A Few Things Ill Considered

A layman's take on the science of Global Warming featuring a guide on How to Talk to a Climate Sceptic.

Wednesday, February 22, 2006

send this to... Digg it! | Technorati | Del.icio.us | Reddit | Furl | Spurl

Climate Scientists Hide Water Vapor

(Part of the How to Talk to a Climate Sceptic guide)

This article has moved to ScienceBlogs

It has also been updated and this page is still here only to preserve the original comment thread. Please visit A Few Things Ill Considered there. You may also like to view Painting With Water, Coby Beck's original fine art photography.



  • At March 15, 2006 8:52 AM, Anonymous Anonymous said…


    Very interesting article.

    I'm trying to understand the reasoning for giving more weight to the impact of CO2 than water vapor. I just published a post on my blog about the interaction of CO2 and average global temps over geologic time and it seems that CO2 has had very little effect on those temps. It's been dropping steadily for 600 million years and yet global temps have remained stable within a 12 degree C range. If CO2 is so important, wouldn't it have more impact on global temps? Isn't it more likely that the water vapor's positive feedback overrides CO2?

    Here's the link if you're intereted:


  • At March 15, 2006 10:35 AM, Blogger coby said…

    It depends on what you mean by "more weight". In terms of the GHE, models correctly give more weight to the effect of water vapor. In terms of climate change forcing, because H2O is abundantly available and quickly responsive to temperature, it is correctly given no weight. This is the distinction between feedback and forcing (see the Real Climate article cited above). Yes the feedback overrides the CO2 effect, but this larger effect would not be there without CO2, so which is responsible? If all CO2 vanished from the atmosphere, all H2O would follow as the temperature dropped to -18oC globally.

    It is worth repeating: no climate scientist, no model ignores or denies the role water vapor plays in the GHE. If some peice of journalism does ignore it, that is one of the unfortunate consequences of simplification of science for a lay audience, accuracy is lost. But the fundamental point that CO2 is the driver, even as H2O is a larger amplifier, is the more important for a layperson and for policy decisions.

    With regards to geological history, I don't believe there are any demonstrable contradictions to greenhouse theory to be found. What we do have is an unfortunate lack of comprehensive and well resolved data. The climate system is complicated, even the configuration of the continents has a big effect, so you should not expect complete correlation between temperatures and CO2 levels throughout such a long and varied history.

  • At March 15, 2006 11:20 AM, Anonymous Anonymous said…

    Can you clarify in a qualitative way why massive emissions of anthropogenic water vapor do not change the relative humidity? The atmosphere on a global average basis is not saturated so it should have the capacity to take up additional water, and instead of precipitating out immediately it should increase the RH.

    I'm not a global warming sceptic, but I find this single issue to be the hardest one to answer.

    Thanks in advance.

  • At March 15, 2006 12:12 PM, Blogger coby said…

    If you pump massive amount of H2O vapor into the atmosphere you are now in an unstable state and the vapor will quickly condense onto dust particles and rain out. Water is always cycling into and out of the air and is in a general balance even if not saturated, this is guaranteed by the global abundance of liquid water. This balance is restored within about 10 days if water were somehow removed or added. 10 days is not long enough to have any climatic response.

  • At March 16, 2006 9:34 PM, Anonymous Anonymous said…

    Hi again,

    "Yes the feedback overrides the CO2 effect, but this larger effect would not be there without CO2, so which is responsible? If all CO2 vanished from the atmosphere, all H2O would follow as the temperature dropped to -18oC globally."

    Thanks for your reply, but the bit I've quoted didn't seem reasonable. After all, 600 million years ago the concentration of CO2 in the atmosphere was 7000 ppm. By comparison, you could say that current levels are as close to no CO2 as we're likely to get and yet the Earth has maintained average global temperatures within a narrow 10 degree range over the phanerozoic eon. How can that possibly be?

    If CO2 forcing is so critical, what prevented the Earth from becoming like Venus when CO2 concentrations were 7000 ppm?

    And why is it AGW proponents think the Earth should stay at the low Holocene temps when average temperatures over the last 600 million years have been 17 degrees C instead of the 9.7 degrees C we're currently at.

    It seems the climate should wants to be warmer than it is now and the upward trend is just the climate system returning to normal.

  • At March 17, 2006 10:21 AM, Blogger coby said…

    Hi Chris,

    The feedback effect decreases as the CO2 concentration increases as absorbtion bands become saturated. eg, once the atmosphere is opaque to IR it does not matter how much more opaque you make it. So while 7000ppm CO2 is 20x current levels, it is less than four doublings. Similarily, the significance of 100ppm rise from ~180 to ~280 in the glacial cycles is greater than the significance of 100ppm rise from 280 to 380 we have done now. So going from 180 to 0 is in no way comparable to going from 7000 to even 6000.

    The reason we don't get a runaway Venus type greenhouse is, I believe but am not 100% sure, because of the abundance of water. As the temperature would rise, cloud cover would increase to the point that enough sunlight would simply not penetrate thereby stopping any warming trend.

