Water vapour: feedback or forcing?

When surface temperatures change (whether from CO2 or solar forcing or volcanos etc.), you can therefore expect water vapour to adjust quickly to reflect that. To first approximation, the water vapour adjusts to maintain constant relative humidity. It’s important to point out that this is a result of the models, not a built-in assumption. Since approximately constant relative humidity implies an increase in specific humidity for an increase in air temperatures, the total amount of water vapour will increase adding to the greenhouse trapping of long-wave radiation. This is the famed ‘water vapour feedback’. A closer look reveals that for a warming (in the GISS model at least) relative humidity increases slightly in the tropics, and decreases at mid latitudes.

How do we know that the magnitude of this feedback is correctly simulated? A good test case is the response to the Pinatubo eruption. This caused cooling for up to 3 years after the eruption – plenty of time for water vapour to equilibriate to the cooler sea surface temperatures. Thus if models can simulate the observed decrease of water vapour at this time, it would be a good sign that they are basically correct. A good paper that demonstrated this was Soden et al (2002) (and the accompanying comment by Tony DelGenio). They found that using the observed volcanic aerosols as forcing the model produced very similar cooling to that observed. Moreover, the water vapour in the total column and in the upper troposphere decreased in line with satellite observations, and helped to increase the cooling by about 60% – in line with projections for increasing greenhouse gases.

To be sure there are still some lingering uncertainties. Some recent data indicates that tropical upper tropopsheric water vapour does not quite keep up with constant relative humidity (Minschwaner and Dessler, 2004) (though they still found that the feedback was positive). Moist convection schemes in models are constantly being refined, and it’s possible that newer schemes will change things . However, given the Pinatubo results, the models are probably getting the broader picture reasonably correct.

*R.S. Lindzen, 1991. Quart. J. Roy. Met. Soc., 117, pp. 651-652

Page 3 of 3 | Previous page

111 comments on this post.
  1. Fabrizio:

    Really interesting. Does the model proof also the effects of the airline shutdown after 09.11? To me it is not clear if you consider only the profile of the vapour in the atmosphere, or if you consider also layering with the coulds and the massive effects the airplane have in modifying it.

  2. Stefan:

    I’ve seen a slightly different “98%” argument made by climate skeptics (e.g., U. Berner in various popular brochures and articles): “98% of the greenhouse effect is natural and only 2% anthropogenic”.
    This is because the anthropogenic greenhouse gas forcing (~2.4 W/m2 until now, here IPCC is cited) is only ~2% of the total (“natural”) greenhouse forcing.
    What these people usually leave out, of course, is that the natural greenhouse effect warms the surface temperature by ~33 ºC (all else being equal, notably albedo).
    A rough and linear back-of-envelope estimate of how large the 2% anthropogenic change in greenhouse effect might be: 2% of 33 ºC is ~0.7 ºC, very similar to what the more detailed and correct calculation gives.
    So, there is nothing wrong with this version of the 2% argument – except that it is often used in a context and in a way designed to mislead the public, i.e., it is used to suggest to a lay audience that “global warming is 98% natural”, so we are not responsible and can’t do anything about it.

  3. John Finn:

    Well done, Gavin

    We’ve finally had an article on the single most important point in the climate change debate, i.e. climate sensitivity. Thanks for that.

    I’ve just got a quick question (for the moment anyway) regarding constant relative humidity where you say

    To first approximation, the water vapour adjusts to maintain constant relative humidity. It’s important to point out that this is a result of the models, not a built-in assumption.

    Now I’d just like make sure I understand what’s been said here. I’m a bit thick, so please bear with me on this. Does this mean that the results of the computer calculations produce a constant relative humidity – as opposed to the program (or model) assuming constant relative humidity to compute the increase in water vapour.

    [Response: I thought Gavin was pretty explicit. The models do not impose a fixed RH. The models are at liberty to produce their own RH. As it happens, what comes out is that the RH tends to stay about the same (its not absolutely constant, of course) - William]

  4. Tim:

    #3 said Does this mean that the results of the computer calculations produce a constant relative humidity? as opposed to the program (or model) assuming constant relative humidity to compute the increase in water vapour.

    That is indeed the case. The constant relative humidity would be produced as a result of calculations that the models make regarding evaporation of water from the surface and then of moving this water about through convection and the dynamics of the model [and raining the water out again].

  5. John Finn:

    Thanks for that, Tim

    So what do the models predict (or project) that the additional water vapour contribution would be for a given rise in temperature.

    For example, if there was a change in GHG (WV not included) forcing which produced a temp rise of 1 deg C – by how much would that increase WV (in ppm) and what would that mean in terms of additional warming.

    [Response: Since it's a coupled feedback process, you can't really separate it out like this. But you can estimate how much more water there would be for a given temperature increase at equilibirium using the Clausius-Clapeyron equation. For the response to 2xCO2, (around 3 deg C) you would expect an increase of about 30% in water vapour amounts. -gavin]

  6. John Finn:

    This is because the anthropogenic greenhouse gas forcing (~2.4 W/m2 until now, here IPCC is cited) is only ~2% of the total (“natural”) greenhouse forcing.
    …..
    A rough and linear back-of-envelope estimate of how large the 2% anthropogenic change in greenhouse effect might be: 2% of 33 ºC is ~0.7 ºC, very similar to what the more detailed and correct calculation gives.

    Not sure realclimate would agree with this. For a change in ghg forcing of 2.4 W/m2 they would expect a warming of around 1.8 deg C, i.e. a sensitivity of 0.75 deg C per W/m2.

    [Response: This was intended as a very rough "back-of-envelope". If you take the IPCC uncertainty range for climate sensitivity, you don't get 1.8 ºC but a range of 0.9-2.7 ºC, and that is with all the feedbacks. Hence 0.7 ºC without feedbacks is roughly in the right ball-park. All I wanted to say is: this quick-and-dirty estimate already shows that a 2% increase in greenhouse effect is not a negligible effect, so people who are telling the public "don't worry, it is only 2%" are making a bogus argument. -Stefan]

  7. John Cross:

    I believe that Essenhigh might have produced some work showing that water accounts for 95 or 98% of the Greenhouse effect. It was an interesting and quite technical look at things but ended up using an average WV content of 4% because he said that if the global warming people can average temperature he could average water content!!???!!

    I took a look for it a while ago but it was no longer on the net. Maybe someone pointed out that WV changes in elevation as well as across the globe and that 4% was way off!

    [Response:If you are referring to this article, Essenhigh's reasoning does not include the variations of water vapour in the atmosphere, nor the multiplicity of absorbing lines for CO2 and water vapour. If you can find something more sophisticated, let me know. - gavin]

  8. John Finn:

    Since it’s a coupled feedback process, you can’t really separate it out like this.

    OK – fair enough.

    But I’m now getting a bit confused over the order of magnitude of the numbers involved. I thought – averaged globally – WV is measured in 1000s of ppm (i.e lots of 1000s in the tropics and much less at the poles). In your response, you say

    For the response to 2xCO2, (around 3 deg C) you would expect an increase of about 30% in water vapour amounts

    This means the increase is of the order of 300 ppm – or have I got something wrong.

    [Response: The mean amount of water vapour in the atmosphere corresponds to about 25 mm of liquid water. At 2xCO2 that might increase to 32 mm or so. The change in ppm will vary a lot depending on where you are, but in the tropics, you might see changes of 1000s ppm (since the current surface values are ~16,000 ppm). - gavin]

  9. Lynn Vincentnathan:

    Let me see if I got it. We emit CO2, which warms the world a bit, and this causes more water to vaporize & warm the world more to a higher (more or less) stabilized level. And reducing emissions, with nature aboring CO2 & atmospheric CO2 reducing, would cool the earth a bit, which would reduce water vapor, cooling the world more to a lower (more or less) stabilized level. So our emissions (or reductions) have an somewhat amplified effect, beyond a purely CO2 effect.

    And this scenario/model does not include the possibility of net positive feedback from nature (up to a much higher stabilized warming) – such as the warming (from CO2 and concomitant WV) reaching levels that cause nature to emit GHGs (from “natural” fires, decomposition, plant reduction, methane clathrates, albedo, etc.)

    Let me know if this is right.

  10. kyan gadac:

    Sounds cool to me Lynn, the critical line is the one about residence time. It’s not the quantity(state) of water vapour that matters as much as the rate(residence time) of it’s cycling. A consequence of this is that water vapour is locally variable(15% – 100% in the temperate zone) depending (mostly) on the wind direction and season.

    In terms of climate change this seems to lead to the sorts of conditions that are prevailing where I live in the south west of Australia . Here we experienced record flooding last week following an equinoctial storm. So that, although the winter rainfall has ben declining steadily since the 1960′s, the average annual rainfall has been less affected due to increasing drought being offset by increasing storminess.

    The deviation is as affected as much as the mean.

  11. Hans Erren:

    Consider the following:
    A large part of global warming is in fact located in Central Siberia and Canada.
    Given increasing population, the amount of water vapour emitted just by heating houses has also increased dramatically. Has this extra forcing by antropogenic water vapour in winter ever been considered? Because this is a synchronous forcing and not a feedback.

    Of course the half life of this antropogenic emission is very short, but the replenishment rate is also fairly constant during winter.

    [Response: Do the sums. Calculate the rate of water vapour injection over the region. An estimate of the fractional change in the concentration can be made by taking that flux and dividing by the regional precipitation rate (the sink for water vapour). Only if that is >> 0 will there be a significant forcing. - gavin]

  12. Dave Dardinger:

    I’m not sure that serious skeptics worry too much about the direct forcing from increased water vapor. What should be an issue of discussion is how the increased water vapor plays out in terms of increased cloud cover. As the now larger amount of water vapor rises it will sooner or later result in cloud formation and this will, during the day, cut off far more visible light than the amount of IR which is blocked from escaping during the night. A good figure for what this negative feedback from water vapor is must be used to offset the initial positive feedback.

    In this regard, it’s also necessary to realize that the forcing from a given amount of additional CO2 or H2O decreases as the total amount of each increases. The rule of thumb I’ve seen is that each doubling of CO2 adds a constant forcing. Does that rule apply to water vapor as well?

  13. Michael Jankowski:

    Re#10:

    “In terms of climate change this seems to lead to the sorts of conditions that are prevailing where I live in the south west of Australia…although the winter rainfall has ben declining steadily since the 1960′s”

    11-yr trendlines for western Australia from the Australian Bureau of Meteorology don’t seem to reflect “winter rainfall has ben declining steadily since the 1960′s” http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/timeseries.cgi?page=cc&variable=rain&region=wa&season=0608

    You can see the area considered “western Australia” here http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/trendmap.cgi?page=cc&variable=rain&region=wa&season=0608&period=1960 and data locations here (seem to be very well represented in the “south west of Australia”) http://www.bom.gov.au/silo/products/cli_chg/rain_trendmaps.shtml , for which the portions of increased rainfall over the 1960-2004 time period (or 1970-2004 time period, if you select it) seems to roughly cancel-out the portions with decreased rainfall.

    As the trendline page states, the avg winter rainfall for the 1961-90 period was 65.37mm. Using the downloaded data, the entire 1900-2004 avg was 66.66mm, roughly the same as the 1961-1990 average. The 1960-2004 avg was 65.50mm. The 1970-2004 avg was 65.15mm. The 1980-2004 avg was 64.38mm. So there was a slight but minimal decline from 1960 to 1970, and then again to 1980. But then there was another uptick, as the 1990-2004 avg was 65.96mm. That doesn’t seem like a lot of variation to me.

    And those figures included 1999-2004, over which the average was just 47.69mm. Those years were weighted more heavily in the prior calculations as the starting time period was moved closer to the present. Eliminating the most recent 5 yrs of data would produce avgs of 67.81 (since 1900), 68.24 (since 1960), 68.77 (since 1970), 69.65 (since 1980), and 78.14 (since 1990). So winter rainfall averages had been INCREASING slightly since the 1960s and up until 1999, after which there has been a large decline.

    Also, using 1900-2004 averages, I come up with a ridiculous standard deviation of 23.79. Seems like you’d have a hard time finding a statistical trend anywhere in that data.

    “The deviation is as affected as much as the mean.”

    Std devs:
    1900-2004: 23.79
    1951-1960: 26.50
    1961-1970: 28.88
    1971-1980: 31.19
    1981-1990: 17.15
    1991-2000: 22.22
    2001-2004: 9.94

    Sorry, but I don’t see any increase in deviations, either. The std dev went-up slightly in the 60s, 70s, and 80s, but has dropped considerably in decades since.

    Now maybe you’re referring to the very “south west of Australia,” and the prior calculations cover to wide of an area. However, the trend maps on the website above show an increase in winter rainfall over most of southwest Australia (0-10mm/decade) with a small portion where there was a decrease in winter rainfall (0-10mm/decade) from 1970-present. 1960-present shows a much larger area of decreased rainfall with a greater magnitude (up to 40mm/decade). Going back to other maps shows similar albeit smaller rainfall decreases. In other words, the far southwest of Australia has seen an overall decrease in winter rainfall since 1960, but this appears to be generally confined to the 1960s themselves. It’s tough to say without actually having data to do calculations, but based on the difference between the 1960-present and 1970-present trend maps, it looks as if much of southwest Australia has seen an increase in winter rainfall from 1970-present and had a severe winter rainfall deficiency in the 1960s.

  14. Eli Rabett:

    The Essenhigh article pointed to by Gavin contains this gem:
    ——————————————
    “Even closer focus on water is given by solution of the Schuster-Schwarzschild equation applied to the U.S. Standard Atmosphere profiles for the variation of temperature, pressure, and air density with elevation (8). The results show that the average absorption coefficient obtained for the atmosphere closely corresponds to that for the 5.6-7.6 µm water radiation band, when water is in the concentration range 60-80% RH – on target for atmospheric conditions. The absorption coefficient is 1-2 orders of magnitude higher than the coefficient values for the CO2 bands at a concentration of 400 ppm. This would seem to eliminate CO2 and thus provide closure to that argument.

    This overall position can be summarized by saying that water accounts, on average, for >95% of the radiative absorption.”
    ———————————————-
    Essenhigh appears not to know that the earth radiates pretty much like a blackbody at ~285 K (http://tinyurl.com/44k2h for a graph) There is about zilch intensity between 5.6 and 7.6 µm (~1300 – 1800 cm-1, the water bending mode) so in fact, there is not much IR to absorb in the bands Essenhigh talks about. Curious what he thinks the water vapor is absorbing at those wavelengths but it ain’t the IR from the earth or reradiated IR.

    Given this blunder, I think we can declare his overall position as similar to a flounder after ten days in the sun.

  15. John Dodds:

    Nice explanation of water vapor.
    Question 1- when the long wave radiation is trapped by water vapor and CO2 etc How much heat energy is trapped? Do the models calculate this based on a concentration AND temperature/humidity dependant equation every 20-30 min cycle? I would assume that the GHG molecules do not saturate, ie trap the maximum amount of energy that they are capable of, just like the regular N2 and O2 molecules will not trap all the (smaller amount of)heat they are capable of, always leaving some room to heat up more as the solar flux gets hotter during the day, or during the season.

