RealClimate logo


Back to the future

Filed under: — gavin @ 30 April 2008 - (Español)

A few weeks ago I was at a meeting in Cambridge that discussed how (or whether) paleo-climate information can reduce the known uncertainties in future climate simulations.

The uncertainties in the impacts of rising greenhouse gases on multiple systems are significant: the potential impact on ENSO or the overturning circulation in the North Atlantic, probable feedbacks on atmospheric composition (CO2, CH4, N2O, aerosols), the predictability of decadal climate change, global climate sensitivity itself, and perhaps most importantly, what will happen to ice sheets and regional rainfall in a warming climate.

The reason why paleo-climate information may be key in these cases is because all of these climate components have changed in the past. If we can understand why and how those changes occurred then, that might inform our projections of changes in the future. Unfortunately, the simplest use of the record – just going back to a point that had similar conditions to what we expect for the future – doesn’t work very well because there are no good analogs for the perturbations we are making. The world has never before seen such a rapid rise in greenhouse gases with the present-day configuration of the continents and with large amounts of polar ice. So more sophisticated approaches must be developed and this meeting was devoted to examining them.

The first point that can be made is a simple one. If something happened in the past, that means it’s possible! Thus evidence for past climate changes in ENSO, ice sheets and the carbon cycle (for instance) demonstrate quite clearly that these systems are indeed sensitive to external changes. Therefore, assuming that they can’t change in the future would be foolish. This is basic, but not really useful in a practical sense.

All future projections rely on models of some sort. Dominant in the climate issue are the large scale ocean-atmosphere GCMs that were discussed extensively in the latest IPCC report, but other kinds of simpler or more specialised or more conceptual models can also be used. The reason those other models are still useful is that the GCMs are not complete. That is, they do not contain all the possible interactions that we know from the paleo record and modern observations can occur. This is a second point – interactions seen in the record, say between carbon dioxide levels or dust amounts and Milankovitch forcing imply that there are mechanisms that connect them. Those mechanisms may be only imperfectly known, but the paleo-record does highlight the need to quantify these mechanisms for models to be more complete.

The third point, and possibly the most important, is that the paleo-record is useful for model evaluation. All episodes in climate history (in principle) should allow us to quantify how good the models are and how appropriate are our hypotheses for climate change in the past. It’s vital to note the connection though – models embody much data and assumptions about how climate works, but for their climate to change you need a hypothesis – like a change in the Earth’s orbit, or volcanic activity, or solar changes etc. Comparing model simulations to observational data is then a test of the two factors together. Even if the hypothesis is that a change is due to intrinsic variability, a simulation of a model to look for the magnitude of intrinsic changes (possibly due to multiple steady states or similar) is still a test both of the model and the hypothesis. If the test fails, it shows that one or other elements (or both) must be lacking or that the data may be incomplete or mis-interpreted. If it passes, then we a have a self-consistent explanation of the observed change that may, however, not be unique (but it’s a good start!).

But what is the relevance of these tests? What can a successful model of the impacts of a change in the North Atlantic overturning circulation or a shift in the Earth’s orbit really do for future projections? This is where most of the attention is being directed. The key unknown is whether the skill of a model on a paleo-climate question is correlated to the magnitude of change in a scenario. If there is no correlation – i.e. the projections of the models that do well on the paleo-climate test span the same range as the models that did badly, then nothing much has been gained. If however, one could show that the models that did best, for instance at mid-Holocene rainfall changes, systematically gave a different projection, for instance, of greater changes in the Indian Monsoon under increasing GHGs, then we would have reason to weight the different model projections to come up with a revised assessment. Similarly, if an ice sheet model can’t match the rapid melt seen during the deglaciation, then its credibility in projecting future melt rates would/should be lessened.

Unfortunately apart from a few coordinated experiments for the last glacial period and the mid-Holocene (i.e. PMIP) with models that don’t necessarily overlap with those in the AR4 archive, this database of model results and tests just doesn’t exist. Of course, individual models have looked at many various paleo-climate events ranging from the Little Ice Age to the Cretaceous, but this serves mainly as an advance scouting party to determine the lay of the land rather than a full road map. Thus we are faced with two problems – we do not yet know which paleo-climate events are likely to be most useful (though everyone has their ideas), and we do not have the databases that allow you to match the paleo simulations with the future projections.

In looking at the paleo record for useful model tests, there are two classes of problems: what happened at a specific time, or what the response is to a specific forcing or event. The first requires a full description of the different forcings at one time, the second a collection of data over many time periods associated with one forcing. An example of the first approach would be the last glacial maximum where the changes in orbit, greenhouse gases, dust, ice sheets and vegetation (at least) all need to be included. The second class is typified by looking for the response to volcanoes by lumping together all the years after big eruptions. Similar approaches could be developed in the first class for the mid-Pliocene, the 8.2 kyr event, the Eemian (last inter-glacial), early Holocene, the deglaciation, the early Eocene, the PETM, the Little Ice Age etc. and for the second class, orbital forcing, solar forcing, Dansgaard-Oeschger events, Heinrich events etc.

But there is still one element lacking. For most of these cases, our knowledge of changes at these times is fragmentary, spread over dozens to hundreds of papers and subject to multiple interpretations. In short, it’s a mess. The missing element is the work required to pull all of that together and produce a synthesis that can be easily compared to the models. That this synthesis is only rarely done underlines the difficulties involved. To be sure there are good examples – CLIMAP (and its recent update, MARGO) for the LGM ocean temperatures, the vegetation and precipitation databases for the mid-Holocene at PMIP, the spatially resolved temperature patterns over the last few hundred years from multiple proxies, etc. Each of these have been used very successfully in model-data comparisons and have been hugely influential inside and outside the paleo-community.

It may seem odd that this kind of study is not undertaken more often, but there are reasons. Most fundamentally it is because the tools and techniques required for doing good synthesis work are not the same as those for making measurements or for developing models. It could in fact be described as a new kind of science (though in essence it is not new at all) requiring, perhaps, a new kind of scientist. One who is at ease in dealing with the disparate sources of paleo-data and aware of the problems, and yet conscious of what is needed (and why) by modellers. Or additionally modellers who understand what the proxy data depends on and who can build that into the models themselves making for more direct model-data comparisons.

Should the paleo-community therefore increase the emphasis on synthesis and allocate more funds and positions accordingly? This is often a contentious issue since whenever people discuss the need for work to be done to integrate existing information, some will question whether the primacy of new data gathering is being threatened. This meeting was no exception. However, I am convinced that this debate isn’t the zero sum game implied by the argument. On the contrary, synthesising the information from a highly technical field and making it useful for others outside is a fundamental part of increasing respect for the field as a whole and actually increases the size of the pot available in the long term. Yet the lack of appropriately skilled people who can gain the respect of the data gatherers and deliver the ‘value added’ products to the modellers remains a serious obstacle.