    As for wanting to keep the temperature low, this is a misstatement of the goal. The danger in the current GW is not due to the difference between a stable climate at average 15oC (your current average temperature numbers are wrong) and a stable climate at average 20 or 22 or 25oC or what have you, it is due to the extremely rapid rate of change and the resulting instability and the loss of biodiversity. Please see this article.

  • At October 30, 2006 6:19 PM, Anonymous Anonymous said…

    You say "The reason we don't get a runaway Venus type greenhouse is, I believe but am not 100% sure, because of the abundance of water. As the temperature would rise, cloud cover would increase to the point that enough sunlight would simply not penetrate thereby stopping any warming trend."

    Err, does this not apply irregardless of the source of CO2 (natural or anthropogenic)? Does this not say that CO2 levels don't matter?

  • At October 30, 2006 7:51 PM, Blogger coby said…

    No, these are non-linear effects. Warming progresses until the temperature is at such a point that differenct processes begin to dominate. In this scenario, once the temperature gets to a certain point cloud making begins to dominate and provide an overall negative feedback.

    But do check the Real Climate article on Venus, it is a complicated issue.

  • At December 27, 2006 10:28 PM, Anonymous Anonymous said…

    I'm a little confused on how CO2 disperses or i guess settles into the atmosphere? Is it spread out evenly throughout, or does it tend to all go to a certain layer of the atmosphere. And if it goes to a certain layer how can they measure the amount by taking core samples from greenland?

  • At December 27, 2006 11:17 PM, Blogger coby said…

    I can not give you any references but it seems to be common knowledge in the atmospheric sciences that CO2 is a well mixed gas in the atmosphere and that it is very uniformly distributed throughout the troposphere. There is too much turbulence in the troposphere for gases to settle out by relative densities. This means that the CO2 concentrations found in ice cores bubbles is a very good indicator of CO2 levels worldwide from ground level to the tropopause.

    Volcanic events very close by would cause spikes, and today the concentration of CO2 in the north hemisphere is a few ppm higher, it takes about four years for CO2 produced largely in the north to cover the southern hemisphere.

  • At January 31, 2007 7:37 AM, Anonymous Anonymous said…

    This is fairly common and fairly straightforward to answer, it just isn't true. This is an effective attack though because it is true that the IPCC report does not spend much time discussing water vapor's greenhouse effect because it is considered as a feedback effect, rather than a forcing of the climate system.


    It is nice to see someone finally admitting that the IPCC throws out data that doesn't fit in with their international socialist agenda for a carbon tax.

    The Hydrosphere is constant (ice+lakes+rivers+oceans+rain+clouds+water vapor). However, water vapor is not constant, one part of the hydrosphere is shifting towards another, constantly.

    Everything on earth is part of a feedback. If CO2 increases, then the probability of forest fires decreases. Feedback. If oxygen increases, then the probility of a forest fire increases, increasing CO2 output. Feedback.

  • At January 31, 2007 12:10 PM, Blogger coby said…

    "If CO2 increases, then the probability of forest fires decreases."

    That's kind of funny, because wildfire records are being broken across the globe. Stupid facts and their liberal agenda.

  • At February 01, 2007 1:53 PM, Anonymous Anonymous said…

    "If CO2 increases, then the probability of forest fires decreases."

    That's kind of funny, because wildfire records are being broken across the globe. Stupid facts and their liberal agenda.


    I meant in a world without human influence. Urbanization, farmland, and people flicking cigarettes out car windows increases the probability of forest fires. However in the absence of human influence, higher CO2 levels decreases forest fires, and on the flip side lower CO2 levels and higher oxygen increases forest fires.

    I doubt the liberal "Scientists" are capable of conceptualizing this simple formula.

    More CO2=less fires
    More Oxygen=More fires

  • At March 13, 2007 4:03 PM, Blogger pc said…

    The problem with this argument is that it is based on an unproven idea with no good theory as to why CO2 is a driver and not a consequence. Simply stating again and again that it just is CO2 is not science.

    If you remove all the CO2 from the atmosphere, plant growth would cease. The plants would die and release CO2 back into the atmosphere. In addition, as the partial pressure of CO2 in the atmosphere drops, the oceans would be forced to release CO2 in order to restore equilibrium. Similarly, as the partial pressure of CO2 increases, the oceans would absorb more. This is just basic science.

    In addition, rising temperatures and/or increasing CO2 levels directly cause more abundant plant and phytoplankton growth, thus using up more CO2. In fact, it has been experimentally shown that increased CO2 levels alone stimulate plant growth.

    This planet could never have survived millions of years without strong balancing negative feedback loops. It has survived asteroid strikes, axis shifts, periods of intense volcanic activity and periods with CO2 levels far higher than they are today.

    You completely fail to convince that CO2 is a driver and water vapor merely an effect.

  • At March 13, 2007 4:36 PM, Blogger coby said…

    Hi pc, thanks for the comment.

    The theory that CO2 is a radiatively active gas in the IR spectrum is extremely well established physics and is the foundation of all kinds of things including the composition and age of the universe. Why do you think H2O is a radiative gas but doubt CO2 is?

