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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

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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Related Arguments

Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

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 651 to 675 out of 883:

  1. I give much thanks to all that have helped me broaden my knowledge of global warming and especially how to deal with the denialist I've been debating for almost a year. I've not quite dealt with a denialist as the one I've presented. I agree with you MA Rodger! This denialist is as an exuberant fool relishing the chase. He is not worth a bean.

    Special thanks to Michael for the link to HHoffman et al 2017.

  2. Hi I'm back to seek more debunking knowledge help from you guys.
    I posted the below graph to debunk a denier who was trying to claim that: Now the same frauds, sorry "experts," that were behind global warming have changed their rhetoric and branding to "climate change."
    Various Measurments of Global Temperature

    Next think you know a loud chest pounding denier jumps in with this wall of questions.


    1. Are you even aware as to what instruments were used to measure temperature in your "graph" and what locations were used?
    2. Do you know how "average" temperatures are statistically massaged?
    3. Do you know how "proxy temperatures" are determined?
    4. Why was there not cooling during the Depression, then warming in WW2?
    5. Is it valid to compare temps measured by digital instruments, compared to mercury thermometer instruments, vs "proxy" measurements?
    6. What is the relative accuracy and standard deviation of each temperature measurement method?
    7. Did you know that man accounts for only 4% of all atmospheric Co2, and that total Co2 is only .04 % of atmospheric gases?
    8. Did you know that the relative contribution of "man made" Co2 (that 4%), compared to water vapor , is 1/1,500,000th?
    9. Did you know that ALL of the carbon atoms in your body (as you are an organic organism) was once CO2? That is the carbon cycle; CO2 is as important to life on earth as water and oxygen, yet the left has labeled it a "pollutant".

    My response/question to each of this deniers claims.


    1. Where can I find this information?
    2. Define: "statistically massaged"
    3. Yes
    4. Not sure how to respond due to the wording of the question.
    5. Not sure if this is even worth addressing
    6. Don't know
    7. False - however I don't know where to find good numbers to debunk this myth.
    8. Show me your sources
    9. False


    This denier is a chest pounding denier who will criticize the instruments, claims the numbers are "massaged", make ridiculous claims about the source of the C in our bodies.

    Below are his favorite statements:

    It is odd indeed when the AGW crowd claims the high ground of "science", then immediately violates every basic premise of actual science:
    1. A hypothesis in not "proven" until the null hypothesis is refuted.
    2. real science welcomes further debate, experimentation, and examination of the hypothesis- cults do not.
    3. real science does not require falsification of data and statistical analysis
    4. real science is indifferent to the conclusions- cults have a very vested interest in outcomes
    5. in real science, those questioning a hypothesis are welcomed, rather than silenced or labeled "deniers".
    6. in real science, action is not taken to "remedy" a problem until a hypothesis is proven
    7. in real science, rarely is there one single cause of natural phenomenon. In the AGW cult, the "villain" or cause of all problems is CO2.

    I am stunned at the minds of people like this!

  3. TVC15 @652 ,

    I am sure you are not really stunned by his* intellectual incompetence ~ but he has enough intelligence to display (via Motivated Reasoning) a barrage of Gish Gallop and rhetorical waffle.

    *almost certainly he is a male ~  since women usually have more sense than to lose themselves in the quagmire of climate denialism.   Prof. Curry excepted: she does a fine job of vagueness and "could-possibly-be" and unjustified sophistry and "confusionism" smoke&mirrors.  In person, I have only ever met one woman who was an extreme denialist ~ she was an elderly geologist (retired).   A few other women seemed to be of the "Yes Dear" type, just going along with their husband's delusions.   ;-)

    TVC15 , in replying to the "intelligent idiot" you mentioned, you have two reasons for engaging with him.   One is to present commonsense factual science to the observers/readers [of course he himself is impervious to reason]  . . .  and the second reason is that you find it intellectually stimulating and fun.

    Plck out and attack one or two of his weaknesses.   Exposing him there, will by association throw doubt on his other points.   Readers will be thinking: a falsehood in one area means he could be a liar in most areas.   But always it should be fun for you (though sometimes partly a chore also).

  4. TVC15 ,

    you have replied to me on the wrong thread.  Perhaps a moderator could move your post into slot #654 in this thread.

    TVC15 , you should be amused when your denier says he is an MD and Engineer.   There are quite a few denialists who claim to be (and possibly are) engineers ~ some of the worst crackpot climate ideas come from ostensible engineers.   ( I myself know a post-doctorate researcher in a biological field, who is a member-in-good-standing of his local Flat Earth Society.   In the end, it is only the real physical evidence which counts. )

    To misquote Alexander Pope : "A little learning is a dangerous thing . . . and many engineers know just enough science to be dangerous."

    If his "MD" you mention is some sort of Medical doctorate, then we are getting into deeper waters ~ and Medical researchers should know better than to apply the confounding-factor-laden biomedical field to the hard-science field of climatology.

