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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Climate reacts to whatever forces it to change at the time; humans are now the dominant forcing.

Climate Myth...

Climate's changed before
Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)

A common skeptic argument is that climate has changed naturally in the past, long before SUVs and coal-fired power plants, and this somehow tells us that humans can't be the main cause of the current global warming. Peer-reviewed research and simple logic show this is not the case.

It's important to know there are a number of different forces acting on the Earth’s climate. When the sun gets brighter, the planet receives more energy and warms. When volcanoes erupt, they emit particles into the atmosphere which reflect sunlight, and the planet cools. When there are more greenhouse gases in the atmosphere, the planet warms. It's worth remembering that without some greenhouse gas  the Earth would be a ball of ice.

These forces are called "forcings" because they force changes in the global average temperature.

Looking at the past gives us insight into how our climate responds to such forcings. Using ice cores, for instance, we can work out past temperature changes, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere. Looking at many different periods and timescales including many thousands of years ago we've learned that when the Earth gains heat, glaciers and sea ice melt resulting in a positive feedbacks that amplify the warming. There are other positive feedbacks as well and this is why the planet has experienced such dramatic changes in temperature in the past.

In summary the past reveals our climate is sensitive to small changes in heat. 

What does that mean for today? Over the past 150 years greenhouse gas levels have increased 40 percent mainly from burning of fossil fuels. This additional "forcing" is warming the planet more than it has in thousands of years. From Earth's history, we know that positive feedbacks will amplify this additional warming.

The Earth's climate has changed in the past and ice cores and other measures tell us why. Based on this knowledge, and other types of evidence we know the human emissions of greenhouse gases are warming the climate.

The 'climate changed naturally in the past' argument is a logical fallacy known as non sequitur, in which the conclusion doesn't follow from the arguments.  It's equivalent to seeing a dead body with a knife sticking out the back, then arguing the death must be natural because people died naturally in the past.  It fails to even consider the available evidence.

Last updated on 4 February 2014 by dana1981. View Archives

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Comments 251 to 300 out of 309:

  1. 250, lancelot,

    To clarify, however, the references to clouds in the AR4 do not give any credence whatsoever to the idea that changes in cloud cover are responsible for the modern warming trend. This is in no way believed or expressed.

    The references to clouds in AR4 pertain explicitly to positive feedbacks and climate sensitivity, i.e. given warming X from CO2, how much additional warming Y will be added to that from clouds.

    AR4 (and scientists) are very upfront about admitting to this area of doubt in predictions, and adjusting error bars appropriately. But the admission is one of mere prudence and honesty, and part of the reason that the currently accepted range of climate sensitivity is between 2˚C and 4.5˚C per doubling of CO2. Part of the reason for that wide range (2.5˚C total) is due to uncertainties about the effects of warming on clouds, and the corresponding effects of changed clouds on warming (although there are other factors, too).
  2. 250, lancelot,

    Measuring energy received at the surface may seem straightforward, but as I said before, it is most certainly not. You must account for:

    1) Local, low lying and potentially transient effects (smog, fog)
    2) Coverage... how do you do it on the oceans, which cover 70% of the earth? Deserts? Inhospitable countries?
    3) Altitude... radiation will be higher for measurements taken at higher altitudes
    4) The past? How do you know what happened before you get your network set up? To what do you compare your new values?

    All of the problems that plague the observational surface temperature record apply as well to measuring sunlight.

    It's just not as easy as it sounds, especially when a satellite can do that and more for less money with less effort and more consistency.
  3. 250, lancelot,

    I mentioned aerosols because your point is not about cloud forcing (whether you realize it or not), but about total solar radiation received at the surface. You are presuming that cloud cover changes are a possible and likely cause (less clouds = more sunlight = more warming). You are then taking it a step further and saying that well, okay, it may not be GCRs, but maybe it's something else.

    That's magical thinking. That's hoping to find a cause, and then after the fact looking for a cause of the cause.

    More to the point, I included aerosols because they can have the same effect as clouds, by reflecting incoming sunlight. Indeed, Hansen proposes this for a reason that warming is not as great as it should be. It's also a reason that the loss of the Glory satellite was a big blow to advancing climate science.

    But a decrease in such reflective aerosols (due, for instance, to improved pollution controls) could in the same way raise temperatures.

    Aerosols (depending on the type) can also have the opposite effect, by absorbing more sunlight and increasing warming, so an increase in such aerosols could warm the earth.

    The point is that scientists are not stupid. They are looking at all of these things and giving them their due.

    On micro-organisms, stony silence and kindness concerning stupidity... ummm, sorry, sort of. When you mentioned it I did look into it, and there do seem to be some very, very interesting papers on the subject of micro-organisms and their impact on cloud formation. But I honestly didn't think for a moment you were serious about it.

    But... while this is an area of interest to the scientists working on it, as of now:

    a) There is no strong, well-defined or reasonably serious mechanism that turns micro-organisms into a major player in changes in cloud formation in the last 30 years.

    b) More importantly, no change in micro-organisms has been identified or even proposed that would suggest that something has happened in the last 30 years to trigger warming.

    Again, it's a case of hunting for an alternate cause when there is no reason to do so, and then in turn still needing to find a cause of the cause.

    Could it be clouds? We have no reason whatsoever to think so (and don't think scientists have not been measuring cloud cover, they have).

    Could it be clouds caused by micro organisms? We have no reason whatsoever to think so.

