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Explaining how the water vapor greenhouse effect works

What the science says...

Select a level... Basic Intermediate

Increased CO2 makes more water vapor, a greenhouse gas which amplifies warming

Climate Myth...

Water vapor is the most powerful greenhouse gas

“Water vapour is the most important greenhouse gas. This is part of the difficulty with the public and the media in understanding that 95% of greenhouse gases are water vapour. The public understand it, in that if you get a fall evening or spring evening and the sky is clear the heat will escape and the temperature will drop and you get frost. If there is a cloud cover, the heat is trapped by water vapour as a greenhouse gas and the temperature stays quite warm. If you go to In Salah in southern Algeria, they recorded at one point a daytime or noon high of 52 degrees Celsius – by midnight that night it was -3.6 degree Celsius. […] That was caused because there is no, or very little, water vapour in the atmosphere and it is a demonstration of water vapour as the most important greenhouse gas.” (Tim Ball)

When skeptics use this argument, they are trying to imply that an increase in CO2 isn't a major problem. If CO2 isn't as powerful as water vapor, which there's already a lot of, adding a little more CO2 couldn't be that bad, right? What this argument misses is the fact that water vapor creates what scientists call a 'positive feedback loop' in the atmosphere — making any temperature changes larger than they would be otherwise.

How does this work? The amount of water vapor in the atmosphere exists in direct relation to the temperature. If you increase the temperature, more water evaporates and becomes vapor, and vice versa. So when something else causes a temperature increase (such as extra CO2 from fossil fuels), more water evaporates. Then, since water vapor is a greenhouse gas, this additional water vapor causes the temperature to go up even further—a positive feedback.

How much does water vapor amplify CO2 warming? Studies show that water vapor feedback roughly doubles the amount of warming caused by CO2. So if there is a 1°C change caused by CO2, the water vapor will cause the temperature to go up another 1°C. When other feedback loops are included, the total warming from a potential 1°C change caused by CO2 is, in reality, as much as 3°C.

The other factor to consider is that water is evaporated from the land and sea and falls as rain or snow all the time. Thus the amount held in the atmosphere as water vapour varies greatly in just hours and days as result of the prevailing weather in any location. So even though water vapour is the greatest greenhouse gas, it is relatively short-lived. On the other hand, CO2 is removed from the air by natural geological-scale processes and these take a long time to work. Consequently CO2 stays in our atmosphere for years and even centuries. A small additional amount has a much more long-term effect.

So skeptics are right in saying that water vapor is the dominant greenhouse gas. What they don't mention is that the water vapor feedback loop actually makes temperature changes caused by CO2 even bigger.

Basic rebuttal written by James Frank

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 5 July 2015 by pattimer. View Archives

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Argument Feedback

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Comments 51 to 65 out of 65:

