have now entered. tomw

  4. I always like when folks state unequivocally that the current global warming is part of a natural cycle. The problem with that that no one can state what is driving that cycle. Mr Watson above thinks it might be the sun, as if all the worlds’ climatologist and solar physicists are too stupid to have considered that notion. Actually, we’re in the midst of a Solar Minimum, and an El Nina — which might account for the recent cooling we’ve seen.

    However, the lack of warming Darwin speaks of is only in relation to the peak year of 1998, which was an unusually strong El Nino event. That was a very hot year! Subsequent years appear cooler when you look at a graph of just the last decade. The past decade is still the hottest on record. See http://climateprogress.org/2008/12/07/very-warm-2008-makes-this-hottest-decade-in-recorded-history-by-far/

  5. I believe that global warming would be a good thing if it happened. The only adverse effect I hear people worrying about it is that it’d melt some of the polar ice and thus raise sea levels. All experts agree that global warming, if it happened, would primarily affect the polar regions, and have little effect on the equatorial and temperate regions. There’s a good analytical basis for that consensus, which I’ll leave you to learn elsewhere. The rise in sea levels, if it happened, couldn’t happen at a rate faster than a few centimeters per decade. That gives people in low-lying areas plenty of time to shore themselves up. At the present time, everybody in low-lying areas already needs, and has, a meter or so of buffer against high tides from storm swells. Over the upcoming decades, they can raise their buffers by the average of a few centimeters a decade. Time is on their side. Raising their banks by a third of a meter in one construction job is enough to keep them dry for a century (or more).

    Meanwhile the cold north regions would get the benefits of more heat and better climate.

    Also, since trees and plants are carbon dioxide consumers, higher carbon dioxide in the atmosphere would be good for plant growth worldwide (not just the polar regions). It would make agriculture more productive. It would make the tropical forests lusher, but not hotter.

  6. @parviziyi It’s not quite like that…

    The climate may be 30–50 percent more sensitive to atmospheric carbon dioxide in the long term than previously thought, according to a study published in Nature Geoscience yesterday.

    “Climate change is affecting water supplies for cities and farms; leading to more severe droughts, hurricanes, and floods; contributing to more intense forest fires; and putting coastal communities at risk,” said Secretary of the Interior Ken Salazar, who is on his way to the global climate change conference convening this week in Copenhagen. “This study and the ongoing work of our USGS scientists will help us continue to build more precise long-term projections and to prepare for the impacts of climate change on our world.”


  7. Mr. Bradley, would you like to buy some beach front property in Arizona? People should not believe anything that the Secretary of the Interior says. Everyone needs to wake up. Our gov needs more monies, “oh this is not a tax, it is for the environment”. WAKE UP. This is all about 1 degree increase per 100 years. Does anyone know that ice evaporates without temperatures above freezing, it is called Sublimation. Have you or anyone else that believes this crap (Al Gore)stopped driving your car? NO. Is there a replacement for fossil fuels? NO. “Save the Planet”, someone tell me from what, what needs to be saved? One person, real data. I say it is from the Weak Minded and Weak Hearted.

  8. ignorance and avarice triumph, as usual

    Who in the 18th or 19th centuries talked about global warming?

    It may come as a surprise to the historically ignorant but — people burned down the forests first, then they burned coal and coke — the great “fogs” of London in Victoria’s time were coal fed smog. By 1900 oil consumption was on its way up — with Standard Oil and conglomerates to come. So, roughly 200 years of dirty air (particulates, oxides of nitrogen, hydrocarbons, CO2).

    Sadly, research in areas where ideology (including religious ideology) triumphs over useful scientific inquiry — like modern evolutionary theory and human-induced global warming — are playgrounds for the monied class supporting the ignorant substructure so carefully manufactured by US public education.

    the anti_supernaturalist

  9. This article deceptively leaves out the fact that the .038% of CO2 in the atmosphere is not all man made. Only .0114% of the atmosphere is man made CO2.
    8 ice ages in the last 1million years. In that time period the planet has spent the majority of its time a much colder planet. Who caused each of those cylces? At the end of the last ice age our planet started warming and melting the polar caps about 80,000 years ago. Who started that and kept it going?

  10. Climate Change

    The name alone should tip you off that something is being slipped over on you. I am reminded of the “war on terrorism”. Climate is ALWAYS changing and ALWAYS will long after man has taxed himself into nothingness. When the earth warms up mankind generally does much better than in the bitter cold. Our earth has been as much as 10 degrees F warmer than it is now.

    Global Warming had to be changed to “climate change” because the earth is not now warming, we are in a cooling trend that many think may last 20 to 40 years. England and Europe just had their coldest winter in MANY years. In Ireland the underground pipes froze solid. This had not happened in over 100 years. IMO it is going to get real COLD. Why? Planes are spraying aluminum coated poly-fibers which is deflecting the suns’ rays. Yes they say they are doing this to prevent GLOBAL WARMING but like much that passes for news this too is false.

    The “climate scientists” have been caught red handed lying, destroying data, losing data, changing data and in other ways changing the “climate model” without emitting a single molecule of CO2.

    We humans are carbon based life forms. We exhale CO2, (soon to be taxed) and inhale the oxygen emitted by the CO2 fueled plants.

    It is FRAUD folks, pure money driven FRAUD.

  11. “By massively increasing the amount of non-water vapor greenhouse gases in the atmosphere”

    We are talking ppm here. Our emissions of CO2 are far from massive and, since Beer’s Law applies to CO2, its effect as a warming gas is almost exhausted (90-95% done). Doubling CO2 might cause 0.01 deg C of warming, not the 0.12 deg C fabricated by the IPCC be altering a thermodynamic constant for CO2 by 12-fold.

    The fact is that there is not enough available carbon to double the CO2 in the atmosphere, but we can try. We might have enough to do 20-30%. The reason is that CO2 partitions 50 to 1 into the oceans such that we would have to emit 51 times the CO2 needed to double the atmospheric CO2 because 50 parts would dissolve in the oceans. It just ain’t going to happen.

    And then we have the half-life or turnover of CO2 in the atmosphere. The IPCC has the half-life at 200 years and NASA says 1000 years. Real research has it at about 5.4 years. Only by pretending that CO2 remains in the atmosphere can the IPCC claim that it is accumulating due to man’s activities. In fact, as the oceans warm, CO2 outgasses and as they cool CO2 dissolves. This is Henry’s Law. The IPCC does not have the power to cancel the laws of nature.

    The unaltered conclusion of the science branch of the IPCC was correct: they cannot detect any footprint of man’s activities on climate.

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