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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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Comments 601 to 650 out of 883:

  1. Salute and thanks to Tom Curtis.

    To my knowledge, it has been just over 6 months since the last comment posted by Tom Curtis.   And I believe, about the same length of time since he posted at his blog "By Brisbane Waters"  [].

    Tom Curtis has been a frequent and energetic poster here at SkS, for 6 years or more.   He has researched / cited / quoted from a great deal of scientific literature, and he has analysed and discussed a great many issues.

    In short, he has been a powerhouse of objective scientific thinking.

    He has fought the good fight, against the lies lunacies & disinformation spread by anti-science propagandists & trolls.

    But over the years, Tom has occasionally referred to long-term unspecified health problems which hampered him.   His recent silence is unprecedented, and presumably indicates that he is too ill to post — or that Father Time has gathered him in.

    And I am sure that I speak for all science-oriented participants at SkS, when I express great thanks to Tom.


    (The moderators will, I hope, agree that this salute to Tom Curtis belongs here in the comments column of Climate Myth Number One , rather than in some difficult-to-find sub-listing.)

  2. Eclectic @601, thankyou for your kind words, and enquiry after my health.  I was advised of the enquiry after my health by Michael Sweet by Glenn Tamblyn in an email, and thought it appropriate to respond (with this being the best place).  As I have advised several of the SkS crew, my health problems have indeed worsened of late.  They are not life threatening, but have made the sustained pace of commentary I had shown in the past unsustainable for me.  As I find it difficult not to rebut silly arguments, or respond to requests for instruction, I doubt I could remain active on SkS in any capacity without being drawn into that high rate of activity, and so thought it best to absent myself completely.  On my last communication with an SkS team member, I mentioned that my health had improved and that I might be able to return to SkS in the medium turn.  Unfortunately it has now taken a turn for the worse, and that now looks less likely, although should my situation stabilize, I would certainly return.  In the meantime, I wish you all well, and succes to SkS and its mission.  

  3. Tom Curtis,

    It is very good to hear from you. I am sorry to hear about your health issues, my daughter has cronic health issues so I know they are a trial. I lived in Acacia Ridge for three years and I smile whenever I hear of Brisbane.

    Good luck with everything. I try to include a citation in all my posts but cannot detail things like you did. I wonder how you kept your patience with those who refuse to even read the data they are given.

    moderator: I accidently posted a duplicate of this on the wrong OP, sorry.

  4. I disagree with your statement that science has a good understanding of past climate changes and their causes. It does not. Also,Milankovitch was obviously brilliant to have figured out the spinning shifts of the earth. I believe he said that it might explain ice age cycles. Wikipedia gave a good explanation of the faults with that theory. I prefer my own theory listed as the Mike Krichew theory of what causes ice ages. So ask yourself the question: where does all the carbon dioxide come from in previous ice ages? I believe it came from warming oceans. This would explain why CO2 levels lag global warming in the data. So, what does the data say about warming oceans today. I have read that they are warming and thus giving off a lot more CO2 than our burning of fossil fuels now. Thus, I argue that even if we stop all fossil fuel burning today it will not stop global warming. 


    [JH] You are already skating on the thin ice of sloganeering by not providing science-based references for your own theories about what caused the ice ages and what is driving global warming.

    Sloganeering is prohibited by the SkS Comments Policy.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  5. "where does all the carbon dioxide come from in previous ice ages? I believe it came from warming oceans"

    Conceded.  However, the rise in atmospheric concentration of CO2 driving the modern warming is NOT coming from the oceans, but from the human burning of fossil fuels.  This we know pretty thoroughly, due to the distinctive isotopic signature of the rise.  Also, we know that the rise in atmospheric CO2 is not from the oceans because the oceans are still acidifying.  This is well-understood by science and not contested in any meaningful way.

    Read this post for background.  If questions, place them there, not here.

    The Koch Industries-funded BEST team found that, WRT 'Is CO2 leading or lagging temperature rise':

    "we know that the CO2 is not coming from the oceans but from human burning of fossil fuels"


    "it is clear that it is the CO2 that comes first, not the warming"

    Due to the thermal lag of the oceans in response to the anthropogenically-forced warming imposed upon them, the world will continue to warm and its climate will continue to change, for decades after the cessation of the usage of fossil fuels.  Again, pretty well understood by science.

    This is a science- and evidence-based venue, with regulars well-versed in the science.

  6. Mkrichew @604 , your Mike Krichew theory was previously called the Murry Salby theory.   To see why Murry Salby was wrong, please read Climate Myth #142 (and elsewhere).

  7. mkrichew, your theory will have some serious hurdles to overcome in order to fit the present warming. The oceans are net carbon sinks at present, not sources; part of the gigantic amounts of carbon dioxide injected in the atmoshere go into solution in the oceans, and lead to acidification. There is an entire thread devoted to the subject on this site. Furthermore, what would be warming up the oceans in the first place? You'd have to find some seriously exotic source of heat to explain the kind of energy accumulation seen across the planet's oceans, another subject that is explored in SkS threads. Even if there was such a mysterious forcing, oceanic chemistry shows that they are not outgasing any CO2. I don;t feel obligated to link any references considering that all these considerations figure in already existing SkS threads. Use the search engine.

  8. " Also,Milankovitch was obviously brilliant to have figured out the spinning shifts of the earth." Not sure what you are trying to say here. He was brilliant, but for calculating the magnitude of the effects without a computer. The orbital cycles discovery is simply astronomical observation and discovery of some of them date back to ancient history (maybe Babylon).

