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Calculating the greenhouse effect

Filed under: — gavin @ 21 January 2006

In another forum (on a planet far, far away), the following quote recently came up:

….the combined effect of these greenhouse gases is to warm Earth’s atmosphere by about 33 ºC, from a chilly -18 ºC in their absence to a pleasant +15 ºC in their presence. 95% (31.35 ºC) of this warming is produced by water vapour, which is far and away the most important greenhouse gas. The other trace gases contribute 5% (1.65 ºC) of the greenhouse warming, amongst which carbon dioxide corresponds to 3.65% (1.19 ºC). The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere, the great majority of which is derived from natural sources. Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming, that is a temperature rise of 0.036 ºC. Put another way, 99.88% of the greenhouse effect has nothing to do with carbon dioxide emissions from human activity8.

We’ve discussed the magnitude of the greenhouse effect before, but it might be helpful to step through this ‘back-of-the-agenda’ calculation and see what the numbers really give. (Deltoid has also had a go at some of these mis-statements).

The quote comes from a lecture by an Australian climate ‘contrarian’ and frequent contributor to the southern hemisphere op-ed pages. Where did he get this from? One might assume that reference ’8′ was a scientific text, but one would assume wrong. It was in fact our old friend at Fox News, who may in turn have picked up his (junk)science from here. It is not clear whether this is the original source, but it’s close enough.

So, starting at the top:

  • “33 ºC” is the difference between the mean surface air temperature of the planet and the blackbody radiating temperature (i.e. the temperature a blackbody would need to radiate at to be in equilibrium with the incoming solar radiation given an albedo of about 0.3). So far so good. While that is one way to assess the strength of the basic greenhouse effect, another one is measure the amount of long wave radiation from the surface that is absorbed in the atmosphere (by greenhouse gases (incl. water vapour), clouds, aerosols, etc.). That is currently about 150 W/m2 and would be zero with no greenhouse effect at all.
  • “95% of this warming is caused by water vapour”. This is sourced to a couple of chaps who may have worked for Accu-Weather, but a) is misquoted – their ’90-95%’ is for both water vapour and clouds, and b) just wrong and c) irrelevant anyway.
    Dealing with b) first, if you remove all water vapour and clouds you still absorb about 34% of the long wave radiation, and conversely, if you only have water vapour and clouds you absorb 85% (calculations here). Thus the effect of water vapour and clouds is between 66 and 85% – the range being due to the spectral overlaps with the other absorbers. These calculations were done with the GISS GCM radiation code, which matches line-by-line codes to about 10% – but the numbers are very similar to Ramanathan and Coakley (1978), and so probably aren’t too far off what you would get with any decent radiation code. I’ll get to ‘c)’ below….
  • “The other trace gases contribute 5% … amongst which carbon dioxide corresponds to 3.65%”. That is just 100 minus 95% of course, but really it should be 15 to 34% – of which CO2 on its own is between 9 and 26% (op cit). If you were to naively estimate the total temperature contribution of the CO2 it would be between 3 and 9 ºC – but see below.
  • “The human-caused contribution corresponds to about 3% of the total carbon dioxide in the present atmosphere,”. This one is blatantly false and is erroneously credited to the US Dept. of Energy in the original source (their Table 1)! The ’3%’ number actually comes from comparing the human emissions with the gross emissions from natural sources while neglecting to consider the large natural sink. Because of the rapid cycling between the biosphere, the atmosphere and the upper ocean, that is an irrelevant comparison – kind of like comparing the interest on your bank account and your salary and expecting to be able to say something about your savings without thinking about your spending. The correct statement is that CO2 is around 30% higher than it was in the pre-industrial period, and all of that rise is due to human emissions (fossil fuel use and deforestation principally).
  • “Therefore, the probable effect of human-injected carbon dioxide is a miniscule 0.12% of the greenhouse warming”. That’s just 0.03*0.0365 of course – but even that is calculated wrong (it should be 0.11% by my calculator). But from our numbers, it would be between 3 and 8%.
  • “a temperature rise of 0.036 ºC”. More like 1-2.6 ºC actually, but although this gives numbers that are in the ballpark of the IPCC estimates (0.6 to 1.7 ºC warming for an increase of 30% in CO2 at equilibirum) this is not a sensible way to calculate climate sensitivty.

Why do I claim this is an irrelevant and not very sensible calculation? Firstly, it assumes linearity – all of the gases contributing according to their effects today when it is obvious that overlaps and saturation effects are large and important, and more importantly, it ignores feedbacks. The calculation above gives the impression that what you are calculating is the change of temperature that would result if you remove all the CO2. But since water vapour concentration is a feedback not a forcing, it can’t be assumed to remain constant as the planet cools. Water vapour does in fact change (roughly keeping relative humidity, as opposed to specific humidity, constant) and this has been shown in the real world as a function of volcanic cooling (Soden et al, 2002) and for longer term trends (Soden et al, 2005, discussed here), and is well reproduced in climate models.

What then is an appropriate calculation? Well, it’s simply the estimate of climate sensitivity for the present climate – how much would you expect the planet to warm if you doubled CO2? We’ve discussed this numerous times before, and in my opinion the best answer so far comes from looking at the difference between the last glacial period and the modern era – this gives a number around 3 +/- 1 ºC at doubling.

For the 30% rise in CO2 there has been so far, that would imply that would represent around 3% of the natural greenhouse effect – a good order of magnitude bigger than that suggested above. Of course, this is at equilibrium and not applicable to a transient change. If one takes into account the human-induced changes in the other GHGs (CH4, N2O, CFCs), you’d get something like double that. Given that even a 5 or 6 ºC cooling was associated with the huge ice sheets 20,000 years ago, and that 33 ºC cooling would reduce our planet to a near-snowball-like state, a potential increase of 5 to 6% of the natural greenhouse effect is not to be sniffed at… nor dismissed as irrelevent with highly misleading arithmetic.

One could make the point that my calculations are ‘just another web page’ no more and no less authoritative than the links above. In some sense that is correct (though I’d argue my sourcing is a little better!). But you will never find a peer-reviewed rebuttal of such a bizarre line of reasoning as we are dealing with here – basically because such a line of reasoning is highly unlikely to make it past peer-review itself. There are innumerable ‘proper’ references to estimates of the climate sensitivity though, and one should indeed hesitate to accept calculations like this example over the mass of peer reviewed studies.