Despite the problems and the undoubted challenges in bringing paleo-data/model comparisons up to a new level, it was heartening to see these issues tackled head on. The desire to turn throwaway lines in grant applications into real science was actually quite inspiring – so much so that I should probably stop writing blog posts and get on with it.

The above condensed version of the meeting is heavily influenced by conversations and talks there, particularly with Peter Huybers, Paul Valdes, Eric Wolff and Sandy Harrison among others.


523 Responses to “Back to the future”

  1. 101
    Martin Vermeer says:

    Ike Solem #100:

    The primary goal is just “creation of the appearance of scientific uncertainty.”

    The best response to this is just to go back to the original topic of the post, which is a lot more interesting than PR efforts (those are handled over at desmogblog).

    I agree Ike. But that isn’t always easy. Consider also new visitors to this site without much background in the science, the most vulnerable ones.

    I admire the way the scientists running this blog sometimes jump in. I admire how they keep their calm — apparently that comes with confidently, both deeply and broadly, knowing your stuff, which distinguishes them from us amateurs. But they cannot be everywhere.

    One technique I have found useful is to feed the troll until he burps up a real blooper, something that even an interested amateur can be made to appreciate the absurdity of, and then jump for the kill. But, unfortunately you have to do that again and again on every new thread where it happens.

    And then there was this wretched female concern troll that professed taking a pity in poor gusbobb… fancy that :-(

  2. 102
    Hank Roberts says:

    Let’s not assume the little colored pixels convey gender accurately.
    We might be visited by a boy named Sue any time and not know it.

  3. 103
    Jim Cross says:

    Regarding models and ENSO, about a year ago I read an article dating from 2001 that intrigued me.

    An Orbitally Driven Tropical Source for Abrupt Climate Change by
    AMY C. CLEMENT, MARK A. CANE, AND RICHARD SEAGER

    “Results from a tropical coupled ocean–atmosphere model show that, under certain orbital configurations of the past, variability associated with El Nino–Southern Oscillation (ENSO) physics can abruptly lock to the seasonal cycle for several centuries, producing a mean sea surface temperature (SST) change in the tropical Pacific that resembles a La Nina.”

    Oddly enough, we appear to very near just such an orbital configuration at this time.

    Gavin stated that current GCM don’t attempt to factor variations to ENSO; however, if the climate locked into either a semi-permanent La Nina (or El Nino), I’m guessing the current models would be drastically off.

  4. 104
    Ron Taylor says:

    Guys, can’t you visualize three or four college students gathered around a computer, laughing uproariously each time they provoke a serious response to their childish provocations? It looks that way to me. I do think there comes a time when the moderators can legitimately put a stop to it under the comments policy. I get so much from RC that it really bothers me when anyone so obviously plays games with it and the good will of the scientists here, and others who are seriously seeking the truth.

  5. 105
    Hank Roberts says:

    > certain orbital configurations of the past …
    > Oddly enough, we appear to very near just such
    > an orbital configuration at this time.

    Citation, please, for this claim? Yes, I did read the abstract and those of the citing papers available to me. I don’t see a basis to say “we appear to very near” (presumably ‘very near to’?)

  6. 106
    gusbobb says:

    I am amazed that people have turned my personal scientific uncertainty into some conspiracy or prank or threat to be dealt with in what looks like a call for me to be deleted. Unless I agree with the mainstream opinion or pledge myself to adopt it, I get demonized. Maybe I just always believed in challenging authority but that’s the only way I come to my personal understanding. And from the get go I have fuly witnessed but not understood why what Martin refers to as the tactic of “undermining my credibility” as the best way to educate me and others.

    I am now reading Part 2 of saturated gassy article and and will have challenges to some assumptions. Think what you may of me, but that is the only way I gain understanding and test my beliefs.

    Chris says :You can see that the 2008 atmospheric [CO2] is well above the previous annual peak.

    So counter-arguments to your speculation are unnecessary since your speculation is based on a false assumption.

    http://www.esrl.noaa.gov/gmd/ccgg/trends/

    Well Chris that last red data point must have jut been added in the last few days because it was not there a week ago. I see it now says May 08, so I suspect that is the case. True the new data point undermines the need for my question.

  7. 107

    gusbobb writes:

    If we assume for a moment that CO2 is a result of temperature change instead of a driver of temperature change,

    In a natural deglaciation, the temperature rises first, then CO2, and the increase in CO2 amplifies the increase in temperature since the greenhouse effect increases. It’s a feedback, not one-way causality.

    That is not what is happening now. CO2 has led temperature for the past 150 years. That’s because we’re producing it artificially and pumping it into the air in vast quantities.

  8. 108
    Jim Cross says:

    Re: #105

    Sorry, pasting the link didn’t work very well. The comment about “orbital configuration” relates to the article cited, which you readily google.

    “The paleoclimate record shows that the pacing of abrupt climate change could be linked to the solar forcing. Heinrich (1988) found that episodes of major ice rafting in the North Atlantic recur on an 11-kyr timescale over the last glacial at times of boreal winter and summer insolation maxima, as in the results shown here. Bond et al. (1999) show that the timing between the ice rafting events decreases as the earth moves into full glacial conditions, but that earlier in the glacial, these detrital events occur on a roughly 11-kyr timescale (G. Bond 2000, personal communication). Our results raise the possibility that the YD is the return to these orbitally paced events once the influence of the ice sheets is diminished.”

    And finally, this is what I was referring to:

    “We note that the modern ENSO (zero forcing) is close to the transition period during which abrupt ENSO shutdowns can occur, suggesting that currently ENSO may be fairly sensitive to external forcing.”

  9. 109
    Jim Eager says:

    Gusbobb wrote: “Well Chris that last red data point must have jut been added in the last few days because it was not there a week ago. I see it now says May 08, so I suspect that is the case. True the new data point undermines the need for my question.”

    It never should have even come up in the first place since the 2008 data is incomplete.

    First it was the graphs of 2008 temperature anomalies, then it was the extent of this winter’s Arctic ice cover, now it’s the CO2 data.

    One has a hard time assuming those who don’t know how to read a graph know much about what they base their arguments on.