    Your comments about self adjustments from biosphere and ocean feedbacks is quite correct at least at the superficial level, but you are ignoring the timescales involved. A CO2 pulse in the atmosphere will take centuries to finally return to original levels, and that is completely ignoring any potential feedbacks from other parts of the system (ie temperatures raised for centuries could result in massve methane releases and loss of signficant low albedo ice sheets etc.)

    The experiments I am aware of that show improved plant growth in elevated CO2 levels require that all additional biological needs are amply provided for. Field experiments where additional nitrogen and moisture is not available have not show similar results. Sometimes the lab does not tell the whole story.

    This planet could never have survived millions of years without strong balancing negative feedback loops. It has survived asteroid strikes, axis shifts, periods of intense volcanic activity and periods with CO2 levels far higher than they are today.

    Quite right. And it has survived near total extinction events where only subterranean bacteria persisted, snowball earth where no ground was left exposed, only thick icesheets. It would survive an all out nuclear war, where every scap of earth was blasted by fire and radiation. It would survive the absolute worst imaginable consequences of catastrophic, ocean sterilising, 100m sea level rising, horrible carbon cycle feedback global warming.

    So what? I am concerned that people and our collective civilisations also survive whatever may be in our near future.

  • At March 14, 2007 6:05 AM, Blogger pc said…

    Hi Coby,

    I don't see how I implied that water vapor was radiatively active and not CO2. Also, as regards timescales for self adjustment, we were talking about hypothetical massive disruptions. Reality dictates vastly smaller changes - we will never remove all water vapor or CO2! In any event, the multi-century timescales mentioned with regard to the carbon cycle refer to the time it takes for overturning and mixing - partial pressure effects are much faster.

    We can argue about many aspects related to climatology (such as rate of temperature increase & measurement statistics, etc.) but these issues tend to be far too complex for most people and to my mind tend to cloud judgment. As far as I can see there are only two primary issues in contention regarding GW.

    1. What is the primary driver?
    2. At what point does GW become catastrophic?

    The effect of the Sun, and the gradual increase of radiation/activity over the last century is not well understood. AGW advocates have discounted this as a factor, which is patently absurd. The Sun affects cloud formation and since water vapor is the most prolific greenhouse gas it seems likely that this effect is significant. I suspect that CO2 is made the scapegoat, partly because it's easier to apportion blame and partly because the Sun's effects are poorly understood.

    The second issue is far more emotive and the media have had a field day producing apocalyptic visions of the future. I'm afraid that many GW scientists are not entirely blameless here. In order to get attention, they have tweaked the models to show catastrophe. I remain unconvinced that even a few degree's rise in temperature will be so disastrous. Mass hysteria over this issue tends to bring much of the science into disrepute.

    I believe that conservation of resources and controlling or reducing pollution are important goals regardless of possible climate change but that the evangelical zeal with which this process is being tackled is extremely dangerous, not to mention costly. In the 1970's, when we were worried about global cooling, some climatologists seriously suggested covering the polar caps with soot in order to melt the ice! What a disaster that would have been. Today they are considering seeding the oceans with iron, or else fancy new bacteria/microbes in order to remove CO2 from the atmosphere.

    To me, this is the worst of all outcomes. We don't truly understand what's going on but we're going to meddle anyway, with possible real ecological disaster.

    Scientists have a duty to remain unbiased and to aggressively pursue all avenues until a general consensus is arrived at. This is not happening with GW.

  • At March 17, 2007 7:49 AM, Blogger coby said…

    Hi pc,

    Also, as regards timescales for self adjustment, we were talking about hypothetical massive disruptions. Reality dictates vastly smaller changes - we will never remove all water vapor or CO2! In any event, the multi-century timescales mentioned with regard to the carbon cycle refer to the time it takes for overturning and mixing - partial pressure effects are much faster.

    No, we will never remove all CO2 or H2O, but we will double the CO2. As this is a radiatively active gas and contributes somewhere between 9 and 30% of the earth's greenhouse effect it is ludicrous to suppose this will not have large consequences. Partial pressure effects only operate at the thin film where air meets water, with 0 mixing this would indeed reach an equilibrim immediately, though it would do so without removing very much CO2. The reality is that balancing of a perturbed carbon cycle can take centuries, there are even historical examples to examine, such as the PETM event.

    The effect of the Sun, and the gradual increase of radiation/activity over the last century is not well understood. AGW advocates have discounted this as a factor, which is patently absurd.

    It is only absurd if it is done without examination. Solar effects are not discouted without examination, in fact the IPCC attributes a significant percent of 20% century temperature change to solar changes. The effect of solar changes on cloud formation and the effects of clouds on the climate are both highly speculative. Ionisation of the air in cloud chambers does demonstrate increase formation of cloud condensation nuclei but it is not clear that in the actual atmosphere in the presence of natural CCN this effect will manifest itself in any significant changes. And even if you can demonstrate an effect on cloud cover, clouds have both a cooling and a warming effect, what will the balance be and how much will that net forcing be?

    Your comment about blaming CO2 because it is "easier" is ridiculous given the 100 history of GH theory and al the mountains of evidence we now have. No one just decided this would be the culprit, it is simply where all the evidence points and what one would expect from the theory.