    Could it be clouds caused by falling fairy wings, as a result of an unexpected increase in the desiduous-winged fairy population? We have no reason whatsoever to think so.

    [Sorry if that last sounded snarky. It wasn't meant to be. It was meant instead to show that science must work by going from observation to hypothesis to experiment to confirmation/refutation. And can not work simply through "but what if..." followed by any and every idea that anyone could consider, simply because they don't like the ideas that we do have, for which we have evidence, and which logically and consistently explain the entire picture without the addition of fairy wings.]
  4. Lancelot -" Is that because readers are much too kind to lambast me for my stupidity in thinking that the airborne biosphere might(repeat might!) have a part to play in climate?"

    There is a considerable literature on the biogenic aerosol effect (naturally-occurring particles such as pollen, sea salt, leaf fragments etc seeding cloud formation). I've read a lot of papers on aerosol formation in the Amazon rainforest region, for starters.

    What is it you think they (biogenic aerosols) are doing? And how do you come to the conclusion the IPCC doesn't know about the published scientific literature?
  5. Tom Curtis 243; Could I add: You wrote: "More importantly, it is far from clear that this is a global phenomenon. Certainly in China the trend has been in the opposite direction towards less sunlight hours. A similar reduction of sunshine has been found in Switzerland, so the observed increase in the UK is not even a Europe wide phenomenon, let alone a world wide phenomenon."

    The Swiss study abstract quotes "general decrease of sunshine duration through to the mid 1980's". That doesn't seem so far off from the general decrease to around 1979-83 on the Met Office chart. (Just eyeballing here). Some data divergence perhaps due to varying definition of 'sunshine' measurement? So perhaps some common ground UK-Swiss?

    In China one would expect a decrease in net irradiance received due to aerosols. I will have to take your word that the paper describes a decrease in actual sunlight hours since 1974, as I don't have access to it.

    DB: Wow!- thanks for the Wild 2009 copy, really kind of you.
  6. Ah, page 6 now.. apologies for missing the latest posts when I wrote 255.

    Sphaerica, I am not trying to put down scientists, and I am sure you have even thought about fairies! But I have not been able to find any consideration of micro-organisms/clouds in the IPCC reports, and there are some interesting papers on the subject, such as http://www.wired.com/wiredscience/2011/05/microbes-make-rain/

    Hence my question.

    I note the difficulties with making ground level (or sea level) measurements.

    Thanks again.
  7. 256, lancelot,

    No worries! I appreciate the interest in the science!

    The main point is that the science now is all about microbes and potential impacts on cloud formation, but there are no signs whatsoever that this translates into any effect on global climate, let alone a non-negligible warming effect related to current climate change. That's just a big leap, that isn't warranted by the state of the literature.

    From the article you linked to (emphasis mine):
    These data add to a growing body of evidence that biological organisms are affecting clouds, notes Anthony Prenni of Colorado State University in Fort Collins, an atmospheric scientist who did not participate in the new studies. Right now, he cautions, “We still don’t know on a global scale how important these processes are.” But research into microbial impacts on weather and climate is really heating up, he adds, so “within a few years, I think we’re going to have a much better handle on it.”
    So it's very interesting, yes. So are any number of avenues and subjects on which the media has yet to report. But it's of no interest in climate science (to me, at least) at this time.

    It's about weather, not climate.
  8. Lancelot -"In China one would expect a decrease in net irradiance received due to aerosols. I will have to take your word that the paper describes a decrease in actual sunlight hours since 1974, as I don't have access to it"

    There are numerous papers freely available on the topic. Try Google scholar.

    The indirect effect on aerosol formation is not what most people may think. In extremely polluted areas the sulfate particles reach a break-even point and start to warm clouds so much they begin to evaporate. This is small relative to the dimming effects, but it is a saturation point of sorts.
    Response: [Sph] Google scholar = http://scholar.google.com, a useful tool for searching specifically for scientific papers by keyword, author, and date range.
  9. lancelot#255, quoting Tom C#243: "More importantly, it is far from clear that this is a global phenomenon."

    Alpert et al 2005 supports Tom's observation:

    we show that this phenomenon, widely termed global dimming, is dominated by the large urban sites. The global-scale analysis of year-to-year variations of solar radiation fluxes shows a decline of 0.41 W/m^2/yr for highly populated sites compared to only 0.16 W/m^2/yr for sparsely populated sites (<0.1 million). Since most of the globe has sparse population, this suggests that solar dimming is of local or regional nature.

    Move over Urban Heat Island, here comes the Urban Dim Island!
  10. lancelot: it is not easy to measure surface radiation fluxes well. Last I looked, a system that will meet BSRN guidelines will cost you around $100k in equipment and sensor costs. BSRN is intended for long-term climate monitoring, and accuracy requirements push modern technology. If you want a very long read (and want to download quite a few megabytes of manual), the BSRN web site has a link to their Operations Manual. (Don't click the link unless you want the full manual!) Be prepared for a huge whack of technical discussion of sources of error, but before anyone decides "we can't measure radiation" keep in mind that the BSRN goals for accuracy are set very high (in the 1 W/m^2 range). It's the Rolls Royce of radiation measurement, not the Chevrolet version. It's part of the Global Energy and Water Experiment (GEWEX), and has been designated as the radiation observing system for the Global Climate Observing System (GCOS).