    Q2:Since the sun on a daily basis warms and cools the atmosphere by 20+ degrees (evaporating the morning dew/water vapor on the grass as it warms!) then how does this daily and variable cycling impact the residence time concept? ie Just how REAL is the water vapor residence time graph above? Wouldn’t the water vapor readjust on the next daily cycle, and continue to adjust during the day as the daily temp and weather fluctuates?

    Related question- Is there any daily cycling of CO2? Is the CO2 concentration temp dependant? Is the amount that dissolves in the nightly washed out water vapor trivial?

    Just wondering!! Thanks.

    [Response: If you look at the difference between the LW going out at the top (240 W/m2), and the LW emitted from the ground (380 W/m2), you get a 'trapped' portion of about 140 W/m2. There is a lot of absorbtion and re-radiation in the middle though. For some frequencies, the absorption is all very close to the ground, and they do saturate, but it varies strongly as a function of pressure and frequency. Another way to look at the residence time is to calculate the mean 'age' of water (how long it has been since that water parcel was evaporated). This gives very similar numbers to the gross calculation given above (i.e. around 10 days), but there are significant areas where the average age is longer (the stratosphere) and where it is shorter (near-surface in the tropics). And finally, for CO2, there is a daily cycling over vegetation (a few ppm), but the (very small) radiative effect is neglected in most models. -gavin]

  16. Joel Shore:

    A hearty thanks to realclimate for doing an article on this. I can’t tell you how many times I have had to explain the idea that, because of its short residence time, water vapor is not a greenhouse gas that we have much direct control over but is an important feedback effect. Now, I can just refer people here!

    In response to #6, I believe that much of the difference between that 0.7 C number and 1.8 C numbers would be that the former is an estimate of the direct effect of the greenhouse gas forcings in an imaginary world without feedbacks and the latter is an estimate of the total effect after the feedbacks are accounted for. (Someone can correct me if I’m wrong.)

  17. Blair Dowden:

    I wonder if someone could clarify the relationship between radiative forcing measured in watts per square meter with a temperature change in degrees celsius. It seems to me that a increased forcing of 2.5 w/m2 should have the same effect whether caused by increased radiation from the sun or increased greenhouse gases. I expect the relationship to be linear, but I keep seeing different values (such as in comment #6). Surely this has a standard, well known value.

    By the way, thank you for providing this good source of information, and especially the chance for feedback.

    [Response: The relation between the forcing and the temperature change is precisely the 'climate sensitivity' which have discussed elsewhere. It is mostly linear, but because of the different physics of the different forcings, there can be differences in how equivalent forcings (i.e. from aerosols or greenhouse gases) get expressed as temperature changes. This has been called the 'efficacy' of each forcing. -gavin]

  18. Lynn Vincentnathan:

    What about a hydrogen economy in which we are generating very high levels of water vapor, and some hydrogen leaks as well. I read somewhere that this may have some negative impact, but I can’t remember.

    Seems by your discussion (I’m not sure) that since the water vapor is close to the ground, only the amount ordained by the warmth of the climate will be held in the atmosphere, the rest precipitating away.

    [Response: See Schultz et al (2003) or Warwick et al (2004) for discussion on the impact of a hydrogen economy. -gavin]

  19. Stephen Berg:

    In response to #12, as the temperature increases, so does the capacity for air to retain moisture, so even if the quantity of water vapour is to increase, relative humidities may not. In other words, dewpoint depressions (T-Td) may remain the same.

    Since RHs need to approach 100% (T-Td needs to approach zero) for clouds to form and since these RHs may not increase despite the aforementioned increases in water vapour, cloud cover may not increase, or if it does, it will not be significant.

    [Response:To be really picky, air doesn't really "retain" moisture: the only thing of importance is the temperature. See http://www.atmos.umd.edu/~stevenb/vapor/ - William.]

  20. John Finn:

    I believe that much of the difference between that 0.7 C number and 1.8 C numbers would be that the former is an estimate of the direct effect of the greenhouse gas forcings in an imaginary world without feedbacks

    … or in a world without imaginary feedbacks :->

    Yes – I suspect you’re right. In fact, Stefan himself has responded to confirm this. However a couple of points are worth noting.

    1. This highlights the dominance of feedback. From the Minschwaner and Dessler paper (referenced by Gavin), actual observations of wv feedback are nowhere near what is being predicted by the GCMs. No (positive) feedback = No big warming

    2. Is the 0.7 value supposed to be observed or calculated? The reported temp rise in the last century is not all down to increased ghg. Also when will the 1.8 deg increase actually happen.

  21. Paul Dwiggins:

    Interesting article. I did not see any mention of the phenomenon of extreme nighttime cooling in arid regions (deserts). This phenomenon is attributed to lack of water vapor in the atmosphere above those regions resulting in a greatly reduced local “greenhouse effect”. Doesn’t this contradict the idea that other molecules (carbon dioxide, etc.) contribute a lot to the whole-earth greenhouse effect?

  22. Eli Rabett:

    Paul Dwiggens comment is the wrong answer for the right reason. Yes, the temperature goes down rapidly in the desert at night because there is little water vapor in the air to capture the radiated IR, but there is a residual, according to Gavin’s table ~ 34%, due to the greenhouse gases. If there were no IR absorbers in the atmosphere the surface temperature would be ~ 256 K or -17 C.

  23. Marc Feldman:

    The important thing about water is, it is saturated over most of the infrared spectrum. That means that 100% of the infrared radiation emitted by the ground is absorbed by the water vapor in the air. Whether there is more or less water vapor in the air sometimes, it doesn’t change the 100% absorption. That is what saturation means.

    Astronomers know a lot about this. It is why infrared telescopes are at extreme sites, on top of Mauna Kea or at the South Pole, where there is a lot lot lot less water vapor and so there is partial visibility at some infrared frequencies.

    So the “greenhouse effect” caused by water vapor is a fixed constant not a dynamical variable, it doesn’t change whether there is more or less water and so stick it into the equations and forget about it — it doesn’t change from century to century. Unless conditions got extreme, like widespread desertification on the one hand or permanent cloud cover on the other hand. (btw clouds contain liquid water not only vapor, so that’s a different discussion.)

    At other frequencies the water vapor does not absorb. The atmosphere is rather transparent at those frequencies. There is some partial absorption by CO2, but it is not saturated because there is much less CO2 in the atmosphere, compared to water vapor. If you put more CO2 into the atmosphere, radiation at those frequencies is absorbed proportionally more.

    Note I made no mention of the residence time of either CO2 or H2O.

    [Response: Parts of the infrared spectrum are saturated, parts are not. The effective forcing from any GHG change (including water vapour) needs to be intgerated over the entire spectrum. An instantaneous forcing calculation for 1.4xH2O over the whole globe gives a forcing of 5.5 W/m2 - demonstrating that over the whole spectrum, water is not saturated. - gavin]

  24. kyan gadac:

    In response to the selective and dishonest use of statistics by Michael Janowski in post #13 I’d refer readers to this map also published at the Bureau of Meteorology site and linked directly from the sites quoted by Mr Janowski. The map clearly shows that rainfall in the far south west has decreased by 50mm/10 years between 1950 and 2000. Furthermore there is extensive and long standing documentation of this rainfall decrease which was first observed back in the 1980′s and has continued.

    Most Western Australians will have seen the regularly published advertisements by the W.A. Water Authority showing the consequence of this decreasing rainfall on catchements over the last 40 years. The authority has a vested interest to conserve water so I suppose they could be exagerating but nobody in the south west seems to think so.

    Mr Janowski is obviously ignorant of the nature of the rainfall in the south west. Specifically he should be aware that the area defined as the south west has a rainfall that varies from 1000mm to 3-400mm. The south west corner(south west of a line from Perth to Albany) where the rainfall exceeds 700mm has a relatively stable climate dominated by winter rain with less than 20% variability in rainfall patterns. To the east of this line and making up more than 1/2 of the south west area on the maps he quoted, the rainfall is sporadic rather than seasonal.

  25. Aaron:

    “To demonstrate how quickly water reacts, I did a GCM experiment where I removed all the water in the atmosphere and waited to see how quickly it would fill up again (through evaporation from the ocean).”

    Hehehehehehehehehehehehe! Thank goodness for computers!

    I hope no extraterrestrial climatologists show up on Earth and decide to do such an experiment in real life… ^_^

  26. grundt:

    Thank you very much for the excellent article and high level discussion.

  27. CharlieT:

    Interesting to think that there is only 1 inch of rain up there!

    From Gavin’s reply to 23: If the cloud/rainfall processes mysteriously altered to reduce the H20 level and feedback by 2.4 Watts/m2. This would require a one-off extra rainfall event of about 1/8 Inch??

    http://www.sron.nl/www/code/eos/atmos/h2o/PWMAY03.pdf seems to suggest that the models do not properly account for ~30 watts/m2 of the radiation balance.(eg Fig.1 caption)
    Tricky to get all the modelling correct, I’m sure, but 30 watts/m2 does seem rather a lot compared to the 2.4 watts/m2 of calculated change.
    Is this wrong?

  28. Paul G. Brown:

    Kyan –

    careful. I think Micheal J. has a point.

    You can get the raw data for winter rainfall here. If you download it and apply your favorite spreadsheet it looks like, while there has been a small downward trend in the 1970-2002 period, the variance of the winter rainfall is so high that the R^2 is only 0.006 – very, very low.

    The difference is that you’re looking at a much smaller region of the state, and there are a number of alternative hypothesis to explain the more pronounced decline in the south-west: deforestation, for example.

    You’re providing evidence of climate change, but it is pretty localized, rather than global. Extrapolating a regional trend is a bit dicey.

  29. dave:

    I was somewhat surprised that Gavin felt the need to post this. I thought that increased water vapour from rising temperatures and water vapour as the principle LW radiation absorber – therefore a feedback and not a forcing – was just obvious. I had never heard a skeptic (needless to say, 3 in the same room – is this possible?) argue against climate change because naturally occurring water vapour is being neglected. I have never seen this used as a strategy in the mainstream press either. So this was a new one for me.

    Other attempts have been made to explain it. I got my initial understanding of the phenomenon from this paper The Long Time Scales of Human-Caused Climate Warming by Jerry Mahlman (formerly head of GFDL and now emeritus at NCAR here in Boulder).

    There is a very good explanation of this topic on pages 9 to 11 of this online PDF document. Also, I highly recommend this document in general for those of us on realclimate who are not climate scientists.

  30. Francis MASSEN:

    concerning gavins comment to #15 (daily CO2 cycle):
    The night/day variations are quite large, often more than 100ppm, when measured at ground level: see http://meteo.lcd.lu/7days_04.png for live 7 days data. A large part from that cycle comes from day/night air movements and temperatures, but vegetation (photosynthesis) plays a big role; see the http://meteo.lcd.lu/today_01.html and compare solar radiation and CO2 (ok, it’s a bit rough, because air temperature variations can not be filtered out..)

    [Response: I stand corrected. The variations do of course greatly diminish in amplitude as you move away from the the boundary layer. - gavin]

  31. kyan gadac:

    Paul Brown in #28 suggest deforestation but that is just simply incorrect for the lower south west where the greatest decrease in rainfall has occurred. This is the one area of the south west that has not been cleared substantially and is still dominated by karri and jarrah forest.

    In W.A. rainfall comes in summer as a result of the summer monsoon and in winter as a result of the movement of the circumpolar front. In the north west and south west extremities these two sources of rain singly dominate the annual rainfall for these regions. Elsewhere rain fall comes from both sources.

    Consequently the decrease that is seen in the lower south west is clearly identifiable with changes in the winter rainfall patterns which are due in turn to the movement of the circumpolar front.

    The decreasing winter rainfall in the south west is due therefore to changes in the average position of the circumpolar front.

    Because W.A. is flat there are no significant orographic affects upon local rainfall. Because it is on the west side of the continent there is less interaction between tropical and polar moisture sources. Because the southern ocean is the only thing for thousand of miles in our weather quarter, changes in our weather could be considered to be indicative of changes in the southern hemisphere.

    IMHO those changes are due to global warming.

  32. Paul G. Brown:

    Kyan –

    an entirely reasonable hypothesis. Thanks for the explaination.

    KR

    Pb

  33. David Jones:

    Not entirely clear how SW Western Australian rainfall trends got onto this discussion, but anyway… just to add to a couple of points. Firstly, the rainfall changes are almost certainly due to large scale circulation changes (the deline is apparent at Rottnest Island, off the coast), and secondly the impacts of this rainfall decline are real and profound – run off has declined by around 40%. The rather large document linked to below has plenty of further info:
    http://www.ioci.org.au/publications/pdf/IOCI_TechnicalReport02.pdf

    BTW, Kleeman and Power (1995) “A simple atmospheric model of surface heat flux for use in ocean modeling studies”, Journal of Physical Oceanography, 25, 92-105. has a very interesting discussion of the temporal and spatial variability of relative humidity in the current climate. Globally over oceans, the relative humidity is almost everywhere near 0.8, despite the enormous variation which exists in temperatures. To the extent that spatial variations are an analogue for climate change, this result suggests that relative humidity (at least over the oceans) is likely to remain fairly constant under global warming.

  34. Michael Jankowski:

    Re#24:
    “In response to the selective and dishonest use of statistics by Michael Janowski in post #13″

    Where was I selective and/or dishonest? I threw out stats for a large number of periods from the available data. I actually felt like it was overkill.

    I did err with a few statements – I goofed and said the trend from 1960-present was as high as -40mm/decade, but it was only -30mm/decade. I obviously spent too much time with calculations you dimissed and not enough time discussing the maps (which I felt were much more obvious). But these do not change the fact that the BofM data and maps conflict with your assertions. If they are a poor source of data, I apologize. I was interested in your post and tried to find information relevant to it, and what I found conflicted with your post.

    “I’d refer readers to this map also published at the Bureau of Meteorology site and linked directly from the sites quoted by Mr Janowski. The map clearly shows that rainfall in the far south west has decreased by 50mm/10 years between 1950 and 2000.”

    First of all, that decrease is not between 1950 and 2000 – it’s between 1950 and 2004 as clearly stated on the map under the title. Secondly, the map does not “clearly show” such a decrease. It is almost HALF of what you claim it is (up to 30mm/10yrs, not 50mm/10yrs as you read it, or 40mm/10yrs as I had written in #13 for the 1960-present period!). Also, we should be careful about how to interpret the data (in addition to your 50mm vs 30mm confusion). The colors represent a range, not a value. The values only occur at the intersection of two ranges. For example, on the 1950-present map, the darkest corner on the maps only represent the range 20mm/decade to 30mm/decade, not necessarily 30mm/decade. The highest value might be only be 20.1mm, 25mm, or it might be 29.9mm, and the highest values would occur at the fringe of the range (i.e., a small area). Nevertheless, we can stick with using the top of the range (e.g., 30mm/decade) as a matter of “worst case” convention for the sake of discussion. But it should be emphasized that this is a “worst case” and likely an exagerration of the actual value.