  1. All that grade school "numerology" isn't going to get you very far Mizimi. re #48 and "water vapour emitted by air breathers". Remember that every molecule of water vapour returned to the atmosphere by metabolic respiration was a water molecule pulled out of the atmosphere by photosynthesis: nCO2 + nH2O ------> (CHOH)n + nO2 photosynthesis where (CHOH)n is generic carbohydrate (CHOH)n + nO2 ------> nCO2 + nH2O respiration re #49 and atmospheric relative humidity. Remember that the bulk of the atmosphere is much colder than 15 oC and so the water content at 50% relative humidity is far lower rather quickly as one ascends re #47/#49 Which paper are you talking about (mizimi: "just re-read that paper....")? You should really give your sources when you start expounding numbers. You make so many mistakes that it would be helpful if you could simply state where you obtained your numbers/ideas from so that we could assess them ourselves. Otherwise it's hardly worth addressing many of your points since they are based on series of unattributed numbers which very often turn out to be incorrect...
  2. Chris: I have difficulty some points you have mentioned. "Water Vapour as a positive feedback" If this were true, then what prevents the water from providing it's own feedback into what is essentially a thermal runaway? As well, it's a well documented fact that carbon dioxide dissolves in rain water, resulting in a typical pH of 6.5. So how can the lifetime of CO2 be so large if it's readily washed out by rain fall?
  3. Chris; the paper is Santer 2007 noted above. And you didn't answer the do climate models incorporate the heat emitted from life which is independant of IR ? Also, as you have previously averred, the WV content of the atmosphere is dependent on P~T, (subject to availability)so when it is removed during photsynthesis it is readily replaced..returning to "equilibrium"; so WV emitted by air breathers adds to the atmospheric content.
  4. Help please! I have not be able to find the paper disclosing the physics of the carbon dioxide and water interactions. Here I see only references to climate models and empirical studies, I would prefer to see the description of the actual phyical chemistry.
  5. According to and atmospheric WV appears to be decreasing at the height where GCM's predict it should increase.
  6. "We have tried to outline some of the unresolved issues concerning water in the atmosphere. But there are others. For example, it is well known that at low temperature pairs of water molecules will stick together to form a weakly bound molecule known as a dimer. The absorption properties of the water dimer at visible wavelengths will be different from those of a single water molecule, but these remain to be characterized. Furthermore, it has so far proved impossible to determine the proportion of atmospheric water molecules that are present as dimers in either laboratory or atmospheric measurements. And we have not even dared to discuss the many problems in understanding clouds. Clouds are highly variable in their make-up, distribution and size. They contain aerosols and mini droplets of water vapour, which have spectroscopic properties that are even more uncertain than those of normal water vapour. " A very interesting read.
  7. Don't know that anyone will come back to this discussion, but just in case... Let's pretend that about 2/3 of the earth is covered in water. If that were the case, shouldn't the atmosphere, in general, already be effectively saturated with respect to WV? What happens when the air becomes over saturated; the water precipitates out. True, if you irrigate a field in a dry region or exhaust WV from a hydrocarbon engine, you add to the WV downwind of that, but that doesn't change the thermodynamic properties of CO2. Nor does it change the fact that water evaporates more when it is warmer. With regard to #2, why would the sea surface temperature remain fixed when it is receiving more IR radiation?
  8. Chris G: Think cycles. The earth rotates so it goes through a heating/cooling cycle. WV taken up during the day will precipitate out at night if it contacts a surface cool enough....dew. Obviously if the temp drops sufficiently the general air mass will reach saturation point ( dewpoint). At sunrise, this saturated air is warmed and the dewpoint rises so the air is no longer saturated and can take up more WV. Whether the mass of air ever reaches saturation point during the day depends on how much water is available to evaporate and also that there is sufficient energy to evaporate it. The Saharan atmosphere is dry because although it has enough heat it doesn't have the water. Tropical forests can almost saturate the local atmosphere as both heat and water are present in sufficient quantities to allow this.
  9. Anybody read this which is an outline of a new climate 'theory' by Ferenc Miskolczi (ex NASA mathemetician) and if so...any comments?
  10. Hello guys. Has anyone considered the basis of a biological understanding of global warming? For instance your assumptions about the behaviour of water vapour are explained in terms of temperature, evaporation and condesation. I have read an interesting article from CSIRO SUSTAINABILITY NETWORK UPDATE – No. 64E is title "The biology of global warming and its profitable mitigation" and written by Dr Walter Jehne. I have a MSWord copy of the article though do not know how to added it to the Articles list.
  11. AldousH: I have read the article summary and in general terms agree with the conclusions. However it does seem to concentrate on deforestation as the prime mover and disregards other matters such as WV emissions from industrial processes, increased evaporation from man-made dams, lakes etc. Whilst these may be (relatively) small, they are not inconsequential; neither is the increase in heat and WV from animal life.
  12. There is considerable evidence that man's activities are changing the distribution of WV with consequential effect on climate. Deforestation has decreased evaporation by around 3000cubic/k/a which is mostly balanced by increases from agricultural evaporation of # 2600c/k/a. To that must be added the estimated loss of 400 c/k/a from industry, commercial, municipal use and reservoirs. The system seems to be in balance. However, the flow pattern of WV has changed, with subsequent effects on climate....this is explored from an agricultural view in "Human modification of global water vapor flows from the land surface." published online at PNAS ( the address is just too long to post) and the authors conclude that until modellers include redistribution of WV, GCM's cannot be considered to adequately describe real world conditions.
  13. Something to consider. The global dew point has been rising faster than global temperature. At the same time the pan evaporation rate has been dropping with an increase in global temperature.
  14. I would like to see all energy inputs and outputs and also the real estimates of the amounts of water in oceans water in atmosphere carbon sources ,co2 production from nature and man methane from nature and man i would lke to see evidence of temperatures in the distant past with co2 levels and if possible water vapour levels say over millenia. my expectation is that atmospheric carbon and water vapour levels are tails of very big dogs in the oceans and carbon sources. that we are dealing with small numbers in a system of much bigger numbers so conclusions we reach about global warming based on atmosheric gases are very problematic. what does co2 energy absorption in its narrow absorption band really have on energy balance.could it be it is reradiated at another frequency to space ? please explain how the green house effect of a gas actually works in detail I can appreciate the effect of WV in that clouds capture heat energy from the sun and nett radiate convect and reflect more heat than if the clouds were not there.water vapour that is not in a cloud presumably is causing a radiation block from the earth. i am not sure of the deatil
    Response: I've recently posted about an analysis of all energy inputs and outputs. and posted on man's co2 emissions. For more on the carbon cycle, see this page on human versus natural co2 emissions.

    Examination of past temperature change alongside CO2 change is examined on the CO2 lags temperature page as well as empirical determinations of climate sensitivity.