    Simply, I don't think it's worth pursuing the instrumentation question.   He's trying to distract you down into a rabbit hole.   Myself, I'd point out to him (and the readers) that thousands of highly-expert scientists have spent decades assessing/ analysing/ cross-checking the various instrumentation aspects of temperatures.   If your denier friend has some definite evidence of gross error . . . then he should frankly point it out, and also publish his findings to the whole world, so that the enormous pyramid of mainstream science comes tumbling down.   But so far, there has been no sign of that happening !

     

    As for the "methodological note" you mention, it is to be found in a rather low-ranking journal, and (judging by the Extract**) it contains a considerable amount of taurine excrement [ usually abbreviated to: BS ].   Actually, I did skim through the body of the "note", and it wasn't nearly as bad as I had expected ~ but it was mostly to do with causation/correlation in a general way and really had little relevance to climate science.   However, the Extract itself mentioned "Popperian" and was largely an attack on the IPCC & mainstream science . . . and I suspect its raison d'etre was simply to be read by & cited by denialists [who wouldn't ever read the body of the note, and wouldn't care a jot for understanding Popper].

    ** The warning sign here is "Popperian".   With apologies for my mixed metaphor ~ but when Popper or Popperian occurs in a paragraph about climate, then your ears should prick up, and you become hyper-suspicious that you are being handed a plateful of BS.

    Popper's philosophy has its virtuous aspects within certain limited circumstances, but little of that is relevant to climate science.   "Popper" and "Popperian" are often these days quoted by denialists who have little real interest in (or knowledge of) the philosophy of science ~ all that these denialists want is a trendy-sounding cudgel to knock real scientists on the head with . . . however inappropriate it may be.   They just want "the optics of it" (if I may use a modern ugly phrase).

    All too easy (for the half-alert reader of Popper) to fall into a semantic jungle, instead of keeping focus on the physical realities of this universe.

    TVC15 , don't let the denialist lead the dance.   Aim for his weak points (which he has tried to conceal).

    Another apology ~ this time for my own long waffle: but there are some gems scattered through it !

  5. Hi Electric!
    I am a bit perplexed as to how I responded to you in the wrong thread??? My apologies to the mods.

    Thank you for the feedback! It's much appreciated.

    I've cornered this denier in the past with respect to his flagrant ignorance sounding where the carbon in our bodies originated. He ran far away. I find it amusing he's back as if he's forgotten. LOL

    I did a search on the author of that open resource paper I linked in the wrong thread and came up with a few hits. Thus why I wanted to hear what others thought about the credibility of that paper.

    Thank you so much for your responses. I often debunk the denialists with the information I find on this site. I love this site and am spreading the knowledge I gain from it as well as from the comment section.

    I am muchb more skilled at debunking the creationists, however human caused climate change denialists are just as amusing. :)

  6. TVC15 @652,

    The usual response I would give to the various accusations using 'Global Warming has been converted into Climate Change because of <some cover-up>' is to point to the name of the UN IPCC which was formed in 1988. So any genuine reason for converting from the term Global Warming to Climate Change would have to pre-date 1988. Most do not.

    The 4% of CO2 attributable to anthropogenic sources has in the past been an account of gross annual emissions which annually were back-in-the-day 6Gt(C) anthro, 60Gt(C) ocean, 100Gt(C) biosphere. Of course, the net emissions yield a 100% anthro as the oceans & biosphere absrob as well as emit (& as they absorb 55% of the anthro emissions, you could say the anthro percentage is 220%).

    The pre-industrial CO2 levels wer 280ppm and they are now 409ppm. So an actual percentage of of today's atmospheric CO2 would be 46% anthro.

    The relative contribution of CO2 to Earth's greenhouse effect (New Scientist has a page on it as probably does SkS if we were to look) is somewhere between 26% (the effect with only CO2) and 15% (the drop in the effect if CO2 were removed). Call it 20% and with water vapour 50%.

    But the 1-in-1,500,000 quoted by the denialist troll is the anthro contribution from CO2 relative to water vapour. If the GHE is 33ºC and half is water vapour, while anthro CO2 forcing is roughly 2Wm^-2, with ECS=3ºC for 3.7Wm^-2. So CO2(anthro) equates to (3 x 2 / 3.7)/(33/2)=0.098 or 1-in-10.

  7. Correction to #656,

    The ECS=3ºC of course includes feedbacks. Without them the CO2 forcing would be 1ºC per doubling. So it reduces to 1-in-30.

  8. TVC15 , if you have past experience in debunking creationists, then you may well have come across the [science journalist] you-tuber Potholer54 who has done many videos on the same subject area.

    Maybe you are not aware that Potholer54 has done 40+ videos on climate science denialism.  Most of them are around 10 minutes long; some more like 15 minutes.   But I heartily recommend them.   He is meticulous in shooting down the denialists' claims & in demonstrating their falsehoods.   He gives his references ~ and he is careful to base his comments on the evidence as determined by peer-reviewed papers in reputable scientific journals (in other words, he does does not act as a talking head spouting his own opinions . . . unlike most you-tubers).

    You will find Potholer54 very useful, because he is skilfully attacking many of the prominent "public denialists", and his videos will cover many of the points that you will wish to use in debating denialists.   He doesn't cover everything ~ but you will find him a very easygoing method of gaining climate scientific knowledge, both directly and indirectly.