  10. 110
    Ray Ladbury says:

    Off topic, but appropos of keeping on topic:
    In the absence of a technological mechanism for viewing only on-topic responses, perhaps one solution would be to direct questions of an elementart/general/tutorial nature to a single thread. The Start Here thread could serve the purpose, although it would become a rather long thread. One could pretty quickly sort out the sincerely confused from the trolls/nutjobs by seeing which ones were willing to conform to the policy after a single suggestion. Indeed, on some forums, an inappropriate entry is cross referenced and redirected to the appropriate thread.
    Personally, I think that Realclimate fulfills many valuable roles. One of these is as a place where lay people can come for an accurate reflection of the science. I’d sure rather they come here than a whole lot of other places. Still, I recognize the need to avoid hijacking a thread, and I am aware that trolls thrive on the anonymity of the Internet.

  11. 111
    Ike Solem says:

    Ah – no conspiracy, gusbob, just an awareness of standard public relations behavior in the modern age, as well as the knowledge that the American Petroleum Institute gave $100 million to Edelman PR services, an avid fan of using online bloggers to get their client’s messages out to the public. People who are genuinely interested in the science don’t repeat standard fossil fuel lobby talking points ad naseum, and college students would probably not be trying to cause dissension on global warming science blogs for kicks – just a guess, there.

    In any case, is there any disagreement over the basic fact that CO2 levels are currently rising some 30 times faster than ever seen in the Antarctic ice cores?

    As far as the lead time, that’s been explained over and over – a little warming leads to a little CO2 increase leads to a little more warming leads to a little more CO2 increase – and we still have quite a bit of carbon locked up in the frozen permafrost.

    It’s like a match. Friction causes combustion of the chemicals in the matchhead, and so we say that friction is the cause, just as we say that Milankovitch cycles are the cause of the glacial cycles of the past few million years.

    Regarding the article that Jim Cross cites, most of the paragraph he quoted from was omitted:

    The model used in this study is highly idealized (see Clement et al. 1999 for further discussion). More complete models are needed to test the infuence of additional processes on the mechanism proposed here. We note that the modern ENSO (zero forcing) is close to the transition period during which abrupt ENSO shut downs can occur, suggesting that currently ENSO may be fairly sensitive to external forcing. Further investigation into the link between abrupt climate changes and orbital forcing of the past, both from a modeling and observational perspective, is clearly important for understanding the nature of abrupt climate change, and also for evaluating the possible future behavior of ENSO.

    Global warming models have a notoriously hard time handling El Nino, particularly the timing, so just because a model run created a “seasonal lock” – well, that means very little, but is interesting. However, Jim Cross’s comments are really a very large distortion of the paper, which has to do with this:

    These studies suggest ways in which the climate in the North Atlantic region can change in response to a La Nina-like SST change at the time of the YD. (the Younger Dryas cold period, some 12,000 years ago)

    .

  12. 112

    Re #85 Gusbob,

    As a moderate skeptic myself (I am pretty sure that more CO2 increases temperature somewhat, but at/below the low side of current GCM’s projections), I have compiled a web page here where is explained that humans indeed are the cause of the recent increase in CO2. Temperature plays a role in month-by-month variability of the increase speed, but hardly in the total increase.

    Based on ice cores (Vostok, Law Dome), the CO2/temperature ratio was about 8 ppmv/°C for long-term (hundreds to thousands of years) changes. Based on the 1992 Pinatubo cooling and 1998 El Niño warming, the short-term variation is about 3 ppmv/°C. Thus temperature can’t have caused more than about 10 ppmv of the total 100 ppmv increase since the start of the industrial revolution…

    All:
    This is about the one-way influence of temperature on CO2 levels, that doesn’t say anything about the influence of CO2 on temperature. If we may believe climate models, the influence is somewhere between 1.5-4.5 °C/2xCO2, or a factor 3 between minimum and maximum effect. But there is little empirical evidence from the past for any of these figures, as in most cases there was an overlap between (leading) temperature and (lagging) CO2 level. With one exception: the end of the Eemian, the previous interglacial. A drop of 40 ppmv CO2 had no influence on temperature or ice sheet growth within the measurement error margins… That doesn’t prove that there was no influence at all, but it points to an influence towards the low side of (or below) the range.

  13. 113

    Re #106 gusbobb:

    … my personal scientific uncertainty …

    Didn’t sound much like uncertainty the first time I heard it… RC is an invaluable, and important, learning resource for those willing to learn. A stubborn unwillingness to look things up combined with a loud mouth degrades the learning experience for everyone else. Yes, that is evil. No, I don’t believe you’re getting a penny from Exxon Mobil. There’s enough private crankiness to go round.

    I am now reading Part 2 of saturated gassy article…

    Good for you! There’s more out there.

    Well Chris that last red data point must have jut been added in the last few days because it was not there a week ago. I see it now says May 08, so I suspect that is the case. True the new data point undermines the need for my question.

    No it doesn’t. Your suspicion was invalid to start with. The new data point just rubs it in.

    Question (no trick question): do you understand why? Once you do, there’s a lot you have learned about the dangers of looking at short pieces of noisy time series. And about the need for statistical significance before jumping to conclusions.

  14. 114
    Geoff Wexler says:

    (Elementary,educational and off topic of lead article)

    As everyone here knows there are different kinds of skepticism ranging from honest questioning to the propagandist and misinforming , and from the naive to the sophisticated. It is sometimes hard to distinguish between a source and a sink of misinformation. Only the latter is interested in learning.

    One quite effective ploy used by the sources of ‘middle level’ misinformation is to offer only a binary choice. According to this view either all or none of the recent warming must have been anthropogenic. You must choose between absolute certainty and complete rejection of the anthropogenic theory.

    Only slightly more subtle, is the discussion which has confused some people is based on the ice core evidence. The discussions on Realclimate have not always been sufficient to remove the doubts which some people have. They are unfamiliar with feedback loops and suspect a fiddle. I think the difficulty here is that it looks like an example of a real binary choice , either CO2 leads or it lags the temperature changes and each has a definite causal interpretation. How do you encourage people to count beyond 2?

    Here is my explanation to these doubters for what is worth; it involves nothing new; just more words and perhaps an extra step and graph. There was more than one cause of the warming during the thaw so the simple choice breaks down. Since the temperature rise is the sum of at least two terms T(greenhouse) and e.g. T(Milankovitch) which behave differently, the simple before and after dichotomy is over-simplified.

    It can longer be said that ‘the temperature’ leads the CO2, only part of the temperature. Whereas the second of these ,the direct term, leads the CO2 change, the first (feedback) term lags the CO2, but only very slightly on this time scale. The feedback term is zero or weak at first, but then grows with time, as it warms up, until it dominates, when the lag becomes invisible on the graph. Temperature and CO2 changes become almost coincident. This version may still be over-simplified but it partially fills in a gap in Al Gore’s film which has been higlighted everywhere especially in the popular blogs in the newspapers.