240 Responses to “Calculating the greenhouse effect”

  1. 201
    Mikel Marinelarena says:

    I notice that some of the comments are a bit too confrontational. Indeed it makes me think that we’re not just talking science here, but ideology as well. Which of course is legitimate but not very helpful at all. In any case, Joel, I appreciate your spending your time to finally satisfy my curiosity and provide with an explanation for the contradiction I had observed. I do find this source pretty reliable, which is why I used it. Not only it showed what seemed to be recent data but it also included various independent measurements (I think that, in fact, we’re all using the same raw data, aren’t we?). The summary you so kindly provided clearly acknowledges and addresses the apparent contradiction and concludes that either physical fenomena exist that the models are not taking into account or tropospheric data need (still further) correction, or both. Quite short of the one-to-nil claim of William’s, I’d dare to say. Besides, I had been told above that the contradiction didn’t exist at all.

    Alastair: not only there are recent studies showing that the Greenland ice-cap is actually growing (but of course someone has hastened to show studies indicating the contrary: this is like a trenches war!) but apparently the same is happening in Antarctica, with an accompanying cooling over the continent included. As for the Arctic sea ice cover, it is becoming smaller in summer and then recovering to the usual dimensions in winter. I won’t bother digging for my sources here, as I’m sure someone will quickly find studies showing that the contrary is true. In any case, I’m sure you know that the Arctic sea ice cover poses no risk at all from the sea-level rise perspective, even if it were to melt completely (which, considering the tilt of the earth, would require a tremendous warming not still predicted by any serious study that I know of).

    Coby and Hanks: if the possibility existed of a net economic gain from shifting now from a source of energy to another, no regulations would be required at all. It would be happening before our very eyes, driven by the energy-producing companies themselves competing against each other (if allowed to). I think that my point can be illustrated rather easily. Let’s imagine, for simplicity, that what is now being proposed is that governments impose a 5% cut in GHG emissions on industry. Not so terrible, you seem to think. Ok, but what about imposing a 50% cut? Would that not make a huge amount of different industries simply shut down, not being able to cope with the cost of such a regulation? Would that not make energy tremendously more expensive? Would it not, in summary, bring about an economic catastrophe? So, if we agree on this obvious point, at what point does an emission cut of x% turn from a catastrophe to a major economic disruption and when does it become a hurdle that will ‘only’ generate less profits, less growth (and yes, unavoidably less employment)? I don’t think that the existence of a cost for any GHG emissions cut is something debatable. Of course, if governments tax the industries or the economies as a whole they can generate revenue with which to create new jobs, say in research or new technologies, but the net economic result will necessarily be negative until more efficient energy-producing technologies are discovered, for which no regulation was required in the first place. And this is so for at least 2 reasons: a) Governments can’t spend as much as they tax, because the very taxation procedure is a (bureaucratic) cost to be deducted from the revenue. b) More importantly, by altering the market prices through taxation the scarce resources will be allocated in an inefficient manner: if GHG-emitting industry is taxed $1 bn by the government, which in turn invests $1 bn in new technologies (and we already know that it will be less than $1 bn) the gains created in the 2nd process will not be enough to compensate for the losses created in the 1st process, for the same reason that if someone destroys the windows of your house the gain for the glaziers when you spend your money repairing them will not compensate for the losses you had to incur in, when you were actually planning to spend (or save) your money in better things.

    But of course, Western economies and big corporations will surely be able to cope with Kyoto-1, no questions about that. It’s just the most vulnerable who will bear the cost, as usual.

  2. 202

    #200 Alastair, I agree we must do what seems to be impossible, reducing CO2, but even harder would be to convince most people to act on it.. #201- Mikel, switching to Hydrogen would be extremely benificial to countries importing oil, making manufacturing of Hydrogen completely homegrown, it would fuel an unprecedented economic revival. for the US, imagine 20% Hydrogen industry, this would make an investment of $50 billion a year strictly in the US, from production to distribution, everything local…

  3. 203
    Don Baccus says:

    #201: “The summary you so kindly provided clearly acknowledges and addresses the apparent contradiction and concludes that either physical fenomena exist that the models are not taking into account or tropospheric data need (still further) correction, or both. Quite short of the one-to-nil claim of William’s, I’d dare to say. Besides, I had been told above that the contradiction didn’t exist at all.”

    Not at all. Christie and Spencer have had to correct their calculations more than once, after other people pointed out their errors and after they stubbornly defended those errors over a period of time. The satellite data now agrees with other data and model predictions within the error bars of uncertainty. And the people who’ve found past errors in C & S have run their own calculations that make the data correspond even closer to model predictions. Given the fact that C & S, when challenged over errors, have each time been proven wrong, they have little credibility left in my mind. When you make silly little errors like flip the sign of a numeric entity, you tend to lose credibility. Life’s like that.

    In short, the contradiction only existed in the sense that proofs that 1 = 0 exist – bad mathematics. The contradiction was based on errors in their analysis, in at least one instance a mathematically trivial and most embarrassing error.

    “Coby and Hanks: if the possibility existed of a net economic gain from shifting now from a source of energy to another, no regulations would be required at all. It would be happening before our very eyes”

    That’s naive economic thinking. That’s like saying “if it were possible to make money over a cheap, worldwide public computer network private industry would invent it”. Well, it was possible, and government, not private industry, invented it and private industry only took it up when legislation allowed for commercial entities to partake and sell services to consumers. Private industry for the most part wasn’t even asking to be part of it. They didn’t share the vision that a lot of money could be made off it. A decade later, an entire new Internet-based economic realm was borne and still grows today.

  4. 204
    Coby says:

    if the possibility existed of a net economic gain from shifting now from a source of energy to another, no regulations would be required at all. It would be happening before our very eyes, driven by the energy-producing companies themselves

    I’m sorry to be so dismissive about this, but it just strikes me as believing in fairy tales. The net economic gain, that I am claiming is just as likely as loss, from a major shift in energy usage also entails major shuffling around of industrial wealth. If you are an energy company in today’s paradigm making, oh let’s say $36.13 billion profits (not revenue) in a single year, why in the world would you be interested in risking your current market position in the least, even considering the fact that you are ideally positioned to dominate in the new paradigm? If you are an innovator with a new fantastic idea that will benefit the consumer but reduce the fossil fuel market, it is more likely that santa clause really exists than you will not meet with opposition from very powerful industry and political forces (oh, look! they are the same people!).