    I agree that the second issue, at what point does climate change become a danger, is more difficult and I must accept your criticism that the mainstream media tends towards sensationalism. So let's not get our scientific information from them. But let's also not forget that the question about what to do about climate change is a question of risk management, so even a very small risk of hugely disasterous consequences must be taken seriously and I do not see how any sincere and diligent investigation of rapid climate change can rule out completely a number of truly catastrophic possibilities.

    Re: 70's, have a look at this article

    I share your aversion to geoengineering, it is hubris and folly on the ultimate scale. But this is in fact what we are undertaking accidentally by altering the chemistry of our planetary atmosphere.

    Scientists have a duty to remain unbiased and to aggressively pursue all avenues until a general consensus is arrived at. This is not happening with GW.

    See here.

    Thanks for the thoughtful comments and sory it took so long to get back here!

  • At April 08, 2007 2:20 AM, Blogger coby said…

    Hi David,

    Water vapour is a big part of the greenhouse effect, it is however not a factor in the causes of climate change. I don't know wht this is hard to understand.

    The abundant oceans ensure that at all times the air will have (roughly speaking) as much moisture as it can hold. Precipitation ensures that the air never retains any additional moisture that might be added by some external factor. Hence it is air temperature which controls the value of this greenhouse effect variable.

    CO2 on the other hand does not leave the air rapidly enough so any added to the atmosphere will remain long enough to alter the climate.

    Thanks for the comment.

  • At April 14, 2007 5:57 AM, Blogger Mike Patterson said…

    Short-term variations in solar energy input have caused climate change in the past and need to be included in any climate model. NASA data indicates the sun is delivering more energy to the earth. This may be the entire reason why the earth is warming. Cloud cover may increase as the earth becomes more humid and reduce the effect of increased solar energy. In any case, CO2 may be just tagging along for the ride with respect to having a significant affect on the temperature of the earth.
    Mike Patterson

  • At April 15, 2007 3:50 AM, Blogger coby said…

    Hi Mike,

    Solar variations are a part of every major climate model, certainly all of those referenced by the IPCC. The full extent of the early 20th century warming can not be explained without it. Yes, NASA data indicate insolation is at a 1000 year high, they however also indicate that there has been only very small changes the last century and no changes (aside from the 11 year cycles) over the last 30 years (since the onset of the satellite era). The observed warming can not be explained without the (fully expected) effects of anthropogenic CO2.

    There is no way that the CO2 rise we are experiencing is a natural response to a natural warming.

    Thanks for the comments.

  • At April 15, 2007 4:04 AM, Blogger coby said…

    Hi v1u1ent

    Thanks for the introduction to HAARP, I had never heard of it and it is intriguing (and tempting to entertain evil conspiracy theories about!)

    Dimming seems to be diminishing and it is certainly expected to diminish with improved anti-pollution technologies, it is however a hard problem and still not well measured. While north america has certainly mad improvements in its air, the notorious "Asian Brown Cloud" visible from space gives you and idea of how China and India are doing!

    Methane from cows and other human agricultural activities is indeed a factor, too.

    Do not worry about the quality of the IPCC document. While it is surely not perfect it is infact one of the most thouroughly reviewed scientific documents in history and your impression of defections is incorrect. I know of only one such person who left because of disagreements about hurrican intensity predictions and this was after the TAR report during preparation of the one not yet released. Many gov't science agencies have been tasked with reviewing the working group 1 report (the one about climate science) and not one has found it to be misrepresenting the stae of climate scinece today (check here for some detail).

    There are a couple of the usual sceptics (such as Richard Lindzen) who participated in the report, but though they may disagree with the projections of the future, they do not have any stated problems with the content or summary of the chapters they themselves worked on.

    Hope this helps, thanks for stopping by!

  • At April 17, 2007 5:53 PM, Blogger JamesB said…

    Let’s look at your statement Colby about CO2 levels. As you have quoted CO2 is responsible for between 9-30% of the greenhouse effect.
    That statement itself is justification for making no radical attempt at limiting CO2 until science gives us better data to work with. Now I could be wrong but from what I’ve read the greenhouse accounts for approx 32 degrees C increase in global temps. That means at the highest possible figure of CO2 effectiveness levels CO2 raises the temps by 9.6 degrees C. Now that’s total CO2 not man made CO2 which is quoted at around 5% of the total. With all things being equal man made CO2 accounts for approx .48 degree C of the greenhouse effect. That’s using the highest quoted effectiveness levels for CO2 (30%). Now double the man made CO2 levels while keeping all other levels constant and you get a temperature rise of still less than 1 degree C. If you double man made CO2 again you get a total temperature increase of slightly less the 2 degrees C or 1.92 degrees C. The above figures are for the highest CO2 effectiveness levels.
    It is unlikely that CO2 effectiveness is that high and the number is more likely somewhere in the middle of the quoted range or around 20%. At that effectiveness level man made CO2 accounts for only .32 degrees C. Double that and you get .64 degrees and double it again the figure is 1.28 degrees.
    Now I’m sure you have an answer for these figures but math rarely lies.
    Remember that these figures all assume all other factors remain constant
    which they of course never do. Another question is how do you explain the two periods in the last ten thousand years when temperatures were much warmer than today? Both events took place long before man made CO2 could possibly have any impact! The earliest the Holocene Max lasted over 3000 years with average temperatures as high as two degrees warmer than today. The quoted CO2 levels from ice core samples remained fairly constant through this period of ten thousand years yet we had two periods of much warmer temps. Another point is that during these warmer periods the temps rose fairly rapidly along the same curve as today. Now if man couldn’t possibly have caused these warming events
    they must be natural. If they were natural why do you believe the current warming trend isn’t?