    The conclusion that atmospheric gases are causing global warming is based on empirical observations. Satellite observations of radiation escaping to space find that less radiation is escaping at wavelengths that CO2 absorb. This is confirmed by surface measurements of downward longwave radiation that also find increasing downward radiation at CO2 wavelengths.
  15. The article states: If extra water is added to the atmosphere, it condenses and falls as rain or snow within a week or two. Similarly, if somehow moisture was sucked out of the atmosphere, evaporation would restore water vapor levels to 'normal levels' in short time. Implicitly that says that humans can not add water vapor to the atmosphere. But from the pure logical point of view this contradicts the very first statement (from the green box): Water vapor is the most dominant greenhouse gas. If it is a greenhouse gas then it will act as such i. e. warm the atmosphere in effect. As a result the atmosphere will hold more water vapor including a fraction of what was added by men. If it's not, then all the talk about feedback is just gibberish and all conclusions from it, including (I assume) all the models, can surely be entrusted to the trash can. Please don't even consider the argument about the tiny amount by comparison. That has clearly been ruled out in the global warming debate. What I'd like to see are some serious estimations about the anthropogenic part when it comes to water vapor. Including besides the obvious ones e. g. the amount of water contained in a swamp vs. a palm oil farm per square kilometer or tropical rain forest vs. Cattle pasture or corn field. So if you start thinking about it there is hardly an end to find even restricted to the respect of land use that might result in releasing water to the atmosphere. Which then leads me to my last point. That is about direct heating the atmosphere by our energy production (of cause from burning fossil fuels and using nuclear - because all other sources are more or less conversions from sunlight). I think this belongs here because in most cases water vapor acts as a transport medium in the process. It gets vaporized by the produced energy and releases it due to condensation in the atmosphere. Due to the overall efficiency of our industry we speak about 50+ % of all energy generated. So far I have been unfortunate in finding anything about that matter so I thought it might be a good idea posting this question here.
  16. h-j-m, there is no actual contradiction between "extra" water falling out of the atmosphere, and the increased temperature due to the presence of extra water vapor allowing more water vapor to stay in the atmosphere. Additional water vapor increases the atmosphere's temperature by enough to allow an increase of the atmosphere's water-vapor-holding-capacity by only a fraction--a proportion less than 1. That resulting increase in water vapor then repeats the cycle, but now only that same fraction of the previous fraction. It is a converging series. The increases are the same percentage each round, but since the percentage of increase is less than 100%, the increase gets progressively smaller until it reaches zero.
  17. h-j-m, the amount of energy added directly to the atmosphere by humans is a forcing of less than 1% of the forcing from greenhouse gases added by humans.
  18. h-j-m, evidence supporting my contention of the triviality of energy humans add directly to the atmosphere is in my two comments on another thread here and here.
  19. h-j-m, I'm sorry, my previous reply regarding extra water falling out of the atmosphere did not answer your question. Please let me try again: There are vast pools of liquid water available to go into the atmosphere, and vast seeds for condensation to help water vapor drop out of the atmosphere. Indeed, both those activities happen constantly. So neither of those is a limitation on the amount of water vapor in the atmosphere at any one time. Humans' provision of more water is only a drop in the bucket. What does primarily limit the amount of water vapor in the (Earth's) atmosphere is the atmosphere's temperature. At a given temperature, adding more water vapor "nearly instantly" forces water vapor to drop out of the atmosphere. "Nearly instantly" in this context means "so fast that there is no time for significant atmospheric heating from the extra water vapor." The opposite happens as well: Water vapor removed from the atmosphere merely leaves room for the other water vapor that is constantly being added. The net effect all those processes is no change in temperature nor in the amount of water vapor. Water vapor is not a "forcing" of temperature. All the above is not just theory; it is observed fact. It was true before humans had even evolved. If it were not true--if water vapor was not limited by temperature--then there would no longer be liquid water on the Earth's surface. It would all have evaporated and none would have condensed. Water vapor could be a forcing if there weren't any liquid water lying around. On some other planet that doesn't have enough water to fill its atmosphere's capacity for water vapor, adding water vapor to the atmosphere certainly would cause that vapor to stay in the atmosphere. But here on Earth, we've got an abundance of water. What's needed to increase water vapor for more than 10 days is an increase in atmospheric temperature. That initial increase can't come from added water vapor (as I just explained), but it can come from anything else--anything that is a temperature forcing. For example, it can come from an increase in the Sun's output, or an increase in greenhouse gases. Once the temperature has increased, less water vapor drops out of the atmosphere. That does indeed then increase the temperature, which is why water vapor is a "feedback" from other causes of temperature increase. But the amount of temperature increase is strictly limited by the converging series I described in my previous comment.