    Think for a moment about Los Angeles, the auto industry and the rail system. Why are millions of productive people hours spent alone in an empty car in traffic jams, why is the air so polluted by exhaust fumes, why is there no light rail public transit system? Because the auto industry bought the rails just to ensure no one could ever use them. That is free market at work. And that results in a loss of quality of life, loss of worker productivity, loss of resources dealing with the effects of pollution.

    Ok, but what about imposing a 50% cut? Would that not make a huge amount of different industries simply shut down, not being able to cope with the cost of such a regulation? Would that not make energy tremendously more expensive? Would it not, in summary, bring about an economic catastrophe?

    I know you followed this with “if we can agree on this obvious point” but I’m afraid I can’t. There are assumptions built into it that need closer scrutiny. For one thing, what time frame are we talking about? Perhaps on the short term some of what you describe would indeed occur (perhaps not) but I think on the long term things will adjust themselves.

    As leary as I am of the utility of such general handwaving as you use above, I am about to respond with the same. So the government imposes a 50% cut, it makes a huge difference and some industries shut down (I am accepting under protest that these industries do not adapt but rather quit). Well, didn’t these industries provide some good or service? Now according to free market principals the demand for these missing goods will skyrocket. So along comes an innovator and entrepreneur with a plan for an alternative or low energy way to provide for this demand and a new company is born. The new infrastructure that is suddenly in demand means more engineering and construction contracts, which demand more manufacturing, all these workers now have more spending money and the demand for luxury goods goes up etc etc.

    Presumably, government would impose these cuts via large taxes, and this would create financial resources that can then be diverted to help the innovators and the adapters, the dinosaurs die out, too bad that’s a) evolution and b) the necessary price for the health of planet and society.

    That strikes me as much more plausible than we all sit on our hands and weep because things are now different.

    Though I appreciate what you are saying, I don’t really find the rest of your post convincing. The bureaucracy is already in place, any additional administrative costs are going to be pennies compared to hundred dollar bills. Repairing the broken window is more economically productive than me saving my money and equally so for me spending it buying something else. (Mind you I don’t buy all the economic gibberish that makes that so, but that is the frame we are speaking within).

    But all these discussions aside, we have to deal with the question “is it necessary?” first. The interruption of that debate with maoning about how expensive it will be is the way a teenager decides what must be done. How hard is it? Oh, well I don’t really need it. That is not the rational way to deal with it. The economic cost of uncontrolled emissions will be huge even if an African is only worth a fraction of what an American is worth
    in the balance sheets of the World Bank.

    Where is that supposedly American “can do” attitude? “We have to drastically reduce CO2 emissions, now!” “Ok, let’s roll.”

  5. 205
    Mikel Marinelarena says:

    Re #203 Don: why is the US Climate Change Science Program still accepting C&S’s measurements? But still, we can leave them out, if that makes you more comfortable. I continue seeing a 5 to 1 measurements difference in favor of less warming in the lower troposphere than on the surface, according to the graphs published and commented by that institution (of course I am aware that what I’ve just typed would only be a preliminary assessment based on rudimentary arithmetic and subject to correction by a properly worded summary!!).

    Yeap, you can have a technology developed not by private but by public funded research, and then rapidly used by the private sector in order to make profits and satisfy our wants (the history of the internet, among others). So what?

    Re #204 Coby: if you’re not convinced by the arbitrary 50% figure I chose just put any other high enough. My reasoning holds equally well. As you said, this is not so important, I brought it up because I was reading that curbing CO2 emissions would have NO cost. So you can disagree from my economic views as much as you want, it doesn’t matter. Still, if you follow your reasoning to the end you’ll find that you’re basically proposing that we all smash the windows of our houses in order to create a buoyant glazier industry, which will indeed generate direct and indirect jobs, create demand for perhaps the goods we produce ourselves, develop brand new window-repairing technologies, etc…

  6. 206
    Hank Roberts says:

    > net economic gain … [worldwide Internet example]

    I can remember seeing projections made — in the 300-baud dialup days — by my local telephone provider, of profits anticipated from the increasing use of dialup modems and the popularity of “bulletin board” systems.

    They calculated the rate of increasing popularity, the total number of individual calls, local and long distance, and the connect time required at 300 baud, and projected a very nice profit from the development over the coming decade or two.

    Individual businesses handle technological change in local terms.

    > smash the windows … to create [economic benefits]

    This in fact counts toward the Gross National Product calculation. The more disasters, the higher the GNP.

  7. 207

    Re #202 by Mikel Marinelarena — Sir, you are assuming there are no costs to global warming. If there are, the loss from switching energy sources might conceivably be less than the loss from not doing so. Until you justify your assumption that staying with fossil fuels has no costs, your whole argument fails.

  8. 208
    Coby says:

    Still, if you follow your reasoning to the end you’ll find that you’re basically proposing that we all smash the windows of our houses in order to create a buoyant glazier industry, which will indeed generate direct and indirect jobs, create demand for perhaps the goods we produce ourselves, develop brand new window-repairing technologies, etc…

    Heh. If I may ensure we have stretched the analogy far beyond it own shattering point: my argument is that there is no way out of the house, we must smash the windows, others are worried about the economic damage caused by doing so. I let the rest of your description speak to my point!

    Cheers,

  9. 209
    Chris O'Neill says:

    Re #201

    “there are recent studies showing that the Greenland ice-cap is actually growing”

    The use of cherry-picked and carelessly interpreted statements like this is a common denialist technique. Of course the Greenland ice-cap is growing thicker where the temperature is well below freezing. This is what you’d expect in such places with warmer and consequently more humid air. The fact ignored by denialists is that Greenland is shrinking at the edges where you’d expect it to melt first. I guess all we can expect from denialists is to endlessly throw up cherry-picked and carelessly interpreted statements like the above.

  10. 210
    Steve Bloom says:

    Re #205: Mikel, I answered your concern about the CCSP report way back in comment 170. The language used by the authors is a bit elliptical and perhaps not obvious to someone who isn’t a native English speaker, but nonetheless it is clear. If the conclusions of the authors aren’t enough for you, I’m afraid you’ll have to read the entire report. I would be willing to discuss it more after that.