    CO2 did come from oceans as they heated up at end of ice age cycles with significant contributions from eurasian swamps as well. If you want a new theory, make sure it matches the observations of methane as well and also accounts for the isotope composition of both in ice cores.

    However, ocean outgassing from current warming is not happening yet - not even close. You cannot seriously posit a new theory that violates basic physical and chemical laws and observations.

    " I have read that they are warming and thus giving off a lot more CO2 than our burning of fossil fuels now."

    You dont say your source but it is clearly untrustworthy. The actual fluxes are well established as the mass of papers associated with that diagram in the IPCC report show.

  9. Unless there is confusion between an outward flux and the net flux. It is "voodoo economics" to have amount of CO2 dissolved in oceans increasing (the reducing pH) while claiming net outflow from ocean to atmosphere.

  10. What I found so astounding about the claim that because climate change happened before and that therefore CO2 is not the cause is a non sequitur. Because on does not follow the other. First of all the far past was significantly different in rate of change and second the distribution and amount of sequistiring green biomass was a whole lot more than it is now. There were intact ecosystems that could balance the change. And ecosystems had ample time to adapt to the change. This is not happening now. Humans are decreasing green biomass a lot. There are even less ecosystems now compared to then. I think this alone debunks a lot of this natural change myths happening now. If I am incorrect please indulge me and explain it to me. 

  11. aemilius89 @610,

    I would correct one thing you say. Yes, humans are reducing the area of the globe which support 'ecosystems'. But, dispite their best efforts, humans are not decreasing green biomass. A significant proportion of our CO2 emissions do result from cutting into the 'green biomass' (this the source of an average of 13% of our total CO2 emissions since AD2000 according to Global Carbon Project global budget). That proportion is a lot smaller than it used to be. It was 62% a century ago and 89% fifty years before that, these large numbers because back then  fossil-fuel-use was in its infancy. Yet these emissions which represent 'decreasing green biomass' have to be balanced against the extra CO2 'land sink' which with the falling proportion of land use emissions now exceeds those land use emissions (GCP figures put the 'land sink'  at 30% of emissions total emissions throughout) and the sink has exceeded source since about 1965.

    Mind, I could go all pedantic and add that had you said 'us humans had decreased the green biomass' this statement would be supported by the GCP data (which goes back to 1860) as the cumulative net loss of biomass in the century prior to 1965 still just exceeds the cumulative net gain in the half century since. We'll need another half decade to achieve parity between cumulative loss and gain. (This timing dependent on a 1860 start date which we could at a pinch get away with as providing a pre-industrial value.)

  12. In my comment 594, I suggested that 'the climate's changed before' or 'climate always changes' is really only half an argument, with two possible misleading inferences, and only one of these is really covered in depth here (although they are both enumerated in the blob points of the intermediate article). I'm hoping this comment might be useful if revising, clarifying or expanding these pages.

    Dr Richard Milne, University of Edinburgh biologist, makes exactly this point and puts these fallacies more clearly and entertainingly than I can in his lecture 'Critical Thinking on Climate Change: Separating Skepticism from Denial', covering both in two minutes, before employing the Scotese graph of temperature over geological time(!), and moving on to his next myth,

    The first implication is 'the climate's changed before... therefore it must be natural', is covered a bit in the intermediate article, and the logical fallacy is deconstructed in very similar terms by John Cook, Peter Ellerton and David Kinkead in their fun video. (By the way, does the assertion that there's no lag actually run counter to the usual explanation of lag but feedback? Probably mentioned elsewhere in these comments.)

    Their paper on critical thinking could equally be applied to the second  implication: 'the climate's changed before ... so it's nothing to worry about'. Milne characterises this as 'A didn't harm B, when B was not present, therefore A cannot harm B'. I'm suggesting that as some people move from 'phase 1' dismissal (it's not happening), through 'phase 2' (it's not us), most dismissives are moving to 'phase 3' (it's not bad), so this second implication is worth clarifying.

    So I think having articles from knowledgeable people on the following would be great, and then they could be hold the findings and be linked from a general page about the fallacies:

    • Previous warming during the Holocene hasn't adversely affected civilisation (in some cases it did, warming was smaller and slower and local, the Optimum was before settlements, we caused some of it through deforestation, the pattern of warming was different, larger future warming is projected to adversely affect ecosystems, food supplies etc.)
    • Previous hyperthermal events like the PETM (or P-T boundary) didn't necessarly lead to mass extinctions or runaway climate change and the Earth was 'resilient'. (Sometimes it does lead to mass extinction, depending on rate of change as well as absolute temperature, weathering will reduce CO₂ only over millennia, most extinctions involved climate change, solar radiation has increased, and our perturbations are on the scale of these extinctions, tended to wipe out megafauna, we have some idea of the extinction and range shift rates, this is a long-term change; much as in the basic article here)

    Tangentially related because I can't think where else to suggest it, probably under 'it's not bad' or 'it's too hard':

    • The projections are imprecise and there are lots of uncertainties about impacts, therefore we shouldn't act until these are resolved, or it might turn out OK (risk management principles; uncertainty means range, not doubt; some range is inevitable; we know more than might be thought; climate change is non-linear and affects some regions more severely than others)

    Finally, I note there's nothing under the 'it's too late' heading in the taxonomy, which is related to the opposite idea, that size of warming is completely unprecedented in the Cenozoic. I occasionally meet overstatements of the kind 'boreal forest will collapse; there will be a permanent El Niño', although these seem individual and not as repetitive as the climate dismissives. Climate Feedback deals with these when they happen, and if there's time, it may be worth seeing how a sceptical analysis looks at those.