  • At April 19, 2007 12:40 AM, Blogger coby said…

    "Now I’m sure you have an answer for these figures but math rarely lies."

    I do in fact have answers but I rather resent the implication that if I do I must be denying the consistency of mathmatics itself. This indicates to me you have your mind well made up and are not really interested.

    I will just make one observation and for the rest refer you to other articles on the site:

    "man made CO2 which is quoted at around 5% of the total"

    I don't know who you are quoting but the current CO2 concentration anomaly is 35% not 5 and it is entirely of anthropogenic origin. You may adjust your arithmetic accordingly, it changes your conclusion. Please keep in mind that though mathematics may not lie, it is easy to misunderstand its relationship to physical processes and draw faulty conclusions.

    Other articles you should read:

    Reread this one and understand what a feedback is vs what a forcing is.

  • At April 20, 2007 10:25 AM, Anonymous Anonymous said…

    Coby: "I don't know who you are quoting but the current CO2 concentration anomaly is 35% not 5 and it is entirely of anthropogenic origin"

    Entirely of anthopogenic origin??? What makes you think that?

    You are no doubt quite familiar with CO2 and temperature reconstructions that go back 100's of thousands of years. All of those temperature fluctuations were natural in origin, yet CO2 concentration still correlates with temperature.

    Why do you suppose that would be, given there were no factories to produce CO2 to raise the temperature of the Earth?

    The Earth has been warming from about 1850, and until around 1980, most of that warming was natural in origin. (Until around 1950, human generated CO2 was entirely negigible.) You raise the temperature of the atmosphere, that raises the temperature of the oceans, the CO2 solubility of the oceans decreases, and more CO2 goes into the atmosphere.

    In fact if you look at the numbers carefully, you'll find that roughly 1/2 of the CO2 "anomaly" is likelyh of natural origins.

    The "5%" is the amount of CO2 emitted into the atmosphere that is anthropogenic in origin, which is an entirely different measure.

  • At April 20, 2007 9:36 PM, Blogger coby said…

    Hi Carrick,

    Please check this article as to how we know the CO2 is anthropogenic, there are in fact many lines of evidence. Perhaps the strongest one is the isotopic signature of atmospheric CO2. Basically this shows us that the extra CO2 is composed of "old" carbon and "new" oxygen, that is to say it is clearly the product of fossil fuel combustion.

    re: 1/2 natural - No, if you look at the numbers carefully you find that we emit into the air 2x the amount that is showing up in the rising concentration. Most of the rest is going into the oceans which are showing a corresponding increase in acidity due to carbonic acid. So it is simply not possible that CO2 is coming out of the oceans (net, there is constant flux) and causing the observed 35% atmospheric increase.

    re: antarctic ice cores - References to the past are informative, but you can not eliminate a contemporary candidate for cause by simply noting it was not a candidate in the past. Comparing CO2 changes today with those in the ice cores is another reason to believe something very different is now at play:


    note both the scale and rapidity of the changes.

    CO2 forcing in the early 20th century was definately less, but it was not negligible. Here is a nice visual of the major components of climate forcing over time:


    Natural components of the warming ceased around 1950's not 1980's.

    Thanks for the thoughtful comments!

  • At April 21, 2007 7:29 AM, Anonymous Anonymous said…


    Let's start by looking at what the data say:the emissions data,

    The curve indicates an total anthropogenic CO2 emissions of around 240 trillions tons.

    From the orange curve, the CO2 levels changed from their so-called historical value of 280 to half of the current value today of 320 by 1975.

    During this period, anthropogenic CO2 emissions amounted to about 20% of the total CO2 emissions, yet the CO2 concentration levels increased by 50%. Pretty hard to reconcile those numbers as being entirely or even mostly huuman generated.

    A second line of evidence is that most of the warming from 1850 to 1980 (and as much as 1/3 of the warming since 1980) is associated with an increase in solar irradiance, and we know that there is correlation between CO2 and temperature, it seems pretty hard to argue that the temperature changes would not have generated more CO2 in the atmosphere.

    Regarding your discussion of acidification of the oceans, that line of reasoning is somewhat stretched, because you are looking at the change in pH of the surface layer, which overtime mixes with the subsurface layer. Thus the pH level of the ocean surface layer is not the same thing as the total CO2 dissolved by the oceans.