    Secondly, you’ve changed the date – you’ve now gone back to the 1950s! The post I was responding to (#10) claimed: “…winter rainfall has ben declining steadily since the 1960′s…”

    Regardless, coupled with trend maps from 1950-present here http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/trendmap.cgi?page=cc&variable=rain&region=wa&season=0608&period=1950 1960-present here http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/trendmap.cgi?page=cc&variable=rain&region=wa&season=0608&period=1960 , and 1970-present here http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/trendmap.cgi?page=cc&variable=rain&region=wa&season=0608&period=1970 , it is STILL clear that the majority of winter rainfall decrease in the far southwest corner occurred prior to 1970. From 1970-present, only a small area has had a decrease in rainfall, and it is on the order of less than 10mm/decade. This is far slower than the rate of decrease from 1950-present (up to -30mm/decade) and 1960-present (up to -30mm/decade), which implies that the 1950-present and 1960-present periods were starting with years much wetter than today’s. The 1950-present and 1960-present timeframes include the 1970-present timeframe. So in order for 1950-present and 1960-present trends to be -30mm/decade and the 1970-present trend to be -10mm/decade, the rate of rainfall decrease has to have tempered substantially relative to 1960 (which, as stated in my previous post, conflicts with your claim that “…winter rainfall has ben declining steadily since the 1960′s…”) or 1950 (which is the period from which you now what to start with). If this were not true, then the 1970-present trend in the corner would be -30mm/decade (or worse) to match the 1950s-present and 1960-present maps. So according to the maps, the 1950s and 1960s saw a dramatic decrease in winter rainfall for the area in question, and things have been relatively “normal” (relative to the present) since 1970. In fact, looking at all maps available, the “best” case one (least decrease in annual winter rainfall) is 1970-present! If climate change is responsible for the 1970-present decrease in rainfall, does it also get the blame for 1900-present, 1910-present, 1920-present, etc, which are even worse?

    Even the most seriously affected portion of winter rainfall in the far southwest part of Australia is -10mm/decade or less since 1970. That’s less than or equal to 1mm/yr. Get out a ruler and look at how big 1mm is. Can you point to that decrease in annual winter rainfall and say that’s due to climate change (which is what you implied in #10), or that it’s even of any significance? Or even outside the realm of measurement error? And since the raw data shows drastically reduced winter rainfall for 1999-2004 for the composite map (which, I acknowledge, is an area larger than the far southwest portion of Australia…still, you said rain variability for most of the map outside of the area in question wasn’t seasonally variable, right?), I wouldn’t be surprised if the 1970-2000 trend, even in the furthest southwest portion of Australia, would’ve been completely flat (or positive!), and brought-down for the 1970-2004 trend by the 1999-2004. I’d have a hard time blaming climate change for a 34-yr trend of rainfall deficiency if the first 29 yrs (or more) of the period don’t have such a trend. Now if you go back to the 1950-present and 1960-present maps, where the decrease in rainfall in the far corner is up to 30mm/yr, then maybe you’d have some grounds to say there’s a significant change in winter rainfall and that climate change could be a contributor. But that 1970-present map shows those effects were basically gone by 1970, which leads me to believe other factors are at play.

    “Furthermore there is extensive and long standing documentation of this rainfall decrease which was first observed back in the 1980′s and has continued.
    Most Western Australians will have seen the regularly published advertisements by the W.A. Water Authority showing the consequence of this decreasing rainfall on catchements over the last 40 years.”

    According to what is shown on the Bureau of Meteorology maps, this decreasing rainfall may have been substantial in the 1950s and 1960s, but not since 1970. If you feel the Bureau of Meteorology is publishing bad or incomplete information, maybe you should share that long-standing documentation with them so that they can correct their data and maps instead of accusing me of lies.

    “The authority has a vested interest to conserve water so I suppose they could be exagerating but nobody in the south west seems to think so.”

    So nothing else has changed in the last 40 yrs that has helped lead to water conservation? Couldn’t conservation of water be due in part to increased water demand due to population growth, agriculture, etc? Couldn’t changes in land-use attribute to increased runoff and decreased aquifer/soil recharge? These contribute to water shortages elsewhere (and are often the cause). It’s not always a factor of decreasing rainfall. Or is the far southwest corner of Australia 100% identical in land use, population, water demand, etc, to what it was 40 yrs ago?

    “Mr Janowski is obviously ignorant of the nature of the rainfall in the south west…”

    I may be ignorant as charged, but if so, then I blame your Bureau of Meteorology for producing maps and releasing data that conflict with reality (at least as you see it). All I know about winter rainfall is southwest Australia is what I can read on maps or download as raw data, and I think most anyone who reads those maps would raise the same questions I did.

    Granted, things might look different if different starting periods were used (e.g., 1955, 1965, and 1975 instead of 1950, 1960, and 1970…we all know about how different trends can be based on the bookends used to present the data!), but that’s a limitation of the BofM website. Still, the regional raw data for which annual winter rainfall data is available seems to support the idea the conclusions would be similar. If there’s better information out there, I’d be happy to see it.

    I’m not saying you’re wrong, just that the info at your BofM conflicts with your conclusions. Feel free to point me in another direction.

  35. Dave Dardinger:

    Re #19

    You need to step back for a second and look at what the claim of H2O feedback actually is. It’s a claim that because of higher temperatures near the surface, additional water vapor will evaporate. But this means that eventually (an average of 10 days according to what has been posted here) this water vapor must return to earth as rain. But to produce rain it must first form clouds. And therefore the water-vapor feedback mechanism requires additional cloud formation. This is as near to a sure thing as we can expect in this entire global warming debate.

    The real question is where and what sort of additional clouds will form and whether or not they will serve as a negative feedback to the water vapor’s positive feedback. I’m a bit disappointed that I didn’t get any substantive response to this question. But perhaps someone will make a response this time.

    [Response: While this makes sense logically, the physics of the situation is very complicated. Whether clouds are a positive or negative feedback depends on where they form (higher clouds have a net positive forcing), how 'thick' they are and how long they persist. You can make innumerable logical deductions about which way the cloud feedback 'should' go, but our current best observations and modelling have not been able to pin down even the sign of the net response. Some models therefore show small negative feedbacks, some show small positive feedbacks - though in neither case are the responses dominant over the more important feedbacks (water vapour, ice-albedo etc.). - gavin]

  36. Eli Rabett:

    In response to #19 and #35. Cloud formation requires sites for nucleation (cloud condensation nuclei or CCN) where water vapor can precipitate out. These can be dust particles, liquid aerosol particles, etc. It is not enough simply to say that additional water vapor will lead to more clouds (however, if the relative humidity is low, and the availability of CCN is not limiting then you will get more clouds given higher humidity). The study of cloud formation still has many “here there be monsters” unexplored areas although troops are massing on the borders with new weapons in the war against ignorance.

    http://www.agu.org/revgeophys/rasmus00/rasmus00.html is an on line review of cloud physics by Roy Rasmussen at NCAR.

    In addition, water vapor exchange in the boundary layer between the ocean and the atmosphere does play a role. You can toss up a number of discussions by googling < "boundary layer" atmosphere ocean exchange>

  37. Armand:

    I see no place for political ideology in Science, do you? If your going to start leaving hints scattered covertly through your messages that you’re a good leftist I’m going to quit regarding anything that’s posted on this website as being relevant to Science. I know that Carl Sagan tried to politicize Science but he made no original contributions to knowledge or furthered understanding of Nature. I hope the aspiring scientists who post here are not going to sink to the level of sociologists lost in the mire of their own verbal solipsism’s.

    [Response: Not quite sure what you are responding to, but you are quite wrong about Carl Sagan. He authored and co-authored over 400 papers in the technical peer-reviewed literature (over 10 a year through his career), as well as the 1000's of popular articles, programs and books that he was more famous for. There are very few scientists who can match such a record. I think this is actually a great example of a good scientist going out of his way to popularise his subject. Something we are attempting to do here as well. - gavin]

  38. Dave Dardinger:

    So Eli, be explicit. Are you claiming that more and more water vapor accumulates in the atmosphere until it just rains out without forming clouds if the levels of CCNs are low or what? We’re talking mass balance here, not some obscure mechanism on how water vapor is converted to water droplets. And just how large would the typical area be which is depleted of CCNs? Given salt from the oceans, dust from deserts, aerosols from trees and industrial operations and soot from fires man-made and otherwise, I’d not think it’s a great area.

  39. Engineer-Poet:

    Francis (response 30):  Where were those CO2 data taken?  How much of the variation is accounted for by plants vs. other sources such as emissions from vehicles upwind?

  40. Eli Rabett:

    Well Dave, if the boundary layer exchange is not important, how do you account for movement of CO2 into and out of the oceans? If there were no CCNs, there would still be a mass-balance equilibrium due to this layer set by the Clausius-Clapyron equation.

    OTOH, you have a non sequitor there as nothing can “rain out” without the formation of clouds. Yet there can be exchange of water vapor in the atmosphere with the oceans near the surface, especially given the turbulent nature of the ocean surface and the presence of salt spray.

    True, I am not going into great or any detail here, but simple googling will toss up a number of aerosol models for clouds, many papers on the role of the boundary layer as well as a raft of studies on the different types of aerosols. Perhaps one of our gentle and learned hosts will provide an article containing the detail you crave.

    FWIW, the largest volume with few CCNs is the upper troposphere and the stratosphere.

  41. Dave Dardinger:

    Uh Eli, the ocean is almost all water. For it to equilibrate with the atmosphere would result in more water vapor entering the atmosphere, not part of the existing vapor entering the ocean. The same is not true of CO2, so talk about non-sequitors! Please explain what you mean by that in this context. CO2 is as it were miscible with the rest of the atmosphere (except perhaps at very high altitudes.) H2O has a maximum [stable] concentration at a given temperature and pressure.

    Now you’re right about there being few CCNs in the upper atmosphere, but at the same time the temperature is so low that it doesn’t take much to cause clouds to form and often they’ll form of their own accord. I don’t deny it’s a complex situation, but that’s precisely why it’s so dangerous for climate change people to imply that all the important details are known and the models are so robust that we can make wise policy decisions based on what we already know.

  42. Stephen Berg:

    “Uh Eli, the ocean is almost all water. For it to equilibrate with the atmosphere would result in more water vapor entering the atmosphere, not part of the existing vapor entering the ocean. The same is not true of CO2, so talk about non-sequitors!”

    Dave, this point is incorrect. The oceans and atmosphere also strive for equilibrium in terms of CO2.

    As the oceans warm (as they are doing today because of increases in global temperatures), the ocean has a reduced carrying capacity for CO2. Therefore, CO2 is released from the oceans into the atmosphere. (Therefore, the oceans can no longer be considered a carbon sink, but a carbon emitter.) As the oceans cool (as has happened in the past), the carrying capacity for CO2 increases, therefore acting as a carbon sink.

  43. Francis MASSEN:

    comments concerning #30 and #39: daily CO2 variations

    I’m absolutely confident in my assertion that CO2 levels vary heavily during a 24 period (CO2 measured at ground level in a “normally” green planted area); these variations surely will be much smaller in a bare plant-less environment. I measure CO2 since over 15 years, with different instruments (all NDIR, but of increasing sophistication, the latest being a WMO agreed MIR9000), and in different environments: underground (in a maze cave), in a forest, and since 1996 in a meteorological station (http://meteo.lcd.lu, sampling inlet 25m above ground level) in nearly rural Luxembourg: rather small town (Diekirch, pop. 5000), no heavy industry, no large emitters upwind, rather low traffic. In my opinion, a big part of these variations is caused by photosynthesis (there is a good negative correlation with solar radiation, much better in summer), another with the usual morning inversion layer at groundlevel. Traffic and industry definitevely are not much involved (we have two “mini” commuter rush-hours at 06:00 UTC and at 15:00 UTC, and at least the last does not show up in a CO2 peak).
    To further nail down my arguments, look here where I assembled other sources of information concerning this daily CO2 pattern:
    http://meteo.lcd.lu/co2_variations/daily_co2.html
    You will find among others a plot of “real” Tennessee data from CDIAC confirming my point of view.

  44. John A:

    Congratulations Gavin, on demonstrating the commonest failure of the beliefs of pro-global warmers on this weblog and elsewhere: that climate models and their program inputs are themselves scientific data and can prove or disprove anything at all. They are parameters for a computer program, not experimental data.

    The distinction, I know, is lost on you. But for the rest of us, the fact that you claim to simulate a climatic event in a simplistic model of a non-linear system like the Earth’s climate does not lead to the conclusion that the model simulates reality or has diagnostic value. For example we do not know the “publication bias” of exactly how many computer runs, twiddles, tweaks, “flux adjustments”, and other parameterizations were done before you got the “right” answer.

    If you’d have actually referred to real experimental data, then I might have been impressed. More impressed if someone else could replicate your work. Really, really impressed if it could so much as predict the next El Nino.

    You even start with a classic straw man argument: that “contrarians … will inevitably claim that water vapour is being unjustly neglected by ‘IPCC’ scientists”. If you’d care to actually read the IPCC TAR you’ll see that the IPCC does exactly that. On its listing of forcings and feedbacks it stacks up the tiny contributions of the other greenhouse gases into a scary mountain and does not even bother to quantify either the role of water vapor or any estimate of the uncertainties in those contributions. (see the IPCC SPM fig.3)

    The IPCC also ignores in that diagram the greatest climate forcing of all: the variation of the solar flux because of intrinsic variation as well as changes in the orbital geometry of the solar system. The IPCC simply implies that the solar contribution (without a scintilla of scientific justification) is more than three times smaller than that from carbon dioxide alone even though such a parameterization is characterized to be on a “very low” level of scientific understanding. How the IPCC got to this conclusion when the clear imprint of solar variation on climate has been described by multiple teams over many years (dear me, and they were peer-reviewed and published in quality scientific journals as well), is simply beyond me. I think the IPCC should get out more from its deterministic, politicized ghetto and smell the scientific air.

    I doubt very much you’ll allow this to be posted, since censorship of opposing views is what realclimate is famous for, but I’m an incorrigable optimist (or just a fool wasting his time).