  20. Dear Tom Dayton, deliberately I war referring to applied logic in my argument because I did not want to delve into the complexities we are dealing with here if only for the reason I don't know enough to argue in any specialized field. But I fear your reply forces me to elaborate on my point. As to my knowledge anything happening in the atmosphere is occurring locally depending on a lot of causes that are satisfied just at the spot. Any method of generalizing and narrowing down to only a few or even one cause (atmosphere temperature in this case) is not appropriate in my view due to the fact that we are dealing with nature here and for quite a long time now it is known that nature no way can be understood in a linear fashion as your argumentation suggests. I might mention that only a few decades ago it was the complexity of the earth's atmospheric system that triggered a whole new branch in mathematical science known as chaos theory. The atmosphere being a chaotic system clearly rules out any notion of insignificance due to amount unless any significance is disproved. Anyway to state my point in a somewhat broader consent: The matter of water and how we handle that should be given a much higher priority not only but also with respect to global warming. The reason should be obvious: The fact that it got harder in the last decades to get access to fresh water due to dwindling surface reservoirs and by now we already started using fossil reservoirs of it poses an immediate threat to mankind's existence as devastating as global warming if not even worse.
  21. h-j-m wrote "for quite a long time now it is known that nature no way can be understood in a linear fashion as your argumentation suggests." The role of water vapor in global warming is not at all "linear." It is rather complicated, and so is scientific knowledge of it. Introductory explanations of it are less complicated to suit readers who "did not want to delve into the complexities we are dealing with here if only for the reason I don't know enough to argue in any specialized field," as you wrote. If you suspect an explanation is unrealistically simple, you should pursue a more complete explanation. That is easy by clicking on the links to scientific papers provided in John Cook's original post, and indeed by clicking on the link I provided in my earlier response to you. One particularly relevant and short article is by Dessler and Sherwood (2009, Science, available for free), which specifically mentions local versus global effects, and which I think you in particular would find very informative and comprehensible.
  22. For one: The reason "I don't know enough to argue in any specialized field" is quite simple due to the fact that next to the majority of what is to be read is not worth it. A lot of it is in my view often stating trivialities cloaked on science language. On the other hand by far too often statements are made that can't stand any initial logical evaluation. Let's take as an example for the latter the wikipedia article on water vapor you referred to. Now let's just take a look at the paragraph on Condensation. I will include my comments in lines starting by the usual comment sign known from programming # continued citation will be marked with an >. It states: Water vapor will only condense onto another surface when that surface is cooler than the dew point temperature, or when the water vapor equilibrium in air has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface. # not necessary because that would depend on the ability of that surface to hold additional heat (energy). > The water molecule brings a parcel of heat with it. # why referring here at molecules when this amount is given in the properties section as 2.27 MJ/kg. I'm too lazy to look up what that would make in watts but I'm pretty sure we are talking about real energy here and not some negligible portion as indicated by the term parcel. >In turn, the temperature of the atmosphere drops slightly. # That is absolute nonsense it implies that the surface it condenses to absorbs more energy (heat) than is set free in the process. > In the atmosphere, condensation produces clouds, fog and precipitation (usually only when facilitated by cloud condensation nuclei). # Does that mean when taking place in the atmosphere no energy (heat) is released at all or maybe absorbed by the condensation nuclei? That would be a rather absurd notion and to my knowledge contradict the first law of thermodynamics. ># I canceled the rest of the paragraph. So far so well (or not so well). I hope this made a bit more clear what I mean when speaking of "not knowing enough". Now, this is what happens in my view: Given the right conditions water evaporates mainly near the earth surface. Due to it's density it then starts a path to higher altitudes. If then again the conditions are right it condenses and continues it's route until at last it comes down again as rain, snow or hail. In the process of evaporating the amount of 2.27 MJ/kg of energy is used. Logic dictates that the same amount has to be released at condensation. I hardly dare saying that it should be obvious that at the point where condensation occurs it's getting warmer. Now given the fact that on average water stays only 10 days in the atmosphere this is a real fast process. Now I'd like to know if you can find something wrong in this statement. Anyway it would prove a better starting point for a real discussion because it is more suitable to uncover differences in the understanding of the basic principles.
  23. Greenman3610 just posted a Climate Denial Crock of the Week on water vapor.
    Response: Thanks for the heads up, I've embedded the video above.
  24. John, the embedded video is just a blank box for me. But I'm using Firefox on a Mac; maybe it's platform-specific.
    Response: Hmm, I see a blank box in Firefox on the PC but it works fine in Internet Explorer. Any YouTube boffins have any solution to this conundrum?
  25. I really don'y buy the positive feedback model of water vapor. All positive feedback loops are unstable. The planet should have gone wildly hot millions of years ago in a positive feedback model. We have to conclude that water is in a negative feedback loop, either alone, as from the reflection of clouds alone, or in concert with other elements.
  26. villar, you can demonstrate non-runaway positive feedback in a spreadsheet: Cell A1: 0 Cell A2: 10 Cell A3: =A2+0.5*(A2-A1) Cell A4: =A3+0.5*(A3-A2) Now copy and paste cell A4 into cell A5 and on down the column for about 15 cells. The formula should automatically adjust to each cell, so each cell's value is the previous cell's value plus 50% of the increase that the previous cell had experienced over its predecessor. The feedback is an increase of each increase, not of the total resulting amount.
  27. "The specific humidity has been increasing over the last few decades near the Earth’s surface (as shown by the 1000 mb data), while it has been decreasing in the upper troposphere (as shown by the 300mb data). The increase in specific humidity at the Earth’s surface (1000 mb) is related to surface temperatures. For all except the far southern hemisphere bands, the effect of the 1997/98 El Nino can be seen in the specific humidity graphs. The decreasing specific humidity in the upper troposphere (300 mb) indicates that the warming at the Earth’s surface does not match the CO2 based warming theory. This is especially so in the northern hemisphere, which has experienced most of the warming in recent decades.....This is a major area of contention in the climate science area, since without the water vapor feedback the CO2 based theory loses its significance."