  15. 115
    Hank Roberts says:

    Martin’s right in #113, Gus, and it’s not a trick question. It may be a chore to understand, but it’s needed so the charts will be understandable. And you’ll start recognizing a lot of the PR talking points, which often use exactly that lack of understanding. “Warming stopped …” is one of those.

  16. 116
    pat n says:

    re #95

    The question about CO2 having peaked after peaks in global warming may
    be explained by having had multiple bursts in methane that were less
    frequent as CO2 accumulation slowed.

    Also note: … Last year alone global levels of atmospheric carbon dioxide, the primary driver of global climate change, increased by 0.6 percent, or 19 billion tons. Additionally methane rose by 27 million tons after nearly a decade with little or no increase. …

    http://www.sciencedaily.com/releases/2008/04/080423181652.htm

    Also, see latest CO2 measured at Mauna Loa:

    http://www.esrl.noaa.gov/gmd/ccgg/trends/

  17. 117
    gusbobb says:

    From A Saturated Gassy Argument “As it moves up layer by layer through the atmosphere, some is stopped in each layer. To be specific: a molecule of carbon dioxide, water vapor or some other greenhouse gas absorbs a bit of energy from the radiation. The molecule may radiate the energy back out again in a random direction. Or it may transfer the energy into velocity in collisions with other air molecules, so that the layer of air where it sits gets warmer. The layer of air radiates some of the energy it has absorbed back toward the ground, and some upwards to higher layers. As you go higher, the atmosphere gets thinner and colder. Eventually the energy reaches a layer so thin that radiation can escape into space.”

    I don’t see that what I said is any different,” #80 CO2 doesn’t trap heat like Al Gore [edit] portrayed in inconvenient Truth. CO2 delays re-radiation back into space.”

    And I understand that when CO2 absorbs a photon that energy will be transformed into an increased kinetic energy. But for how long? (and why the edit of my 2-word description of the cartoon characters???)

    Camping in Death Valley one feels how quickly the day’s heat escapes. One way to quantify the time delay for heat escaping would be a comparison of changes in average temperatures at 4 AM local time vs other average day time or 24 hour temperatures. The change in daytime temperatures are confounded by the sun’s input. If the release of heat is just delayed by CO2 we should see very little change in the average annual temperatures as time intervals approach 4 AM local time. . If the heat is truly trapped we would see the 4 AM average temperature mirror the average daily temperature. Are there studies of the temperature change at various times, after sunset, etc?

    From A Saturated Gassy Argument “Moreover, researchers had become acutely aware of how very dry the air gets at upper altitudes — indeed the stratosphere has scarcely any water vapor at all. By contrast, CO2 is well mixed all through the atmosphere, so as you look higher it becomes relatively more significant.”

    I am curious about this generalization. On top of Mt. Whitney, (14000 ft) you can see cirrus clouds overhead and heavy breathing reminds you that you atmospheric density has dropped by close to 50%. Also CO2 is more dense than other major atmospeheric components. I thought that despite being a well mixed gas, that CO2 concentrations get lower the higher the altitude in addition to the lower density. The condensation of water vapor into clouds suggests it increases the density of the water. So within the cloud layer I would expect water vapor to have increased in importance vs CO2. The cloud layers may be as high as 12 km. Once above the cloud layer, the density of CO2 would be so small, I would not expect these upper CO2 layers to detain much radiation.

    My other questions are once a molecule of CO2 absorbs a particular wavelength it will radiate the energy out randomly but at lower frequencies. What percentage of these re-emitted frequencies can then be absorbed by CO2? That would lead me to suspect that absorbance at ground level by CO2 would be most efficient and then the layers of CO2 above would miss most of the re-emitted photons from below.

    If some one could clear this up, it will help my continued reading and understanding.

  18. 118
    gusbobb says:

    # Ferdinand Engelbeen Says: As a moderate skeptic myself (I am pretty sure that more CO2 increases temperature somewhat, but at/below the low side of current GCM’s projections), I have compiled a web page here where is explained that humans indeed are the cause of the recent increase in CO2. Temperature plays a role in month-by-month variability of the increase speed, but hardly in the total increase.

    That is my position as well. I see CO2 has added to the average temperature but smaller amounts than argued. And I have no doubts that humans are responsible for the recent increase in CO2 concentrations. I just believe the role of the sun is not properly valued.

  19. 119

    Re #116 Patn (and #95 Lynn):

    Methane was following temperature with far less lag than CO2 in the past (as seen in ice cores). And is near flat in current levels since about 1998. The 2007 increase (probably caused by a warmer Arctic) is hardly significant in the graph:

    http://www.esrl.noaa.gov/gmd/ccgg/iadv/

  20. 120
    catman306 says:

    Off topic:

    Conservative talk radio host Neil Boortz asks this question:

    Even if the climate is warming, is that a bad thing? What IS the ideal temperature for the earth?

    Don’t worry, I know the answer. But I fear that many of his listeners do not. Perhaps someone could help with their education.

  21. 121
    Jim Eager says:

    Re Gusbob @ 117: “Camping in Death Valley one feels how quickly the day’s heat escapes.”

    And why? Because there is less water vapour in the air column above a desert.

    “If the heat is truly trapped we would see the 4 AM average temperature mirror the average daily temperature. Are there studies of the temperature change at various times, after sunset, etc?”

    Why do you think regular posters here answer questions and provide links if you don’t bother to read them?

    Yes, night time temperatures have increased in correlation with the rise in daytime temperatures.

    “I thought that despite being a well mixed gas, that CO2 concentrations get lower the higher the altitude in addition to the lower density. The condensation of water vapor into clouds suggests it increases the density of the water.”

    No, it suggests a very real drop in both temperature and pressure with altitude, both of which reduce the amount of water vapour that can exist, so it condenses into water droplets and freezes into ice crystals. CO2 does not condense in Earth atmosphere.

    “Once above the cloud layer, the density of CO2 would be so small, I would not expect these upper CO2 layers to detain much radiation.”

    You would be wrong.

    “My other questions are once a molecule of CO2 absorbs a particular wavelength it will radiate the energy out randomly but at lower frequencies.”

    No, the same wavelength.

    “What percentage of these re-emitted frequencies can then be absorbed by CO2?”

    Therefore potentially all of it.

  22. 122
    Martin Vermeer says:

    Re #117 gusbobb: here some answers that are within my knowledge.

    If the release of heat is just delayed by CO2 we should see very little change in the average annual temperatures as time intervals approach 4 AM local time. . If the heat is truly trapped we would see the 4 AM average temperature mirror the average daily temperature. Are there studies of the temperature change at various times, after sunset, etc?

