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What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Greenhouse gasses, principally CO2, have controlled most ancient climate changes. This time around humans are the cause, mainly by our CO2 emissions.

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)

Greenhouse gasses – mainly CO2, but also methane – were involved in most of the climate changes in Earth’s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer. When CO2 levels jumped rapidly, the global warming that resulted was highly disruptive and sometimes caused mass extinctions. Humans today are emitting prodigious quantities of CO2, at a rate faster than even the most destructive climate changes in earth's past.

Abrupt vs slow change.

Life flourished in the Eocene, the Cretaceous and other times of high COin the atmosphere because the greenhouse gasses were in balance with the carbon in the oceans and the weathering of rocks. Life, ocean chemistry, and atmospheric gasses had millions of years to adjust to those levels.

Lush Eocene Arctic 50 million years ago

Lush life in the Arctic during the Eocene, 50 million years ago (original art - Stephen C. Quinn, The American Museum of Natural History, N.Y.C)


But there have been several times in Earth’s past when Earth's temperature jumped abruptly, in much the same way as they are doing today. Those times were caused by large and rapid greenhouse gas emissions, just like humans are causing today.

Those abrupt global warming events were almost always highly destructive for life, causing mass extinctions such as at the end of the PermianTriassic, or even mid-Cambrian periods. The symptoms from those events (a big, rapid jump in global temperatures, rising sea levels, and ocean acidification) are all happening today with human-caused climate change.

So yes, the climate has changed before humans, and in most cases scientists know why. In all cases we see the same association between CO2 levels and global temperatures. And past examples of rapid carbon emissions (just like today) were generally highly destructive to life on Earth.

Basic rebuttal written by howardlee


Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Last updated on 6 August 2015 by pattimer. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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Myth Deconstruction

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MD Past

Please check the related blog post for background information about this graphics resource.

Further reading

RealClimate article published by Prof. Stefan Rahmstorf on July 20, 2017:

The climate has always changed. What do you conclude?

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Comments 376 to 400 out of 883:

  1. I also read the second figure in question to be natural output. He phrased it as "the modern mean annual rate of Mantle co2." So I have the concepts but got led astray by dividing by 12 in my attempt to get to the modern atomic weight and then try to convert that when all I had to do was multiply by 12.  So 6,000 GT divided by 2.13 would mean a theoretical atmospheric input of 2817 ppmv over that (plus minus) 1,000,000 million year time period  less whatever the Earth's carbon sinks could then reabsorb. Mclean strongly implied a weaker feedback mechanism in describing the ocean's of the day as being warm, deep and with slugish circulation. So a conservative number might be closer to 40%. That would imply the the ppmv towards the end of the period was around 2012 ppmv.   The other author'(s) paper, however, stated that the ppmv was pretty consistant at around 350-500 ppmv until, right at the KT mark, it shot up to 2300 ppmv. Darn: it would seem both of these sources can't be right.   I was looking, in all of this, for an aproximation of the tipping point when the ocean's heatsink mechanism just shuts down. It would seem all the author's numbers agree about ppvm being roughly in the  2000-23000 range indicating dead oceans below at the end of the sequence. The Ma period numbers preceding are wildy divergent. The second paper looked for 4600 Gt to be thrown up by an impact to get to 2300 ppmv.

    4600Gt divided by  the current anthrogenic number of 8.2 is 560 years to dead oceans.  That is worrysome indeed, but I wish there was more consensus on the background data as there seems to be on current data. In both of the papers I cite, the ppmv figures in the long term neatly support each author's hypothesis but both can't be correct. One would think peer review would catch major discrepencies such as these. Thanks for the help. I am just a laymen who can read fairly technical data but strugeles a bit with the math.

     

  2. pheidius @376, I am unable to comment further unless you do in fact cite the two papers, ie, either list their names, authors, date and journal of publication; or provide a link to the abstract including those details.

  3. Hi,
    Sorry about the delay but, yes, the papers are available. I would have included them at the onset but I was confused by the insert and source tabs. The Mclean paper is available on this page http://filebox.vt.edu/artsci/geology/mclean/Dinosaur_Volcano_Extinction/pages/studentv.html  as a pdf on a link called McLean (1994)

    The second paper I referenced is here

    7836.full.pdf


    I have mulled over the discrepancy because its magnitude is glaring. The pertinent facts, as I see them, are that while both camps seem to agree that a ppmv of 2000-2300 marked the bitter (acidic) end of the line at the KT boundary E.G. dead oceans, they clearly disagree on the ppmv preceding the heat sink's 10, 000 year collapse. Mclean's numbers would indicate a millennium long sharply punctuated yet steady uptick where the second author(s) see a steady 350-500 ppmv for the Ma and only then see a massive jump in the final 10,000 years.