    One of the main reasons that the surface layer is increasing in acidity (or more accurately, becoming less alkaline) is because the current increase in the rate of human-generated CO2 is overwhelming the ocean's ability to absorb it. Sorry I don't have time to look up references, but I'm thinking of work by Inez Fung.

    By the way, if you compare models with data, they fail to do a satisfactory job in explaining the 0.4C temperature rise from 1905 to 1945. Also, it turns out that the difference in slope (change in temperature with year) for the 1975-current warming trend is statistically indistinguishable from the prior warming trend.

    That said, the main reason we think that the current warming trend is not natural is because the small increase in solar irradiance from 1975 to current is much less than from the first half of the century. This pretty clearly implicates human activity as a culprit in the most recent global warming trend.

    Regarding your ice core data, I'm certainly not arguing that the current CO2 levels don't have a dominant human contribution! I'm simply pointing out that we know historically that CO2 changes tend to follow and are positively correlated with natural temperature changes. That is an established fact.

  • At April 21, 2007 6:47 PM, Blogger coby said…

    Hi Carrick,

    I have no quarrel with your referenced graph and appreciate that you take the time to cite quality sources. However, I think you are misinterpreting, or maybe over-interpreting the two lines. First off, it would be useful to know what their data source is, what exactly it is including and when the dataset began vs when what it represents began. Secondly, let's not forget methane emissions, which this doesn't seem to include, and which breaks down into CO2 on a decadal timescale.

    There is a data set maintained by Crowley et al that gives total carbon emissions going back to the 1750. While I am sure it would not disagree with your graph it would augment our understanding of anthro emissions. The data is here which I found (my bookmark was stale) from this page with tons of other useful stuff.

    I am not sure I get how you arrived at this:

    "During this period, anthropogenic CO2 emissions amounted to about 20% of the total CO2 emissions"

    I suspect you may be forgetting that the emissions are cumulative, so even a flat blue line would go with a rising orange one.

    About solar attributions, the IPCC has solar forcing at about 50% of pre 1950 warming and the 2001 report (don't know about the latest) put the post 1970 solar at maybe 10% IIRC. I know there has been alot of research lately, but I believe that the Max Plank Institute's conclusions of no significant solar forcing trend since the 1950's is still the most well supported finding. Satellites have been monitoring things very closely now for 30 years and the trend (aside from the 11 yr cycle) is barely there, 2% or something similar. It is a complicated thing though as it is not purely a quantitative thing, solar irradiance, changes in relative frequency components also have different effects.

    I agree that acidification will be primarily in the surface layer, it takes many centuries for the ocean waters to overturn completely. This is also the layer that interacts with the atmosphere in the carbon cycle. BTW, this is another reason to eliminate oceanic CO2 outgassing from warming as a source of atmospheric changes, this (expected eventually) effect also takes centuries. That is one of the leading hypotheses for the mechanism at work in the glacial-interglacial temperature driven CO2 rise, the ~800yr lag is very similar to the ocean overturning timescale.

    Regarding model hindcasts, I think that the models do in fact handle the whole of the 20th quite well:

    Is this the comparison you were thinking of? If not, I am curious as to why you thought the models had trouble with the early 20th.

    Regardless, we seem to agree on the most recent warming being pronouned and anthropogenic, which I think is the more important conclusion. It is harder to reconstruct the past than observe the present, but harder still is predicting the future!

    Thanks again for the intelligent discussion.

  • At April 23, 2007 10:04 AM, Anonymous Anonymous said…

    Coby, my link is from ORNL, which I'll note your link tracks back to as well, so I would guess it is the same reconstruction. I don't have time to go back and check right now, I have the complete document that this figure was taken from lying around someplace. If I get a chance and don't get too distracted, I'll go back and post it.

    In terms of how I got the numbers, I integrated the rate of anthropogenic CO2 emission to measure the total CO2 emitted versus time, then compared it to the % change in concentration level. There are of course peer-reviewed articles that make the same general observation, but the point is obvious and reproducible for anybody who can compute areas under curves.

    Recognizing that the carbon cycle is very complex, so there are reasons that the simple comparison could be off (going either way of course), the chart suggests that only 20% of the total anthropogenic CO2 emissions occurred in the same period where 50% of the total change in atmospheric CO2 concentration were observed.

    I'm perfectly comfortable admitting that I'm no expert on the global carbon cycle, but I'm equally comfortable suggesting that the data on the face of it don't tend to support your contention that 100% of the CO2 rise is anthropogenic in origin.

    I have no doubt your original train of thought for your comment that I objected to was in opposition to natural sources like volcanos being a dominant source, a common red herring brought up by doubters. As I've said, of course I agree that most of the recent (post 1975) surge in CO2 is human in origin. The data are quite undeniable on that.

    Regarding the IPCC and reconstructed temperature, one of the games the IPCC played was to overlap various climate models to widen the suggested uncertainties for a given time period, but this fails to account for correlations in errors over time of individual models. If you dial a parameter to improve the temperature agreement in one decade it tends to push other decades farther out of agreement.