    Actually the IPCC report contains language on the DTR, or Diurnal Temperature Range. It says

    “• A decrease in diurnal temperature range (DTR) was reported in the TAR, but the data available then extended
    only from 1950 to 1993. Updated observations reveal that DTR has not changed from 1979 to 2004 as both
    day- and night-time temperature have risen at about the same rate. The trends are highly variable from one
    region to another. {3.2}

    So the answer appears “yes”. We do see trapping.

    I am curious about this generalization. On top of Mt. Whitney, (14000 ft) you can see cirrus clouds overhead and heavy breathing reminds you that you atmospheric density has dropped by close to 50%.

    Yes… but those are clouds made up of ice crystals. There is very little water vapour up there, and what little there is, can be made to freeze out very easily: the low temperature means that the saturation water vapour pressure is also very low.

    Also CO2 is more dense than other major atmospeheric components. I thought that despite being a well mixed gas, that CO2 concentrations get lower the higher the altitude in addition to the lower density.

    No, that would only happen if the atmosphere were stagnant — and even then, very very slowly. The real atmosphere is well mixed by currents, both horizontal and vertical. I found it surprisingly difficult to find a Web reference on this, apparently because it is self-evident. But look at this for how well mixed the atmosphere is in the horizontal direction. There are graphs for stations at different latitudes. The annual “ripple” is due to vegetation on the Northern hemisphere.

    Closer to the ground, to vegetation and urban areas, you will find greater variations in CO2 concentration.

    The condensation of water vapor into clouds suggests it increases the density of the water. So within the cloud layer I would expect water vapor to have increased in importance vs CO2.

    Within the cloud, relative humidity will be close to 100%. Never more. The cloud itself is liquid water in the form of droplets. Note that the higher up you go, the less the concentration of water vapour is that corresponds to 100% relative humidity.

    The cloud layers may be as high as 12 km.

    Yes, but at those heights you will get those wispy cirrus clouds made of ice crystals. And at those low temperatures they may even form from air containing only minute traces of water vapour.

    My other questions are once a molecule of CO2 absorbs a particular wavelength it will radiate the energy out randomly but at lower frequencies.

    No… don’t look at individual molecules, that’s not fruitful. They collide and exchange energy with other molecules all the time. According to Kirchhoff-Bunsen, an air parcel will radiate at the same frequencies that it absorbs on. So, in frequency ranges where CO2 is opaque to radiation, the heat will slowly migrate upward by emission-absorption-emission as in the Saturated Gassy Argument description.

    Also, it is not fruitful to look at the effect of greenhouse gases as a temporal (delay) effect. Rather it is a spatial (barrier) effect. Consider that the heat has to be transported from the Earth surface to the “edge of space” where it may be radiated out. The latter always occurs at the Stefan-Boltzmann equilibrium temperature of 255K. In order to transport the heat, whether this happens radiatively (as described above) or convectively (along the so-called adiabatic lapse rate, some -5C/km of height), you need a temperature gradient to drive the heat transport. For the adiabatic lapse rate, the “edge of space” being at 6 km, you find that you need a temperature difference of 30C, making the Earth surface temperature 255+30K=285K. This is the natural greenhouse effect.

    Now add CO2. The “edge of space” will push upward as air gets more opaque, and the surface will get warmer.

    It’s like adding blankets to the bed you’re sleeping in. A heat camera on the outside would observe the same temperature, at which the top blanket manages to get rid of your body heat; but underneath you’re sweating more and more, the more blankets are added. I would say “heat trapping” or “thermal blanketing” is an apt term.

    Hope this helps (a little).

  23. 123
    Consumer says:

    From the Dept. of stupid questions:

    1. What is the lag between the release of CO2 and when it starts trapping heat?
    If I exhale today, does that molecule start blocking radiation of solar heat immediately?

    [Response: There is no lag. However, there is a lag for a change in emissions to affect the atmospheric concentration, and there is a lag for the change in concentration to affect temperatures. Note that the CO2 you exhale doesn't count since that carbon came from the atmosphere itself fairly recently (the last year or so). - gavin]

    2. Is this lag time the same for CO2 and CH4?

    [Response: The 'no lag' is the same. But perturbations of the total CH4 concentration in the atmosphere reacts faster to changes in emissions. A decade or so rather than decades to centuries. - gavin]

    3. It is my understanding that the arctic has been 5-6 degrees warmer than present, and some of the GIS remained intact. Do we know what the effect of this higher temp was on the marine methane deposits?
    Do we know how old these methane deposits are, and what temperature ranges they have survived?

    [Response: Likely small (look at CH4 concs during the Eemian. But no, and no. - gavin]

    4. Could melting of the GIS help keep the North Atlantic waters cold enough to prevent the methane
    release – as a negative feedback?

    [Response: Not likely. It could slow the rate of warming in the N. Atlantic though. However, I don't know where you are really coming from - has someone suggested that marine methane hydrate release is likely or expected? Because although there are uncertainties, it doesn't appear to be an imminent problem - though it is one that people are concerned about. - gavin]

    5. Can someone give me an easy-to-understand answer on my main question on Hansen’s new paper?
    I still can’t figure out how if glaciation happened with CO2 levels at 425ppm that we are seeing so much
    warming at 385ppm.

    [Response: First off there is a difference between equivalent CO2 and actual CO2. Plus you have to factor in 'unfavorable' orbital configurations (not what we have now)... - gavin]

    6. Does methane evenly distribute in the atmosphere like CO2?

    Let’s be honest, I have many more stupid questions, but I’ll stop there for now.

  24. 124
    Hank Roberts says:

    Gus, when you quote, attribute the quotation — right click on the timestamp, copy/paste — and say who you’re quoting.

    Any thread here will have copious droppings from at least one hobbyhorse, usually more than one, as well as much speculation from ordinary readers like me, as well as cites to real science. Help keep track.

    Anything quoted comes from a context and should be read that way.

  25. 125
    Hank Roberts says:

    Martin, thanks, this helps me — we went ’round and ’round on the earlier threads in which those of us with insufficient math were trying to understand radiation physics using prose.

    Your posting above helps, clear and concise

    > it is not fruitful to look at the effect of
    > greenhouse gases as a temporal (delay) effect.
    > Rather it is a spatial (barrier) effect. Consider
    > that the heat has to be transported from the Earth
    > surface to the “edge of space” where it may be
    > radiated out.

  26. 126
    Lawrence Brown says:

    Gusbobb says in #117:” I don’t see that what I said is any different,” #80 CO2 doesn’t trap heat like Al Gore [edit] portrayed in inconvenient Truth. CO2 delays re-radiation back into space.