  28. Mizimi, unfortunately who wrote that page failed to notice that using the very same ESR utility it can be easily found that the upper troposphere has indeed warmed. An obvious question then arises as to how can specific humidity drop while temperature rises. It looks more like a convection issue. P.S. The first graph shown in you link has been demonstrated to be wrong quite a while ago. But you know, things keep hanging around forever over the internet ...
  29. Riccardo - thanks for the PS pointer. I recently read a paper ( which I seem to have lost) showing that there has indeed been an unexpected increase in convective turnover in the tropics...must try and relocate it. Just as a side issue... the amount of WV is not just T dependant - you have to have a source. No source in the Sahara so it's dry even tho' T is high. Lots of water in the tropics so it's humid. Also, in general terms, the atmosphere could hold a lot more WV -if the contact surface area between air/water was increased - without an increase in T. Air conditioning spray humidifiers do just that.
  30. Just a thought, are any of you familiar with global dimming. The article states that there has been an increase in WV in the atmosphere which has been recorded since 1988. If this is true then in essence there should be greater cloud cover which acts as both a negative feedback mechanism and a positive feedback. I cant remember where but i read that the suns rays have a greater impact on the evaporation of water than a rise in temperature alone. Something about the excitement of water molecules. So the increase in cloud cover and aerosols act as both a positive and negative feedback mechanism not exactly canceling each other out though. Apparently global dimming is half as strong as global warming. I'm sure that if i have made an error some where in my logic you will correct me.
  31. "Anthropogenic use of water is less than 1% of natural sources of water vapor..." Thus starts a paragraph about water vapor to state somewhat later: "Radiative forcing from anthropogenic sources of tropospheric water vapor is not evaluated here ..." How can some one come to the conclusion we are dealing with science here. By the way these statements are taken from the IPCC's 4th Assessment Report.
  32. If I can comment the discussion of Chris G and Mizimi: It is very interesting and I am amazed by the level of details being analyzed. Nonetheless my impression is that keeping an eye (and mind) focused on details prevents sometimes from noticing more relevant obvious facts which can render the details insignificant. The neglected factor seem to be the stabilising impact of oceans. While it is true that raising temperature of atmosphere increases its capacity to hold more WV thus raising its potential for more efficient GH effect - to fill this capacity requires liquid water reservoirs of elevated temperature. Primary source of globe's VW are oceans, whose heat capacity is several orders of magnitude higher than that of atmosphere and it would take millenia for the air to warm them up. Over the lands water sources are less massive and thus can more readily make use of raising evaporation conditions. However - taking into account high mobility of atmosphere and effective mixing - the warming effect will be diluted (with the probable net effect being enhanced removal of moisture from lands to oceans). As to the C02 - again it is the temperature of the oceans that determines water-air equilibrium concentrations. Antropogenic CO2 will in consequence mostly go to the oceans, and again - taking into account their far greater capacity then that of atmosphere - it should not accumulate to significant long-term levels in atmosphere making its impact on climate transient. How than can be explained the rising concentrations of CO2 in the air - observational fact beyond doubt? Either it is really of antropogenic origin and then it seems to be a small problem (as it is on its way into ocean) or - CO2 is released by the warming ocean (for which I - and perhaps we - miss information), a process that can be of far more dangerous consequences.
  33. lepton writes: Antropogenic CO2 will in consequence mostly go to the oceans, and again - taking into account their far greater capacity then that of atmosphere - it should not accumulate to significant long-term levels in atmosphere making its impact on climate transient. Well, that's true, as long as you can accept a timescale of tens of thousands of years as "transient." Yes, most of the CO2 we add to the atmosphere will end up in the ocean but given the thinness of the mixed layer and the slow rate of movement from the atmosphere to the mixed layer to the deep ocean, that will take a long time to happen. In the meantime, atmospheric CO2 will almost certainly exceed 2X preindustrial levels, if not 3X. How than can be explained the rising concentrations of CO2 in the air - observational fact beyond doubt? Either it is really of antropogenic origin and then it seems to be a small problem (as it is on its way into ocean) or - CO2 is released by the warming ocean (for which I - and perhaps we - miss information), a process that can be of far more dangerous consequences. Actually, it's quite clear that CO2 is going from fossil fuels to the atmosphere to the ocean, not the opposite direction. See, e.g., the following papers: Takahashi et al. 2009. Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans. Deep Sea Research Part II: Topical Studies in Oceanography, Volume 56, Issues 8-10, April 2009, Pages 554-577. Sabine, et al. 2004. The Oceanic Sink for Anthropogenic CO2. Science, Vol. 305. no. 5682, pp. 367 – 371. Yes, as it warms the ocean can hold less CO2, but CO2 is rising faster in the atmosphere, so there's a net flux from the atmosphere to the ocean. More than anything else, it was studies of the process of CO2 uptake by the oceans that set off alarm bells about global warming in the 1970s and early 1980s. Until then people thought most of the CO2 we emit would end up in the oceans. When it became clear that this would take a long, long time to happen, people began to realize that this is a big problem that we're facing.