    Sphaerica: Please don't try to tell me that it can all be done by satellites. They give great spatial coverage, yes, but accuracy of surface radiative fluxes can't come close to good surface-based measurements. BSRN provides data at one-minute intervals, 24 hours per day, 365 days a year. A literature search for BSRN references will probably provide you with mostly satellite papers, all desperate for good ground-truth data.
  11. May I just say that I really appreciate the well-considered (and well-mannered) comments to my questions on this site.

    Sphaerica: When I wrote before I was 'half serious' I was referring to my somewhat flippant suggestion of breeding microbes to seed clouds. That idea, even if feasible, wouldn't go very far of course.

    I do have a purely scientific interest as you say, but there are larger interests too. (-Snip-).

    Report of an Ad Hoc Study Group on Carbon Dioxide and Climate, Woods Hole, Massachusetts July 23.–27, 1979 to the Climate Research Board , Assembly of Mathematical and Physical Sciences, National Research Council:

    “We conclude that the predictions of CO2-induced climate changes made with the various models examined are basically consistent and mutually supporting. ... Of course, we can never be sure that some badly estimated or totally overlooked effect may not vitiate our conclusions. We can only say that we have not been able to find such effects.”

    (-Snip-)

    CO2 is a GHG. 100% certain.
    Natural forcings exist. 100% certain.
    All possible natural forcings or long term effects on climate have been identified and accurately quantified. __% certain. (Fill in the gap?)

    muoncounter: Dimming is an urban island phenomenon, ok. Not sure how that relates to the question of net irradiance at surface level globally. From Bob Loblaw's posts I suspect the situation is: we use satellites because they are there. But gee whizz, if we could use actual surface monitoring, we would be so much more certain that our estimates are correct.

    GCOS looks really interesting. Re sphaerica's comment that oceans cover 70% of surface, I don't see why BSRN type monitoring couldn't be done from ship decks. Use some of that £18bn perhaps?
    Response:

    [DB] Ideology snipped.  Stick to the science, please.

    Your Woods Hole report is badly dated.  Various scientific organizations, including the National Academies last year, have greatly linked the certainty of climate change/global warming (as fact) to its human attribution (greater than 90% likelihood).

  12. 261 - lancelot

    "So if it turns out in a few years that something has been 'totally overlooked', climatologists will be about as popular as bankers!!"

    It's worth noting - taking the long view - that CO2 as the key to global warming was, in the '70-'80s, the "other factor". You might also want to ask; if it had been overlooked and, indeed, the anthropogenic origins of the observed warming had been overlooked... just how popular would the climatologists been?

    If you're going to do counterfactuals; Imagen a future generation suffering from land-loss, a crippled bio-sphere, extreme weather etc. Just how popular will our generation be if we had overlooked the anthropogenic side of the equation and possible mitigation policies and if we don't act on them?
  13. lancelot @261, our understanding of what will happen in the near future does not just depend on projections from known physics. We also have the record from the past. The advantage of the record from the past is that we do not need to know all the factors involved to read that record. We do not need to know what the cloud feedback is, for example, for that feedback has been integrated into the results by the best model available to us, ie, the real world.

    Given that, it is worthwhile examining two particular events, the Paleocene-Eocene Thermal Maximum (PETM), and the Last Glacial Maximum.

    The PETM was a warming event at the boundary between the Paleocene and the Eocene. Boundaries between geological eras are marked by significant changes in fossil assemblages, ie, by extinction events followed by repopulation with new species. In this case the extinction event was probably brought on by the release of a large amount of methane, which was oxidized to form CO2 and H2O, with the CO2 showing up clearly in the geological record. The effects are summarized in the abstract of one review article as follows:

    "During the Paleocene-Eocene Thermal Maximum (PETM), 56 Mya, thousands of petagrams of carbon were released into the ocean-atmosphere system with attendant changes in the carbon cycle, climate, ocean chemistry, and marine and continental ecosystems. The period of carbon release is thought to have lasted <20 ka, the duration of the whole event was 200 ka, and the global temperature increase was 5–8°C. Terrestrial and marine organisms experienced large shifts in geographic ranges, rapid evolution, and changes in trophic ecology, but few groups suffered major extinctions with the exception of benthic foraminifera. The PETM provides valuable insights into the carbon cycle, climate system, and biotic responses to environmental change that are relevant to long-term future global changes."


    The interesting thing here is that best estimates show that the climate response to a doubling of CO2 evidenced by the PETM is 3.6 degrees C per doubling. That is a climate sensitivity of 0.973 degrees C per Watt/m^2 of forcing.

    In contrast to the PETM when temperatures where substantially hotter than today, at the LGM they where substantially colder. Again the climate sensitivity can be calculated from known forcings at the LGM and the known temperature difference. Most estimates in doing so come close to that by Hansen and Sato, with a value of 0.75 +/-0.25 degrees C per Watt/m^2. That represents an estimate of 2.775 (1.85-3.7) degrees C per doubling of CO2 (compared to the IPCC estimate of 2.8).

    Again, I emphasize, no assumptions about feedback values from water vapour, clouds or anything else go into these calculations. The Earth just does what it does, and the comparison between known forcing and known temperature response yields the climate sensitivity.

    But despite the significantly different continental arrangements, and the very different temperatures, the climate sensitivity estimates from these two periods are in the same ball park, and indeed, in the same zone as the IPCC estimates.

    When it comes to the basic feedbacks, it is certainly possible that scientists have missed something. Evidence is strong, for example, that they have been underestimating ice and snow albedo feedbacks (positive). They may well also be overestimating the cloud feedback (possibly positive or negative). For that to create a significant problem for their predictions, these errors need to mostly line up in the same direction.