    “And I understand that when CO2 absorbs a photon that energy will be transformed into an increased kinetic energy. But for how long? (and why the edit of my 2-word description of the cartoon characters???)”

    There are different levels of understanding of the effects of GHGs on Earth’s surface temperature depending on how detailed the explanation. “A Saturated Gassy Argument” gives a high level of scientific explanation. Others, who adress mainly an audience of non-scientists, may use words such as a “blanket” or “trapping” effect, rather than go into scientific detail about back radiation and energy balance. Why do these more simplified explanations bother you?

    As to your next question about why the edit,it’s because the word you use is inflammatory,an insult, it’s an ad hominem attack. Ad homs add nothing to the discussion, regardless of the source.

  27. 127
    Consumer says:

    Thank you for the quick response.

    1. If there is no lag, why is there a lag between concentrations and temperature. Is this a lag between concentration and net heat, or between net heat and temperature?

    4. I was thinking of the article linked to by #95 Lynn:

    **Meanwhile, back in the present, we seem to have awaked the big monster (23 times more potent than CO2), who is poised to bear down on us. Methane is now gassing out off Siberia.

    See: http://www.climateark.org/shared/reader/welcome.aspx?linkid=97317

  28. 128
    Ray Ladbury says:

    Gusbob, per my earlier suggestion, I will try to compose a coherent reply that addresses some of your queries and misconceptions over in the “Start Here” Thread to avoid hijacking the main thread. Hopefully, this will serve as an incentive to you and others to avail yourselves of the other offerings vectored by that thread.

  29. 129
    Ray Ladbury says:

    Gusbob, spoke too soon. Start Here Thread is closed. Let’s go back to the “A Day when Hell Was Frozen” Thread:
    http://www.realclimate.org/index.php/archives/2008/02/a-day-when-hell-was-frozen/langswitch_lang/sw

    A tutorial post would be quasi-on-topic there.

  30. 130
    Chris Colose says:

    Consumer,

    the lag is for the same reason that a swimming pool doesn’t heat up immediately on a hot day– it takes time to heat the planet, and especially water (with a high heat capacity) and covers 70% of the planet. If the planet had no atmsophere and no oceans, than it would change temperatures much quicker, and be more sensitive to things like changes in the sun (hotter days, colder nights).

    As gavin mentions, the methane feedback might be harmful over centuries, but for now I’d be more worried about the increases in greenhouse gases (mainly CO2).

  31. 131
    pat n says:

    Re #119, #116, #95,

    I think the 2007 is significan – in light of:

    … “Of particular concern are potential positive feedbacks
    that could amplify increases in the concentrations of greenhouse gases
    — water, CO2, methane and nitrous oxide (N2O) — effectively escalating
    climate sensitivity to initial anthropogenic carbon input”.

    Jan. 2008, Zachos, Dickens & Zeebe on “An early Cenozoic perspective
    on greenhouse warming and carbon-cycle”

    http://www.es.ucsc.edu/%7Ejzachos/pubs/Zachos_Dickens_Zeebe_08.pdf

    It still seems logical to me that bursts of methane from thawing
    permafrost and heating of wetlands can explain an apparent warming-CO2
    lag in some past episodes of warming.

  32. 132
    Ron Taylor says:

    Gusbob, I think I was a little too critical of you before. You seem to be getting the message. Just pose your questions in the form of “questions from a humble learner,” instead of as assertions challenging the competence of the scientists here. It will really work for you.

  33. 133
    Lowell says:

    I have two comments to make.

    1. For a Paleoclimate discussion thread, there is a remarkable lack of discussion regarding the Paleoclimate (which does not seem to be correlated with CO2 levels much at all throughout climate history.)

    2. Methane concentrations in the atmosphere have stabilized and are probably falling now so all the doom and gloom discussion about Methane releases are not supported by the facts.

  34. 134
    greg smith says:

    As a scientist (geologist) who is neither a sceptic nor a warmer I visit sites such as this to get an appreciation of where the science regarding AGW is heading. After reading many of the posts here I can get an appreciation of how Copernicus or Darwin must have felt. You should collectively hang your heads in shame at the close mindedness expressed here. It is arrogant in the extreme to assume that you can effectively model something as complex as the atmosphere and its interaction with the earth and the solar system using the current state of computers and knowledge of how the ocean or any other process that you haven’t yet become aware of works and yet be so certain and dismissive of anyone such as gusbob who dares to put his hand up with different ideas.
    Geology teaches me that nothing is “ideal” or constant in the scheme of things and that the earth will go on regardless. Don’t forget that we are just passengers on this large billiard ball with a thin plastic coating that is the atmosphere.

  35. 135
    Chris Colose says:

    Lowell, check out some of Dana Royer’s work for the connection between CO2 and climate over million-year timescales. The supergreenhouses of the Cretaceous, snowball earth, glacial-interglacial cycles, the PETM, the hot earth during the faint sun, the evaporated oceans of Venus, the history of Mars, and many other examples all have CO2 in them in some way or another. You could say the relation of carbon dioxide to planetary climate is like evolution is to biology.

    MEthane does appear to be levelling off, but it’s hard to say with high confidence what the future trends will be. In any case, the methane from human activities is a bit of a separate issue from the deep ocean methane feedback, which is supposedly a response to warmer temperature and occurs over centennial timescales.

  36. 136
    Aaron Lewis says:

    I do not always agree with Gavin, but he has more patience than any saint. However, like a saint, I fear he is a naïve when dealing with the professional agent provocateurs that come in and steal his column inches.

    Column inches with readership have value, and I fear that professionals are stealing them. That is theft and wire fraud.

    Wire fraud is a law with teeth. In this case, it might not be prosecuted under the Bush Administration, but Bush’s tenure is shorter than the wire fraud statute of limitations.

  37. 137
    Hank Roberts says:

    Lowell,

    Your first para. states a belief but is very vague. What’s your source for it? Why do you rely on that source?

    Compare what you believe to what you read here for example
    http://www.ncdc.noaa.gov/paleo/globalwarming/temperature-change.html

    or at least the picture from the beginning of that long page:
    http://www.ncdc.noaa.gov/paleo/globalwarming/images/temperature-change.jpg

    Your 2nd para. is a belief, but doesn’t follow logically from the stated fact. You appear to assume the only thing that can cause an increase in methane is the prior release of methane. Not true.

    Methane clathrate stability is related to the slow warming of the seabed with increases in ocean temperature.

    “It would take around 2300 years for an increased temperature to diffuse warm the sea bed to a depth sufficient to cause clathrates’ release ….” en.wikipedia.org/wiki/Paleocene-Eocene_Thermal_Maximum

    That change lags air temperature and CO2 is the forcing most directly involved. By the time that amount of warming is ‘in the pipeline’ (look up “committed warming”) it’ll be a different world already.