  34. to villar at 20:21 PM on 2 December, 2009 Any positive feedback is the source of instability, by definition. I do regret that so many climatologists have so minimal knowledge of process control. Not every positive feedback blows a sytem up. It can also make it oscillate, like in simple systems with phase delay. In climate - an obvious complex set of interwoven processes - a positive feedback like VW induced GH effect - generally will drive conditions to the point when other (up to then dormant) processes will activate, possibly turning on some negative feedback. The very fact that Earth's ecosphere still exist after so many evidences of past climate extremities proves that (regardless of any positive feedback) our globe can always find equilibrium (if only local).
  35. Ned at 13:23 PM on 21 February, 2010 writes: "More than anything else, it was studies of the process of CO2 uptake by the oceans that set off alarm bells about global warming in the 1970s and early 1980s. Until then people thought most of the CO2 we emit would end up in the oceans. When it became clear that this would take a long, long time to happen, people began to realize that this is a big problem that we're facing." Thank you for valuable references. However - as a physicist (not climatologist) - I can hardly understand why the time scale of the process of the CO2 reaching equlibrium between atmosphere and ocean concentrations process might be any different from that of WV evaporation rate due to ocean-air temperature differences. Both processes are based on the same molecular mechanisms. Perhaps the culprit is the ocean surface layer - warmer than the bulk, so evaporating more willingly, at the same time accepting less CO2?. Might it be that the significant factor is the mixing of ocean? Both on surface by waves and in bulk by currents?
  36. A year ago, Mizimi wrote: A few sums ....various sources give our annual energy usage from FF as around 14 terawatts. That's almost certainly the power directly associated with combustion of fossil fuels, not the radiative forcing from the CO2 produced by that combustion. But, more or less coincidentally, the annual increase in radiative forcing is probably pretty close to that 14 terawatts worldwide. (Based on these data from NOAA, it looks like the annual increase is 0.03 watts/m2 which works out to about 1.5E13 watts over the planet as a whole. Mizimi continues: Looking around the Australian Bureau of Statistics gives the following population figures.... People 21 million Horses 400,000 Kangaroos 23 million Camels 400,000 Cattle (dairy and beef) 26 million Sheep 20 million Rabbits 250 million Simple maths - multiplying numbers by the basal metabolic rate at rest of each species gives a daily heat emission of 315 x 10E9 watts or 114 x 10E12 watts per annum. Whoa, do you understand the meaning of the word "watt," Mizimi? A basal metabolism of 1 watt is 1 watt, whether you measure it over a period of days, weeks, years, or millennia. If you're going to convert the metabolic data to watt-years, you need to do the same conversion for the radiative forcing! Let's redo those calculations. I can't find actual data on the metabolic rates of kangaroos etc., but I see that sheep are about 50 watts, cattle about 330, and humans about 78. Using Mizimi's population figures, that works out to a total basal metabolism of 1.1E10 watts, several orders of magnitude less than the figure that Mizimi quotes. I don't think adding in the kangaroos and rabbits would make up the difference :-) The annual increase in radiative forcing from greenhouse gases is 1360 times larger than that. In other words, every 6.4 hours we're adding a radiative forcing to the climate system that's approximately equal to the combined metabolism of all the people, cattle, and sheep in Australia. Two caveats in closing: (1) If that seems like a silly comparison, blame Mizimi not me. (2) Apologies for responding a year late ... but Mizimi's original post was so severely erroneous and had gone uncorrected for so long that I thought it would be good to set the record straight.
  37. Ned, i am interested in your refute of Mizimi's calcualations in post #86. I was wondering if you could answer a question for me. I am no where near the level of discussion on this board. Your first point has to do with the definition of a watt. A watt is equal to one joul/s. The definition of a watt includes a specific amount of energy over a specific period of time. j/s. Why then is it inappropriate for an individual to calculate the total increase in heat or energy over a period of time (a year) based on the length of time given in the definition of a watt? Second, my understanding of radiative forcing is limited. I beleive it is defined as the change in irradiance at the tropopause. It is determined relitave to a base period (usually 1750). The IPCC defines radiative forcing as follows: "Radiative forcing is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism. In this report radiative forcing values are for changes relative to preindustrial conditions defined at 1750 and are expressed in watts per square metre (W/m2).":36 Neither my previous definition nor the IPCC definition refer to change per unit of time. As such how and why would Mizimi have to calculate radiative forcing-years? sure one year may have an increase in radiative forcing, and another a decrease, but they are all relative to 1750 and are not necessarly cumulative. To better explain myself and my understanding of radiative forcing i will use simplified means. Say year XXX1 has a radiative forcing value of +1. this would mean that it is +1(w/m2) over 1750. Assume year XXX2 has a reading of +1 as well, year XXX 3 has a reading of +2, the cumulative radiative forcing is + 2 not +4, right? Love this series of posts, sorry if i am dumbing it down too much.
  38. Okay, first of all I think that evaluating the impact of CO2 by comparison to the metabolism of Australian livestock is not necessarily the optimal way to visualize it. Kind of like weighing yourself and then converting to units of ladybugs based on a sample weight of a ladybug in grams found somewhere on the internet. But, since you asked ... Tadh writes: Why then is it inappropriate for an individual to calculate the total increase in heat or energy over a period of time (a year) based on the length of time given in the definition of a watt? Actually, it's not at all inappropriate in the right circumstances. My monthly electricity bill reports usage in kilowatt-hours. That is appropriate for a quantity that fluctuates over time, like household electrical usage. In this case, it's not necessary, since for both the animal metabolism and climate radiative forcing data we have just an annual average. When Mizimi writes "... a daily heat emission of 315 x 10E9 watts ..." that's not "daily" ... it's 315 x 10E9 watts full stop. When she/he multiplies that by 365 to get "114 x 10E12 watts per annum" that's actually "114 x 10E12 watt-days per annum", though Mizimi doesn't seem to understand the meaning of these units. Now, doing that conversion merely complicates things unnecessarily, since "114 x 10E12 watt-days per annum" is exactly the same as "315 x 10E9 watts" (ignoring leap-years). However, the real problem is that Mizimi converted the metabolic data to "watt-days per annum" but didn't convert the radiative forcing to the same units. In other words, one side of the comparison got multiplied by 365 but the other side didn't. Hope this helps. Let me know if it's still confusing...