  13. Responding to jesscars from here:

    Sigh, "OK, so you are saying that the effect of CO2 on the temperature is only minor. "

    No, he was saying the CO2 direct contribution to ice ages is 0.5C. Mostly it is an amplifier (feedback) converting a change in northern NH albedo into global event.

    Historically CO2 can change for many reasons, depending on which events you are talking about. Volcanoes, change to sea temperature (CO2 solubility), changes to vegatation cover, long term carbon sequestration in rock, freeze/thaw of tundra swamps, operating on time periods of seasons to eons. The pliestocene ice-age cycle is driven by milankovich.

    Climate is always a response to sum of all forcings. (solar input, albedo, aerosols, GHGs). Past climates are considered by looking at what changes to all of them. Complicating matters is that temperature change triggers feedbacks - you cant change temperature without also changing CO2, CH4, water vapour and albedo.

  14. We are told at the end of the video that climate is understood.  If that is the case, then why are climate models not capable of reproducing climate history over the past 35 years?

  15. Waterguy13 @ #614 ,

    What source do you base your comment on?   The earlier mainstream climate models have done a fairly good job with their projections during the past 30 years or so.   They can be criticized for minor inaccuracy, in that they A) somewhat overestimated the tropical mid-trospheric "hot spot" , and B) underestimated arctic warming,  and C) underestimated sealevel rise.

    But on the whole, they have done quite well.   In comparison, Dr Lindzen's model has done appallingly badly [he predicted cooling!] . . . and Lindzen still has difficulty acknowledging the reality of the actual ongoing global warming.

    Waterguy13 , you very much need to explain your strange comment.

  16. The "science" statement here seems incredibly overly bold and lacking in sufficient supporting scientific corroberation.

    "GHGs, principally CO2 have controlled most major climate changes"?

    That seems like quite a leap of faith. It seems like changes in solar behavior, volcanism, impacting comets and meteors, seismic activity, and who knows what else would be tough to rule out.

    The accompanying video appears to address a strawman argument in that skeptical references to prior climate change, specifically warming are not to argue that "therefore current warming must also be natural" but rather that it may be natural, or at least mostly natural.

    On the skeptics' side an opposing science versus myth scenario plays out, where an AGW argument is offered that "it must be anthropogenic since the current/recent warming is unprecedented in magnitude and/or rate." Well, that just isn't true, is it?

    The claim appears to assume high confidence in our understanding of all the various ocean systems' natural heat cycles with periods ranging in scale from decadal, to multidecadal, to century scale, and millennia scale. But aren't we now just beginning to learn about the various systems and cycles of ocean heat transport?

    The science claim appears to also assume high confidence in our understanding of various natural albedo cycles and feedbacks, and also of multiple cyclic and random solar behavior, and also geomagnetic influences.

    If Earth's natural climate response includes a combination of various natural cycles of various periods, then shouldn't we be having a very careful comprehensive look to identify ALL of such cycles, and then very thoroughly analyze ALL of them jointly rather than just dismiss each in turn for failing to fully cause recent observed behavior?

    How do we know that what we've recently witnessed in the observed temperature record isn't mostly just the result of a so-called perfect storm scenario, a coincidence of multiple cyclic peaks? If we cannot know that, then how can we know that equilibrium climate sensitivity to a doubling of atmospheric CO2 isn't a benign or even beneficial 1.5°C, not the claimed 3°C?

    That is the point of referring to proxy temperature records that indicate greater magnitudes of temperature and greater rates of temperature change. It is to say, hold on amigo, maybe we best not jump to such a bold conclusion prematurely; cause there's likely a lot we still don't know concerning climate, and so shouldn't we take some more time to be sure we comprehensively understand nature before calling the international 911 climate change SWAT team?

    It appears to me that this particular myth-busting is premature.

    The next 20-30 years of observations may prove highly informative, one way or the other.  If needed, we can pretty easily pump aerosols into the atmosphere while we ramp up nuclear power plants and renewables.  No?  

    Party on and be excellent to each other my brothers! And sisters, if there be any of the finer gender here. :)


    [PS] Please look at articles under the "arguments" to understand why the statement is soundly based in scientific observation and not a leap of faith. Better still, try reading the IPCC WG1 report to understand what the science actually says. Uninformed statements about what you presume science assumes do not helpful to any discourse. You would see that the science has actually carefully examined all known influences on climate and quantified these with error bars.

  17. Ed,

    You say "It seems like changes in solar behavior, volcanism, impacting comets and meteors, seismic activity, and who knows what else would be tough to rule out."  Fortunately, scientists have been working hard on these questions for the past 100 years.  They have been able to make the difficult observations you have apparently missed.  Looking at all the data we see that, in fact, scientists have shown that CO2 was responsible for almost all of past catastrophic climate change.

    Read the references that the moderator linked to find out how all this is known.

    I note that you have cited zero scientific reports in your post.

  18. Dear PS:

    That was a quick response!  Thank you for that.

    "...try reading the IPCC WG1 report to understand what the science actually says. Uninformed statements about what you presume science assumes do not helpful to any discourse. You would see that the science has actually carefully examined all known influences on climate and quantified these with error bars."

    I'm not uninformed.  I'm a well-published (dozens of peer-reviewed papers) science professional who's become interested in this subject.  I've read the recent WG1 report, noted the error bars and confidence levels, and that's a big part of the reason for my posting here.

    After some forty years of additional observations, intense scrutiny, supercomputer modelling, satellite technology, and massive capital investment, the stated range of estimated equilibrium climate sensitivity (ECS) to a doubling of CO2 remains unchanged at 1.5°C to 4.5°C.  