  11. 211
    PHEaston says:

    RE No. 209. “The use of cherry-picked and carelessly interpreted statements” is certainly not good argument. So you have taken one short phrase out of a 4-paragraph comment and attacked it, out-of-context with un-substantiated statements. Where are your references?(a request we so often hear to those who dare challenge the AGW case). Its this type of attitude that most damages the pro-AGW argument.

  12. 212
    Chris O'Neill says:

    Re #211

    The one short phrase stands on its own without context as you would see if you read the context. The study about the Greenland ice-cap was probably Recent Ice Sheet Growth in the Interior of Greenland which says

    “The averaged results indicate a net increase of 6.4 cm/year in the interior areas above 1500 m. Below 1500 m, the elevation-change rate is -2.0 cm/year, in qualitative agreement with reported thinning in the ice-sheet margins.” The summary implies that there is about 0.5 cm/year bedrock uplift. The summary concludes by saying

    “Modeling studies of the Greenland Ice Sheet mass balance under greenhouse global warming have shown that temperature increases up to about 3C lead to positive mass balance changes at high elevations (due to accumulation) and negative at low elevations (due to runoff exceeding accumulation), in agreement with these new observational results. However, after that threshold is reached, possibly already in the present century, losses from melting would exceed accumulation from increases in snowfall – then the meltdown of the Greenland Ice Sheet would be on.”

    You can also check http://news.bbc.co.uk/1/hi/sci/tech/4660938.stm which refers to “Arctic Climate Impact Assessment” published by the UK Government to see how the area of Greenland’s summer melt zone has increased. Click on the Greenland map. This reference had already been mentioned in #200.

  13. 213
    Coby says:

    PHEaston,

    I believe I provided the reference above showing Greenland losing ice mass:

    http://www.nasa.gov/vision/earth/lookingatearth/grace-20051220.html
    “In an update to findings published in the journal Geophysical Research Letters, a team led by Dr. Isabella Velicogna of the University of Colorado, Boulder, found that Greenland’s ice sheet decreased by 162 (plus or minus 22) cubic kilometers a year between 2002 and 2005. This is higher than all previously published estimates, and it represents a change of about 0.4 millimeters (.016 inches) per year to global sea level rise.”

    Which was a response to another poster simply “recalling” studies but providing no references. So I may be missing something, let me know, but so far I am not aware of any references being provided to support the notion that Greenland ice is showing ant net increases.

    As for context, the “4 paragraph comment” only dealt with Greenland in one paragraph, and comment #209 certainly presented enough to fairly characterize it so your attack is a little questionable.

  14. 214
    Dano says:

    Re: #211 [PHE]

    If I may,

    My comment here is your answer wrt Greenland [currently# 100]. In a nutshell: 1., 2., 3., 4. , 5., 6., 7. (the context for the issue).

    This is all, of course, common knowledge and we shouldn’t expect Mr O’Neill to have to provide atomistic detail for every statement, esp. for topics that we should all know; That is: if you don’t know this, then the highlighted statement in 209 is the crux of the competence of the arguer and its use is easily justified (not that I’m doing it, but I had the information you seek on my clipboard and the argumentation is so simple to interpret).

    HTH,

    D

  15. 215
    Ken Robinson says:

    Coby:

    Re: 195

    Of course I don’t know anything about the dynamics of ice sheets. I rather doubt that anyone here knows the first thing about the dynamics of ice sheets. That doesn’t preclude the application of simple common sense.

    The Greenland ice sheet’s thickness is measured in KILOMETERS. Scientists are debating its mass gain and loss in terms of CENTIMETERS, and the total mass balance still seems to be in debate. The reference I provided indicated that most models predict a GAIN in total mass under global warming scenarios for a considerable period into the future.

    But let’s set THAT reference aside, and take at face value the numbers in the reference you prefer, of a loss in ice mass of 162 cubic kilometers annually. Shocking. Alarming. Now let’s look at the size of the ice sheet in question. According to the Encyclopedia Brittanica;

    “The largest ice sheet, the Greenland Inland Ice, is second in area only to the Antarctic Ice Sheet. It extends about 1,570 miles from north to south and has a maximum width of some 600 miles and an average thickness of about 5,800 feet, reaching 11,000 feet in the middle of the island. It covers an area of more than 650,000 square miles, nearly 80 percent of Greenland, and is contained within a basin by the mountains around the margins.”

    If I’ve done my sums correctly, that’s a surface area of about 1.68 million square kilometers, with an average depth of about 1.77 kilometers. 1.68 million times 1.77 is just under 3 million cubic kilometers. That’s a lot of ice.

    One of the references Dano provides states that:

    “The Greenland ice sheet may disappear within about 1,000 years, raising Earth’s sea level by about 20 feet, and the glacial breakdown mechanisms being studied could speed that up considerably.”

    Coby, you say that one of the researchers you “recall” suggests a timeframe of a few centuries. But let’s not be too pessimistic, and let’s use a thousand years as a nice round number.

    Hmmm. To melt all that ice in the space of a thousand years would require a loss of 3 million km3 divided by 1000 years equals 3000 cubic kilometers per year. That’s a rate of loss 18 times greater than the loss cited in Coby’s reference (which is “higher than all previous estimates” and therefore more accurate I suppose. It’s contradicted by my reference, but so what).

    You say linear extrapolations are naove (although the loss rate cited in your reference seems to be a simple linear regression of the data, for all of three years). Fair enough. Let’s take the opposite approach. Explain to me please, how we’re going to go from losing 162 km3 to an AVERAGE of 3000 km3 annually. That’s one heck of a feedback loop. And keep in mind, Coby, that we’re not going to see 3000 km3 of ice loss anytime soon (ie not in the next year, or decade, or century). Therefore, logically there will have to be an even more vastly accelerated rate of loss in the future if we’re going to get rid of the entire ice sheet anytime before 3000 AD. What will cause such an exponential rise in the melt rate? Where are the data to support such a proposition? Perhaps we can find an expert in ice sheet dynamics who can explain it to us in detail…

    And by the way, according to a survey of Greenland’s temperatures published in the International Journal of Climatology (http://polarmet.mps.ohio-state.edu/jbox/pubs/Box_2002_Greenland_Temperature_Analysis.pdf) , the SUMMER mean temperature in the middle of Greenland (where the ice is thickest, averaging something like 3 km deep) is -14.9 degrees C. The annual mean temperature in this location is -29.7 degrees. Clearly, this ice will never melt. The only way to get the WHOLE sheet to melt is to move ALL the ice to the edges and melt it there. That’ll be a neat trick for an ice sheet “contained within a basin by the mountains around the margins”. Sure, parts of it can flow down to the coast. But ALL of it? Again, I would ask for help from an ice sheet dynamics expert in understanding how this will happen, since my amateur brain is incapable of developing a scenario to account for this…

    I’ll just mention in passing that the same survey of Greenland temperatures (almost all of which are coastal sites) did in fact find a significant warming trend over the 20th century. It appears that the majority of this warming occurred prior to 1940. In fact, some of the temperature increases back in the 1930′s must have been very alarming, since they match (or even exceed) today’s observed temperature increases in terms of rate and magnitude. It’s astonishing that civilization survived, really.