  39. Ned, Thanks for the quick reply. You certainly gave me a better understanding of what Mizimi did with the metabolic rate, and how it affects the resulting answer. However I am still a bit lost on the radiative forcing. I think I know where I am going wrong. Radiative forcing would need to be changed in the same way metabolic influence would need to be due to the fact both are expressed in watts? But isn’t the radiatve forcing just relative to a set period, not a predictable increase? In order to do RF-Years wouldn’t we have to apply the change from year to year, and not the actual RF number? Thanks! By the way, apparently I weigh approximately 3,995,933 ladybugs. (wiki says .021 grams per ladybug)
  40. Well, you outweigh me a bit; I'm 3,780,000 ladybugs as of this morning. It's been a long day here and I'm a bit addle-brained right now, but I think you're talking about two separate issues. One is the units involved in comparing radiative forcing to gross Australian livestock metabolism, and the other is how to account for changes in radiative forcing over time.* Is that right? If so, I think we've taken care of the first part (units should be consistent on both sides, either comparing watts to watts or watt-days per year to watt-days per year). Then the other question is about radiative forcing and how to handle changes therein over time. If CO2 and everything else were constant, RF would be constant too (and there'd be no need for this website!) Unfortunately CO2 is increasing, so the RF associated with CO2 is likewise increasing over time. Now, I may have screwed up the calculations somewhere, and I'm too tired to re-check this, but apparently when I wrote that original reply to Mizimi I'd calculated that annual increase in RF as 0.03 W/m2 over the whole earth. (I would not be the least bit surprised to learn that I'd made an error somewhere there, but let's assume it's correct). Now, the RF itself doesn't "accumulate" from year to year, though the energy resulting from it does (until the earth comes back into radiative balance with its exoatmospheric environment). But you can still look at the annual increase in RF caused by the annual increase in CO2, and compare the power of that RF increase with some other thing (like Australian sheep metabolism). Of course, I may be confused about what you're saying, or I might be screwing up the calculations. Or I might be suffering from a case of DK effect. But this is how it seems to me. * This is a sentence that has probably never before been composed in all of human history!
  41. John, The link to Soden 2005 doesn't work. At least for me, it redirects to a search page. Is this the article? One thing would make this web page even more excellent is if you'd list the full references, so that if a link doesn't work, you can try to find it yourself (if not on the web than maybe at a library); at least the abstract. Regards, Simon
    Response: No, that wasn't the article I was linking to although it does look like an interesting paper. The paper I'm refering to is An Assessment of Climate Feedbacks in Coupled Ocean–Atmosphere Models (Soden et al 2005). Thanks for letting me know about the bad link.
  42. Good discussion guys! It appears from the comments in general and reading of various paper quoted innthe Arguements,that the critical longer term measurements behind the IPCC consensus understanding of the CO2 forcing and amplification of the dominant water vapour greenhouse effect and feeed backs are not yet available. So although many suspect or actually believe that CO2 has a strong influence on pushing higher atmospheric temperatures, we dont actually know this to be true as a scientific fact. Arguements were made that increased CO2 has caused a little warming which then causes water vapour increases that sustains and amplifies the warming. But surely as Mizimi has rightly emphasised in many ways, water vapour is the dominant GHG as part of the natural evaporative cycle, so it's always been operating and the anthropogenic CO2 increase has just caused some minor additional warming! How does one differentiate the various contributions to GW? Fundimentally then what is the hard proof that CO2 is the dominant factor in GW?, leaving aside model driven assertions that are by default somewhat suspect because factors chosen or their levels may not be represenative of the real complexities involved. I have read the Carbon isotope proposal showing the increased carbon in CO2 mostly comes from burning fossil fuels-and that seems reasonable, but doesn't in itself prove AGW. Climatologists may be sure that their data tells the story well enough, but so far it does not convince me, though I admit to being worried by the evident belief expressed by many authors. However, asserting that CO2 must be the main cause of AGW because nothing else fits the bill- is not geood enough! The science on this must be more clear cut and definitive than at present, especially when major global policy affecting future world economic growth and energy use is at stake.
  43. Thanks for the comment, Bob Close. First, on the very narrow point of CO2 vs water vapor: As a thought experiment, imagine that you could somehow remove all the water vapor from the atmosphere, and prevent any more water from evaporating into the atmosphere (but you keep CO2 constant). Now, alternatively, imagine that you removed all the CO2 from the atmosphere, but kept water vapor constant. (Yes, both these alternatives are physically impossible on our world, but use your imagination). The world with no water vapor (but normal CO2) would get much colder than the world with no CO2 (but normal water vapor). So in that sense, you could say that "water vapor is more important than CO2 in warming the planet". However, neither of those is a realistic scenario. In the real world, we are doubling CO2 concentration. This has the effect of warming the planet somewhat. Water vapor then acts as a feedback, increasing the warming started by CO2. So we end up with our natural base temperature (t0) plus some new warming from CO2 (dt1) plus some additional new warming from the water vapor feedback (dt2). But in terms of assigning responsibility for that warming ("whodunit?") ... both dt1 