     I think I see a possible way to explain this difference. In doing further research, I am seeing some current rump climatology research, which undermines a critical assumption that Mclean may have used. The current working assumption, in most climatology models, is that the Earth reabsorbs around 50% of the Co2 emitted and that the remainder is added to the heap, as it were, thus causing an ever increasing ppmv. This may be a key assumption that Mclean did not question and used in the exposition of his model. The other authors used a more direct measurement of ppmv for the Ma(the size of leaf stomata). This would support the rump research, which postulates that the Earth’s sinks absorbs Co2 regardless of the amount emitted, keeping the ppmv in the 300-500 ranges.


     I am trying to ground my take on this on the older and longer data sets.  In comparing the two sides, one used an assumption to approximate ppmv for the Ma in question while the other used a form of indirect measurement that has wide acceptance in the field of geology. This brings me back to the salient question with which I began.  The Ma preceding the KT boundary extinction event saw 10-25 % higher co2 levels annually yet the ppmv fluctuated between 350-500.  I understand the risks involved in a 90 percent annual increase yet I am struck by the fact that the second set of author(s) paper required the instantaneous release of 4600 Gt on top of 1,000,000 years of a 25 % increase before the sinks failed catastrophically over a period of 10, 000 additional years.  In terms of percentages, the 90 Gt number which you described, as a 90 % increase over baseline constitutes only a .019 % annual increase relative to the near instantaneous increase wrought by 4600 gt.(not to mention the other colossal atmospheric effects of a bolide collision).  


    I am, by no means, taking a hard and fast position here. I do see another unquestioned assumption as well as other implied and, as of yet,  unexamined data sets and models in the position taken by the second paper for the need for an additional 4600 Gt to precipitate disaster.   I will have to reread this paper carefully and look closely for the source(s) of this modeling.

  4. Is anything in this link useful information?  Thanks. http://www.timelinetothefuture.com/index.php/en/prepare/possible-earth-events/sun-a-heat

    Response:

    [TD] No, not a single thing.  Really.  For each of the arguments that page makes, you can find the actual scientific evidence summarized in a Skeptical Science post.  EIther use the Search field at the top left of any Skeptical Science page, or click the View All Arguments link next to the thermometer below that, or click the Arguments link in the blue horizontal bar at the top of any Skeptical Science page.  Note that most posts have different levels of detail in different tabbed panes--Basic, Intermediate, and Advanced. Here are just a few examples:  "It's the Sun," "It's Cosmic Rays," "We're Heading Into an Ice Age," "We're Coming Out of the Little Ice Age."  (Okay, Skeptical Science does not have rebuttals for all the contentions made in that page; we don't have a rebuttal to the contention that the Earth will stop rotating and then start rotating in the opposite direction.  Here's an answer to that one:  That would happen only if a planet-sized body smashed into the Earth, offset from the center, and in the direction opposite the Earth's spin.  But if that happens, I'm perfectly willing to stop worrying about CO2 levels.  Because I'll be dead.  Along with everything else.)

  5. " The current working assumption, in most climatology models, is that the Earth reabsorbs around 50% of the Co2 emitted and that the remainder is added to the heap, as it were, thus causing an ever increasing ppmv."

    This is an extremely simplistic and short term view of carbon cycle modelling, and only true for very short term (around 100 years). Both modelling and paleoclimate studies point to significant positive carbon cycle feedbacks as sinks are saturated. You might like to look at:

    Le Quere, C., C. Rodenbeck, E.T. Buitenhuis, T.J. Conway, R. Langenfelds, A. Gomez, C. Labuschagne, M. Ramonet, T. Nakazawa, N. Metzl, N. Gillett, and M. Heimann, Saturation of the Southern Ocean CO2 sink due to recent climate change, Science, 316 (5832), 1735-1738, 2007.

    Schuster, U., and A.J. Watson, A variable and decreasing sink for atmospheric CO2 in the North Atlantic, J. Geophysical Res., 2007.

    Ultimately, as the oceans warm, they outgas CO2.

  6. Actually for a good look at current understanding of carbon cycle and its evolution, look at Chp6 (esp 6.4) in the just released IPCC AR5.

  7. You also cite "some current rump climatology research". This is a curious term. Could you perhaps give some cites for this "rump" research?