    But I digress…

    I know, I know. Glaciers will flow faster, and melt faster, and big chunks will come flying off. Well, maybe. But I haven’t seen any actual data, nor a plausible mechanism, in the literature, or the references provided to me, to indicate that 3 million cubic kilometers of ice will disappear in a thousand years. Or, as you “recall”, a few centuries.

    I’m not saying some ice won’t melt. I’m not saying that big chunks won’t come off. I’m simply saying that the vast bulk of the Greenland Ice Sheet is going to be around for a long, long, long time. Go ahead; call me naive some more.

    Cheers.

  16. 216

    About the Greenland ice cap:

    The retreat of the ice cap in Greenland is mainly at the edges and is directly coupled with summer temperatures around Greenland. Most of the ice cap in the centre is too high and doesn’t get melting temperatures, not even in summer. As temperatures get higher, the increased humidity also increases snowfall (as is also the case in Norway, where glaciers are growing).

    Of more interest is to have a look at the history of Greenland glacier retreat and temperatures. All Greenland stations are at the edges, as the inland ice is uninhabitable.
    From the largest Greenland glacier in Ilulisat (Jacobshavn) the breakup point (where the glacier breaks into icebergs) is known since 1850. The move of the breakup point to more inland is probably the direct result of warmer temperatures.
    The move of the breakup point started already before 1850 and was fastest in the period 1929-1953, before GHGs had much of their influence. Moreover, the Greenland temperatures after 2000 just reach the temperatures seen in the 1930-1940′s, with a cooler climate in between (which seems to be connected to the NAO)…
    As the breakup point moves, the counterpressure/resistance reduces and the glacier is moving faster. I suppose that is the case for all Greenland glaciers now.

    It seems to me that the NAO has more influence on the Greenland glacier melting than general global climate, and that GHGs played a minor role, based on the long retreat of the glacier and the fact that the melting was faster in the 1930-1940′s.

  17. 217
    Chris O'Neill says:

    Re #215

    “the SUMMER mean temperature in the middle of Greenland (where the ice is thickest, averaging something like 3 km deep) is -14.9 degrees C. The annual mean temperature in this location is -29.7 degrees. Clearly, this ice will never melt.”

    I’m not a glaciologist but I do know some things about Greenland that make the above a brave assumption. The middle of Greenland has about 3km of ice and it is also about 3km high. As you might guess, this means the bedrock is not very far from sea level and in fact a lot of it is below sea level. Without the ice Greenland would be like a large lake surrounded by land most of which is fairly high. So even though the ice in the middle may never melt as long as it stays 3km high, it’s a different story if for any reason that ice was reduced to a lower altitude, say 1.5km. It’s interesting to see that some research has shown that if the ice was removed from Greenland, it would not re-establish the ice-cap at current or pre-industrial temperatures. So the ice-cap on Greenland is a bi-stable or hysteresis process and thus there is some critical temperature above which the ice-cap will proceed to disappear. No-one knows what this temperature is but James Hansen offered the guess that it is probably at least 2 degrees C. This say nothing about how long such melting takes. It’s hard to say because melting is such a non-linear process. One other thing James Hansen said was that the ice-cap melting process rapidly accelerated as it proceeded, so it is very slow to begin with and very fast towards the end.

  18. 218

    Re #217:

    According to different models, the increase of sea levels due to melting Arctic icefields/glaciers is between 0-6 cm for this century. See Oerlemans ea.. But that is based on a constant increase of GHGs/temperatures. In the case of the Greenland ice cap, that is far from settled. For the mean yearly average temperature trends (of the edges), the 2000+ temperatures hardly reach the 1930-1950 trends, but the more important summer (June-July-August) temperatures still seems to be below the 1930-1950 level. See the until 2005 updated Greenland temperature trends.

  19. 219
    Ken Robinson says:

    Re 217

    Chris, thanks for the note. Maybe I’m just dense today but I’m having difficulty following what you’re saying. You say “So even though the ice in the middle may never melt as long as it stays 3km high, it’s a different story if for any reason that ice was reduced to a lower altitude, say 1.5km.” How could this happen without melting 1.5 km of ice? This seems to me to be a prodigious thing in itself. Also, you mention something about a temperature of 2 deg C after which the cap will begin to melt. By this, do you mean an average annual mean temp of 2 degrees in the middle of Greenland, or a summer mean temp of 2 degrees, or an increase of 2 degrees in one of these means? Would you mind clarifying your points for me?

    Incidentally, by “this ice will never melt”, I mean within this millenium. And for a long time afterward, I expect.

    Thanks;

  20. 220
    Chris O'Neill says:

    Re #219 and #217

    Losing the first half of the ice from Greenland would be relatively slow because initially most of the ice loss has to involve glacier transportation down to the ablation zone but as the ice becomes lower the size of the ablation zone becomes larger and the rate of ice loss becomes larger. If the central plateau gets down to 1.5km then nearly the whole lot may be in the ablation zone so it would melt many times faster than it could now. So even though the first half might take hundreds of years to melt, the last half is likely to melt in a small fraction of the first half’s time.

    By 2 degrees C, I meant 2 degrees of warming from pre-existing temperatures to cause Greenland ice-cap melting. You can read what Hansen has to say in http://pubs.giss.nasa.gov/docs/2003/2003_Hansen.pdf page 30. On checking it, I notice Hansen actually says 1 degree and that others have said 2 degrees.