and dt2 are a result of the increase in CO2. If we hadn't burned any coal or oil, we would still be at t0. The same would be true if there were some other event that caused warming (or cooling). For example, 65 million years ago a bolide impact on the Yucatan peninsula injected a lot of dust, aerosols, etc. into the stratosphere, which cooled the planet, which in turn reduced the amount of water vapor, which cooled the planet further. None of that cooling would have happened without the bolide impact, so even though some of the cooling involved water vapor, we still would say that all of the cooling was caused by the impact event. That initial cooling was followed by a rapid and extreme warming, caused first by CO and other shorter-lived greenhouse gases, then by CO2 which lasted for many centuries. Much of this new carbon came from the carbonate rocks that were vaporized at the impact site, injecting lots of carbon into the atmosphere. Once again, this warming was amplified by the water vapor feedback, but none of it would have occurred without the presence of CO, CO2, etc. So on both the downswing and the upswing in temperatures, water vapor acts as a feedback amplifying the change in temperature that is created by some other forcing (greenhouse gases, aerosols, solar variations, etc.)
  44. Ned wrote: "As a thought experiment, imagine that you could somehow remove all the water vapor from the atmosphere, and prevent any more water from evaporating into the atmosphere (but you keep CO2 constant)." But that's the rub, you could not prevent water from evaporating, at least not unless you also get rid of the ocean -- nay, all liquid and frozen surface water. Ned: "Now, alternatively, imagine that you removed all the CO2 from the atmosphere, but kept water vapor constant." A far more interesting thought experiment. If you instantaneously removed CO2 you could not keep water vapour constant because removing CO2 would reduce the temperature of the atmosphere, thereby reducing the amount of water vapour the atmosphere could hold, causing a portion to condense and precipitate out. This would in turn cause a further drop in temperature, and so on in an amplifying feedback loop. Temperature would eventually stabilize with substantially more ocean surface being frozen over, possibly even a global snow or slush ball earth state, greatly reducing albedo and cutting off a substantial portion of evaporation such that there would be relatively little water vapour in the atmosphere. In other words, CO2, which does not condense out of earth's atmosphere, makes it possible for there to be appreciable water vapour in the atmosphere, thus CO2 is, in the words of Richard Alley, the 'control knob' of the greenhouse effect.
  45. #94: Interesting! Now imagine that a decrease in water vapor in the atmosphere would cause fewer clouds to form. As a result, the Sun can warm the surface more than when clouds got in the way, which puts more water vapor back into the atmosphere to form clouds. Imagine a planet with no cloud cover. What would the surface temp be? If the answer is "hot", then clouds could rightly be said to have a cooling effect. If not, then the opposite would be the case. Which is it? Clouds have often been said to be where the biggest disagreement remains. Is the net effect of clouds to a positive or a negative feedback? I'm not aware that this has been settled.
  46. daisym, I believe that some types of clouds are understood to have a net cooling effect, and some a net warming effect. The difficulty, I believe, is in figuring out the relative contributions of those types of clouds in any given scenario. Realclimate has a post addressing clouds' role in albedo changes. It has another post on the role of aerosols in triggering cloud formation. And it has another post on the purported role of galactic cosmic rays in triggering clouds.
  47. daisym, there is a good explanation of clouds and climate at the NASA Goddard site.
  48. In a different thread, cruzn246 made this claim relating to Water Vapor concentration (after I stated it represented about 0.4% of the atmosphere): "Actually this is wrong. It ranges from 1 to 4% with the average being between 2 and 3%" Those figure are for surface value. In the entire atmosphere it's 0.4%. "but no one is really sure what that average is on any given day." True, but irrelevant. The water is already part of the weather system, contrary to fossil fuel CO2 which is being added to the atmosphere. "According to NASA, they say the increase in water vapor is probably playing a bigger part in warming now than CO2, but they will not put numbers on either as far as the amount each is contributing." Water Vapor acts as a positive feedback to CO2-caused warming. It has a bigger impact on GW than CO2, but we are not adding new water to the system. We are adding more CO2, which increases the heat, which causes more water to evaporate, which further raises temperature. We all know this. Why do you come here on your high horse and tell us things that we already know as if you had the "killer argument" against AGW? All you're doing is highlighting your own ignorance for all to see. "The difference in an atmosphere with a strong water vapor feedback and one with a weak feedback is enormous," Dessler said." Note the use of the word "feedback." Basically, this articles agrees with the science presented here, and disagrees with you. I know it's common for less experienced deniers to mistakenly provide evidence that goes against their position, but this one's pretty obvious... "I think all you need is a simple climate shift that has nothing to do with CO2 to put more water vapor in the air." Please provide evidence of such an unknown climate shift. Put up or shut up.
  49. "Please provide evidence of such an unknown climate shift. Put up or shut up." The shift of the PDO and NAO at about the same time in the late mid 70s put us into this warm spell. Good enough? There are signs they both may go negative again at the same time and that could put us right back into the type of weather we had in the middle of the century.
  50. @cruzn246: wow, you're really goign through the gamut of debunked arguments, aren't you. What's next, it's because of Solar Irradiance? The PDO is currently *negative*, why would it warm us? It's also a cyclical phenomenon that doesn't show a long-term trend, which we are experiencing. "Good enough?" Not by a long shot. It's Pacific Decadal Oscillation Instead of randomly posting graphs you clearly don't understand, I suggest you actually start learning some science. Again, it's clear you have no idea what you're talking about, and are simply trolling on this site.

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