  8. This is a major point made repeatedly by my "opponent" one which I'd like answered as well if at all possible. Thank you again for your time.

     

    "The period that we were talking about is the Younger Drayas / Preboreal

    Which in conjunction means that we are talking of the transition from the Younger Drayas to the Preboreal.

    This is an example of a D-O event. (Everyone calls them that because the names of the original people Dangaard -Oestinger? are hard to say/remember).

    The point of that is that there have been THOUSANDS of these transitions. They occur every 1100-1500 years.

    Think with common sense for a minute. If these transitions have been occuring every roughly 1500 years for thousands and thousands of years.

    If that is true - why do you think THIS temperature change is man caused? Especially since we are roughly due for a transition? Remember these temperature changes have been seen for more several tens of millions of years - and in none of them were men around to cause the change.

    In all of them, the CO2 levels changed; the atlantic and the pacific oscillations occurred.

    In addition to that, Al Gore (et.al) has basically said that the temperatures the earth is seeing now is unprecedented. This is just simply factually untrue. Look at the K. ice cores - where we have an unbroken temperature record for like 1,000,000 years. Temperatures *higher* than the ones we see now have been seen every 50,000 years or so.

    Followed by steep plunges in temperature (ie, drops of 12oF). The period of life that we regard as normal is only the very tip of the mountain - most of the time the temperatures of the earth are much, much colder. Hence sabertooth tigers and mammoths.

    Now, regarding the two skeptical science articles about correlation & lag.

    I quite agree that there is a correlation between co2 and temperature. Where I differ is that I do not believe that Co2 is causal.

    But I need to refine that statement again.

    As the vostok cores show (and every other ice core) is that Co2 follows temperature change. Again, this is a simple reflection of Henry's Law - which climate scientists are trying very hard to ignore.

    In that second skeptical science article, they cherry pick exactly *one* transition, that was known to have asymptomatic co2 event to prove therefore that ALL transitions are induced by carbon.

    Thats flat out deceptive.

    Look back to the Quaternary paper I quoted. It claims that it is clear that there are SIX main drivers of climate change - as opposed to AGW -which claims there is only one.

    If you look at the Quaternary paper - as well as others - you will see they claim that the temperature difference attributable to the change in CO2 is between 1.1 and 2.0 degrees.

    (Also many D-O events occur that have precisely that range of temperature changes; as well as the current temperature change).

    The quaternary paper is nowhere near alone in claiming documenting D-O transitions - there are literally hundreds of papers saying the same thing.

    Going back to the skeptical article you quoted (again, not a science paper, but I'll live). Look at the graph. Notice that the temperature change occurred differently in the arctic and the anarctic.

    Doesn't that just scream to you that something is involved other than Co2? Since CO2 distribution is fungible & normal? And indeed - something else IS involved - the ocean water temperatures are huge drivers of climate change.

    Again, even the hansen paper you quoted said that climate change could be caused by orbit shift.

    So contrary to what you have thought, I do not disagree with the fundamental fact that CO2 absorbs in the infrared.

    Contrary to what you may have thought, I do not necessarly believe that Co2 doesn't play some role in global warming. It may.

    But if so, it is one of many drivers of climate forcing.

    And what I said before is still true - the role of co2 outside the troposphere and the effects of carbon migration through the atmosphere are mostly unknown, and that nasa has documented that CO2 in the upper atmsphere cools the planet.

    And the effects of aerosols - as one of your skeptical articles alludes too, plays a much larger role than the AGW accepts. This by the way is the nature of Svenmark's & Cern's & others research."

  9. tkman0 - 'This is a major point made repeatedly by my "opponent"...'

    Actually, that's an entire series of bad denial myth points, a veritable Gish Gallop. If your 'opponent' has an actual point, please indicate what that is. As it stands you have mentioned the climate has changed before, CO2 lags temperature, the erroneous strawman of claiming that CO2 is the only driver of climate, it's cosmic rays, it's aerosols, and the questionable assertion of repeated D-O events - and I may have missed a few. 

    That is not 'a major point'. It's a shopping list.

    I hate to say this, but your posts have increasingly taken on the appearance of presenting your own opinions, not those of an 'opponent', ramping up in absurdity as initial errors are pointed out. I would strongly suggest looking at the list of the Most Used Climate Myths on this website regarding your most recent, and future, posts - it may save some time.

  10. I apologise, they're honestly not my own opinions, despite the fact that I can see how it was mistaken that way. I'm personally debating this guy on a website and these are the points he has sent to me and I'm just seeking a more professional explanation. The "main point" I was trying to point out was his reference to these D-O periods which I have no previous knowledge about. I'm sorry for posting the entire message he sent my way, I'll try to cut it down to the more basic points next time. And the reason why I'm posting these on his behalf is because I'm informing him while learning a lot myself in the meantime. 