    Climate omniscience seems still a very long way off.  Don't you agree?

    If I get a chance, I'll post links to some of the recent literature dealing with as yet unquantified natural forcings and feedbacks.


    [PS] Range for ECS (which is problematic because of feedbacks) has nothing to do with attribution of cause which you were querying. Scientific critique of the attribution chapter in the WG1 is welcome. Be sure to comment on the appropriate topic - use the search function to help find one. If you had read WG1, then why all the false presumptions?

  19. Ed the Skeptic @616 : you say you are not uninformed ~ yet you seem unaware of the absurdity of suggesting that the modern-day rapid global warming could be caused by "multiple cyclic peaks" of warming.   (e.g. Dr Curry's frequent "hints" that oceanic cycles are the majority cause of recent rapid warming, are similarly absurd.)

    The "multiple peaks" hypothesis is unphysical [=absurd] because:

    A.  Oceanic currents merely redistribute heat energy, giving negligible overall change through a full cycle.  (Unusual events, such as the Younger Dryas, produce a forcing feedback via albedo change ~ but that is not-at-all the case in the present circumstances.)

    B.  There is no evidence of significant positive [=planetary heating] effect from other cycles or Natural Variations that you mentioned, during the recent 50 years of rapid surface temperature rise.  And the real temperature rise is still going up steeply.

    C.  If the oceans were producing the observed surface heating, then there would be some consequent cooling of the upper ocean.  But actually the opposite is occurring ~ the oceanic water is warming [Oceanic Heat Content is increasing over many decades].

    D.  Even assuming that a "perfect storm" is presently existing ~ leads to the necessity of having a simultaneous Unknown Mysterious Cooling Factor which counteracts the known planetary warming effect of our recent atmospheric CO2 rise (and other GHG's).   Some Mysterious Cooling Factor that nicely follows/matches the rising arc of CO2.   Clearly absurd !

    Ed, our past climate change tells us global warming occurs when there is a reason causing the change.   The evidence is strong enough to indicate that we should abate the present [Greenhouse] cause.

  20. Ed says earlier in the thread "changes in solar behavior, volcanism, impacting comets and meteors, seismic activity, and who knows what else would be tough to rule out."

    Certainly not for recent times. None of these is a factor in the changes we are currently experiencing. Solar activity is actually lower now than it was in the late 20th century (see related threads where PMOD data can be found). Comets and asteroid strikes have a way of getting noticed. Even tiny nuclear weapon tests in North Korea can be detected by our seismological equipment. "Who knows what else" seems to be falling in the category of cosmic rays and Leprechauns (see applicable thread, except for Leprechauns), rather surprising from one who claims an extensive scientific background.

    Perhaps, like a lot of other people, Ed has difficulty accepting that we humans are responsible for a truly geological scale event. Going up in total atmospheric CO2 content by a 100 ppm within the 2ish decades since I started teaching weather for pilots is simply astounding, and a lightining fast geological freak event. Anyone who doesn't see that has a problem with quantitative thinking. Human activity releases about 100 times more CO2 per year than all volcanoes together (see applicable thread). If all of a suddent we started witnessing that kind of volcanic activity, year after year, there would be absolutely no doubt about its scope, consequences, and the urgency of the situation.

  21. I've read the other myth-busting pages.  Lots of good information on many of them.  I hope to engage on some that appear deficient from my semi-informed perspective.  I have no dog in this hunt other than truth and scientific integrity.  I'm disappointed by the personal commentary that some se fit to include. 


    Defendping consensus scientific orthodoxy ought be done with humility, lest you join the ranks of the scoffers and naysayers who pilloried the likes of Copernicus, Galileo, Einstein, and LeMaitre.

    I'm not seeing lots of hard scientific evidence here on this myth-buster topic,  just mostly declarations.  Thus my posting.

    This myth-busting deals with natural climate variability, yes? Isn't the uncertainty about ECS exactly directly related to that?  It's wide range informed by some decadeal to millennial scale proxy temperature records—GISP2 stands out—would seem to indicate a significant uncertainty related to this topic, no?  That's the only intended point.

    Can anyone engaged hereing please explain the apparent certainty on the issue offered here on SKS relative to figure 8.14 and 8.15 of AR4 WG1?  

    Has anyone seen the NASA data showing significant decadal reduction in global cloudiness from around the 1980-2000 time frame, dropping from roughly 70% to 65% in two decades?  That drop in cloudiness corresponds with an apparent increase in global surface solar radiation of roughly 4 W/m^2.  

    Where is that addressed in the AR4 WG1 tally of radiative forcing information included in the aforementioned figures 8.14 amd 8.15?


    [DB] Baiting snipped.

  22. The above-mentioned cloudiness data for your convenience:

    LINK 1

    Correlation with temperature change:

    LINK 2

    This is data is not being shared to divert topic, just to ask where it is included in the above-mentioned IPCC AR4 WG1 figures.


    [DB] Shortened links breaking page formatting

  23. Ed @ 621/622 ,

    you don't really advance your case (whatever it is) by waving a rhetorical hand in the direction of Copernicus, Galileo, Einstein, and LeMaitre.

    Copernicus and Galileo were (strictly speaking!) representing the scientific consensus of their age (an age of very few scientists, indeed).   Their opponents (shall we label them denialists?) were a group of rich & powerful men (in the upper echelons of the Papal state) who supported an evidence-deficient position. Easy to see a parallel with the rich & powerful magnates of the upper echelons of the fossil fuel industry . . . plus c'est la meme chose.   Even more irony, in that the modern-day Pope denounces those same science-deniers.