    What is troubling about the assumption that these errors will fortuitously come out in our favour is that it is also an assumption that the Earth's climate sensitivity is, fortuitously, approximately half or less of what it is when the Earth is hotter (PETM) or colder (LGM) than it currently is. That somehow, and with no physical basis for assuming so, we just happen to be in a goldilocks zone of low climate sensitivity even though hotter and colder conditions are known to have high climate sensitivities. What makes the heroism of this assumption even greater is that it is known that throughout the entire existence of vertebrates on Earth, from the late pre-Cambrian to the present, climate sensitivity has never been far from 2.8 degrees per doubling of CO2. Over 540 million years of high climate sensitivity, but it just happens when we start emitting CO2 at industrial scales, we happen to be in a goldilocks zone of low climate sensitivity?

    That, at least, is what the so-called climate "skeptics" would have you believe.
  14. 261, lancelot,

    2 things.

    First, I'm getting the impressions from your posts that you're currently in a "yeah, but what if" mode. You are looking as hard as you can for alternative explanations, but you're starting to run out of ideas (as have the deniers/skeptics). This is fine, and the path you have to take to some degree.

    But you should be leery of resting a position on ignorance (i.e. it might be those impossible to define natural forcings, or just plain something we haven't thought of yet). That's not science, it's magical thinking.

    There is also a whole lot to learn. Molecular physics, atmospheric physics, how the myriad proxies work, past climate change events, ocean mechanics, how ENSO works, how models are constructed etc., etc.

    Your time would be much better spent studying what we do know rather than trying to pin down what we don't know in order to give a wave of the hand attribution of climate change to something other than CO2.

    The science is fascinating, in and of itself, and you will understand the gaps in our knowledge (where they are, and how deep) much better by learning what we do know than what we don't know.

    Second... apologies for having parts of your post snipped, but unlike WUWT and many other denial sites, we like to stick exclusively to the science. Occasional this rule must be bent because of current events or the topic of a post (such as public policy), but as a rule, physics doesn't belong to a political party or have a socio-economic reason for warming the planet, so those factors aren't worth discussing.
  15. Sphaerica, no problems. You are right to curtail, but I am not running out of ideas. I had a specific list of questions, I have now gone through it. The topic question was: What does past climate change tell us about warming? Part of the answer would be: Identify all natural causes which may have caused warming, and which may still be causing warming. Once they have been carefully and rigorously eliminated, it leaves only AGW.

    The list of the 'possible others' was:

    1 Solar irradiance - yes of course, but variations are not powerful enough to account for recent variations.
    2 Does Solar activity/GCR influence cloud formation? Answer - perhaps, but no firm evidence for that theory yet.
    3 Is cloud formation influenced by the biosphere? Answer - perhaps,some interesting studies in hand, but no firm evidence of a significant effect yet.
    4 Earth heat, release of mantle heat underwater? Answer - no evidence.
    5 Increase in surface irradiation (TSI) due to any other unknown cause, as yet undetected. Answer - the subject has been discussed in another thread. TSI data is incomplete and there seem to be no historic proxies. So, no evidence either way on that.
    6 Fairies (joking)

    That was my entire list of 'suspects'. I have had clarification on all, for which many thanks to all. In summary, on the basis of current evidence: Past climate change and assessment of all conceivable natural causes tells me that AGW looks a 95% certainty.

    My point about bankers? Well, all professionals carry responsibility for their advice and decisions. I am one. I have to make decisions too, some of them determined by an assessment of the AGW case. If AGW predictions are correct, the world will be grateful for your advice. It not, the world will be quite unhappy about wasted resources. No judgment there, just the way life is. Good luck.
    Response:

    [DB] Here we are, a flurry of responsive comments later (all subsequent to your comment with unsourced graphics).  I remind you again of the need to provide sources for these asserted graphics as others having to point out the issues with these is dragging this whole thread off-topic.

    Or else I will have to clean up this thread a bit.

  16. FYI, there is evidence on TSI... evidence that there has been no corresponding increase coincident with the warming of the last 30 years. That's why they started reaching for GCRs and other special effects. Except that there are proxies for that, too, and they don't appear to have had that sort of climate effect in the past, so why would we think they suddenly have a large effect now?

    And, lastly, if such an effect is large, then it implies a high climate sensitivity -- and a big part of the skeptic argument today has turned to a begrudging admission that it is warming (unless some new evidence says it's not or it's stopped), a begrudging admission that CO2 is the cause (unless some new idea says maybe it's not), but an adamant belief that any such warming will not be too great because climate sensitivity is low and the planet has a natural negative feedback to constrain temperatures to a narrow range (this despite the evidence of great swings between glacial and interglacial periods, and other proxy evidence of past extreme if much slower changes in climate, observational evidence of positive feedbacks in today's warming world, and well conceived and modeled mechanisms that would point to the currently estimated sensitivity of 2˚C to 4.5˚C).
  17. 265, lancelot,

    Sorry, I just realized that you used TSI incorrectly, and I responded to my instant interpretation of the acronym, not what you meant by it. TSI stands for Total Solar Irradiance, and has to do with the amount of solar radiation (all frequencies) hitting the earth at TOA (top of atmosphere). It does not refer to the amount of radiation actually reaching the ground.
  18. 267 No, my apologies, I meant Total Surface Irradiation.