  11. Also these D-O periods dont seem to be referenced on the website, which is mainly why I'm asking in a comment, to send him a more specific answer.

  12. tkman0 - Dansgaard-Oeschger (D-O) events occur during glacial periods. The interglacial equivalent is that of Bond events, discussed here. When considering those against recent climate change, however, Bond events are regional (showing in regional records such as Greenland or Antarctic ice cores), and in fact often include warming in one hemisphere (North or South) and cooling in the other. Recent warming is global, which just doesn't match the signature of a Bond event. 

    If your previous posting is any example, your opponent is clearly attempting to throw everything in the 'skeptic' myths but the kitchen sink in the hopes that something will stick. I find that sort of scattershot approach, rather than explaining an objection in detail, to be a signpost of denial - since any individual myth quickly runs aground due to errors of fact.... 

  13. Thank you very much KR, I appreciate the assistance. Tbh ive spent the last little while debating him, and his typical method seems to be to throw as much misinformation out there so that it makes it extremely dificult to debunk each argument on a case by case basis. 

     

    However he does keep coming back to the fact that just because there is a correlation between CO2 and temp doesnt make it causational. I point to the fact that we have never seen this level of atmospheric CO2 before but he simply denies it. He's largely a lost cause, I'm simply humoring him because it's fun to watch him squirm with the facts thrown at him over and over. I'll try to keep to the articles themselves and only resort to comments when explicitely necessary. Thanks again.

  14. tkman0, I have little to add to KR's comments re Dansgaard-Oeschger events.  I will, however, show this graph from wikipedia:

    The original caption reads:

    "Comparison of temperature proxies for ice cores from Antarctica and Greenland for 140,000 years. Greenland ice cores use delta 18O, while Antarctic ice cores use delta 2H. Note the en:Dansgaard-Oeschger events in the Greenland ice core between 20,000 and 110,000 years ago, which barely register (if at all) in the corresponding Antarctic record. GRIP and NGRIP data is on ss09sea timescale, Vostok uses GT4, and EPICA uses EDC2."

    I, however, want to draw your attention to the radical difference in magnitude in the perturbations due to D-O events durring the last glacial, and those during the Holocene - even in Greenland.  If your interlocuter knows enough to know about D-O events, he also knows about the minimal impact during the holocene of their (possible) equivalents, and that consequently that the current warming in not a D-O event, or a Bond Event

  15. tkman0 @383 quotes his interlocuter as saying:

    "Doesn't that just scream to you that something is involved other than Co2? Since CO2 distribution is fungible & normal? And indeed - something else IS involved - the ocean water temperatures are huge drivers of climate change."

    I am not even sure what your interlocuter is saying when they say "...CO2 distribution is fungible...".  Are they saying that any distribution will have equal effect on climate?  That it doesn't matter whether you have a Venusian or a Martian atmosphere when it comes to climate, its all the same?  That is the literal meaning of what they write.

    As to "... CO2 distribution is ... normal", that is clearly false when "normal" defined by comparison to the last 10 thousand, or indeed the last 5 million years.  That is, you have to go back to a time when the apes whose descendants are modern humans were just differentiating from the apes whose descendants are chimpanzees and gorillas to find a time when that claim is anywhere near correct.

    My primary concern, however, is the last sentence.  Given that ocean temperature is a part of climate, indeed, a major part of climate, that sentence reduces to:

    "Ocean water temperatures are huge drivers of ocean water temperatures"

    or possible:

    "Change in climate is a huge driver in climate".

    Your interlocuter can only avoid the evident circularity of the claim by assuming feedbacks are very large such that any change in ocean temperatures will result in further changes in ocean temperatures in the same direction, and of substantial magnitude.  That is, they must assume climate sensitivity is very large.  Far greater than IPCC values.  Without that assumption, his claim is vacuous due to circularity, and therefore cannot represent a causal relationship.

  16. tkman0, regarding causation, your denier is (irrationally, of course) consciously ignoring the experimental evidence that was woven together to form the theory that was then supported and improved by more experimental and other empirical evidence, and used to build models that unquestionably accurately predicted Earth's temperature trajectory.  Links to that evidence already was pointed out in replies to you.  That behavior is common among deniers.  So you might as well give up on your denier, unless dealing with him is educating or entertaining you.