    Regarding the warming that has actually occured in Greenland in the last hundred years, regional effects could have the same magnitude as global average warming in the last 60 years (0.5 degrees C). As long as these are not negatively correlated to any level of global warming, it is not likely that Greenland will escape most of the future global warming which will most likely be a lot more than we’ve already had (0.8 degrees C since 1920).

    [Response: The '2 C' number being talked about is from the pre-industrial (not present-day), and Hansen is talking about a further 1 C - not too different. -gavin]

  21. 221
    Mikel Marinelarena says:

    Re #160 Dr Connolley: I’ve just realized that you commented this post of mine. When I said that “I am in no position to discuss your or Wikipedia’s assertions” what I meant was that I am obviously too ignorant to engage in a discussion with you over the issues at stake. I may dare to judge some “sceptic” scientists’ opinions reasonable but I have the utmost respect for scientists working in such complex areas as GCMs and devoting their efforts to better understand climate. Perhaps it was unnecessary from your side to reply that I was talking “nonsense”. Whatever makes a prestigious scientist misinterpret and overreact to a candid comment by a well-meaning observer?

    As for the links you requested, here is one: http://www.tcsdaily.com/article.aspx?id=042505C

  22. 222
    Mikel Marinelarena says:

    If I may summarize again my personal conclusions on this whole debate:

    1) CO2 is a trace gas in the atmosphere, measurable only in parts per million. However the observed 30% increase in its concentration can produce, ceteris paribus, a modest warming of the average temperature on the surface of the earth. This warming is estimated by Gavin Schmidt at almost 1 oC.

    2) According to the very Wikipedia article William pointed to, the AGW theory predicts a warming of the lower troposphere by a factor of about 1.3 over that of the surface. This has not been observed by any satellite or radiosonde, even after the correction of some detected measurement errors. The surface temperature increase of the last 3 decades itself is at the very low end of the AGW predictions, reaching about 0.187 oC/ decade. Prior to that, it was actually decreasing.

    3) Michaels (http://www.tcsdaily.com/article.aspx?id=042505C), Lindzen, Balliunas and many other climate scientists interpret that the AGW theory predicted a larger warming of BOTH polar regions than the global average, which is also not being observed on the South Pole (in spite of the constant bombardment in the media about a “melting Antarctica” as prove of AGW being real). Gavin and Eric (http://www.realclimate.org/index.php?p=18) and Cecilia Bitz (http://www.realclimate.org/index.php?p=234) contend that, in fact, the polar amplification does not apply to the SH and their models never predicted it. Gavin asserts that “we fully expect Antarctica to warm up in the future” while Cecilia Bitz does not think that we should expect to see any significant warming in Antarctica until the 2nd half of this century. I am not convinced either way here. What does the AGW theory exactly predict as regards polar amplification for the various GHG concentration scenarios? What DID it predict in the past? It shouldn’t be difficult to find out who is right on this one.

    4) Prof. Jon Jenkins expressed some interesting criticism in this thread on the AGW theory. His scepticism about how GCMs are being used (shared by many scientists inside and outside climate research) is of particular importance to me. As long as the time-honored Scientific Method is not abandoned (observation -> formulation of a theory -> quantitative predictions -> independent empiric validation), the capability of computers to manipulate data can be very useful. But computer models cannot be used to make predictions and also to validate theories. The latter would fall outside the Scientific Method. Until predictions are empirically validated anything produced by a GCM will be nothing better than predictions based on a given theory or set of theories.

    5) Many AGW adherents seem to believe in some sort of “Oil Industry -> libertarian politicians -> don’t know what -> conspiracy” and in their ability to prevent the development of cheaper ways of producing energy not only in the US, but apparently anywhere else in the world. I don’t feel that any amount of reasoning would make them change their mind. But I do hope that the amount of scientists working in climate research and sharing such views is negligible.

    Finally, the AGW theory may well be right, which we should be able to find out sooner rather than later (in another thread on this same website I see some scientists already debate on the best ways to tweak the earth’s thermostat!! http://www.realclimate.org/index.php?p=246#comment-8227) but in the meantime some sceptic opinions seem well founded. Dismissing or ridiculing them does not add much credibility to the AGW theory.

  23. 223
    Chris O'Neill says:

    Re #222 2)

    “According to the very Wikipedia article William pointed to, the AGW theory predicts a warming of the lower troposphere by a factor of about 1.3 over that of the surface.”

    Where in http://en.wikipedia.org/wiki/Satellite_temperature_measurements does it mention a factor of 1.3?

    In spite of the conclusion “This has not been observed by any satellite or radiosonde, even after the correction of some detected measurement errors”, the wikipedia page actually says “Climate models predict that the troposphere should warm faster than the surface, so all but the Spencer and Christy version of the satellite record are compatible with this and the surface records.”

  24. 224
    Steve Bloom says:

    Re #221: Mikel, if you scroll through all of the comments you’ll find that “my side” corrected you multiple times on your misinterpretation of the CCSP report, but somehow the point never seemed to sink in. To respond as you have by linking to Pat Michaels, who promotes on the linked page his recent book “Meltdown: The Predictable Distortion of Global Warming by Scientists, Politicians, and the Media” is not only unpersuasive but peculiar. Part of the reason I directed you to Steve Schneider’s page on contrarians was so that you could figure out who some of those people are and not waste your (or our) time with their stuff. (Had you looked, BTW, you would have found out that Pat’s activities are funded by the coal industry.) Instead, you responded to my suggestion by tossing out an irrelevant (and incorrect) ad hom about Steve Schneider. This seemed less than constructive on your part.

  25. 225
    Mikel Marinelarena says:

    Re #223 Chris: click on the graph and read below. In fact, I didn’t have a clue what the exact difference between surface and lower troposphere temperature ought to be until William provided his Wiki link and, following his suggestion, read it thoroughly. BTW, One surprising thing I noticed is that the exact radiosonde measurements are absent from that Wiki article. My link from the CCSP does include them: http://www.climatescience.gov/Library/sap/sap1-1/public-review-draft/sap1-1prd-exsumfigs.pdf. Check them and judge by yourself.

  26. 226
    Mikel Marinelarena says:

    Re #224: Steve: I never addressed the CCSP report so I can hardly have misinterpreted it. If you want your point to finally sink in I suggest you describe specifically how I am misinterpreting the analysis of the lower troposphere and surface measurements the CCSP publishes in the link I provided, see comment above.