    Moderator: Point noted. My first use of graphics, possibly the last.
    Response:

    [DB] It is not the usage of graphics to make a point that is the issue (indeed, graphics are extremely powerful in conveying of complex information and ideas).  The issue in play is that the source of the graphic needs to be made transparently clear.  And if the graphic is "home-baked-bread" then the methods used to create it (the "recipe", if you will) must be made available to the reader as well.

    But thank you for providing the requisite information.

  19. Tom Curtis: Thanks for your post 263. PETM is a big subject area in its own right and I have yet to venture into it in depth. With my usual Sherlock Holmes hat on I would just ask, have all other possibilities first been eliminated?

    What little I know of PETM comes mainly from Bryan Lovell in 'Challenged by Carbon' (a book kindly recommended to me by Prof David MacKay) in which Lovell selects the PETM event of 55 Ma as the prime evidence for CO2 warming.

    To quote him:
    _________________________________
    Prof G Dickens [presumably Dickens G R 1999, Nature, 401, 752-755] ... reaches several conclusions:

    1 The first of their conclusions is that a large quantity of carbon was released into the ocean-atmosphere system
    2 The second is that the temperature of the water at the bottom of the ocean increased rapidly by more than 4 deg C from 11 to 15 deg C , over the same short period.

    Norris & Rohl [1999] conclude:

    3 For just a brief period, .. temperatures at high latitudes and in the deep oceans soared by 5 - 7 deg C. [some contradiction of numbers here]
    _____________________________________

    I have not read the papers cited, but just considering those two factors as described, the primary event seems possibly to be heating of the bottom of the deep ocean. CO2 could not cause such a rapid effect directly. It seems very possible from those statements that a major geological event in the mantle or crust under the oceans released a large amount of heat directly into the deep oceans. A huge release of carbon from the mantle or crust in form of methane at the same time is indicated. Heating of the deep oceans would lead to a rise in air and surface temperatures, as well as a further release of stored CO2 in the oceans. No doubt the airborne CO2 would create a serious GHG effect, but how much of the surface warming could have in fact been caused by deep ocean water warming?

    Would that affect the sensitivity estimate?

    I hope I am not just saying 'yeah if', but putting forward a valid question here.
  20. Moderator: Is there any way to find one's past posts? I am getting a bit lost with the many different threads.
    Response: [Dikran Marsupial] The easiest thing to do is to look back through the recent comments. However, it is generally a good idea to limit the number of discussions you participate in simultaneously. Science is best discussed in depth rather than breadth (at least to begin with), the best way to do that is to conduct a single narrow thread of discussion at a time and avoid digreessions.
  21. lancelot - if you want to get into ideaological matters, how about taking the challenge here?
  22. lancelot - It takes something like 0.5-1 ka (thousands of years) for the deep oceans to equilibrate to a temperature change. The PETM event, quite possibly driven by a massive clathrate release, lasted 20 ka, with the effects persisting for 200 ka - plenty of time for the enhanced greenhouse effect to equilibrate.

    Not extra heat at the bottom of the ocean - we would see the geologic signs of that (volcanism, lava, etc?) quite easily. But a carbon release that increased the greenhouse effect.

    The extra CH4 (then oxidizing to CO2), massive GHG increase, leads to atmospheric and ocean surface heating, with ocean circulation bringing that to the depths. The math works out - no extraneous sub-benthic heat sources needed.

    ---

    I have to say that you appear to still be hunting for anything but CO2, rather than following the evidence. That's an inherent confirmation bias, searching for a particular explanation rather than paying attention to what the data supports. That attitude will lead you astray...
  23. lancelot - As an addendum to my previous post:

    The Earth fully equilibrates to changed energy conditions in a fairly short time, geologically speaking (~500-1000 years, including deep oceans). The only way for a temperature change to last 200 ka is for either the input energy or the temperature dependent rate of outgoing energy (as per the Stefan-Boltzmann relationship) to be different - a forcing change.

    Hence your PETM "sub-ocean heating theory" would require a 200 ka 5C warming of the ocean bottom. There's no evidence for that, and in fact significant evidence against it (there would be considerable changes in ocean core data, for example). Whereas we have plenty of evidence supporting increased GHG effects, including the timing of CO2 recovery matching the end of the PETM.

    Follow the evidence, lancelot - not your preconceptions.
  24. Might I suggest to anyone reading this thread to to take the time and re-read Tom Curtis' post at #263. A great, and impotant post! And Tom, it might be worthy of a new blog post if the balance of both cold (LGM) and warm (PETM) climate sensitivity has not been explicitly covered before?
  25. KR, fine, I simply put what seemed to be a very obvious question, from a position which I had clearly stated, based on reading the statements quoted by Brian Lovell, and without the benefit of a detailed study of the PETM. The statements quotes were not backed up by detailed supporting evidence such as you have quoted. My question invited any rebuttal with contrary evidence, such as yours. That does not, I think, make me a narrow minded denialist. I may however be a bit persistent in seeking answers.

    Just another question though, how can you be certain of "no geological signs" in the ocean floor from 55ma ago? Lot of sediment since then, and it's a big ocean.
  26. 275, lancelot,
    Just another question though, how can you be certain of "no geological signs" in the ocean floor from 55ma ago? Lot of sediment since then, and it's a big ocean.
    Research ocean cores. See how they are used to establish various aspects of climate, life, etc. See how they are dated (by looking at the different, distinct layers of sediment).