    [Response: This kind of tiresome posting is exactly the kind of thing we try to avoid on this site. Mainly because it adds nothing but noise to the debate. However, as an exercise in reasoned discussion, I will take the time to point out the numerous problems with your point of view.
    - I have not claimed to 'prove' anything. Given a system like the Earth's climate, the best one can hope for is a reasonable match to observations. Radiation models (such as I used here) have matches to line-by-line observations good to about 10%. All I did was demonstrate in those models the importance of various terms. That the results are similar to those from a completely different model (RC78) written over 20 years ago should indicate that they are reasonably robust.
    - Climate models cannot be "used to prove anything at all". The proof of that is that no-one has ever made a model that cools when greenhouse gases increase.
    - Given that you clearly don't believe a word I say, I don't know why I'll bother to point this out, but no tweaks, adjustments, twiddles or other runs were done to get these results. None. Not one. The proof is that the source code for the model and the input data I used are all available on the GISS model website. Anyone is perfectly at liberty to demonstrate for themselves that the answers are what the model gives. Given your penchant for audits, I would have thought that you would have already started...
    - A straw man eh? How about this particular gathering only a day after my article? (William Kininmonth paragraph 11). I would also point out that it is bad debating style to claim that an argument is a straw man, and then go ahead and use it.
    - This may surprise you, but I have actually read the whole of IPCC WG1, not just the Summary for policy makers. More to the point I actually understand what is being shown in the figure you highlight. These are the estimated forcings on climate - things which change the radiative transfer through the atmosphere, and to which the climate responds. Water vapour, since it responds so fast (as illustrated above) acts as feedback and not a forcing, and so quite sensibly does not appear on the diagram of forcings. Why you think there are no error bars on the figure is a little more mysterious, since they are quite plain in my view. For the well-mixed GHGs the error is the total error for all the gases and it's small because we actually know quite a lot about GHGs...
    - Orbital forcing over the period 1850 to 2000 is neglected in the figure for the obvious reason that it is small, and in particularly in the global mean, very close to zero (and with very little uncertainty).
    - Long term solar forcing estimates by contrast are indeed rather uncertain, and so your confidence that they must be must larger than accepted by IPCC is curious. Uncertainty works both ways remember. The numbers used by IPCC come from reasonable extrapolations of the measured values of solar irradiance during the satellite era - and there's much more than a scintilla of scientific evidence there (Lean et al, 1995, Lean 2000, Foukal 2004 etc.). I have actually written a number of papers on the solar forcing of climate, and your claim that the observations imply a much larger recent solar forcing is simply not supported by evidence. Cooling during the Little Ice Age for instance is completely consistent with the 'IPCC' forcing (solar and volcanic), canonical climate sensitivity and the historical temperature data (within the uncertainties of each) (see here). If you have a direct line to someone who has demonstrated otherwise, let me know.
    - I cannot comment on your optimism. But I have formed an opinion on your foolishness....
    -gavin]

  45. Francis MASSEN:

    comment concerning #30 and gavins remark:
    sorry gavin, I misunderstood the meaning of your “I stand corrected” (blame my poor English)… so we may close the debate on daily CO2 variations. It is strange that online hourly or live CO2 measurements seem to be extremely rare (and/or difficult to find), whereas data with daily and monthly CO2 means are plenty….

  46. Dave Dardinger:

    re: #42

    I didn’t say there wasn’t a tendency toward equilibrium with CO2. I said (or rather implied) that it results in CO2 being taken up by the ocean rather that vice-versa. This is not the case for water vapor. Instead water vapor enters the atmosphere and would continue to rise in concentration if it wasn’t for the fact that water eventually condenses and thus returns to the oceans.

    And CO2 doesn’t enter the atmosphere from the oceans on net. It may be that the total amount which can be take up will eventually plateau, but don’t confuse such a future event with the present situation. In fact, the amount of CO2 entering the ocean has been rising, as it would be expected to.

    Furthermore, if you look at the balances for the surface waters compared to water returning from the depths, there is actually more CO2 rising that being conveyed to the depths. This is because phytoplankton converts CO2 to biomass and eventually this rains into the depths. At some point it’s possible that this situation will reverse and the water being taken to the depths will be richer in CO2 than that upwelling, but there’s still quite a way to go before that happens.

    What may be confusing you is that the % of emitted CO2 being absorbed by the ocean is now smaller than it was in the past. But the actual amount being absorbed is still increasing.

  47. Mike Doran:

    Failing to look at the RATE at which water phase changes is based on assumptions that this RATE is the same throughout the dynamic. It is not. That RATE varies ELECTRICALLY.

    See

    http://www.ichmt.org/abstracts/Vim-01/abstracts/04-01.pdf

    If you are interested in the mechanism involved, visit us at the tropics thread at TWC bb.

    Mike Doran aka Purple Heart

  48. Mike Doran:

    Steve,

    You make the incorrect assumption that the rates of CO2 exchange with the ocean is constant when it indeed is not.

    There is an good Nature paper on the subject by Bates et al with the study of Hurricane Felix descussing CO2 uptake.

    Further, hurricanes offer the most intense large scale electrical couplings on earth, between ionosphere and ocean, and those couplings change surface pH, which then varies uptake rates at the most significant times–when they impact cloud microphysics processes.

    If you are not looking at large scale electrical features and biological activity, you don’t know spit about CO2 and climate. CO2 is ELECTRICAL and hyper critical in gas exchange from surface lows in determining relative conductivities. The earth is very much alive in this context.

  49. Mike Doran:

    John A. (post 44 response)

    Have you taken into consideration along with your orbital discussion gravity changes? That is discussed in this paper here, for instance?

    http://www.pnas.org/cgi/content/full/070047197

    This in my view gets to orbital patterns and how roiling gas exchange and CO2 functions (which the biosphere modulates) in the oceans and which impacts conductivities. So looking merely at the sun misses both that the LIA is a function of the moon orbit and misses that the relationship to CO2 is DEPENDANT. A set of double blundering.

  50. Lynn Vincentnathan:

    RE #44 & models (which I know were covered earlier on this site), I was thinking about correlations v. causation. In sociology we often use surveys & load up lots of variables (as controls for the variables of interest). That’s because in the real & highly complex world it is difficult and/or unethical to do experiments on human social behavior. Experiments give the strongest proofs of causation. Correlations & other association stats do not prove causation (as tobacco companies so gleefully used to claim, until celluar level proof of tobacco causing cancer came along), but correlations do give good indication of causation, when other (thought to be) impacting variables are controlled for, and when using good hypotheses & thought – e.g., about which variable comes 1st & which comes 2nd. It’s better than no study at all and a “know-nothing” stance.

    I don’t know if this is analogous to climate change studies, but an important point is that we have only one earth on which we all depend for our lives, so it is totally unethical to experiment on it — and we really should stop emitting so many GHGs (at least those we can reduce cost-effectively — which would be more than a 50% reduction for the U.S. given current technology) & halt this experiment right away before we prove just how harmful GW can be.

    Predictive climate models seem like the second best approach, after the all out “see if we can greatly harm the earth” experiment, sort of like surveys in the social sciences — though H2O and even wind behave more predictably than people — they don’t have all sorts of mindsets and weird motives. So climate models should be much better than what the social sciences can come up with (unless, of course, you add in the human factors).

    By the way, even if water vapor were somewhat of a forcing (which I’m sure glad it is not) or volcanos started spewing out massive GHGs, that would still not get us off the hook about our need to reduce our own GHGs. That’s like saying it’s OK to kill a few people, because Hilter killed millions. Focus shifting or changing the topic (e.g., from CO2 to H2O) is a dishonest tactic in argumentation, commonly used in marital disputes.

  51. Stephen Berg:

    In response to #48, this paper seems to suggest that SSTs are a factor in atmospheric CO2 concentration:

    http://www.ph.unito.it/~ferrares/2002_a_study_of_yearly_and_seasonal.pdf

    From the article’s conclusions section:

    “…[atmospheric] CO2 concentration fields, calculated in the recent years over an area including Europe, northern Africa and the Boreal Atlantic Ocean, display a seasonal cycle that seems well related with the seasonal variations of SST.”

    “…during Spring, the fields exhibit
    medium and low values, but during Summer the increase
    of the SST (stronger near the Tropic of Cancer) seems in
    good agreement with the appearance of intense maxima
    of atmospheric CO2 concentration over the southern
    part of the extratropical Atlantic Ocean.”

    With oceans warming as a result of climate change, you would assume that the same would be true, not just on a seasonal basis, but annually and decadally, as well. In other words, as the global mean temperatures increase (which should and does result in an increase of SSTs), so should atmospheric CO2 concentrations.

  52. Raymond T. Pierrehumbert:

    For additional information on water vapor feedback, I’d like to point out the article I wrote on water vapor for the CalTech General Circulation Symposium, “On the relative humidity of the Earth’s Atmosphere” It’s posted on my web site (geosci.uchicago.edu/~rtp1) under “publications.”
    Eventually, it will come out in the general circulation book published by Princeton University Press

    This article has some calculations which bear on the old “98%” myth. By my calculations, in the Tropics, CO2 is more like 1/3 of the greenhouse effect, and it’s pretty clear that if you took it out the Earth would fall into a snowball state.

    Some other things in that article that may be of interest include:

    * A calculation of how much the climate would change if water vapor were completely removed, if water vapor were forced to be saturated, and if water vapor content were half that produced by standard parameterizations,

    *An analytic argument saying why relative humidity should stay roughly constant as climate changes, together with some GCM studies shedding light on the way the argument works.

    Enjoy!

    –Ray

  53. Raymond T. Pierrehumbert:

    As one of the authors of the TAR chapter on “Physical Processes and Feedbacks,” I can state definitively that water vapor feedback was not ignored in TAR. We read and considered several dozen key articles on observation and modelling, and I can assure you the discussions in our drafting sessions were lively — particularly in view of the fact that Dick Lindzen was also an author on this chapter. I think we were quite clear about the nature of the possible uncertainties (notably regarding the role of microphysics in transport), but also about the reasons for believing that models are probably not too badly wrong with regard to water vapor feedback.

    By the way, the characterization of Minschwaner’s paper as saying that observed water vapor feedback is less than that in GCM’s is a gross oversimplification and over-interpretation of their result. Among other things, their observations apply only to the very upper part of the troposphere, which accounts for only a small part of the total water vapor feedback.

  54. Mike Doran:

    From the above article:

    “How do we know that the magnitude of this feedback is correctly simulated? A good test case is the response to the Pinatubo eruption.”

    Again the example is confounded with the complexity of large scale electrical features on cloud microphysics, and then back to the reverse, the affect of the varying chemistry of microphysics on large scale cloud dyanmics. Pinatubo is perfect example because not only does the SOx drop the phase change temperature of heat trapping cirrus, for instance, but the ion content of forming clouds is altered or was altered and then in DC fields the microphysics affect of large scale DC fields is altered per the China paper. Think of it this way–the ions in the super cooled droplet will migrate in the DC field to the opposite pole charge–negative ions toward relatively positive ionosphere and negative ions toward relatively negative oceans–and you get asymmetries of cloud microphysics. If the microphysics becomes relatively too asymmetrical, the cloud mass in the relatively strong DC field has no chance of competing against forming clouds where the asymmetries do not exist. The result is that if the ion content is greater from, say, SOx disolved to sulfur acid, these asymmetries become more extreme.

    I am a student of hurricanes, and Pinatubo is particularly important with respect to Hurricane Andrew for this vary reason, in terms of cloud and wind levels, as well as intensities.

    But what is even more interesting following Pinatubo is the 1997-8 El Nino. Conductivity patterns, largely biological, flow from a nutrients and upwellings in relation to both the cooling that followed the eruption as well as the SOx consumed by sulfur loving microves and relativel bloom activity in relation to that nutrient. Pinatubo gives a sense of both the input and the modulation by the living earth.

    “They found that using the observed volcanic aerosols as forcing the model produced very similar cooling to that observed. Moreover, the water vapour in the total column and in the upper troposphere decreased in line with satellite observations, and helped to increase the cooling by about 60% – in line with projections for increasing greenhouse gases.”

    But again this is confounded by the microphysics impact by large scale electrical features. Okay. How to explain? Appreciate that these DC fields are basically virtual capaciter behaviors between the ionosphere and the oceans–those as the two ‘plates’. The static fields in the ionosphere are held in pattern by the earth’s magentic field . . . and, of course, the oceans are conductive. The microphysics of clouds–they are inbetween ionosphere and ocean where the DC field exists. However, also inbetween is WATER. Water, in droplet or vapor or ice form, has an impact on how the magnetic fields flow. This impact, mathematically, is expressed by dielectric constant. It turns out that water is about 80 times the dielectric constant to air. What that then means is, like Pinatubo, increases in CO2 and other human inputs have changed the global electrical circuit, which then impacts cloud microphysics behaviors, and changes water content, which in turn has its own electrical significance. Climate change.

    “Moist convection schemes in models are constantly being refined, and it’s possible that newer schemes will change things . However, given the Pinatubo results, the models are probably getting the broader picture reasonably correct.”

    The models change because the context of CO2 as a gas exchange and water content is changing. There are, of course, other natural electrical changes that occur as well. For instance, in the hurricane season there is a pattern called the QBO which is a wind in the tropics–caused by induction not unlike an electric engine on the light upper atmosphere. Dr. William Gray has made a living using that as a factor for his hurricane forecasts, but, like the Nirvana song about the man with a gun, but he don’t know what it means, Dr. Gray sees a factor but does not know why it impacts the hurricanes the way it does. That impact is really a switch in the global electrical circuit, which then impacts the ionosphere and hence how these electrical couplings and microphysics patterns occur.

    [Response: You appear to be confusing a number of issues here. The first order impact of Pinatubo was the direct effect of increased reflective aerosols in the lower stratosphere. This was very clearly observed and has been shown to explain very well the subsequent cooling of the planet. There were of course secondary effects (for instance on stratospheric ozone) that are also of great interest. Increases in upper tropospheric aerosols due to settling may have affected cloud microphysical properties too (through the standard aerosol indirect effects). Impacts on the global electric circuit due to the increased number of ions is an intriguing possibility, but a demonstrated (rather than hypothesised) connection to cloud formation and climate remains elusive. Regardless of whether such a mechanism exists, it was not the dominant effect after Pinatubo. With respect to the QBO, you should read the classic papers by Lindzen (and others) demonstrating very clearly that the mechanism is related to gravity wave-mean flow interaction and has nothing to do with electrical induction. -gavin]

  55. John Finn:

    Gavin, in your response to John A, you say

    Given a system like the Earth’s climate, the best one can hope for is a reasonable match to observations

    From the Minschwaner and Dessler paper (referenced by you), observations suggest the following increases in water vapour in the upper troposphere

    3 ppm/K +/- 1.2 ppm/K
    1.5 ppm/K +/- 1.7 ppm/K (excluding 1997-98 El Nino data)

    What do the IPCC models predict – 30 ppm/K? Whatever – it’s likely to be of that order for a constant RH.

    So let’s say that some, possibly hypothetical, scientist had developed a model several years previously which predicted an increase in water vapour of, say, around 1.7 ppm/K. Would he be dismissed as just another crank contrarian?

    [Response: I checked both the GISS model response to interannual SST variations (1990-1999) and the response to 2xCO2, and your estimate of what the models predict for the tropical upper troposphere mean humidity is about right: 20-28 ppm/K at 180mb (smaller above that, larger, below). I haven't done the calculations for any other model, so there may well be differences among them. I strongly doubt that any of the modelling groups will be described as 'cranks' if their numbers are closer to the MD04 estimates. Upper tropospheric processes are a known source of uncertainty, as acknowledged very clearly in IPCC, and getting more data and improving the models for this region are active areas of reasearch. They are however only a very small part of the overall water vapour feedback. - gavin]

  56. DrMaggie:

    Re #45: “It is strange that online hourly or live CO2 measurements seem to be extremely rare (and/or difficult to find), whereas data with daily and monthly CO2 means are plenty….”