  17. tkman0 - It's pretty simple. Increased CO2 causes less IR to go to space at any surface temperature (physics, in particular spectroscopy).

    A bit of Milankovitch warming causes the oceans to release some CO2 (temperature/solubility relationship), and considerably more warming results - a release of perhaps 20ppm/degree C - acting as a feedback. Our use of fossil fuels releases a great deal of CO2, and entirely without surprise warming results from that - in this case as a first cause. It doesn't matter whether the cause of CO2 increase is a bit of previous warming and ocean release or the result of millions of SUVs - the spectroscopic result of increased CO2 is that the climate will warm

    Not just correlation, but rather causation from physical principles (Fourier, Tyndall, Arrhenius all over 100 years ago) - with the correlation observed later (now) just as predicted. 

  18. @Tom Dayton, 

    It's personally very entertaining as odd as that may be. But also I'm learning a LOT in the process, so I hardly see this endeavour as worthless. But thanks for the admice anyway :)

  19. tkman0 @393, given an interest in learning about global warming, I believe that the best approach is to start reading the history of the science.  Here are some good resources from SkS:

    Climate Science History Interactive Tool

    Introducing the History of Climate Science

    The History of Climate Science

    Behind the Lines:  Herschel's Discovery of Infrared

    Two Centuries of Climate Science, Part 1, Part 2 and Part 3.

    You should supplement reading those pages by targetted questions about aspects o the science discussed in the history that you do not understand.  This will give you a far broader knowledge base than answering detailed questions in response to a denier.  It will also show just how narrow is the focus, and how ignorant of the history of the discipline those deniers are when they start denying things proved decades, or even centuries ago.

    Finally, I believe a good, clear explanation of the basic physics helps understand everything more clearly.

    If you try to learn by debates with deniers, you will find they repeat previously refuted claims, contradict themselves and do not have a clear idea of the subject.  Refuting them may be interesting the first time, but it will leave you with an unbalanced understanding of the science.  As it is also the several thousandth time various of the people helping you have refuted those same points, a more sensible approach would be refreshing for them as well ;)

  20. This for me highlights one major problem for sceptics and parents

     

    As the planet cools into an ice age, CO2 is transported to the deep oceans, helping to cool the planet.  As the planet again warms at the end of an ice age, this CO2 is released from the oceans into the atmosphere, helping the warming process along.  How and why CO2 gets stored and released from the deep oceans is something scientists are still working on.  Increased wind, driving more ocean circulation and changes in marine algae that take in CO2 may be parts of the process.

     

    From this 'educational' site

    Does this class as misinformation?

  21. Vonnegut, I'm not sure why you would think that might be "misinformation". The only part I'd question is, "How and why CO2 gets stored and released from the deep oceans is something scientists are still working on." It is well established that colder water absorbs more CO2. I suspect what they are questioning is how the CO2 then gets mixed into the deep ocean, but I'd think that would happen inevitably happen over time... leaving the relevant mechanism just the warming and cooling of the water itself.

  22. Vonnegut @395.

    Question 21 on the web page you link to doesn't provide the best answer in the world but the whole exercise is trying to be attractive to kids at the same time as keeping to the straight and narrow. (Thus Question 4. Do people farts contribute to climate change, too?) And it does fail to answer some questions it poses (eg Question 7) despite answers being readily presentable.

    Question 21 is in error by failing to differentiate between CO2 uptake into the oceans (which is mainly a temperature thing) and the transfer of that CO2 into the deep oceans (which is better understood than is suggested by the question). But this isn't the sort of detail you would expect to throw at kids. I see no case for classing it as "misinformation".

    BTW, thank you for the demonstration of how my cold oceans question works with deniers.

  23. So If I understand this correctly, Co2 is released from the oceans with extra heat so the oceans will become more alkaline, or more acid if it gets colder and more co2 is dissolved in the oceans?

  24. Vonnegut:  Not necessarily.  Oceans always release CO2 and absorb CO2--both processes.  Oceans are able to hold less CO2 the warmer they are.  Whether the net effect is more CO2 in than out depends not only on the temperature but on the atmospheric partial pressure of CO2--how much CO2 is in the air.

  25. Vonnegut, of course my answer was only about the really short term in versus out of CO2 from the oceans.  Over longer periods, other processes remove "CO2" (really, the chemical byproducts of CO2) from the ocean into sediments.  That is covered by the OA is Not OK series, and also by other posts such as the place of that process in the even longer period cycling through the crust--explained in "Understanding the long-term carbon-cycle: weathering of rocks - a vitally important carbon-sink."

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