    Put a bit more succinctly, you need to compare the predictions of individual models, not an aggregate of the models. When you do, for example here, you find a 0.2 C disagreement between model and data for the period. Actually the same discrepancy is shown in the IPCC figure you linked, but the line thickness in their figure falsely suggests that this 0.2C is not very significant. Actually it's a pretty huge error, nearly 50% of the observed change from 1905 to 1945. Try plotting the difference between e.g. observations and any of the individual models (they don't like showing that for good reason) and you'll see what I mean. Although the models do a relatively good job in reproducing 1980-2000, they simply fail to give a good account of the 1905-1945 trend.

    Further, if you look at the blue curve (Canada model) you will see that tuning the model to improve the agreement for mid century has the effect of over estimating the global warming at the end of the century. That's an illustration of the correlated-errorrs point I was making earlier.

    Regarding this comment it takes many centuries for the ocean waters to overturn completely, I'd love to scrutinize your source on this. Now I will agree that it is generally accepted wisdom that the deep ocean currents turn over in the period of centuries, the upper ocean layers decades. But ocean surface layers take nowhere near centuries to turn over. I think the interval is measured in hours, not years.l Otherwise, the assumption of a "well-mixed layer," which has generally been established in the oceanic community as a valid assumption, would be completely false.

    That said, while the general explanation I've heard for the historical relationship between atmospheric CO2 and global mean temperature is from CO2 solubility, that probably is too slow a mechanism to explain the relatively rapid change in CO2 levels from 1850 to 1975. There are certainly other natural mechanisms besides the ocean CO2 reservoir, and certainly other natural feedback loops between temperature and CO2. Possibly one could write a popular book just on the global carbon cycle and especially the effect of the biosphere on it.

    If you compare the lead/lag of CO2 variations against temperature changes, you find there are nearly as many examples of CO2 variations leading the temperature changes as the opposite. As you know, on average CO2 lags temperature change by about 800 years (it varies depending on who does it, the correlation is rather broad and flat, so the number is pretty squirrelly), it is untrue to suggest that natural fluctuations in CO2 always follow temperature fluctuations.

    (Interestingly, most of the guys who make this claim never go beyond offset plotted images of CO2 fluctuations against reconstructed global mean temperatures. They are basically arguing from a subjective position, rather than a quantitative one.)

    Coby said: Regardless, we seem to agree on the most recent warming being pronouned and anthropogenic, which I think is the more important conclusion. It is harder to reconstruct the past than observe the present, but harder still is predicting the future!

    We are in total agreement on this part.

    My position is the following:

    1) the extent of past human interference with global climate is likely somewhat exaggerated, 2) the dangers of future human-induced climate change are greatly exaggerated (for example, I heard Ira Flatow a couple of weeks ago talking about the East coast being under water in 50 years---which is complete piffle), 3) the numerical global climate do a poor job of past reconstruction and are unlikely to be very reliable in predicting the consequences of future human activity.

    That said, this doesn't make it any less important for us to get our human generated CO2 emissions under control. If anything, less reliable climate models (especially in the details, like the critical question of the stability of the WAIS) actually make it more important that we reduce our CO2 emissions!

    I can't imagine a worse experiment than to be pumping enormous amounts of CO2 in the atmosphere, and really having no good way to predict how the Earth's climate will be affected. That is absolutely the worst example of a very poor uncontrolled experiment that I could possibly imagine.

    I just think some of the extreme exaggerations of the threat, such as from Al Gore's Inconvenient Truth, hurts our credibility when discussing this with the public. This is a point many other scientists agree with me on.

    Enjoyed discussing this with you!

  • At December 13, 2007 1:59 PM, Blogger Will Nitschke said…

    I've never heard of this particular objection among intelligent sceptics. (i.e., anyone who is worth debating and will have their minds changed by the evidence.)

    I have heard repeatedly the silly phrase, 'water vapour is the number one greenhouse gas' which is true for what it's worth, but it's not clear if this phrase is worth anything scientifically, for the good reasons you've pointed out.

    However, this may also be another 'straw man' argument for the reason that it doesn't appear to be a genuine objection from most intelligent sceptics. Of greater concern (whether true or not) is how well computer models can account for feedback effects in relation to cloud cover. And what overall significance this may or may not have as a negative feed back effect. I will look at the rest of your site to see if I can find anything on this particular topic...

  • At February 28, 2008 8:35 AM, Blogger barry said…

    Hi all,

    I've been debating this issue for about 6 months, and I won't festoon this post with links, because there aren't any I've found on the web that get to the kernel of the matter - radiative absoprtion - and certainly not broadly enough to satisfy.

    The way greenhouse gases retain heat is by absorbing, re-emitting, and reabsorbing and re-emitting infrared radiation welling up from the Earth's surface. If the GHGs weren't there, the infrared radiation would escape to space and we'd be living (or dead, rather) on a very cold planet.

    CO2 absorbs upwelling infrared radiation (IR) mainly (but not only) in the 15 micron wavelength range. But water vapour (WV) absorbs in many bands, and significantly part of the 15 micron band. If you looked at an absorption graph, you'd see a 'spike' for CO2 in the 15 micron range, and a 'slope' cutting across the 15+ micron range, being the WV absorption.