    I agree that ad-hominems should rather be left out of the debate. Pat Michaels has never made any secret of his wanting to continue benefiting from the achievements that the American economic system and the technological society have brought about. He does belong to groups endorsing those agendas. Why are some people so uneasy about that? I thought that it was worth while pointing out that Schneider had previously endorsed Global Cooling because the very existence of such a recent AGC scare endorsed by the same activists and some scientists is a KEY reason to understand why many people are sceptical about AGW now. If you think that I am making false statements against Schneider please check this webpage and correct not me, but his author, William Connolley: http://www.wmconnolley.org.uk/sci/iceage/ponte.html

  27. 227
    Joel Shore says:

    Re #222 point 5: As I explained to you before, it does not take any sort of “conspiracy theory” in the common usage of the term to suspect that scientists have various biases and that there will be a few scientists who will particularly stubbornly stick to their beliefs for whatever reasons, thus providing fuel for libertarian think-tanks and the fossil fuel industry (who most of these scientists seem to have some close association with). This sort of thing has in fact been true time and again on other issues, whether it be depletion of the ozone layer or the dangers of smoking (and in fact, some of the same characters have even been involved)!

    What constitutes a true conspiracy theory is believing that the mainstream scientific consensus as reflected by the IPCC, National Academy of Sciences (of the U.S. and similar bodies in many other countries), the councils of the AGU and the APS, etc. can all be hijacked by a political agenda, as many deniers of global warming suggest.

    This is why it is important in climate change, or any other issue, to listen mainly to what is being said by the peer-reviewed scientific community as a whole and not simply to cherry-pick the viewpoints of a few scientists who hold the viewpoint that one happens to favor. Doing this is a recipe for disastrous policymaking, as the current U.S. administration amply demonstrates.

  28. 228
    Steve Bloom says:

    Re #226 (MM): The CCSP report describes the entire history of the various data sets. That is *not* the same thing as saying they are all valid. As noted, the authors state that any remaining discrepancies are far more likely to be remaining errors in the data than in the model predictions, which is a polite way of saying that S+C’s stuff is likely still somewhat wrong (and noting that Christie himself signed on to that statement). Let me know if there’s anything else that’s unclear about this.

    The Schneider quote you refer to does not endorse global cooling. Rather, he endorses the idea that the public should be educated about the potential for substantial instability in the climate. The scientific basis for the claims in the book are somewhat spurious, much more so in retrospect, and William’s comment is essentially that it’s too bad that Schneider’s quote could be *misinterpreted* to endorse the specific claims made by the book. The full quote is:

    “The dramatic importance of climate changes to the worlds future has been dangerously underestimated by many, often because we have been lulled by modern technology into thinking we have conquered nature. But this well-written book points out in clear language that the climatic threat could be as awesome as any we might face, and that massive world-wide actions to hedge against that threat deserve immediate consideration. At a minimum, public awareness of the possibilities must commence, and Lowell Ponte’s provocative work is a good place to start.”

  29. 229
    Hank Roberts says:

    And remember to suspect hidden funding. Decades went by before journals reported on how science was being manipulated by the tobacco industry. Money corrupts.

    http://www.ajph.org/cgi/content/abstract/96/1/20
    http://tc.bmjjournals.com/cgi/content/full/14/4/217
    http://tobacco.health.usyd.edu.au/site/supersite/contact/pdfs/jech_drope.pdf

  30. 230
    Mikel Marinelarena says:

    As it turns out, if you click on the History tab of the Wikipedia article William sent us to: http://en.wikipedia.org/wiki/Satellite_temperature_measurements the leading contributor, if not the author, is himself! He’s actually one of Wikipedia’s administrators, having authored pretty much everything having to do with climate change on that website. I really think that he should have clarified this when he mentioned that article. I’m not very impressed.

    [Response: Nor am I: you have nothing at all to say on the content, just reporting the easily-observed fact that I wrote some of it. Come back when you can find something actually wrong with it - William]

    Re #228 Steve, we’re talking semantics here (again,…) Alright then, let’s put that Schneider’s endorsement of Ponte’s infamous book was not a specially ringing one. Everybody happy now?

    As for the CCSP link I provided http://www.climatescience.gov/Library/sap/sap1-1/public-review-draft/sap1-1prd-exsumfigs.pdf I see that you continue refusing to address it and refer me again to the CCSP summary. You have 8 comparisons between surface and lower troposphere temperatures and all of them but one show a smaller warming of the troposphere than the surface. How do you personally reconcile this with the summary you once and again cite?

    All of this ties in with two of Lindzen’s criticisms of the IPCC. A) Its summaries don’t summarize very well the real consensus among scientists and B) when data are found that do not validate predictions the immediate reaction is to try and correct those data, rather than correcting the theories they challenge. Shouldn’t we all feel very happy if eventually we found out that the world is not really going to warm as we so much feared???

    [Response:A) is nonsense. B) If you're talking about the satellite record again, you need to stop scratching this itch, and face the obvious: that those suspicious of the satellite record from S+C turned out to be right; and the S+C data wrong - William]

  31. 231
    Mikel Marinelarena says:
    [Response: Nor am I: you have nothing at all to say on the content, just reporting the easily-observed fact that I wrote some of it. Come back when you can find something actually wrong with it - William]

    [Response:A) is nonsense. B) If you're talking about the satellite record again, you need to stop scratching this itch, and face the obvious: that those suspicious of the satellite record from S+C turned out to be right; and the S+C data wrong - William]

    Dr Connolley,

    Nothing further away from my intentions than engaging in one of those never-ending rows I have found you get entangled in at Wikipedia, where a certain amount of verbal abuse also seems to be present.

    So I will not come back if I’m not welcome on this website but just for the record, in my search to find out whether there is any substance in the sceptic scientists’ contentions, I have pointed out 2 concrete issues on your Wikipedia article: 1) Even after correcting S+C’s measurements, the 1.3 larger warming of the lower troposphere is not validated by available MSU data. 2) Radiosonde measurements are absent from that article. I have found a CCSP webpage where they are accounted for and the discrepancy is even more obvious: the troposphere warming is actually lower, not greater.