    Einstein and LeMaitre advanced the physics/astrophysics science ~ but they did not trash the pre-existing body of science.

    # Attacking the consensus scientific orthodoxy [especially in climate matters] ought to be done with humility [and genuine skepticism], lest you join the ranks of the Dunning-Krugerites.


    "Uncertainty" about ECS (currently the most probable ECS figure being around 3 or 3.5 degrees) is an interesting scientific question ~ but in no way justifies delaying on decently fast transition to a nett-zero-emission economy.   After all, we citizens/voters/politicians/parents ought to be intensely practical in prudent risk-managing. 

    My apologies, but my little laptop is struggling to access "figure 8.14 and 8.15 of AR4 WG1".   Perhaps, Ed, you would be kind enough to upload those charts and explain how you think they undermine the mainstream position.

    Strangely, the same goes for Dr Humlum's "climate4you" illustrations.  (I have no difficulty accessing the WUWT and Climateetc websites.)   On the little I know of Dr Humlum: he has (scientifically speaking) a poor track record indeed.   * That is not to say he must therefore be wrong, on the cloudiness issue.  But it seems the somewhat-related "Iris Hypothesis" of Prof Lindzen has fallen flat on its face.  And on a second point: a "cloudiness drop" providing a warming forcing of "roughly 4 W/m^2" has much the same problem I mentioned above in post #619.D  . . . that if true, then there must also be some Unknown Mysterious Cooling Factor that nicely follows/matches the rising arc of CO2's warming forcing effect.   Which seems absurdly unlikely, if not quite impossible.

    (And which would leave only another 5 impossible things to believe before breakfast.)

  24. The IPCC figures mentioned @621 are:-

    IPCC AR4 Figure 8.14.

    IPCC AR4 Figure 8.15.

    The graphics linked @622 are reporduced by the denialist website climate4you from the now defunct International Satellite Cloud Climatology Project but discussion of these data would be best transferred to a more appropriate thread - SkS Could global brightening be causing global warming?

  25. Ed,

    You claim that you are "semi-informed".  You are citing resources that are  at least 10 years out of date.  The current IPCC report is AR5 or the 2018 supplimental report.  Perhaps the discrepancy you notice is caused by SkS being up to date while your reference is out of date.

    You are clearly echoing some other web site you have read.  Can you cite and link that web site directly so that we can see the entire argument?  SkS probably addressed this myth in an OP 10 years  ago when it was first raised.  It will be easier for us to directly address the source instead of rehashing the argument again.

    When you claim to be semi-informed attacking consensus scientific orthodoxy ought be done with humility,  If the best you can find is a 10 year old web site that is no longer active you might want to reconsider how strong your argument is.

  26. Can somone please explain in great detail why  the mass balance (the annual CO2 concentration growth is less than the annual CO2 emissions) and the declining O2 concentration are both strong indicators of GW ? I was reading the post by Tom Currtis in 7/25/2012 and these were items number 3 and 6.

  27. alonerock @626,

    It would be better to put your enquiry on the thread below the OP by Tom Curtis. And note the list is followed by explanation of each item, although they do perhaps need a little effort to understand (& currently have a missing graphic for item 6).

  28. "This myth-busting deals with natural climate variability, yes? Isn't the uncertainty about ECS exactly directly related to that?"

    Um, no? Using past climate to estimate ECS is plagued by the uncertainties in both estimates of past global temperature and past forcings. Naive estimates of TCR from short-term measurement do suffer from internal variability (not to be confused with natural climate variability in forcings).

    Model estimates of ECS must deal with feedback - and the range there is largely due to the difficulties with clouds in current hardware. Ie not only how much does cloudiness change with a change in temperature but also change in high-level versus low level cloud (one is a positive feedback, the other is a negative feedback). Again, all of this is discusssed at length, with references in the IPCC WG1, (see table 9.5 for instance).

    "Natural variability" is of two kinds - one is the internal variability due to uneven heating of wet planet. This is essentially weather and evens out over a 30 year time scale (hence climate being 30 year averages).

    The other is natural climate variability due to changes in natural forcings - predominantly solar (both in strength and orbitally-induced variations in latitudinal distribution), and volcano aerosols.

  29. I should also add that scientists are inordinately attached to conservation of energy. You cant magically increase the Ocean Heat Content without adding the energy from somewhere. The change in GHG easily account for this. Pretty hard to figure a way of doing this from a change in any known natural forcing.

  30. Very nice site.  However, as I've also been reading from various Noble prize winning scientists who insist on exactly the things this site purports to 'debunk' I think I consider you debunked instead.... unless you have a Noble prize in scientific fields germane to the subjects. 


    [TD] Fittingly, you misspelled "Nobel." The only Nobel prize winning scientist that I'm aware of denying human-caused climate change is Ivar Giaever. He has no training, background, or scientific publications on that topic. He readily admitted:

    "I am not really terribly interested in global warming.  Like most physicists I don't think much about it.  But in 2008 I was in a panel here about global warming and I had to learn something about it.  And I spent a day or so - half a day maybe on Google, and I was horrified by what I learned.  And I'm going to try to explain to you why that was the case."

    A fuller explanation of breadth and depth of his incorrect opinions is in an article here on Skeptical Science.

  31. Let me guess James, you spent haf a day on Google too?

  32. "Those abrupt global warming events were almost always highly destructive for life, causing mass extinctions such as at the end of the Permian, Triassic, or even mid-Cambrian periods."