    For those interested in looking at flux data (including CO2) from studies of various ecosystems, there is actually quite a lot of data available for downloading on the web. One example is the data archive of the EUROFLUX and MEDEFLU projects: http://carbodat.ei.jrc.it/data_arch_info_eur.cfm. Depending a bit on the measurement site, data is available with a number of different time resolutions, from half-hourly to yearly. Datasets can be downloaded freely (e.g. as formatted ascii files), and there are links to documentation about the various parameters. (We used data from this site in an applied ecosystems modeling course I attended last year, with great success.)

  57. Mike Doran:

    Gavin,

    There indeed was an albedo impact from the eruption. The assumption you make in ‘determination’ of what is primary and what is secondary is in relation to how long an effect takes place. Volcanic inputs are actually quite short termed given the microphysics ongoing impact by the ocean.

    The oceans are huge. A volcano eruption in relation to the oceans is tiny. Within a short time the SOx emissions from the volcano are modulated away, fall out of the atmosphere. Even short term microphysics properties are more a function of ocean saltiness than the SOx in the air. The best example of that is Hurricane Andrew–which is the most proximate and recognizable storm in relation to the Pinatubo eruption. Then the 1997-8 El Nino is a reflection of upwelling from cooling leading to algae blooms from upwelling and increases in nutrients to the surface of the oceans and the Sox as a nutrient leading to sulfur loving blooms–and the living earth feedbacks which caused a warming event. Water vapor is about control, modulation, dampenings–from the perspective of a living earth. Your analysis that volcanic inputs are a primary forcing, from the standpoint of inputs only–in this case, SOx, then, misses the context of human activities.

    “With respect to the QBO, you should read the classic papers by Lindzen
    (and others) demonstrating very clearly that the mechanism is related to
    gravity wave-mean flow interaction and has nothing to do with electrical
    induction.”

    I wouldn’t trust Lindzen’s view of atmospherics without electrical cloud microphysics properties. He, and other scholars in the field, lack the ken required to analyze the problem. See:
    http://groups.yahoo.com/group/methanehydrateclub/message/1816

    The QBO is entirely about such an electrical switch which impacts cloud microphysics, or water vapor. The QBO
    reverses from the TOP down. IOWs, the upper part of that wind slows and starts to reverse first. Lower atmospheric wave conditions would merely cause bottom down reversals . . . The reason this top down reversal occurs as such is that there is an ELECTRICAL FIELD switch FIRST which is followed by movement first of the least dense aspect of the atmosphere by induction, because that part of the atmosphere has the least amount of momentum to mass and therefore the force exacted can move on it. The changes in microphysics globally as a result then causes a feedback in the global electrical circuit which then eventually results in a switch, and the process reverses. Rossby waves, all these features which Lindzen and others address are forced by these switches in the global electrical circuit. They confuse condition with sign.

    Presently the oceans are too salty for nucleotide complex sortings in clouds to have a significant forcing impact per the China paper. Life has grown . . . has been sorted to become so complex that chemistries are now contained in cells. Cells that in cumulation have significant enough conductivity meaning over chemical diffusion that there can be electrical modulation without the nucleotide complex modulating inside the cloud parasols, and the aid of saltwater spray as what was previously â??noiseâ?? against a signal of these complexes has become an aid for a living earth, made of cells, in its modulations. The earth has been designed to have saltier oceans! Of course, there are diatoms and other cellular life that find themselves as cloud nucleatation particles, and that is part of the modulation, but purely from a chemical standpoint, the oceans are now too salty to allow direct cloud microphysics control or design by nucleotide complex.

    Modulation without cells cannot take place if the cloud has too much salinity in it blown up from the ocean per the China paper. Membranes evolved because they contain chemistries over diffusion, and that then has a significant ELECTRICAL meaning in cumulation. Yet, in the cloud parasol a membrane will prevent the sorting by size, shape, mass and charge of the nucleotide complex as the parasol super cools and forms or not into a cloud droplet/particle. This led to sexual reproduction, which is a complexity that connected symbiotically nucleotide complex (male) to membraned life (female egg). The complexity of a living earth in relation to water content in the air and volcanoes are the sulfur loving microbes. These are amoung the first life forms, in the catagory extremophiles or archae.

  58. John Dodds:

    Re #15, 30 & 56.
    Wow, neat data about how daily CO2 actually rises from the baseline ~390ppm to over 500ppm on many nights, along with the relative humidity, and then falls back to baseline as the sun warms the air up. It is just like seeing the results of an actual run of a simulation program but with a daily solar forcing function.

    Seems funny how the daily CO2 concentration in air goes INVERSELY with temperature or solar radiation, when on the yearly ice core data CO2 temp and water vapor all go in the same direction. Also how a daily fluctuation can be 50 times larger than the annual increases which form the basis for the Global warming projections. Makes you wonder if the Global simulation programs might have forgotten or over/underestimated something small, or are missing a process we do not know about.

    I understand that the accepted explanation for CO2 cycling is primarily normal plant respiration, but on some warmer nights we only got 5% changes instead of 25% changes in CO2. Also you can see rain effects, and Francis says you can even see the afternoon rush hour commute. (pollution spike). Nice job Francis, thanks for the info.

    Open Question: do the ocean plants/algae do the same thing? Is there any evidence of a daily CO2 cycle over water. or does it all get absorbed & never get to the air?
    What does this daily cycling do to the residence time for CO2? Or is residence time really a computer simulation term that refers to the time it takes for a perturbation to return to the preexisting condition, and not the actual residence time of a molecule in a particular location?

    I assume that since this is presumably a cyclic phenomenon then it zeros out, as does the yearly ~5ppm CO2 cycle that is measured in Hawaii and is ignored in the annual averaged values used in the 200 year global warming computer models.
    Francis, what is the annual variation in your baseline CO2 levels? Is it also on the order of 5ppm summer to winter like Hawaii (which would have a larger ocean influence)

    Does this wide variation in CO2 impact the accepted CO2 in air measurements? Is the daily cycling accounted for? My first guess would be yes, since the Luxembourg data baseline at ~390ppm is comparable to the accepted global average of 380+.

  59. Dave Dardinger:

    re Gavin’s response to comment #35

    Sorry I didn’t respond to this before, but it’s hard, when a thread gets so long, to notice that a response has been added to a message you posted 20 responses before.

    While I appreciate the problems with determing cloud feedbacks, your response is still rather a brush-off than an answer. It amounts to saying, nobody knows what the true answer is, but we’re sure it’s small. An actual answer would consist of explaining why it must be small, or if that’s too complicated, at least a link to a site which does go into details of the complications. BTW, this means something other than what you’ll find in the IPCC site. They list a lot of things, but not the details, which are needed to understand whether or not the findings pass the smell test. E.g. if you simply state that high level clouds give positive forcing, as you did, you need to say what the reason is. If it’s “They’re thin and let a lot of visible light through but trap almost all the outgoing IR” then you need to reconsider this in light of the increased absolute humidity, which would presumably make such clouds thicker and less able to let light through. I’m not saying that this is an actual proposed mechanism, but I hope it illustrates what I was hoping for in an answer.

    [Response: Sorry about that, but I do have a real job, and so responses here sometimes have to wait. As I stated above, cloud feedbacks are complex and I cannot do justice to them in a response here. A good review is available from the National Academies though. There is of course a connection between it being thought of as small and it also being uncertain - if it were a really large effect it would be more obvious in the data and we wouldn't be arguing about it. Water vapour feedback for instance is clearly seen in the data (Soden et al, 2000). -gavin]

  60. David H:

    Despite its somewhat unprepossessing title this thread has been one of the more informative though the original question is rather semantic. Jeff Severinghaus, discussing ice core studies in December, said “In other words, CO2 does not initiate the warmings, but acts as an amplifier once they are underway. From model estimates, CO2 (along with other greenhouse gases CH4 and N2O) causes about half of the full glacial-to-interglacial warming.”

    So CO2 is also a feedback. For different reasons a warmer world, however caused, means more CO2 and more water vapour. What is hard to dispute is that mankind can and probably has artificially increased CO2 but can’t do much about water vapour. The question between proponents and those Gavin calls contrarians is whether the likely increase in CO2 will be a problem for us.

    This thread and everything I have read so far makes me think we are a long way from having sufficient certainty to warrant the actions being proposed. It is promising to see that John A’s comment was published and Gavin should realise that the price of freedom is not only eternal vigilance but having to put up with the tiresome business of responding to those who challenge his views. We do not need a scientific Taliban

    But if I might say so, contrarians do not have a monopoly on folly and obfuscation. The British House of Lords is conducting an enquiry into global warming and have heard arguments on both sides from creditable witnesses. Notable and directly relevant to this thread was the statement (according to the uncorrected draft transcript) from Kyoto proponent and one time head of the Confederation of British Industry, Adair Turner, who said “We know that that CO2 plays a fundamental role in the climate. Basically, if there was not CO2, we would be as cold as Mars or somewhere like that, and we would not have human life”

    Statements similarly economic with the actuality were made by the previous and current chairmen of the IPPC. Sir John Houghton describing 20th century warming said “Then, if you get to the middle of the century, you find the temperature rise stops somewhat!??”. When asked how much of 20th century warming took place in each half of the century Dr Pachauri said “The bulk of it took place in the second half of the century.”

  61. Ferdinand Engelbeen:

    Some more comment on water feedback…

    I have the impression that the Pinatubo eruption is not a good (anti)surrogate for global warming caused by GHGs. The main effects of the eruption were in the lower stratosphere and the higher troposphere, while CO2 acts mainly in the lower troposphere. There were changes in ozone concentration, temperature (the change in temperature in the troposphere was larger measured by balloon data and satellites than at the surface) and in jet stream position (see: Rutgers).

    The change in SST during the peak Pinatubo event is even smaller than the global surface temperature drop (see: NOAA page 41), and not distinguishable from the (solar/ENSO induced) noise in SST trends. It seems that the change in water vapour in the total air column is not correlated to the sea surface temperature, the origin of most of the water vapour…

    At the other hand, sea air temperatures in the (sub)tropics have increased in the last decades (see: Chen, Carlson, Del Genio) with 0.085 K/decade. No matter which was the cause of the warming, this caused faster Hadley cell circulation, leading to a negative trend in clouds, upper troposphere humidity and more loss of heat (2.8 W/m2 net loss to space over the whole 30N-30S band). This could mean that GHG warming of the oceans, at least over the tropics, has a negative feedback from drying the upper troposphere (leading to less clouds), instead of a positive one from more water vapour…

    More interesting reading: http://www.gesource.ac.uk/worldguide/html/883_articles.html
    and http://www.sron.nl/www/code/eos/atmos/h2o/PWMAY03.pdf

    [Response: There are no perfect surrogates. If there were we'd not be arguing about this! Each different kind of variability (seasonal, ENSO, volcanic. solar etc....) can be used to test different aspects of the model's responses and feedbacks. Pinatubo is useful for the water vapour feedback because it was a global cooling (as opposed to compensating warm/cool patterns) and there were clear measurements of the effect. There were reductions in tropical SST because of the eruption, but it is clearer if you look at the monthly values - the peak cooling of about 0.25 deg C in the 20 S-20 N band was towards the end of 1992. Surface air temperatures cooled more (0.5 deg C) because of the increased cooling over land (which does not have the heat capacity of the ocean). Pinatubo is in fact much more useful than the trends you mention because we know exactly what the driver was. - gavin]

  62. John Dodds:

    Re: Why consider Water vapor… in the opening paragraph, and #29 Dave who has not heard the Water Vapor arguments:

    The “honorable” State of California in Code section 42801.1. defines Grennhouse Gases as :
    “42801.1. For purposes of this chapter, the following terms have the following meanings:…
    (h) “Greenhouse gases” include all of the following gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.”

    ie NO WATER VAPOR.

    Californians are prohibited by law from considering water vapor as a greenhouse gas, and this is the basis used to recently pass the Vehicle Emissions Regulations that mandated increased vehicle efficiency in order to reduce CO2 and global warming. AND is being implemented in several other states and Canada.

    I am not sure how the California University researchers get around this law when doing climate research.

    PS this is NOT a misplaced item from the Doubts about the advent of Spring, April 1st post.

    [Response: Since this is not from a science textbook, but from the law regulating greenhouse gas emissions, it makes sense that they do not include water vapour as one of the emissions they are interested in controlling. It would have been much worse to include it for these purposes. Remember context is everything. - gavin]

  63. Mike Doran:

    58 wrote:

    Q: “Open Question: do the ocean plants/algae do the same thing? Is there any evidence of a daily CO2 cycle over water. or does it all get absorbed & never get to the air?”

    A: http://groups.yahoo.com/group/methanehydrateclub/message/2428

  64. Dave Dardinger:

    re response to #59

    Thanks for the link, I’ll see what I can learn there. But the very first sentence in the summary on the first page of the chapter rather undercuts your position: “Cloud feedback and its association with water vapor feedback and lapse rate feedback appear to be the largest contributors to uncertainty in climate sensitivity….”

    If cloud feedback is small and at the same time the largest contributer to uncertainty, then no wonder you warmers feel so cocky! But I think it needs more discussion.

  65. John Dodds:

    Gavin, Re 62 response
    I can’t believe that you think it makes sense that greenhouse gases are legally defined to not include water vapor in the context of greenhouse gas emissions.
    What could be “much worse” than reality?
    What if the entire rule making and the subsequent regulations are thrown out because they illegally include the greenhouse gas effects of water vapor feedback in calculating effects and cost benefit analyses etc?
    The law does not believe in context- just what the law says.

    I can understand making a practical law that says do not monitor the greenhouse gas water vapor.

    Did you also support the Indiana Legislature when they defined Pi as 3.0 to make calculations easier?

  66. Brian Jackson:

    Re #60

    Statements similarly economic with the actuality were made by the previous and current chairmen of the IPPC. Sir John Houghton describing 20th century warming said “Then, if you get to the middle of the century, you find the temperature rise stops somewhat!??”. When asked how much of 20th century warming took place in each half of the century Dr Pachauri said “The bulk of it took place in the second half of the century.”

    I’m not quite sure why you think they are being “economic with the actuality”, since their comments seem to be in line with the data.

  67. Peter Hearnden:

    Re 65, well, John, we’re 66 post into a thread (and excellent initial post – thanks Gavin) and surely you’d need ‘selecto vision’ specs on not to know one of the crucial point is WV is a feedback not a forcing? Or maybe you can name some significant anthropogenic WV emissions for me – with estimated forcing?

    Your last comment is what I’d call tiresome, just what are you trying to imply?

  68. Michael Jankowski:

    RE #62&65, there are also proposed legislations (and maybe even some passed ones) which classify CO2 as a “pollutant.” Obviously, this could also have serious ramifications if taken literally and applied to a number of different things.