    15 micron absorption of IR by CO2 is practically saturated in the middle of the 15 micron range, but there is more absorption possible either side. Adding more CO2 'fattens' the spike - a bit like painting a wide black stripe across a window, adding more CO2 is like adding a fine line of paint either side of the wide stripe, which prevents more light (IR) passing through the window. WV's absorption profile laid over this would be like painting a diagonal stripe that cut across the original one. If the wavelength values are increasing to the right, WV would cover the whole right hand side of the window and slope across the original stripe. If you can picture this, that leaves mainly the left hand slope of the CO2 spike (very steep) available for absorption. Here is where most of the action is.

    In the actual atmosphere, WV fluctuates dramatically. In arid areas, over deserts and the poles, the WV absorption profile is less pronounced. The CO2 15 micron 'spike' stands out more, and therefore the absorption of IR by CO2 is more pronounced.

    At this point in the debate, honest skeptics want hard data from spectral absorption studies. There are hundreds, stretching back to the 1950s, when the US airforce began measuring the upper atmosphere for military purposes (thereby discovering that the atmosphere has many layers, and is not a single slab, as was thought until then). Early studies were ground based at high altitude, from weather balloons and high-flying aircraft. Satellites were later used for spectral analysis, measuring from the top of the atmosphere down, and perpendicular to the surface of the Earth at altitude. Time series studies exist showing a rise in CO2 levels, and changes in thermal activity. Here is some of the hard data honest skeptics are looking for - at this resolution.

    There is a database (HITRAN) that gives spectral absorption data for various gases. Like WV and CO2, there is some overlap in which gases absorb what wavelength of radiation. In Earth's atmosphere, there is a 'window' between the 8 and 12 micron band where there is virtually no absorption going on, and through which IR radiation passes out from the surface to space virtually unimpeded. Adding more CO2 impinges on this clear part of the spectrum, at the 12 micron end.

    However, the study is so complex, with instruments usually only capable of studying a few bandwidths at once, and the layers of the atmosphere needing to be taken into account, that you'd need to read a mountain of studies to get a whole picture. At Spencer Weart's website on the history of climate studies, he recommends that one would need to go to a library and read at least one fat book on atmospheric radiative transfer to get the kind of data and understanding needed to get a fix on the drill-down 'facts'. He also points out that much of the spectral analysis was done 40 years ago, and many of the studies have not been transferred to the internet. IOW, to get to the guts of this issue, at the resolution of radiative transfer and absorption profiles, including times series and under different humidities, is probably impossible via the web. Not to mention that most studies that are available cost money to view.

    There is a lot of pseudo-science on the topic. When a paper is cited, check the author's credentials. There are quite a number floating around written by (for example) neuroscientists (TJ Nelson), computer engineers (Petschauer), and experts in geomagnetics-regarding-military-weapons (Slade somebody-or-other, via the late John Daly's website).

    I guess I want to warn you that absolute resolution on this, if pursued honestly, rigorously and to the enth degree, will leave the querant unsatisfied if they restrict their travails to the web. And I thought I'd point this out to you, Coby, because it's well to acknowledge limitations when acting as a conduit for information.

    My take - I think it is unreasonable to think that mainstream climate theory is ignoring the role of water vapour in the atmosphere. I searched for the phrase (with the European/Australian spelling of 'vapuor') in the pdf files of the 2001 and 2007 IPCC reports. I got hundreds of hits, but the IPCC reports do not detail the spectral properties of WV and CO2 - that is too fine a resolution for the purposes of the report. For that information you not only have to go to the studies listed in the relevant chapters, but also the studies those studies reference, and the studies those studies reference and so on, and pretty much all of these are pay per view.

    You have to be extremely bloody dedicated, or slightly mad to get to the absolute bottom of this. I haven't made up my mind which category I fall in.

    Hope this post was useful, or at least, that I spare some sincere sojourner the hours of googling i went through. On the way, though, i learned a lot of vicarious arcana and useful stuff to understand what goes into the study of this particular subject.

    May good tidings and intellectual honesty make a home in your hearts and minds,


  • At February 28, 2008 9:02 AM, Blogger coby said…

    Thanks alot for all that Barry, and your other useful comments. I am planning to transfer the content of this site to my new ScienceBlogs home soon, otherwise I would be highlighting several of your contributions. Hopefully I will have time to update as well as transfer and can bring up some o your points then.


  • At May 23, 2008 1:06 PM, Anonymous Anonymous said…

    """This planet could never have survived millions of years without strong balancing negative feedback loops. It has survived asteroid strikes, axis shifts, periods of intense volcanic activity and periods with CO2 levels far higher than they are today.



    Poor reasoning. The actual planet is not put at risk by the climate but extant life can be put at risk. There were at least five major extinction events and evidence exists that at least some were caused by climate instabililty.

    You only need to look back 10k years to the ice age to know that many large mammal species went extinct. That has been repeated many times.

    Now, you might argue that biodiversity will eventually recover after a serious culling but that would occur on geological time scales and wouldnt do us much good.

  • At July 11, 2008 10:48 PM, Anonymous Anonymous said…

Post a Comment

<< Home