    For example, consider this excerpt about how cores can be taken:
    The Chikyu (Japanese for planet "Earth") seen above, cost $540 million and is a colossal 57,500-ton, 210-meter-long white ship developed to drill deep below the ocean floor. Besides being the most sophisticated laboratory on the seas, the science vessel boasts the tallest drilling derrick at 112 meters above the waterline and a drill pipe that is 9.5 kilometers long--22 times the height of the Empire State Building. The borer drills through 7,000 metres of crust while floating in seas up to 2,500 meters deep. Its drilling system uses a 380-ton protective casing over the wellhead that is about the size of a six-story office building. It shields the vessel against eruptions of methane gas and pressurized fluids and allows for the secure retrieval of nine-meter-long core samples.
  27. 275, lancelot,

    Oh, and... a lot of real deniers come here trying to "trip up" the science by offering half-baked ideas that they assume scientists haven't considered. A lot of your questions come across in that vein, because of the way they are phrased.

    You'll probably raise less hackles if you take a little more care in how you phrase your questions, by making it clear that it's an honest question as opposed to a rhetorical question intended to convey doubt to lurkers (i.e. aimed at other readers rather than the people of whom you are asking the question).

    For example, your "how can you be certain..." question might be better phrased as "how have scientists ascertained that..."

    I know it may seem annoying, but it's important to come across as truly interested in the answers, and giving scientists their due respect, rather than making it appear that you have, in your spare time, out-thought the professionals and come up with something they can't possibly have considered.
  28. lancelot - Forminifera species ratios, sedimentation types/rates, isotopic balances, other signs. Forminifera species ratios are quite sensitive to environmental conditions, for example, and have been used to construct multiple paleotemperature records, including sea rise on the order of millimeters/year.

    And if the ocean floor heated up non-uniformly, the signs of such heating would be even more clear where it did happen.

    But seriously - there is no evidence to suggest a 5 °C heating of the ocean floor lasting 200 ka. That's the evidentiary equivalent of fairies, of claiming climate change is due to wars among the Mole Men, of magic wands.

    Actually reading Katz, Dickens, et al 1999, they state:

    "Long-term global warming during the late Paleocene pushed the ocean atmosphere system past a critical threshold, causing warm surface waters to sink and intermediate to deep ocean temperatures to rise by 4 to 8C. This warming propagated into the sediments, converting once solid CH4 hydrates into free gas bubbles. This dissociation resulted in an increase in pore pressure at depth, leading to sediment failure and the release of massive quantities of CH4 into the ocean." (emphasis added)

    From this they feel a circulation change pushed surface water quite quickly into the depths, warming the benthic waters and triggering the clathrate release. .

    "Methane release would have occurred on continental slopes ... adding carbon to all reservoirs of the global exogenic carbon cycle and substantially shoaling the depth of carbonate dissolution in the ocean. ... Over several hundred thousand years, global carbon and oxygen cycles gradually retumed to equilibrium conditions after the LPTM, although marine and terrestrial ecosystems were forever changed. "

    Again, note the carbon cycle disturbance. There are also in this paper descriptions of ocean cores that show sedimentation supporting this scenario.

    I would strongly suggest, lancelot, that you read the papers you have pointed to - it looks more like you're grabbing the first interesting quote without looking at the context, and hence presenting a misinterpretation of the work.

    There's a big difference between asking "Hey, somebody said XXX, I don't know if it's right or wrong?", and presenting skeptic arguments and (in this case) misinterpretations of papers as your opinion.
  29. Lancelot - have a look at this article here for more on PETM. The evidence for CO2 being culprit is in the ocean acidification which also constrains the size of change. I would also suggest looking at
    "Carbon dioxide forcing alone insufficient to explain
    Palaeocene–Eocene Thermal Maximum warming"
    Richard E. Zeebe, James C. Zachos and Gerald R. Dickens
    2009 for an idea of the constraints (though I disagree with some of their conclusions).
  30. Sphaeriica, if I make a statement, and someone says "how can you be certain?", I dont take offence. I explain why I feel confident in making the statement. So I don't quite see your point.

    KR please note the preface in my post 269. I clearly stated my ignorance at the outset, I quoted in full the basis for my question. Anyway, question raised, answer given, thanks for the scientific evidence which you have given to negate ocean floor heat release as a possible partial contribution to the PETM warming. Have you considered that every time some non expert says , maybe it isn't CO2, and you give a reasoned answer to explain why it is, it actually strengthens the public perception of the Co2 theories?

    Scaddenp will take a look, thanks,
  31. 276 , by the way, amazing engineering, really fascinating to hear what goes on in deep ocean exploration. Was honestly interested in how one would could possibly know what happened 55mya and 7 miles down under the ocean. Impressive.
  32. 280, lancelot,

    This isn't a normal venue. In a classroom, or a party, or at lunch, when you do as you describe you are right.

    But in climate change there are a large number of very, very arrogant, angry and ignorant people. They waltz in here with personal theories based on a gross misunderstanding of the science, stating everything from proof that the globe hasn't warmed to the idea that GHG theory violates the laws of thermodynamics and more.

    One (-self-snip-) even claims that he's proven that current warming is coming from the interior of the earth.

    Most people who comment here but do not already understand the science are not here to learn, or asking reasonable questions and looking for answers (as I presume you are).

    Most people who comment here but do not already understand the science instead have an axe to grind, and believe that they have all of the real answers, and that they'll show those dang, silly scientists a thing or two about logix and clear-headed thanking.

    Hence... a perfectly ordinary sounding question is likely to touch some nerves with people who have already been rubbed raw with what could, at best, be called a parade utter and complete nonsense.