    This is the weakest part of the argument. Why should humans fear abrupt changes when we have demonstrated extrordinary resilience to such changes in the recent past? The future looks even brighter, we have the capability to grow food for two or three earths, Saudi Arabia is growing wheat, Russia will soon be able to grow enough wheat for the entire planet. There were just a handful of deaths due the 'polar vortex'. El Nino and La Nina are just weather channel jokes countered by cranking up the AC or the heater. Just what is this event which we cannot handle? Show us from recent past.

  33. rxrankings @632,

    When you say "we have demonstrated extrordinary resilience to such changes in the recent past," you presumably do not consider the Triassic as "the recent past." So what "such changes" are you referring to?

  34. MA Rodger, I think that the worst that happened in human times was the Toba eruption, but I could be wrong. Humans and other mammals show evidence of genetic bottlenecks in the wake of that event although there is controversy as to the true global effect of it. In any case, it was a far cry from anything like major object impacts or large igneous provinces. 

  35. By recent past I meant the examples I gave: "Saudi Arabia, being a desert and able to grow wheat"; "Russia, able to grow wheat in Siberia (previously) thought impossible and probably able to grow enough in the whole country to feed the entire planet". Dinosaurs and Mammoths couldn't grow wheat or travel in Ships to warmer climates, they used to die if it became too hot/ too cold or too dry. Humans book a ticket, crank up the AC, turn on the heater or eat wheat instead of meat. Tomorrow if the whole of Europe turned into an oven and Antarctica melted, it would take less than 10 years for a continent wide migration and resettlement. If we have enough fossil fuels, humanity could survive for centuries on a desert filled planet. Show me the impact of Global warming and I will show you the current technology that can handle it.

  36. Philippe Chantreau @634,

    Toba has been associated with the genetic bottleneck theory in which proponents see the human population dropping to less than 10,000 people. With modern technology, the survival numbers would likely be higher than 10,000 but the mortality rate (the percent of humanity who perish) would be infinitely higher.

  37. rxrankings @635,

    When you first use the phrase @632 "in the recent past" (which I quote @633) you are referring to humanity "demonstrat(ing) extrordinary resilience to (abrupt) changes in the recent past." I assume growing wheat isn't the sort of "abrupt change" that would provide this "demonstartion (of) extraordinary resilience" you speak of.
    And in terms of "demonstrating" stuff, you demonstrate a poor grasp of the energy requirements needed to melt the Antarctic ice cap. Today's global energy use (132,000TWh) is enough to melt 1,600 cu km of ice. Antarctica has 26,500,000 cu km of ice so melting it in 10 years would be an interesting project. What's your plan for obtaining this level of energy in the next 10 years?

  38. rxrankings at 635 "Russia, able to grow wheat in Siberia (previously) thought impossible"

    This is false. The chief crops of neolithic Siberia (8000 BCE and after) included millet, wheat, barley and hemp.

  39. MA Rodger,

    I am aware of the Toba bottleneck theory, but there is considerable debate as to the true impact of the event. The genetic bottleneck around that period is a relaity nonetheless, and is found in several other primate species.

  40. "With modern technology, the survival numbers would likely be higher than 10,000 but the mortality rate (the percent of humanity who perish) would be infinitely higher." — How can you say that?Show me a climate event in the past 30 years that has killed at least 1 million people directly. Even in severe droughts we have most people dying from poverty and unable to afford food, NOT lack of food. I can make a bold statement and say ALL climate related deaths in the past 30 years are due to lack of technology awareness or poverty or being careless. There has not been a storm that concrete and steel cannot handle. So my question is, with all the warming we have had in 30 years, no one has died, why should I believe you when you say another 5 degree rise in temperature will kill billions??


    [DB] Please note that at Skeptical Science there are thousands of active discussion threads on just about every topic related to climate change science.  As such, users are encouraged to confine comments to the topic of the thread on which they are place.  Further, it is incumbent upon those making hyperbolic assertions to then support them with citations to credible sources.

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

    Off-topic snipped.

  41. Philippe Chantreau @639,

    We do agree that the Toba genetic bottleneck theory is not entirely convincing. The genetic finding is well established, that there were few humans on the planet in those days but if Toba created such a bottleneck it needs better evidence to become established given that there are plenty other factors were at work that could have kept human population low through those times.

  42. Hi Skeptial Science,

    First let me say that I LOVE this site as it's helped me to debunk the human caused climate change deniers.

    I keep running into one denier who keeps repeating this: 

    "The average global temperatures for seven of the previous Inter-Glacial Periods was 66.2°F to 73.7°F not the current 58.4°F and CO2 levels never exceed 292 ppm CO2.

    The temperatures in Greenland during the last Inter-Glacial Period were 14.4°F warmer than now, in part, because the average global temperature was 15.3°F warmer than now, and CO2 levels peaked at 287 ppm CO2.

    So, how can you possibly state with absolute certainty that temperatures will not rise another 7.8°F to 15.3°F on their own?

    The reason it was 14.4°F warmer in Greenland than it is now is because during the last Inter-Glacial Period, the average global temperature was 73.7°F and not the current 58.4°F."

    "You should also know the Greenland Ice Sheet always melts, and the Western Antarctic Ice Sheet always melts, and that sometimes the Eastern Antarctic Ice Sheet undergoes substantial melting, like it did during MIS-5 and MIS-11, and that it may have had substantial melting during other Inter-Glacial Periods, but the data has not yet been evaluated.

    In short, nothing abnormal is happening very slowly."

    How to respond to what appears to be inaccurte cherry picking?