    Permafrost above the seabed warms faster, making it more imminent as a source of methane — you can look it up. There’s no ‘wisdom’ option, you still have to choose what you read, but try the first few dozen hits:

    http://www.google.com/search?q=permafrost+methane

    What source are you relying on for what you believe?

  38. 138

    RE #133, what I’ve read (and it’s also highly stressed by AGW denialists) is that warming episodes of the past, whatever their initial causes, led to an increase in GHGs.

    I also read some years back that CH4 levels have been steady over the past many years. However, this does not mean they will always stay steady. Recent studies in Siberia indicate that methane is now outgassing in Siberia, presumably from melting ocean hydrates and permafrost, so it may be that CH4 levels will start increasing.

    See: http://www.climateark.org/shared/reader/welcome.aspx?linkid=97317

    My meager understanding has it that CH4 only lasts in the atmosphere about 10 years (unlike CO2, a small portion of which can last up to 100,000 years), and then the CH4 degrades into CO2 and other things?? The problem then is the rate at which CH4 goes into the atmosphere. If this is very slow, no problem, it could maintain a steady level, but if it should get into the atmosphere a lot faster, compounding the amount of CH4 before it can degrade, then the warming effect could really jump up, since CH4 is about a 23 times more potent GHG than CO2.

    One of the new things about this current global warming episode is the speed with which we are pumping GHG into the atmosphere. I think in the past it took hundreds (maybe thousands) of years for the warming to happen.

    What’s slow is our ability to size up a problem and respond in a timely fashion. I’m thinking the evacation efforts during Katrina (they did know the hurricane was coming and that many lived below sea level); or 9/11 — it seems the FBI or CIA agents did know something fishy was going on in flight schools. Bureaucratic and societal inertia. That’s the name of our game. No matter how fast our computers get, no matter how much we know from paleoclimate and current climate science and physics, we’re just dumb slow in our response. Except when it comes to pumping GHGs into the atmosphere — we’re fast in that.

  39. 139
    JCH says:

    “After reading many of the posts here I can get an appreciation of how Copernicus or Darwin must have felt. …” – greg smith@134

    Just me, but I think what you understand, greg, is how the doubters of those two men must have felt.

  40. 140
    Hank Roberts says:

    > Copernicus or Darwin

    “Alas, to wear the mantle of Galileo it is not enough that you be persecuted by an unkind establishment, you must also be right.”

    – Robert Park. (Stolen from the header of Conspiracy Factory blog)

  41. 141
    Richard Pauli says:

    Re: 133 #2 Methane releases… if not a scientific citation, at least accept a recent Chicago Tribune article:

    “Chersky, Russia – Sergei Zimov waded through knee-deep snow to reach a frozen lake where so much methane belches out of the melting permafrost that it spews from the ice like small geysers.”

    http://www.chicagotribune.com/news/nationworld/chi-siberia-loner_rodriguezmay05,0,7326792.story

    Freezing to show warming trend
    Though dismissed in Russia, scientist’s climate research in remote Siberia is heating up discussions in the West

  42. 142

    #138, Fast and furious at dumping Lynn, the masses extraordinarily lethargic in seeing a freight train going to crash at 1 MPH, and are paying extra gas $$$ to make it go faster. The big story Up Here in far away Arctic lands is the big blue sky ever so lasting till tonight, AH such souvenirs…… From cosmic ray theorists, proclaiming more clouds during a solar minima? Where are these guys? GCR theorists care to comment?

    Going back to CO2 and greenhouse gases, I was very impressed during winter just past, by the lack of total cooling as autumn big blue turned dark during the long night. The surface might have been cold for a brief moment during mid winter, to the delight of vengeful contrarians, but alas they don’t really understand climate science, and now, nothing but blue sky, ever so steadily warming as the sun rises till solstice day. AGW is a rock solid theory, all those so far trying to discredit have failed, too bad for all of us, many press outlets don’t see it the same way.

  43. 143

    Re #134 greg smith: Both Copernicus and Darwin were well acquainted both with the ideas their theories were to replace, and with the observational record. About gusbobb, we’re working hard on getting him there too ;-)

    BTW I find rather unhistorical the implication that modelling the revolutions of the heavenly orbs, or the origin of species, were any less arrogant undertakings in their days than general circulation modelling today.

  44. 144
    Jim Cross says:

    Re #111

    Ike, there wasn’t any attempt to distort by leaving out the context of a sentence. My reply was to Hank’s request for a citation regarding the current orbital configuration and its possible effect on ENSO.

    The article is not just about the YD. It is rather about a 11 thousand year orbital influence on ENSO.

    In regard to “idealized” models, all models are idealized. The model of the article I cited covers time periods of thousands of years whereas the GCMs in the IPCC report operate on decades and centuries. This to me seems to create scaling problem in trying to employ the observations and models of the paleo-record to the models we are trying to use to predict future climate.

    What’s more, we know dramatic changes can and do occur in the paleo-record, however, the current GCMs are heavily biased towards the conservative. That’s understandable. It’s the safe play – like bet-ting on red and black on a rou-lette wheel and gamb-ling that the green zero doesn’t come up. Odds are it won’t during the next few decades. Eventually, however, the zero will come up. It could be a sudden melting of the Antarctic ice sheets, a mysterious shutdown of the THC, a super volcano, or perhaps even a global energy and economic crisis leading to a dramatic reduction of greenhouse gases.

    Note: Odd hyphenated spellings above are to bypass the WordPress spam filter.

  45. 145

    gusbobb writes:

    I thought that despite being a well mixed gas, that CO2 concentrations get lower the higher the altitude in addition to the lower density.

    No. It’s well-mixed at least through the troposphere and stratosphere, which is pretty much 99% of the mass of the atmosphere.

  46. 146

    greg smith posts:

    As a scientist (geologist) who is neither a sceptic nor a warmer I visit sites such as this to get an appreciation of where the science regarding AGW is heading. After reading many of the posts here I can get an appreciation of how Copernicus or Darwin must have felt. You should collectively hang your heads in shame at the close mindedness expressed here.

    Somehow this doesn’t sound like a geologist talking to his colleagues. Especially at the mention of Galileo so beloved of pseudoscientists. Where did you get your degree and when?

    It is arrogant in the extreme to assume that you can effectively model something as complex as the atmosphere and its interaction with the earth and the solar system using the current state of computers and knowledge of how the ocean or any other process that you haven’t yet become aware of works and yet be so certain and dismissive of anyone such as gusbob who dares to put his hand up with different ideas.