    Note also the fine-print so prevalent in carefully-worded legal docs (my caps): ***FOR THE PURPOSES OF THIS CHAPTER, the following terms have the following meanings:…
    (h) “Greenhouse gases” include all of the following gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.***

    Additionally, it doesn’t state that water vapor is NOT a greenhouse gas. It simply states that the term “greenhouse gases” includes CO2, CH4, etc. It doesn’t state that those are the ONLY greenhouse gases recognized by the State of Cal. And coupled with the context of “for the purposes of this chapter,” it is certainly not illegal for Californians to consider water vapor to be a greenhouse gas.

  69. Tom Huntington:

    Open Question regarding the distinction between water vapor as a feedback versus a forcing:

    How do climatologists view atmospheric water vapor derived from evapotranspiration of irrigation water? By one estimate (below) global irrigation is about 3,500 cubic km of water per year on 2.5 million sq km of croplands. I realize that water vapor has a very short residence time, but this irrigation-induced increase in ET (a human alteration of the water cycle) is not something that is likely to go away any time soon, in fact, it is increasing, albeit at a decreasing rate. IF irrigation contributes to a short-term (but, effectively continuous) significant increase in water vapor, would this consitute a measurable forcing in its own right?

    http://home.alltel.net/bsundquist1/ir1.html

    [Response: This is a very good question. Personally, I would consider this a land surface change (similar to the chopping down of a forest to be replaced by cropland) that has an indirect effect on water vapour. Others have different opinions. These kinds of indirect forcings are however difficult to characterise on the standard 'forcings' bar chart, since they don't necessarily have a significant 'instantaneous' radiative forcing. One way to get around that is to use more complicated calculations for the forcings, for instance seeing how the radiation reacts to the change if you allow the whole column to adjust (while keeping surface temperatures constant), but this becomes more model dependent than the standard definition. -gavin]

  70. Dave Dardinger:

    Follow-up to #64

    I’ve now read the chapter gavin suggested and have a couple of remarks and one quote.

    1. The chapter has the same flaw as the IPCC documents available in terms of discussing the subject under discussion. It’s a very high-level discussion, listing subject of interest and needing further research, but it only lists other papers to be looked at and doesn’t give any details. Anyone wanting to poke under the hood, as it were, is forced to find many articles and read them. This means it’s only of real use to a full-time researcher and not the layman (no matter how well trained scientifically). What I’m looking for is essentially a set of text-books which let a person look at actual data, equations and even simplified models if necessary. Not that anyone has time to look at everything, but it’d be useful if a person could dig as deep as desired in one limited area without having to spend great amounts of time and money to prepare for it.

    2. The chapter is well worth reading for anyone who thinks climate scientists have things well in hand when it comes to understanding clouds et. al. The chapter is practically an unending series of apologies for how much is not known. Nor does it state a la Gavin that these are minor details which won’t have much effect on our understanding of climate change if and when they’re addressed. (A lot of the problem involves needing many years of data to test models and observe natural variations).

    To illustrate, here’s one striking quote from the middle of page 26:

    “If the structure or area coverage of clouds change with the climate, they have the potential to provide a very large feedback and either greatly increase or decrease the response of the climate to human-caused forcing. At this time both the magnitude and sign of cloud feedback effects on the global mean response to human forcing are uncertain.”

  71. Joseph O'Sullivan:

    The California law

    You have to read the entire chapter to understand the greenhouse gas clause.
    The scientists at Realclimate and scientists who comment at the site know that non-scientist sometimes get the science wrong. Lawyers and people in the regulatory field see the same things with laws and regulations.

    Reading laws and regulation is like reading a contract or a credit card statement (lawyers write these too). You have to read the entire thing, including the fine print, even though it is truly tedious. The chapter is titled California Climate Action Registry (Chapter 6, sections 42800-42870). The section cited by John Dodds gives the definitions of greenhouse gases which Michael Jankowski notes are for the purposes of the chapter. The next section is 42810, the Purposes of the California Climate Action Registry
    ( http://caselaw.lp.findlaw.com/cacodes/hsc/42810.html )
    To summarize, the purpose of the chapter is to encourage and record voluntary reductions of the greenhouse gases as defined in the earlier section.

    An environmental law takes science into consideration but also has to consider what is politically, technologically and economically feasible. This could account for the exclusion of water vapor in the definition.
    Science and the law is a messy area and like climate change has been increasing politicized. The Center for Progressive Regulation has a lot of info on this ( http://www.progressiveregulation.org/ ), and in the interest of full disclosure, one of the legal scholar/attorneys in the Center was one of my law school professors.

    The law covering vehicle emissions is another law. The UCS has a good summary of this issue at:
    http://www.ucsusa.org/clean_vehicles/cars_and_suvs/page.cfm?pageID=1396
    There are ongoing lawsuits about this issue and other efforts to curb greenhouse gases. Generally some states are proposing regulation trying to curb CO2 and other pollutants and they are being opposed by the EPA, other states and industry primarily on the grounds that the governing law, the Clean Air Act (CAA), does not include CO2 as a regulated pollutant or that only the federal government and not state governments can regulate these areas. It’s too early to tell how these suits will come out and how the efforts to reduce CO2 and other emissions will be effected

    The National Academy of Science has reviewed air pollution regulation (Air Quality Management in the United States (2004) online at: http://books.nap.edu/catalog/10728.html ), and stated “economic assessments of the overall costs and benefits of AQM in the United States indicate, despite uncertainties, that implementation of the CAA has had and will probably continue to have substantial net economic benefits.” The NAS also stated that a key challenge facing air quality management (AQM) will be “adapting the AQM system to a changing (and most likely warmer) climate”.

  72. John Dodds:

    Re 68
    Michael & Gavin,
    My position is that I heartily support & approve of and agree with Gavins topic here on water vapor (see comment 15.)
    However I was pointing out to Dave #29,and supporting Gavin’s opening statement, that not everyone believes that water vapor is a greenhouse gas.
    The example being the State of California , which in Sec 42801 defines Greenhouse gases (for the purpose of the 42801 chapter) as to NOT include Water vapor. The 42801 chapter was originally written (I think in the 90s or maybe 2000) for the purpose of monitoring Greenhouse Gas Emissions – for which obviously monitoring water vapor does not make sense.
    HOWEVER, California also issued the law AB1493 in 2002. This is the law that required that the Vehicle emissions be evaluated to see if there was a greenhouse gas and global warming impact, and if so then they should be controlled – hence the basis for California to regulate CO2 auto emissions (as a pollutant) by mandating what the auto efficiency must be, when the US EPA claims that what they are really doing is controlling auto efficiency which the courts have ruled is a Federal mandate. Ab1493 invoked the 42801 definition of Greenhouse gases – ie Greenhouse gases do not include water vapor, for the purposes of the Law AB1493 (controlling vehicle emissions).

    To me this is stupid illogical and just plain wrong. It is as wrong as defining Pi to be 3.0. Regulating Greenhouse gases IS the Legislatures perrogative. Defining the reality that water vapor is not a greenhouse gas is not.
    If you are going to look at a subject and then force the Ca residents to spend billions of dollars to implement it, then you need to look at ALL of it. and honestly.
    Water vapor, as Gavin pointed out, is a greenhouse gas, AND terribly important as a feedback. It is also an anthropogenic emission (eg you eat hydrocarbons & breathout CO2 and water vapor, auto and airplane exhaust includes water vapor, electric power plants belch out water vapor and CO2 etc etc, BUT Natures feedback mechanism makes it ridiculous to try to control it.

    My statement was that if, by law, you do not consider water vapor a greenhouse gas, then how can you count the water vapor feedback as a greenhouse gas effect?

    My response in 65, was the total incredulity that Gavin in 62, could justify the scientificly invalid definition of greenhouse gases, when in the his opening paragraph he indicates that it is a greenhouse gas.

    Up until this point , I had thought that Gavin et al at RC were reputable, reasonable logical ethical scientists. But to admit reality and then ignore it in another context makes me wonder. Maybe Michael Crichton does have a point or two.

    John Dodds

  73. Tom Huntington:

    Regarding Comment 69
    Gavin- Thank you for your response and for this very informative topic. If anyone knows of a bar chart similar to the forcings bar chart in the IPCC TAR WG1 Figure 6.6 (or updated in Figure 28 in Hansen et al. “Efficacy of Climate Forcings” submitted to JGR in January -http://www.giss.nasa.gov/data/simodel/efficacy/Fig.28.pdf)
    that would include the various feedbacks (rather than forcings) please pass that information on.

    I think such a chart would be a useful summary in this discussion even if the levels of uncertainty are very high. I suggest this in the spirit of comparing apples to apples, as it appears myself and others in this thread are trying to do. As I understand it the major feedbacks are (1) water vapor in both troposphere and stratosphere, (2) changes in the albedo, of snow, ice, and sea ice, and (3) changes in the properties of clouds.

  74. Eli Rabett:

    I think John Dobbs is completely missing Gavin Schmidt’s point. The rapid interchange of water vapor and water through evaporation and condensation means that on the time scale of decades and centuries, water vapor concentrations are responses to other forcings rather than being drivers.

    In that context, what the California legislature did was perfectly logical They listed greenhouse gas emissions which were to be studied and perhaps controlled if they were shown to have a potential impact on global warming. You might try and fault it for not distinguishing between greenhouse gases and greenhouse gases that were to be evaluated and perhaps controlled, but that would be splitting hairs. To use John Dodd’s example AB 1493 required evaluation of vehicle emissions to see if there was a greenhouse gas and global warming impact. Water vapor concentrations cannot be controlled by limiting vehicle emissions or increasing vehicle emissions (you could plant or cut down a whole lot of trees….???). This is obvious even to members of a state legislature, so one wonders what the point of bringing this up was. Kind of the kind of point Michael Crichton makes as far as I can see.

  75. Dave Dardinger:

    I hate to rain on your parade, John, but I think reason for the distinction between H2O and CO2 is quite clear. CO2 sticks around a good while while H2O rains out quickly. Therefore how much H20 is released is meaningless unless it is both constantly being released and the amount released is an appreciable % of the total H2O in the atmosphere. Autos and power plant emissions of H2O don’t pass this test. I’ve worked through the math before and it’s tiny.

    This is not to say that I share the warmer’s fear of increasing CO2, but the debate should be primarily aimed at the things which matter, not trivialities and semantics.

  76. Ferdinand Engelbeen:

    I am not that sure that water is not a primary driver for temperatures, at least on land, as result of irrigation. See the work of Christy and Norris at: http://ams.confex.com/ams/pdfpapers/68739.pdf

    The summer minimum temperatures in the Californian Central Valley increased with 1-2 K since the mid-seventies, while stations at the bording foothills (200-1000 m high) nor mountain stations (>1000 m) show such a trend. Maximum temperatures in the valley show a small cooling trend. This all may be due to irrigation.

    It seems that some stations surrounded by irrigated land need corrections for this phenomenon, as good as is the case for the UHI effect of growing towns…

  77. David H:

    Re #66
    The choice of the phrase ‘economic with the actuality’ was to avoid suggesting either of the IPCC men deliberately misled. Both the questions and the answers have to understood in the context of the assertion that increasing CO2 will cause increasing temperature. If you take the mid century year of 1950 the trend is definitely down not up on both the graphs to which you link. If you take the trend from 1939 to 1975 it is also a decrease. Describing it as “the temperature rise stops somewhat” is just spin. CO2 rose steadily but temperature most definitely did not. However, for the counter argument, through that period the solar cycle lengthened. The correlation with solar cycle length as shown at http://www.arm.ac.uk/press/200years-on-the-Net.html is far more convincing than the CO2 theory. Apart from that mid century period the solar cycle has steadily shortened from 1890, which is the coldest period shown on your graphs, to the present. The solar cycle length has never again been as long as it was in 1890 and I don’t need science to tell me we now have a more active sun than I have seen in my lifetime. Just think about skin cancer.

    My quarrel with Dr Pachauri is the word “bulk”. The rises in temperature either side of the mid century point on your graphs are similar and I do not think an objective scientist would use the word bulk. This, however, is not true of the rise in CO2 in the same period.

    The quarrel sceptics and contrarians have is that every piece of data is spun to point in the direction of CO2 to such an extent that even adroit operators like Adair Turner come to think and pronounce publicly that CO2 is only thing that determines how warm our planet is. Almost daily until the start of our election campaign we have been told that CO2 is the “principle greenhouse gas”. Significantly, global warming is not in the electors top 10 interests and no major party is proposing anything serious. Anyone want to predict the UK Green vote?

  78. Joseph O'Sullivan:

    John Dodds does bring up a very good point and is absolutely right that the best and most comprehensive science should be the basis for laws and regulations, especially expensive ones. However there are many other things that influence the law making process. In addition to science issues there are economic, political, technical issues and even timing (i.e. we want to pass a law now, but the science is not fully developed). There are also legal concepts like the role of state vs. federal government and property rights. Environmental regulation involves many complex issues and makes a lot of work for lawyers. In a naked bit of self-interest, I think it is a great system that improves my employment prospects.

    In the current issue, AB 1493 (its at http://www.arb.ca.gov/cc/ab1493.pdf ) as a matter of law declares that greenhouse gases would have negative effects on California and should be regulated. The California legislature instructed state agencies to set greenhouse gas emissions for autos, examining the technology available and economic effects. The definition of greenhouse gas excluded water vapor for, and only for, auto emissions.
    The issue should be if water vapor emissions from autos should be regulated, not if water vapor should be considered a greenhouse gas to determine possible climate effects.

  79. Andrew Watkins:

    Re: #34

    Michael,

    Im not sure where the reduction in rainfall in SW Western Australia came into this, but i think people are a little off the track with timing. The greatest reductions are in the May-July period (See: http://www.ioci.org.au/publications/pdf/IOCI_Notes_Series2.pdf), laregly driven by the late arrival of the Autumn rains. You can see this trend in the simple trend maps for Autumn at the BoM site, e.g:
    http://www.bom.gov.au/cgi-bin/silo/reg/cli_chg/trendmap.cgi?page=cc&variable=rain&region=wa&season=0305&period=1960

    I think the BoM web site does a fine job in showing this, but agree it would be nice to be able to see any period you wanted.

    The IOCI reports suggest that based upon climate modelling and analysis of past synoptic conditions, the most likely cause for this change in precip is a global warming induced shift in the atmospheric circulation patterns. Land clearing has also been considered, however it cant realistically explain the broad scale changes in the circulation at this stage.

    Whichever way you look at it, SW W.A has a disasterous drying trend.
    Cheers…

  80. Michael Jankowski:

    Re#79, I will try to keep this brief as it probably is a little off-topic.