  43. Artemsis, the proposition is puzzling and it would help if you could get more information on what informs your denier. Estimating a global mean temperature through the Quarternary is not a simple proposition and it looks to me as if a no. of data sources have been mis-interpreted. The temperature of Greenland at LIG cf present might also be confused about what is "now" (The meaning of 0BP in ice core records). In short, we need the references used by the denier that back the above claims.

    Beyond that there is some sleight-of-hand in the argument. Climate does not change on its own. It changes in response to changes in net forcings and the ice ages are no different. The ice age cycle is due to orbitally-driven changes in the distribution of solar insolation in the northern hemisphere, which are amplified into global change by CO2 and albedo feedbacks. Temperatures in NH polar regions can indeed be warmer in interglacials with lower CO2 because the incoming insolation for that region is much higher than today. This is not a global change however. More importantly, the milankovich forcing is now decreasing. Without our anthropogenic CO2 we should be slowly cooling. It is important to realize however that this change is very slow - milliwatts per century - compared to emission CO2 forcing which is more like 1W per century. Even without our emissions, the next glacial would have been 50k into future. (Berger and Loutre 2002)

  44. TVC15 @642,

    What this denialist is saying in proper numbers is that seven previous interglacials had global average tmperatures between 19ºC & 23ºC when present global averages are put at 14.7ºC. So that would put these prior interglacials +4.3ºC to +8.3ºC relative to today.

    There is a graph in the screed below this thread showing none of the past four interglacials topping +4ºC above the 1960-90 average. (Two are a tad above +3ºC and two a tad above +2ºC). But the graphic is unreferenced so not that helpful but indicative that the denialist is talking nonsense. (I have the thought that the graph looks a bit like Vostok ice core data which means it still requires adjusting for polar amplification to provide global temperature.)

    Yet even the EPICA ice core data (which covers back to eight previous interglacials) doesn't manage the '+4.3ºC to +8.3ºC relative to today' for seven prior interglacials. Only five of last eight were warmer than 'today' and the warmest, the Eemian, was +4.8ºC which should be perhaps at least halved to give a global value and account for polar amplification.

    EPIC & Vostok ice core data

    One of the problems with identifying a Greenland temperature for the Eemian is that Greenland pretty-much melted out in the Eemian. Yet to see this as a global temperature thing is a step too far. Yes, it would take very little increase in global temperature to set Greenland melting out (something like +1.5ºC above pre-industrial) but the Eemian had a far stronger Milankovitch cycle warming the Arctic which would suffice just as well, even with a lower global average temperature.

    Generally though, the denialist is spouting nonsense numbers. So the questions of import - Where does he get these nonsense numbers? Which nonsense factory?

  45. Scaddenp and MA Rodger,

    I'm starting to think this denialist is being paid to spread myths and move goal posts.

    When I asked for references I was told that its a "government source, or from Nature, NOAA, National Geographic or any peer-reviewed paper"

    So essentially they could not provide a concrete reference for the nonsense numbers.

    I also looked for a timeline of the last 8 interglacial global temps and could not find a good source.

    Below is a typical argument of a denialist. 

    It's not just Greenland. It's also Baffin Island:

    From applications of both correspondence analysis regression and best modern analogue methodologies, we infer July air temperatures of the last interglacial to have been 4 to 5 °C warmer than present on eastern Baffin Island, which was warmer than any interval within the Holocene.

    Vegetation and climate of the last interglacial on Baffin Island, Arctic Canada

    4°C to 5°C corresponds to 7.2°F to 9.0°F

    And in eastern Siberia:

    Our pollen-based climatic reconstruction suggests a mean temperature of the warmest month (MTWA) range of 9–14.5 °C during the warmest interval of the last interglacial. The reconstruction from plant macrofossils, representing more local environments, reached MTWA values above 12.5 °C in contrast to today's 2.8 °C.

    Continental climate in the East Siberian Arctic during the lastinterglacial: Implications from palaeobotanical records

    12.5°C is 22.5°F warmer.

    So, this is not a regional phenomenon occurring only in Greenland. It's global.

    And, if you've noticed, the climate-nutters refuse to acknowledge the science, because it contradicts their belief system.

    The Milankovitch Cycle has nothing to do with it.

    Originally, Glacial Periods lasted 40,000 to 42,000 years and Inter-Glacial Periods lasted 12,000 to 15,000 years.

    What does that have to do with the Milankovitch Cycle?

    Absolutely nothing.

    Oh, wait a minute, I get're looking at the 40,000 to 42,000 year Glacial Period and thinking it jives with the 41,000 year Cycle, which is just one of three Cycles.

    It should be very obvious, because peak-to-peak, the cycle is 52,000 to 57,000 years.

    I often wonder where these types of minds come from. It's interesting that creationists argue in the same manner. I often wonder how the human mind can allow itself to be completely deluded with self-righteous beliefs.

  46. TVC15 @645,

    The denialist appears to me as an exuberant fool relishing the chase. He is not worth a bean.

    On the source of his numbers - You could ask him if it is that he cannot remember where these numbers are allegedly lurking and thus he sets out so many possible sources. Or is he saying there are so many sources that he is spoilt for choice? All we need is one credible reference to be able to judge his preposterous claims on interglacial global average temperatures. Perhaps he should also set Wikipedia straight. They, despite using Antarctic EPICA ice core data unajusted, still have nothing like the temperature record alleged by this denier in their account of the Geological Temperature Record.

    The rest of his rant is basically saying there is interglacial warming yet to appear in the present Holocene interglacial, and this based on the level of deglaciation at the height of the Eemian deglaciation. Perhaps he can set out the mechanism he sees as providing this warming-yet-to-appear.