    Hence, a sensitivity to such a response is advised. You might not want to go to the trouble to carefully word your questions, but you might give someone like KR a break when they presume that you are possibly asking these questions with a hidden agenda, hoping to trip people up or to sow doubt.

    At the same time... people here at SkS probably should back off and give newcomers a little more slack before flipping out on them.
    Response:

    [DB] "At the same time... people here at SkS probably should back off and give newcomers a little more slack before flipping out on them."

    Agreed.  Give the benefit of the doubt, with the action mentioned after the word "before" in your back pocket.

  33. Sphaericq, thanks for the gentle advice. I note that KR told me I was raising a Skeptical Argument , my caps. I suspect that is the touchy point. I have read nothing up on the PETM except Brian Lovells book. My question honestly came out of my own head, as an immediate reaction to the events as described, not off some website. But if the question, as I now suspect from KR's phrase, is a regularly used SA, I can see how KR would react to someone apparently churning out an old mantra.

    I do appreciate being given the benefit of the doubt. My purpose in using this forum (for which many thanks for allowing me) is to clarify my personal understanding. I entered here rating significant AGW as around 50% certain, now I would rate it as 80 to 95% certain.

    Lastly, I have seen criticism of some of my posts on the lines of , why dont you read up in depth on the subject before coming here with questions. Simple answer, I would love to, but life isn't long enough. That is why one asks the experts.
  34. lancelot - If I've misinterpreted your posts, overreacted, my apologies. What I was reacting to is in large part the series of different skeptic arguments you have presented, pointing every which way. That can be very hard to distinguish from the behavior of a Concern Troll.

    I will note, however, that the vast well of knowledge does reward those who put in some effort. In my last post I spent ~20 seconds on Google Scholar using the search term "Dickens G R 1999, Nature" from your post (clicking on the first PDF), roughly two minutes looking through the abstract, initial sections, and conclusions - and found clear information completely dismissing a 'heat from the crust' scenario.

    That's two and a half minutes. And this is not my professional field.

    Alternatively, using the "Search" box here on SkS, with the term "crust", links to some relevant threads discussing particular climate issues, such as the recent Heat from the Earth’s interior does not control climate.

    I'm glad you are actually looking for information on climate change. Far too many take a personally/ideologically attractive position, stick their fingers in their ears and sing 'lalala", as I'm sure you've seen. I would encourage both your curiosity - and perhaps a bit more use of search capabilities.
  35. KR I will use google scholar in future, it looks good. iI have in the past tried to download papers such as Dickens from the AAAS site and for some reason the site repeatedly fails to register me. So only the abstracts are viewable, for me. When I have seen full articles, often as a non expert the language and terminology can get quite dense and very hard to follow. I simply don't have the hours in the day to learn the language. At the same time, i need to make some decisions which are to a large extent dependent on theIPCC advice for policy makers. For that reason I have taken time over the last 6 months to fully understand the subject in as much depth as possible, in order to feel confident about applying the advice. Learning mainly on the web, that inevitably exposes one to a lot of arguments and apparently valid questions, from all sides, some of them very plausible. Muller, Svensmark, Kirkby.. Appinsys... I felt it was quite important to be clear in my mind and to subject the questions in my mind (some of them independently arrived at by the way) to expert grilling. I wish of course I had the time to do a climate science degree and even to understand a tenth of the content of some of the papers! But this forum has been very helpful, and patient. I have actually gone through my finite list of 5 query subjects now so I doubt that I will need to ask any more, unless some surprises come up. Of course as we know, life is full of surprises!
  36. 285, lancelot,

    Three things.

    First, while it seems daunting at first, you will find that as you look at more and more actual papers (just briefly!) it will get easier and easier. Admittedly, KR's ability to do what he did in 2 1/2 minutes did come from a lot of practice. But it does get easier.

    Second, on finding papers... I've found that while most papers are behind paywalls, you can almost always find a copy for free download from somewhere. Usually including the term "+pdf" in the Google search terms will find you an option or two... but not always.

    Third, on learning on the Internet... that can be very, very dangerous, especially with the vast number of denial sites out there who want to spin the science from their own perturbed (and wrong) point of view, but do so with the confident tone of someone who is teaching you fact rather than their interpretation, misinterpretation or misrepresentation of the facts. You need to be very leery of what you read and what you trust.
  37. 285, lancelot,

    For learning properly I might recommend Raypierre Humbert's book Principles of Planetary Climate. I have not read it myself yet. I simply have a whole lot of respect for Raypierre.

    Amazon lets you look at a fair number of pages inside the book to give you a feel for it.

    If you do pick it up, let me know how it reads. I won't have time to do so myself for quite a while (looking at my schedule, I'm planning on getting to it by my fourth reincarnation from now).
  38. lancelot - One thing I've found helpful on Google Scholar is the links to "All N version". Often this points to alternative sources, pre-prints, author's copies, etc., when just an abstract is available on a journal page. Full text isn't always available, but it's helpful.

    If nothing else works, I follow the "Cited by N" link, and try to get a feel for that particular topic from those either using that paper as background, expanding upon or refuting the results.
  39. lancelot : "Muller, Svensmark, Kirkby.. Appinsys..."

    Seeing that you go to Appinsys, I can now see how you could have been confused or uncertain previously !
    A website whose 'Global Warming' page contains 28 instances of 'alarm' and 3 uses of the word 'lie', should give pause to anyone thinking of using that site.
    Not only that, the About page ends up by calling Obama a "liar" !