    What is arrogant about it? Atmospheric models work. They’re not perfect, but they don’t have to be. You’re assuming that we have to have perfect knowledge of the atmosphere to say anything about it at all, and that’s just not true. And it’s hard to believe a geologist wouldn’t know that. Even a geologist has to know something about the atmosphere, if only to understand weathering and geochemical cycles.

    Geology teaches me that nothing is “ideal” or constant in the scheme of things and that the earth will go on regardless.

    What part of “geology” says that?

    Don’t forget that we are just passengers on this large billiard ball with a thin plastic coating that is the atmosphere.

    We know.

  47. 147
    Ray Ladbury says:

    Greg Smith, Your attitude represents such a profound level of ignorance, it belies your claims to be a scientist. Not only are you seemingly unaware that we model complex systems all the time, you don’t even seem to be aware of the purpose of modeling. We model the relativistic collisions of Uranium atoms. We model the explosions of supernovae. We model percolation of oil, water and other fluids through rock and soil. We model the dynamics of DNA molecules consisting of hundreds of thousands of individual atoms. I personally have modeled cratering on icy satellites. We model these systems not to reproduce every detail of their dynamics on the computer, but rather to gain insight into their dynamics. The fact that you are so unnerved that you throw up your hands when confronted with a complicated problem merely shows that you are unwilling to invest the effort to understand anything. Yours is an attitude that is profoundly anti-scientific.

  48. 148
    Chris says:

    Re #133 Lowell

    Of all of the potential variable influences on climate during the long history of the Earth, atmospheric greenhouse gases do seem to have the dominant influence:

    Thus the Earth’s cool and warm periods match rather well with the periods in which proxy measures of atmospheric CO2 were, respectively low and high. This data has recently been comprehensively compiled by Royer:

    e.g.:
    D. L. Royer (2006) CO2-forced climate thresholds during the Phanerozoic Geochim. Cosmochim Acta 70 5665-5675

    see also:
    Came RE, Eiler JM, Veizer J et al (2007) Coupling of surface temperatures and atmospheric CO2 concentrations during the Palaeozoic era Nature 449, 198-201.

    and very recent analyses of paleoproxy CO2 data (fossil leaf stomatal index) indicates a climate:CO2 coupling throughout the Miocene:

    Kurschner WM et al (2008) The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems Proc. Natl. Acad. Sci. USA 105, 449-453

    And if one considers catastrophic events in Earth’s history associated with extinctions, for example, the most dominant correlate is massive tectonic events, at least one consequence of which is large increases in the atmospheric greenhouse gas concentrations:

    So, a very recent reanalysis of the argon-argon dating “clock” has established, for example, that the massive Permian Triassic extinction correlates with the massive volcanic events associated with the formation of the Serbian Traps (see Science 25th April 2008)]. The end-Cretaceous extinction correlates with the tectonic events associated with the Deccan Traps formation, although an asteroid impact was involved too! The Paleo-Eocene Thermal Maximum extinctions with the tectonic events associated with the opening up of the North Atlantic at a plate boundary. The Triassic-Jurrasic extinction (201.6 mya) associates with the massive volcanic outpourings of the central Atlantic magmatic province…and so on…

    …and the first great glaciation in Earth’s history seems likely to have resulted from the evolution of the earliest photosynthetic organisms that produced oxygen which, having oxidised enormous amounts of iron salts to iron-oxide, was released into the atmosphere where it oxidised the methane that was “helping” to keep the early Earth warm, and thus caused a marked cooling….

    e.g.:

    Beerling DJ et al. (2002) An atmospheric pCO(2) reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils; Proc. Natl. Acad. Sci. USA 99 (12): 7836-7840

    Keller G (2005) Impacts, volcanism and mass extinction: random coincidence or cause and effect?; Austral. J. Earth Sci 52 725-757.

    Kelley S. (2007) The geochronology of large igneous provinces, terrestrial impact craters, and their relationship to mass extinctions on Earth ; Journal of the Geological Society 164, 923-936

  49. 149
    Timothy Chase says:

    Lynn Vincentnathan (138) wrote:

    My meager understanding has it that CH4 only lasts in the atmosphere about 10 years (unlike CO2, a small portion of which can last up to 100,000 years), and then the CH4 degrades into CO2 and other things?? The problem then is the rate at which CH4 goes into the atmosphere. If this is very slow, no problem, it could maintain a steady level, but if it should get into the atmosphere a lot faster, compounding the amount of CH4 before it can degrade, then the warming effect could really jump up, since CH4 is about a 23 times more potent GHG than CO2.

    A ten year residence time?

    Usually, but not always. It depends upon the size of the pulse. A larger pulse could use up the OH radicals – and then it may stick around a little longer.

    Please see:

    When methane (CH4) enters the atmosphere, it reacts with molecules of oxygen (O) and hydrogen (H), called OH radicals. The OH radicals combine with methane and break it up, creating carbon dioxide (CO2) and water vapor (H2O), both of which are greenhouse gases. Scientists previously assumed that all of the released methane would be converted to CO2 and water after about a decade. If that happened, the rise in CO2 would have been the biggest player in warming the planet. But when scientists tried to find evidence of increased CO2 levels to explain the rapid warming during the LPTM, none could be found.

    The models used in the new study show that when you greatly increase methane amounts, the OH quickly gets used up, and the extra methane lingers for hundreds of years, producing enough global warming to explain the LTPM climate.

    “Ten years of methane is a blip, but hundreds of years of atmospheric methane is enough to warm up the atmosphere, melt the ice in the oceans, and change the whole climate system,” Schmidt said. “So we may have solved a conundrum.”

    Methane Explosion Warmed the Prehistoric Earth, Possible Again
    December 10, 2001
    http://www.giss.nasa.gov/research/news/20011210/

    Schmidt, G.A., and D.T. Shindell 2003. Atmospheric composition, radiative forcing, and climate change as a consequence of a massive methane release from gas hydrates. Paleoceanography 18, no. 1, 1004, doi:10.1029/2002PA000757.
    http://pubs.giss.nasa.gov/abstracts/2003/Schmidt_Shindell.html

    [Response: Thanks for the plug (but really, there is no need!). Note however, that the 'hundreds of years' involves two effects - one is the increased lifetime (which would occur, but is limited to a few decades at most), and the second which is an assumption of continuous emissions. You can't do it by increased lifetime alone. - gavin]

  50. 150
    Hank Roberts says:

    Jim, you apparently have the actual article, not just the abstract. Can you quote exactly what orbital parameters that says are currently the same as at some past time when an abrupt change happened? There are _lots_ of variables, like the planet’s inclination, how oval or circular the orbit is. Which do they specify and which are similar?


Switch to our mobile site