    Hard though I’ve tried, I haven’t managed to get any explanation for these apparent inconsistencies. I’ve only been referred once and again to the expert’s summaries or to C+S’s admittance of their having committed some errors, which does nothing but reinforce my suspicion that Lindzen might be right in his above-mentioned criticisms.

    Unlike you, I have no itches to scratch. Whatever happens to the AGW theory, I will continue to be a happy man. Only I’d really hate to see the natural landscapes I so much love change abruptly by AGW, hence my interest in the subject. Speaking of which, you are welcome to come back to the Pyrennees when you so please. We are enjoying one of the best ski seasons ever, due to the unusually cold winter.

    [Response: S+C are not the only analysis of the MSU data. RSS and Vinnikov et al (2006) have alternate analyses of the same raw data, both of which give significantly more warming in the tropopshere than S+C. Thus there is uncertainty in the satellite results. Over the 25 years of the record, climate models show significant variability in tropical tropospheric temperatures - the mean ratio over all models and all ensemble members is indeed 1.3, but the value in any particular realisation (of which the real world is just one of course) varies (as you have seen in the CCSP figures). The range of ratios in the models and the range of estimates from the different satellite analyses overlap - which implies there is no longer an inconsistency between them. Prior to the last set of corrections to S+C, there was. There is no longer. Please read the two posts on the subject from last year (here and here), and better still read the Santer et al (2005) and Sherwood et al (2005) papers in Science for more information. -gavin]

    [Response:1) Gavin has done this 2) did you read past the first para? - William]

  32. 232
    Joel Shore says:

    Re #231: Since William didn’t say it explicitly, note that the 2nd of the two RC articles that he linked to deals with the issue of the radiosonde measurements.

    Also, I have to admit that I am a bit skeptical about your claim of having “no itches to scratch” by which I presume you mean no biases. I think your posts have made it quite clear (to me at any rate) that your views on economics issues mean that you have strong feelings about policies like the Kyoto Protocol and, therefore, that you might have strong feelings in regards to the science that provides the evidence that we have to seriously reduce our greenhouse gas emissions. I am not denigrating you for having such a bias but I think it may be a bit disingenious to claim to have none.

  33. 233
    Mikel Marinelarena says:

    That’s alright Gavin. But following your rationale, the wider the range of ratios in the model outputs, i.e. the more inconsistent they are with each other (or the larger the discrepancies between different observation analyses) the more overlapping there will be and thus both will be “compatible”. One can even envisage one situation where, as long as the average of the former shows AGW, the AGW theory/ies can remain unchecked, pretty much regardless of what actual observations show. I’d rather see models showing consistent predictions and these being validated by the best available historic data. In the meantime, you should tolerate some scepticism. You see, some of us remember the global cooling scare (among so many others) or the NASA “long term weather predictions”.

    Re#232 Being an economist, I can’t help having my views on certain economic issues, can I? However, I very much doubt you value a naturally stable climate more than I do. The problem I see, as an economist, is that, regardless of my personal priorities, people like my children or the less disadvantaged will also have to pay for the pricey climate insurance policy that is being implemented.

  34. 234
    Coby says:

    There was no “global cooling scare” coming from the scientific community that even remotely resembles the warnings and consenus that exist now about AGW. I’m sure you are familiar with all the links that demonstrate this. Here are a couple again:
    http://www.realclimate.org/index.php?p=94
    http://www.wmconnolley.org.uk/sci/iceage/

    Do tell what you have in mind when you slip in “(among others)” given that the one concrete example you have is bogus.

  35. 235
    Hank Roberts says:

    Are there any climate models that give results consistent with what the current ‘skeptics’ say are the facts?

    Is there a model somewhere that shows this global cooling risk as a real thing and includes assumptions about things so it comes out that the global temperature will stay approximately the same if we burn all the carbon at the present rate, by offsetting some other force?

    It seems odd that there’s no Coal Industry Climate Model, or something along those lines. I’d think they’d have one or several to show.

  36. 236

    #216 Ferdinand, I gather you may add that the “edges” of the Greenland ice sheet not only melts in the summer but gathers a certain temprature by being immersed during the long night air having certain temperatures. Lets say that the dark season average temperature sutrrounding Greenland at 1000 meters has increased by 10 C, (a practical number now a days), that would mean 2 things: 1- summer warm air contact conduction would require less heat to gather a further melt, and 2, the very chemistry of high pressure ice probably changes in the long run if its core temperature is warmer. So, this saying that top of the ice sheet average summer temperature of -14.5 C misses the mark, and does not explain the real causation of Greenland’s greater ice shedding.

    Through my experience with optical effects, mirages, on top of hills or mountains having differing temperatures with the air, I can literally see such dynamics. For instance a hill immersed in -40 C weather for 3 weeks, creates a great show
    of mirages when warmer air envelopes it, creating illusions, not so known like horizon lines, where a complete horizon beyond the other side of the hill from the observer is minituarized in a fine line less than 1′ of arc thickness. What this mirage means is that the hill is significantly colder than the air, and retains such temperatures properties for significant periods of time. Conduction is a very significant process with Greenlland ice likewise, and warmer air, still well below zero degrees C, plays a significant role. Even exacerbated by recent shortage of multi year ice of the Arctic ocean, there is perhaps a greater feedback effect caused by warmer air than previously thought, and the difficult focus. research, over great ice sheet dynamics must be accelerated.

  37. 237
    Coby says:

    Another factor I wonder about: I think I have read that the temperature at the bottom of the Antarctic ice is only a few degrees below zero due to geothermal heat and an insulating effect of the ice between the much colder surface air and the ground. How much does the surface need to warm before the geothermal heat will melt the ice from the bottom (if at all possible)?

    I don’t know if the situation is the same in Greenland, though I don’t know why it shouldn’t be…(thinner ice?)

  38. 238

    #237, Coby good point, rather all the above, there are some ice walls 100′s of meters high, always soaking what heat made available, its becoming clearer how North Americas massive 2 mile high pan continental ice sheet disappeared during the last glaciation period.

  39. 239

    [...] and temperature, while the human influence on the greenhouse effect is a “small” 1% (a highly dubious figure). But as discussed earlier, the prevailing view is that it’s ultimately temperature [...]

  40. 240

    [...] and temperature, while the human influence on the greenhouse effect is a “small” 1% (a highly dubious figure). But as discussed earlier, the prevailing view is that it’s ultimately temperature [...]


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