    In sensible speak, the reason for the Eemian being warmer than the Holocene is down to the reduced glaciation driven by high latitude Northern insolation. It is, of cource, a dynamic system so the timing of this insolation within the ice age cycle is critical. The denialist seems to fail to grasp that timing is everything and is bogged down by considering the duration of any particular swing in the Milankovitch cycles.

    Temperature & insolation through ice ages

  47. TVC15 @645,

    Picking up on the denialist's assertion that his position would be supported by "any peer-reviewed paper," I have been unable to find the full text of Hoffman et al (2017) 'Regional and global sea-surface temperatures during the last interglaciation'  (which is of course one such paper) but its abstract (below) doesn't give any room for the denialist's bold assertions about blindingly hot Eemian global average temperatures which @642 the denialist describes as "15.3°F warmer than now" or +8.5ºC relative to today.

    "The last interglaciation (LIG, 129 to 116 thousand years ago) was the most recent time in Earth’s history when global mean sea level was substantially higher than it is at present. However, reconstructions of LIG global temperature remain uncertain, with estimates ranging from no significant difference to nearly 2°C warmer than present-day temperatures. Here we use a network of sea-surface temperature (SST) records to reconstruct spatiotemporal variability in regional and global SSTs during the LIG. Our results indicate that peak LIG global mean annual SSTs were 0.5 ± 0.3°C warmer than the climatological mean from 1870 to 1889 and indistinguishable from the 1995 to 2014 mean. LIG warming in the extratropical latitudes occurred in response to boreal insolation and the bipolar seesaw, whereas tropical SSTs were slightly cooler than the 1870 to 1889 mean in response to reduced mean annual insolation." [My bold]

  48. MA Rodger, thank you so much! I am not a climate scientist but I do hold 3 science degrees in the field of medical science. I love this site as it has helped me learn so much about areas of climate change that I was unaware of.

    This denier posts walls of misinformation and rants just as you have read and since most people in the world are not well versed in science, they think he sounds great and knowledgeable. It's astounding the things he's says. He tried arguing CO2 is a dissolved and released gas in seawater, and that it's based on Boyle's Law. I was astounded and knew immediately I was dealing with a layman attempting to come off as being knowledgeable in science.

    I often wonder where he gets his misinformation from.

    He is constantly trying to push these concepts:

    My position is that CO2 levels are irrelevant. CO2 levels are a lagging indicator. Temperatures increase, then CO2 levels rise. Temperatures decrease, then CO2 levels drop.

    There are many articles that all say the same thing.

    What were CO2 levels during the last Inter-Glacial?

    EPICA Ice Core data for the last Inter-Glacial period shows CO2 levels never rose above 286.8 ppm CO2 (peak at 128,609 years before present).

    Because CO2 levels peaked at 286.8 ppm CO2 and temperatures in Greenland were 14.4°F warmer than present and on the opposite side of Earth temperatures were 22.5°F warmer than present, you cannot claim CO2 drives the climate.

    In fact, that refutes global warming.

    Here we show that the south GIS was drastically smaller during MIS 11 than it is now, with only a small residual ice dome over southernmost Greenland.

    If we go back to MIS 11, we find CO2 levels peaked at 283.5 ppm CO2 at 411,071 years before present.

    If you look through EPICA Ice Core Data, CO2 levels never peaked more than 292 ppm CO2 over the last 800,000 years.

    Prove, with absolute certainty, that if CO2 levels were back down to 287 ppm, temperatures in Greenland would not rise another 14.4°F and temperatures in Siberia would not rise another 22.5°F.

    If you are unwilling to do that or cannot do that, then you have proven global warming to be a fatally flawed theory.

    Given that CO2 levels are currently in excess of 400 ppm CO2, why haven't temperatures risen?

    You say they have? Yeah, 1.4°F over 140 years, but, I've already proven that temperature fluctuations of 20°F in a matter of years is not unprecedented.

    I think Skeptical Science should add this denier’s myth claims to the most used climate myths. This denier makes some of the strangest claims and draws odd conclusion’s based on what appears to be cherry picking and lack of basice science understanding.

  49. MA Rodger and others interested:

    I think the full text of HHoffman et al 2017 is here.

  50. TVC - first thing to remember is the old saying that you cannot reason a person out of position that they were not reasoned into. Deniers will deny. You can however demonstrate to other bystanders that their position is not based on science. You could ask if they could consider that any evidence will change their mind. Chances are the answer is "nothing".

    The CO2 lags argument is already in Skpsci. See here. and this is really where this discussion belongs. The argument relies on believing you can choose which bits of chemistry and physics apply at will.

    In short, CO2 is both a feedback AND a forcing. Anything that causes temperature to rise will eventually cause CO2 to rise as well (and vice versa) but on timescales of centuries to a thousand years (time for ocean mixing). Our adding CO2 from emissions will eventually cause CO2 to be releassed from natural sinks making matters worse. In ice age cycle, it acts to convert a local event (change in insolation in NH around 65N) into a global event. Locally the milankovich forcing is large. If you look at MA Rodgers graph, the Milankovich forcing changes insolation at 65N by 10+W/m2 between glacial and interglacial. The forcing from doubling CO2 is around 4W/m2. The difference is that change is local for milankovich (I note the deniers examples to "prove" it was global were all NH higher latitudes), but global for CO2. I should say ditto for water vapour but feedback is much faster. Your denier is pulling a strawman argument, claiming CO2 is supposed to explain all climate change. Climate science by comparison claims that all physical laws apply at all times and climate responds to net forcing, not one single factor.

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