    With regard to your first link (IOCI report), I have a MAJOR problem with how they presented/interpretted the data. There is certainly an overall downward trend from 1925-2003 in Fig 2. When you have a downward trend, the mean at a later period within that timeframe is generally going to be lower than the mean at the beginning of the period. As an oversimplistic example, draw a downward trendline, and split the line into two segments (anywhere along the line). The mean across the first segment will be higher than the mean across the second segment, even though there was no change in trend. This is similar to what is presented in Fig 2 of the link, comparing the 1925-1975 mean vs 1976-2003 mean. This does not itself imply that there was some sort of drastic change in 1975/1976. Even in the case where you have a steeply declining trendline for the early period and then a flatter trend for the later period (even possibly going up!), you can have the same situation where the mean for the later period is much lower than that of the early period. Anyhow, I find it absurd to draw and/or present the conclusions they did using such methodology. I’m curious if Gavin or one of the more “expert” people feels as strongly as I do about this. I also think this method of comparing means for two time segments heavily skews the conclusions on page 2.

    Page 2 does refer to “a global change in the atmospheric circulation” for 1975/1976, so that does support why they selected those two timeframes. However, from eyeballing Fig 2, you could get similar results stopping the first period in the early or late 60s, the early 50s, the mid 40s, etc, so it doesn’t seem like the 1976-2003 timeframe really is exceptional in the context of the 20th century. Maybe there are more statistical elements behind the scenes that would show such a thing, and maybe my eyeballing is way-off, but I think this note ignores analysis which could be legitimate and relevant and instead uses oversimplistic methodology which is flat-out insufficient, quite misleading, and could produce incorrect conclusions.

    With regard to your 2nd link, the timeseries charts for “western Australia” don’t seem to show a declining trend for winter rainfall since 1975, and the autumn rainfall trend seems to be consistent with pre-1975 autumns and actually going upwards (www.bom.gov.au/cgi-bin/silo/reg/cli_chg/timeseries.cgi?page=cc&variable=rain&region=wa&season=0305). Annual rainfall is also on the increase. Granted, these are not specifically for only the “south west of Australia,” so it’s possible decreases in the south west of Australia are compensated for by increases in rain elsewhere in western Australia. So on to the trend maps…

    In looking at the 1960-2004 trend map you linked to, there clearly is a decline in autumn rainfall in the south west of Australia, up to 15-20mm/decade. I don’t dispute that rainfall in autumn (or winter) in the south west of Australia has been decreasing over time. But what I found was that the 1970-2004 trend map shows a decline of only up to 10-15mm/decade, which indicates that the decreasing rainfall trend in autumn has actually slowed in the south west of Australia post-1970. Isn’t that a good thing? The rainfall is still decreasing, yes, but that rate of decrease slowed…yet your first link (IOCI report) implied everything was pretty much fine until 1975/1976 and then fell apart. When you look at the other maps, you’ll find even more information to dispute the position of the IOCI report. The 1950-2004 map looks almost identical to the 1970-2004 map in the south west. Ditto for 1940-2004. Using only the trend maps as a source of info, it appears that autumn rainfall in the southwest of Australia declined from 1900-2004. However, this rate of decline peaked in the 1960s, and the decline rate of 1970-2004 is quite similar to that of 1940-2004 and not much worse in highest magnitude than that of 1920-2004. So it’s tough to see from those links the basis for arguing that there’s been a drastic change in the 1970s.

    I must maintain the caveat that not being able to select specific start-and-end points with the trend maps can produce some misleading conclusions. But I think they (along with the IOCI data) show enough to suggest that the decline in autumn rainfall in the south west of Australia over the past 3 decades is more of a continued trend over much of the century than a sudden change.

  81. Jeff Norman:

    All this talk about evaporation, water vapour and precipitation and not one mention of enthalpy, heat of vapourization and heat transfer.

    Evaporated water rises up in the atmosphere where it achieves a heat balance with the molecules that make up the surrounding air. If there is an imbalance the water will change phase from the vapour state to the liquid state releasing the heat of vapourization which energizes the air molecules, increasing their temperature.

    Warmer air “retains” more water vapour because it is cannot absorb the incremental heat energy from the incremental water vapour.

    According to the CRU, the Earth’s surface temperature has increased. According to the discussion above this means more moisture should evaporated at the Earth’s surface. This vapour has to go somewhere. It doesn’t appear to be accumulating in the atmosphere so it must be precipitating out and falling back to Earth, leaving the heat energy in the atmosphere.

    Where is all this heat energy going? According to the MSU data (even the RSS interpretation) it is not staying in the atmosphere. Does this mean the atmosphere is better at shedding heat into space than the models suggest?

  82. Francis MASSEN:

    answer to #58:
    here are the yearly averages I measured the last 3 years on the same location:

    year /annual___/JanFeb___/JunJul___/delta
    year /mean_____/mean_____/mean____(summer-winter)
    ————————————————————————
    2002 398.0___381.7___384.1___2.4
    2003 402.0___404.5___394.2___-10.3___heatwave summer
    2004 407.5___393.1___401.4___8.3

    I used the MIR9000 sensor from Environnement SA (a French company).
    I have a problem with the 2001 data (the sensor was down during a hefty 10% of the time, so the yearly mean is questionable). The years 2002 to 2004 (sensor uptime nearly 100%) show an increase of about 4 ppm/year, which seems more or less double the Mauna Loa means). I would have preferred a negative delta (summer – winter) for all years, but the data don’t respect this wishful thinking…

  83. Dan Allan:

    Debunking contrarians sure gets tiresome. You never seem to get anywhere. I don’t really get this crisis over a California law that says that, for the purposes of regulation, WV should not be considered a GHG. What is the big conspiracy theory? Are they proposing that there is not enough regulation, and we should begn immediately to regulate WV emissions? Do hey think scientists a purposely surpressing critical data that WV really is a GHG? I don’t get it.

    Regarding post 77, how many times does one have to repeat: Nobody has ever said that CO2 is the only forcing, so nobody ever expected a temperature chart to follow a trendline of CO2 concentration in the atmosphere without incorporating other forcings. In fact, if historical temperatures tracked in perfect parallel to CO2 in the atmosphere, that would be a serious PROBLEM for most GCMs. What is incontrovertible is that when you add the CO2 forcing you wind up with a temperature trendline that is closer to historical reality than without it.

    I would also like to know which part of the CO2 / Global warming argument is being disputed:

    1) CO2 is accumulating in the atmosphere due to human activity – this is basically proven fact. I know of nobody who seriously disputes it.
    2) CO2 is a greenhouse gas that will cause the atmosphere to warm as its concentration increases. Does anyone seriously question this?? This seems to be pretty basic science.

    There is plenty of room for debate about positive and negative feedbacks, how much or how little the atmosphere is likely to warm in the future, etc. But it would be nice if wasn’t necessary to continually go back to square one to persuade those who see a giant cabal that there is no grand conspiracy.

  84. Dave Dardinger:

    But what good does it do to try talking about feedbacks when I get no responses worth discussing? Gavin claims the feedback from clouds are known to be small and then cites a link which basically contradicts what he just claimed.

    So what’s the next subject up for discussion? Clouds? Of course not. It’s Ozone. Like skeptics are going to get fired up about that subject?

  85. Dan Dorritie:

    This is not a comment; it’s a question (or more).

    In discussing the global warming potential (GWP) of various greenhouse gases (GHGs), climate scientists frequently employ compilations of “integrated time horizons.” (Example, the 1990 IPCC report, “Climate Change”, table 2.8, p. 60.) GWP compares the warming potential of other GHGs to that of carbon dioxide, but they are compared according to time horizons of 20, 100, and 500 years. (I do recognize that these particular time horizons have been used because they are the most useful, and that, depending on one’s purpose, other time horizons could also be used.) Let’s take methane. Methane (including its indirect effects, which are irrelevant to my question) has a GWP of 63 for a time horizon of 20 years. Methane also has an atmospheric residence time of less than 10 years. So what does the 63 represent? Does it mean that if we start with equal amounts of carbon dioxide and methane, the amount of warming produced by that methane will be 63 times that of carbon dioxide, despite the fact that it will all be gone in less than half (under 10 years) of that 20 year time horizon (whereas much of the carbon dioxide input will still be around)? Does the time horizon therefore reflect both the intrinsic balance of solar radiation input, thermal radiation output, as well as the length of time that each gas will remain in the atmosphere?

    And, practically speaking, why choose to examine GWPs on the basis of one time horizon versus another? Should we therefore worry about the immediate warming effects of methane (because they are “big”) but not so much about the longer-term effects (because they’re less)?
    Despite some investment of personal time on attempting to answer this question, I’ve not located any adequate discussion of the matter. . . and article after article presumes that that the answer is either self-evident or common-sensical. It’s not.

    Many thanks,
    Dan

    [Response: Lifetimes are more complex that a simple number might indicate. There is some discussion at http://www.grida.no/climate/ipcc_tar/wg1/133.htm. A lifetime is more an e-folding time that a time for complete disappearence, so I think that saying there would be no methane left after 10 years is wrong (disclaimer: not my area of expertise). The exact defn is given in the TAR: http://www.grida.no/climate/ipcc_tar/wg1/247.htm. The resason for looking at different time horizons is that the "total" warming effect is different for long and short lived gases. The "instantaneous" effect of a certain amount of methane is more that the same amount of CO2; but if you integrate the warming over some time horizon - perhaps 100 years - then the balance shifts. This is useful is you need to balance methane/CO2 emissions and their effects - William]

    [Response: With respect to methane in particular, there are a number of issues. Firstly, the 'residence time' (total atmospheric content divided by total sources (or sinks) ) for methane is around 8.4 years. However, because of a non-linearity in the CH4-OH chemistry, the time scale for a perturbation to decay away is around 10 years. This is the time for a perturbation to decay to 1/e of it's initial value, and so after 20 years, there will still be around 13% of the initial pulse. Thus the integrated forcing due to methane needs to take the molecule per molecule greater impact into account, and also the changes in abundance. - gavin]

  86. Francis Massen:

    reply to #83:
    my mixed sympathy to Dan Allen who gets upset debunking contrarians. BUT: when you read media on GW, you (almost) never hear anything else than CO2 bashing (even here in Kyoto friendly Europe, the 5 other gases are almost never spoken upon: nearly all political forced strategies go into reducing CO2, THAT BIG AND ONLY CULPRIT!). No wonder that the fine points of climate science get lost, and that someone who does no agree to this very biased view rightly claims his opposition!

  87. Stephen Berg:

    Francis, if you looked at this link, you would see why CO2 is the primary target by policymakers in Europe:

    http://www.giss.nasa.gov/data/simodel/efficacy/Fig.28.pdf

    It is the most prominent greenhouse gas that is causing the human-induced climate change problem.

  88. Eli Rabett:

    I hate (OK, I love) to make more work for others, but there is an important article in the Journal of Chemical Physics 122 (11) 114309 (2005) by Cormier,m Hodges and Drummond on measuring the water vapor continuum absorption. It shows (or makes a real good attempt at showing) that the mid IR continuum absorption for water vapor is a couple of orders of magnitude lower that a commonly used empirical model (CKD 2 4). So, my question is how would that affect Gavin Schmidt’s table?

    This looks like a really good experiment.

    [Response: Indeed. This is a bit more complicated than just putting in a new number and testing it though, but I will consult further and report back at some point! - gavin]

    [Update: After some discussion, the consensus appears to be that the uncertainties in the continuum are on the order of a few W/m2 of absorbtion (this is about 2% in the numbers in the table). The data (even including this new paper) are pretty diverse and hard to measure. Thus independent replication of any new result is necessary before the codes will be changed. The GISS radiation scheme uses a theroretical basis (Ma-Tipping) for the continuum absorption and this is at least as good as any other scheme out there compared to the data. However, this is a definite source of significant uncertainty, although it's impact on the sensitivity or water vapour feedback is less important. -gavin]

  89. John Dodds:

    Re Forcings chart (#87?)
    It is precisely because of the unquestioning acceptance of the “Forcings Chart” that Gavin had to write this Water Vapor topic in the first place.
    It is a chart of apparently arbitrarily (but logically) defined forcings in order to make the computer models work.
    It is NOT a chart of the the causes of global warming, but many people seem to use it that way.
    There is also something called feedback, (see above) which is apparently primarily water vapor which will result in more warming as a result of increasing temperature from all of the factors in the chart. There is also a feedback greenhouse effect from existing CO2 responding to increased solar energy etc which doesn’t seem to get mentioned often. etc etc.
    In fact if you make a similar “Causes of Warming chart” in W/m2 then the water vapor feedback dwarfs the CO2 column. Hence as Gavin pointed out, when you get 3 sceptics together, they always bring up water vapor as being neglected.
    The forcings chart is IMHO unfortunately biased towards making CO2 the biggest reddest box on the chart. It is highly misleading.
    A more fair Causes chart should show water vapor and all feedbacks, and then indicate that there is no practival way to control water vapor, just like there is no practical way to control the sun, and no practical way to control the natural part of the ~380ppm of CO2.

    I have several questions about the Forcing chart, which I hope Gavin can address when/if he does Forcings vs Feedback as a discussion topic. (Good luck in explaining that one!!- hope you do as good a job as you did for water vapor!)
    1. It seems to me that a forcing is defined as an external change to the system. eg the sun adds heat, man adds CO2 to the air, etc. My basic question is what is external? what is the system?
    eg1 The sun causes all of the greenhouse effects due to its energy input and trapped reflected energy. Are all of the GH gas “forcings” therefore really feedbacks? Why not?
    eg2 Manmade CO2 is produced from burning fossil fuels previously caused by the sun which are already, or should be, included in the Earth total energy balance, just like CO2 is included in limestone and corals and dissolved in water, and (negative or cold) energy is stored in ice and glaciers etc Are we therefore defining the “system” to be only the atmosphere, so forcings are then external changes to the atmosphere? In which case why is melting ice not a forcing? (my answer – because it is already accounted for in the computer model & you don’t want to double count it)
    A New thought just struck me, is “the system” the computer model and not the earth or air ecosystem? If this is so, then a chart of forcings (without feedbacks) makes no sense whatsoever, since it is so arbitrary and depends on how the programmer accounted for things.

    2, Does the CO2 in the Forcings chart include the natural feedback of the CO2 increases due to solar warming? – ie the sun warms, ice melts, more land/sea is available for plants to produce CO2, which is the normal mechanism that has resulted in all of the previous warmings & CO2 increases from the previous ice ages?
    I assume that the CO2 column does NOT include the water vapor feedback from increased temp due the CO2 forcing. – does it?
    Does the CO2 forcings column include the CO2 feedback from increased greenhouse effect (from the 378 ppm of old CO2) from the increased and varying solar warming?

    Now considering these questions, I begin to wonder, just what good is the current forcings chart if it does NOT include all the relevant feedback effects?