    How could you (or anyone) consider that site a useful and unbiased one ?
  40. Lancelot:

    Rather than attempting to access and read a slew of peer-reviewed papers, I recommend that you first read and digest books and reports that essentially synthesize the science of climate change. You really need to understand the forst before you start analyzing each and every tree in it.

    In terms of textbooks, I highly recommend the Fourth Edition of Global Warming: The Complete Briefing by John Hougton, Cambridge University Press, 2009. It is written in plain English so to speak.

    Another excellent resource is the recent set of reports prepared by the National Academies of Science under their America's Climate Choices initiative.

    To access these reports, click here.
  41. lancelot - I would also recommend The Discovery of Global Warming for an overview of the topic, not requiring a technical background.

    And in looking at the 'series of tubes', the interweb, I would suggest discounting any sites with obvious political or ad hominem ranting. Such as, for example, "Appinsys". The ability for anyone to publish to the web means that quality checking is ever more important.
  42. 292, lancelot,

    Didn't notice Appinsys in your list.

    The site is a travesty. You will get nothing but confusion and misinformation there.
  43. Thank you all for the wealth of suggestions for further reading. To be honest, From now on I will tend to rely on IPCC advice and reports, in which I now have much more confidence.
  44. Out of interest, and for future reference in any discussions with colleagues, what would be specific examples of wrong information (as distinct from polemic) in the appinsys site? It was the most convincing skeptic site i came across, the arguments being supported by a lot of impressive graphics. Sorry if off topic here, but I am never quite sure which thread to move to for digressions.
  45. lancelot#254: Replying here, a thread that deals in facts; a strong counterpoint to appinsys.
  46. 294, lancelot,

    I dont' want to waste too much time dissecting their nonsense, because just looking at it makes my skin crawl, but you should note that they are very, very good at taking actual scientific data that is accurate, but presenting only that data that fits the conclusions they wish to establish.

    I'll just do a couple.

    Their page trying to claim that warming is not global.

    This page goes to great lengths cherry picking plots to try to show that warming is merely a northern hemisphere problem.

    Their conclusion:
    Conclusion: The empirical data show that warming in recent decades is a northern hemisphere phenomenon – in particular an Arctic phenomenon –with no significant warming in the tropics or southern hemisphere.
     
    It is not a global phenomenon.
    The fact is that because of the unequal distribution of land masses the warming in the two hemispheres is always dramatically different. This does not mean that the southern hemisphere is immune or not involved, merely that it responds differently in the short term.

    The conclusion that warming will be greater in the Arctic is, in fact, a tenet of the current science -- research "polar amplification."

    At the same time, much of their evidence relates to the differences between the Arctic and Antarctic ice and temperatures, but these are apples and oranges. One is a large sea virtually hemmed in by land, while the other is a large, mountainous area of land surrounded on all sides by ocean. The southern hemisphere is dominated by ocean, while the northern hemisphere is dominated by land. Of course they are responding differently!
  47. 294, lancelot,

    appinsys MWP

    This section goes to great length to try to claim that the MWP is global and had temperatures greater than we are seeing currently, when this is patently false.

    Part of their argument:
    This IPCC statement is at odds with the findings of other scientists. For example, research at the Harvard-Smithsonian Center for Astrophysics report on a recent paper using proxies, which verifies the occurrence of the MWP: [http://cfa-www.harvard.edu/press/pr0310.html]
    The linked paper by Willie Soon (an astrophysicist, not a climate scientist) is notorious for it's failings, and the resulting resignation of half of the publishing journal's editorial board in the ensuing controversy.

    They go on to say:
    Many studies can be found exhibiting the MWP. One example is shown in the following figure.
    This is a common skeptic trick, and a great example of presenting individual proxies that for that one location seemingly show similar warming, yet their graphs stop before more recent temperatures.

    Another common problem is that the MWP is very loosely defined as occurring from 950 to 1250 AD. The warming in any particular location might be a 50 year span peaking at 1000, 1100, or 1200 AD. They're all treated as contemporaneous. Can you imagine if current temperatures were computed by taking the highest temperature in a 300 year span from each separate location on the globe?

    In their example shown here the peak is just prior to 1000 AD.



    They also term this a "Northern Hemisphere" reconstruction even though 9 of the 14 proxy sites used lie above the 60˚ north, and 13 of the 14 above 45˚ north. It's more appropriately a sub-arctic reconstruction.

    And yet even their graph hows that current global temperatures exceed those around 1000 AD at that latitude. If you were to instead plot temperatures in the same band, you'd see this:



    [Source: GISTEMP... click on the image to view]

    Imagine the 1 to 3 degree increase added to the Cook graph, which are representative of the same sites used in his study and on his graph, instead of the temps appinsys added.

    The Cook paper is available here.
  48. 294, lancelot,

    I don't have any more time for appinsys... have to chauffeur the teen daughter around town.

    But if you have any particular section of appinsys you'd like me to rip up, just let me know. It can be a fun diversion.
  49. Sphaerica, Thanks , I guess that writing that response was the equivalent of root canal work for you. I get the point!
  50. Lance @ 293

    Over the past couple months I have been reading both here and at JoNova's blog trying to acquaint myself with the state of the debate.

    Even if I were absolutely scientifically, numerically and logically illiterate, one thing would stand out. One side is full of desperation, anger, ideology, rhetoric and ignores questions. The other side is a little testy at times, a little left-biased at times but generally patient, responsive and comprehensive.

    SkS makes it really easy to pick who to trust.

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