    [Response: You ask some very good questions, and in truth the answers are sometimes a little fuzzy. In a zeroth-order practical sense, you can define as a forcing as a change in anything that isn't calculated prognostically in your system. So for instance, O3 can be a forcing in a simple model, but in a model that calculated atmospheric chemistry, it would be a feedback (while the forcing would be the emission of precursor molecules). In common parlance, forcings are assumed to apply to the basic dynamical GCM system (i.e. that includes winds, temperature changes, water etc.) but not including the bio-geo-chemistry or interactive vegetation that many of the newer Earth System models come with.
    You also need to remember what forcing 'bar charts' were designed to do. The idea was to have a metric to compare different effects and be able to assess how the climate will react when given combinations of the forcings without having to do the calcuations every time. Since water vapour (and ice albedo, and clouds and long-wave radiation and evaporative cooling....) will change as a result of all the forcings, it doesn't make sense to associated a water vapour feedback say only with CO2. If one makes the assumption that each forcing really is equal (which it isn't really), then including the water vapour term would simply multiply all the lines by whatever the gain is. It is a cleaner calculation not to include that for any of them.
    Now with respect to any of the constituents that have an anthropogenic component and a climate related feedback (i.e. CO2, CH4, etc.) it is a little difficult to seperate the two. The standard method is to take the observed concentrations and simply use that (which assumes (correctly in most cases) that the natural feedback term is small). Alternatively, you use the emissions data and the bio-geo-chemical models (which can calculate the natural feedback term) and re-apportion the forcings (which must add up to the same number as in the first case) between the different emissions. I was a co-author on a recent paper that tried to do this for methane (Shindell et al, 2005) which actually demonstrates that methane is actually undervalued on the standard chart! (but that is compensated for by a negative forcing from NOx).
    You may be right in thinking that a more expansive discussion of this is required..... - gavin]

  90. graham dungworth:

    The original work done on heat transport by water vapour in the atmosphere is by Tyndall.

    Tyndall, J., 1859, Note on the transmission of heat through gaseous bodies, Proceedings of the Royal Society, London, 10, 155�158.

    Quote “acts more energetically upon the terrestrial rays than upon the solar rays; hence, its tendency is to preserve to the earth a portion of heat which would otherwise be radiated into space”.Tyndall’s work predates Arrhenius’work by almost two generations and he estimated in his 1859 paper that water vapour absorbed 16000 fold more infrared heat than dry air. Despite its low residence time in the atmosphere he regarded it as the most important “GHG”.

    The 88% also comes from a book reference
    Peixoto, J. P. and A.H. Oort, 1992, Physics of Climate. American Institute of Physics, 520pp.

    Perhaps the 98% ref was a ” back of an envelope calculation” combination of this 16000 fold estimate and the ratio of respective residence times!

  91. Mike Doran:

    Heavy math respecting tropical storm dynamics and SSTs (sea surface temperatures):

    http://groups.yahoo.com/group/methanehydrateclub/message/2434

    http://groups.yahoo.com/group/methanehydrateclub/message/2435

    Mike

  92. Andrew Boada:

    The extent of my knowledge of climate science comes from the 101 course I took and the text book I read, so my depth of knowledge isn’t very great. However, I was wondering: couldn’t it be said that water vapour isn’t a forcing agent simply because the amount of water vapour in the atmosphere is dependent on the temperature of the air, not vice versa? Also (from my anecdotal observations) humid air seems to require more energy to raise its temperature (is this correct?) If true, then even though humid air would cool more slowly at night, it would also heat more slowly during the day. Water vapour seems just to stabilize air teperatures.

  93. Mike Doran:

    http://news.bbc.co.uk/2/hi/science/nature/4495463.stm

    Interesting.

    [Response:Well obviously I think so! I will do a summary of the results soon... - gavin]

  94. John Dodds:

    Gavin, a follow-up to #89 about the Forcings Bar chart, in the water vapor feedback http://www.realclimate.org/index.php?p=142#comments, section of RealClimate.org, (I am using the 1750-2000 chart @ http://www.giss.nasa.gov/data/simodel/efficacy/Fig.28.pdf ):
    I can see why a chart of the “forcings” (or causes) should not include the feedback “effects” of water vapor. BUT I think you need to be able to address ALL the effects somehow if “The idea was to have a metric to compare different effects and be able to assess how the climate will react when given combinations of the forcings without having to do the calcuations every time.”

    Now I have a question: Is the 1.5W/m2 attributed to CO2, strictly from the forcing part of the CO2 (ie the addition between 1750 and 2000 – or nominally the ~90ppm difference between ~290ppm of CO2 and the current 380ppm)? OR does it include the change in W/m2 due to the increased CO2 “feedback” as a result of the positive Solar irradiance forcing acting on the preexisting ~290ppm of CO2 also? ie Is the 1.5W/m2 strictly due to Anthropogenic causes or is there a piece of it (290/380=75%)due to the solar forcing on natural CO2 also? (because if the natural part is included then the use of this box to guesstimate effect from anthropogenic (which #87 is trying to do) over estimates the effect). Same question applies to all the greenhouse gases. And the other forcings?
    Just what are the magnitudes of the natural GHG feedbacks from the solar forcing? (so that I can accurately determine how much of the temperature rise (or total W/m2) was due to the solar forcing and how much was due to the anthropogenic forcing.)

    [Response: The 1.5 is purely from measured CO2 changes. I don't understand why your think there should be solar influence mixed in it - W]

    Then questions on the Sun box in the Forcings bar chart.
    The solar irradiance actually oscillates over time. Is the 0.3W/m2 a net value difference between 1750 and 2000?
    Would the number be significantly different if you had gone from solar trough to peak (~1820 to 1998)? ie is the choice of time interval a hidden consideration in this chart so that you can’t use this history snapshot to project the solar part (& its feedbacks) into the future?
    If the chart had gone for example from 1942 to 1970, when the net sun W/m2 would have been negative, during cooling, what would the CO2 box(es) have been – positive or negative?

    [Response: Firstly, remember its not *measured* solar - its reconstructed from proxies with more or less certainty. I presume its the avg over the 11y cycle. From 42-70 the CO2 forcing was +ve, of course (you have remembered sulphate aerosol, haven't you?) - W]

    Similar questions apply to the Forcings vs Time chart. http://www.giss.nasa.gov/data/simodel/F_line.gif .
    ie Does the light green CO2/GHG line include the result of solar forcing of the natural CO2 component? or is that an effect that is also missing like the water vapor feedback, and needs to be added to the solar forcing in order to get the total solar + feedback effects. Does this then result in a more intuitively logical conclusion that the solar forcing with feedbacks dominates the Anthropogenic CO2 forcing effects, just like the sun dictates shorter and longer (daily, yearly, little ice age, and presumably ice age) temperature cycles?

    I think it would clarify the whole picture if you created “Forcings And Feedbacks” Bar (and Time) charts, with a water vapor box above or below each of the other CO2, CH4 , sun, clouds etc components. tying the WV box to each component indicates its dependence on that component (ie its a feedback from that component, not a forcing) BUT it allows the user/public to add all the values up to get the total W/m2 impact from all the other forcings and feedbacks. Also each of the GHGs would be broken out to show anthropogenic or natural and the natural components should be associated with their forcing, which is the sun. (My guesstimate of this chart would show the solar forcing to be responsible for 75-80% of all the 1750-2000 W/m2 effects.)
    Right now the forcings bar and time charts give a very incomplete picture- lots of pieces are missing or not expressly broken out, so the public can not accurately see the relative magnitude of the components. I do not see how you could use them to accurately assess the future impacts

    Finally a very subtle but important question: The Forcings bar chart, or the proposed Forcings and Feedbacks charts are a historical explanation of what caused what etc. However a chart trying to project the future, does not care if the existing GHGs were anthropogenic or natural. Any estimate of the future impact depends on the existing conditions (eg CO2 @380ppm) and what the future forcings will be. ie If the sun cools off next year (a negative forcing), but CO2 increases 2ppm (similar to what it did in 1999 and 2000), what will be the dominant “forcing/cause” and the effect on temperature? Won’t the negative sun forcing on all 380ppm of CO2 dictate what the temperature does since it far outweighs (380/382=99.5%) the 2ppm CO2 forcing increase? – as it did in 1999. Are we not then at the mercy of the sun, and the only thing that anthropogenic CO2 etc does is magnify (by GHG feedback) whatever the sun is forcing? Therefore, a future 2x rise in CO2 over 50 years has the potential to change the temperature BUT only as a multiplier/feedback on the magnitude, and direction, dictated by the orbitally modified solar irradiance forcing. ie Raising the CO2 levels for the next 50 years ALSO raises the potential that the temperature will go a few degrees lower WHEN the next solar cooling happens. Increasing GHG levels has only widened the band for the temperature range by a fraction of one or two degrees, similar to the way that the Earth precession tilt and eccentricity (see Zachos 2001 fig 1C, pangea.stanford.edu/research/ Oceans/GES206/papers/Zachos2001.pdf – or google: Zachos 2001), have narrowed the range by several to ten degrees over the last few thousand years.

    [Response:This all seems a bit strange to me - you're implying a dominant role to the sun, when the evidence seems to be that solar changes are rather small. If CO2 rises, that doesn't imply (as you seem to believe) that a subsequent reduction of solar would cause a greater cooling than if CO2 was lower - W]

    Doesn’t this then dictate that the majority of the results of any future temp projection are dictated by the estimate of what the sun will do in the future? (Pay attention Drs Lean and Solanski etc!) And by what the unknown and not evaluated longer term solar irradiance cycles, and orbital and Milankovitch multiplying factors and their associated feedbacks, do to the solar forcing? (A Strange concept that the GHG increases result in major feedbacks to the solar + Milankovitch factors such that they may really explain all of the ice age cycles in spite of being so small!)

    It can’t be this simple. Have I missed something?
    John Dodds

    PS If all the above is valid, then have I succeeded in unifying the valid (with uncertainties) IPCC Science Data ( but not the political position) with the skeptics who do not believe that CO2 is the major cause of global warming ? If so, then as an unaffiliated, unemployed amateur scientist (actually an engineer) I will gratefully accept all accolades rewards & remunerances. :) – BIG smile! :).

  95. Welcome to Reasic, Phil. « Reasic:

    [...] effect. This then leads us to the conclusion that excludes water vapor as an option because it is a feedback, not a forcing: While water vapour is indeed the most important greenhouse gas, the issue that [...]

  96. Sizzling study concludes: Global warming 'hot air' - Page 4 - Volconvo Debate Forums:

    [...] absorbance of between 9 to 26%. We’ve already covered the importance and relevance of water vapour before but of course, you never actually learn from these articles even though you claim to be someone [...]

  97. Alexander Cockburn versus Al Gore « Louis Proyect: The Unrepentant Marxist:

    [...] those interested how climate scientists deal with water vapor, I recommend the RealClimate website. It explains very clearly that water vapor is a “feedback” rather than a [...]

  98. co2 blog » Blog Archiv » Wasserdampf: treibende Kraft beim Treibhauseffekt?:

    [...] Original von Gavin Schmidt (NASA Goddard Institute for Space Studies in New York) bei RealClimate [...]

  99. Hypography Science Forums - Co2 Acquittal:

    [...] link goes into pretty good detail, and also helps raise your understanding on the issue quickly: RealClimate Water vapour: feedback or forcing? Sorry to hear about your hand. Maybe you can learn to type with your toes? All the best. [...]

  100. tribe.net: www.realclimate.org:

    Re: Clinton and Obama: Failures on War and Global Warming…

    " Water? "

    Water vapor is a feedback mechanism in climate change..
    If you……

  101. Skeptics - Page 2 - The Environment Site Forums:

    [...] in discussions of climate as a positive feedback on other longer-duration warming phenomena. Here is a sensible discussion if you are interested. If you are not, note that water vapour considered [...]

  102. Hydrogen Highway's Dead End. FINALLY ! - Page 2 - PriusChat Forums:

    [...] for anything of this sort is realclimate.org. A discussion of water vapor is given here. RealClimate These guys are climate scientists, so if you’re looking for a quick explanation, this isn’t it, [...]

  103. Physics of the Greenhouse Effect Pt 2 « Climate Change:

    [...] by the Clausius-Clapeyron relationship (further discussion on water vapor feedback here, here, and at realclimate. This means two important things: First, the influence of water vapor on the 33 K greenhouse effect [...]

  104. Stop the Denialists before it’s too late « Fermi Paradox:

    [...] vapor is indeed a very important greenhouse gas, see here for more. It is included in the models, of [...]

  105. Water vapour: Biggest GHG? - Page 2 - The Environment Site Forums:

    [...] Originally Posted by prashamk I found the following while surfing around: Can the experts put some light? The 95% figure is very wrong. True figure is about 66% or 36% depending on whether you count the overlap. (IE if you remove the water vapour and leave everything else, you reduce the GE by 36% or so, if you remove everything else and leave the water vapour you leave about 66% of the GE.) That is without considering clouds, which, as you point out, ameliorate the effect. (See: Water vapour: feedback or forcing?) [...]

  106. Water vapour: Biggest GHG? - Page 3 - The Environment Site Forums:

    [...] like "not making up the figures"). Water with clouding is only 81% of the total GHG’s. RealClimate Thanks BW for letting me revise it. Which one relates to our climate change the most?? [...]

  107. Global Warming: A Whole Lot of Mistakin’ Going On « 4 No One:

    [...] c, Water. Source: realclimate.org (estimates 67% to 85% of greenhouse affect), and Freidenreich and Ramaswamy, Solar Radiation [...]

  108. Global Warming - Page 77 - Volconvo Debate Forums:

    [...] effect than CO2(humiidity and cloud cover). But water vapour is more of a feedback component. Technical stuff [...]

  109. Is There Experimental Proof of CO2 Warming? - Page 2 - The Environment Site Forums:

    [...] for 2.5W/m^2. For total GHG’s and their effects upon the planet, then this is good reading. RealClimate __________________ Sustainability – is the environmental/economic and social interests combined. [...]

  110. Is There Experimental Proof of CO2 Warming? - Page 6 - The Environment Site Forums:

    [...] RealClimate Clouding is one factor they haven’t fully evaluated as yet, but with water vapour and clouding they are really only 66 to 85% You’ll have to read the article to explain. But water is a feedback only because we can not artificially increase or decrease water in the air. By warming the ocean though, we are removing a forcing that creates clouding and rain and can lead to a further rise in temperatures. By deforestation we are removing a fast source of evaporation (by transpiration) that helps cool the lower land levels and creates rainfall (especially monsoonal rain). __________________ Sustainability – is the environmental/economic and social interests combined. http://www.theage.com.au/frontpage/2…/frontpage.pdf [...]

  111. Half truths « My view on climate change:

    [...] -          Water vapor is the most important greenhouse gas (dwarfing the effect of CO2.) Again, even though the first statement is in principle correct, the second is dead wrong. Water vapor doesn’t change due to increased emissions, but it changes in response to the increase in temperature: warm air can hold more water vapor. Therefore water vapor works as a positive feedback: If the climate warms, it causes even more warming, and vice versa. Water vapor is in a fast equilibrium with the biosphere, and it is not a climate forcing (cause), but rather a feedback (reinforcing effect). If we wouldn’t have changed the climate, water vapor would not have changed either. The effect of water vapor is definitely included in climate models: A large part of the warming from CO2 occurs indirectly via water vapor as a positive feedback. See also here and here. [...]