    Yet there's more ~ his videos are done in a humorous style (which I find very entertaining).

  9. Thanks MA Rodger and Electric,

    I've been watching Global Weirding with Katharine Hayhoe on YouTube.

    I've never heard of Potholer54 I will indeed check him out!

    MA Rodger and Electric I appreciate all the new things I'm learning from you both!

  10. I searched this site and came across this page.

    Global warming theory isn't falsifiable

    However it's not like the other myth pages as it does not explain the myth.

  11. TVC15, please comment in the threads of the posts you are commenting about. I will respond to your comment there.

  12. TVC15 @652: Re. your denier's Gish Gallop list of 9 points: The tricky thing is that parts of these statements contain bits of truth. For example, point 9:

    9. Did you know that ALL of the carbon atoms in your body (as you are an organic organism) was once CO2? That is the carbon cycle; CO2 is as important to life on earth as water and oxygen


    This is true, but so what. He's using just enough sciencey stuff to show that he can be "trusted" and then he draws illogical conclusions. Here he concludes that since CO2 is such an important building block of all life on earth it can't possibly be a "pollutant". Water, as he points out, is also a fundamental necessity, but you can still drown in the stuff. Too much of it all at once can destroy your house. The dose makes the poison.

    Anyway, be careful of just labeling his statements as "False!" Instead, be mindful of where his misdirection lies and point out, for the sake of the lurkers in the conversation, his flawed logic. Acknowledge things he says which are correct (this will also show the lurkers that you are reasonable) but then show where he is trying to be misleading.

  13. David Kirtley @662

    I told the denier this: 

    I find it amusing as well that you don't understand that the Carbon found in carbon based life is not from CO2. You should know that Carbon is very abundant on Earth and of the 92 naturally occurring elements (except for elements 43 and 61), only six of these elements make up some 99% of all living tissue. Ever heard of CHNOPS?

    You might want to look up where elements originate.

  14. TVC15 @663. I'm not following you. The elements originate in stars. The Earth was made of "star stuff." But I usually eat plants and animals, not rocks.

    Plants take in CO2 from the atmosphere, photosyntesize, and build the stuff of plant tissue from that. Animals, including me, eat plants. Other animals, including me, eat animals which ate plants. We transform the plant/animal material into the stuff of our animal bodies. All that carbon origianlly came from the atmosphere.

  15. Hi David @ 663,

    This denier loves to say that the Carbon in our bodies *orginated* from CO2.  This is not accurate.

    The building blocks of life come from elements and elements orginated from stars.

    Origin of Life’s Building Blocks in Carbon- and Nitrogen-Rich Surface Hydrothermal Vents

    As I pointed out to this denier show me where CO2 is mentioned in this paper as being how carbon based life originated.

    Origin of organic compounds on the primitive earth and in meteorites.

    I hope this helps to clarify.

  16. LOL now the deniers are using this article to claim global warming is a hoax!

    Big U-turn: Key melting Greenland glacier is growing again

  17. Sorry, TVC15, that doesn't clarify it. Yes, ultimately all carbon on earth comes from stars. We both agree about this. But the origins of life are not relevant here. I don't know what chemical pathways led to the origin of life, or if this involved CO2 or not. But today, right now, my everyday existance depends on atmospheric CO2.

    The question is: where did the carbon in my body come from? If you follow the trail it is clear that the carbon in my body came from the food I ate: plants and animals. Those animals get that carbon from the plants they eat. And all plants get that carbon from the CO2 floating in the air.

    None of this is inaccurate or controversial. It's Biology 101. Yes, you can follow the trail back to the ultimate origin of the element carbon inside the nuclear furnaces of stars. But why? The question is about life on Earth now.

    Your denier has stated some true facts about the carbon cycle and then tried to use this to draw an invalid conclusion about whether CO2 can be classified as a pollutant. Now you, by focusing on the ultimate origin of carbon in stars and now bringing in info about the origins of life, have totally missed the real misinformation that he is trying to push.

  18. David@667,

    I don't follow how what I posted does not clarify?

    In fact when I challenged the denier with what I posted here he stopped posting over and over the same manta that CO2 is a basic building block of life. No CO2 is not a basic building block of life.

    Then he came back with the Carbon in carbon based life originated from CO2.

    He stopped spreading his misinformation after I debunked both of his inaccurate statements.

  19. @668 : let it slide, TVC15 .

    In the end, it's rather futile to debate the origin of metabolic carbon ~ since the terrestrial carbon cycle moves C around continuously [not counting fossil carbon]. As David Kirtley says, its ultimate origin is from some distant stellar source, pre-dating our own sun.

    If anything, one might say that lifeform C in evolutionary terms originated from lipids and/or carbonates/bicarbonates in the primordial ocean.   And there can be other arguments too . . . all getting a bit Angels on a pinhead.   But your denier friend wasn't entirely wrong in his point about carbon ~ though it certainly was a pointless point he made.

    I hope you've had time to enjoy a few of the Potholer54 videos on climate science.   He has five [FIVE] on the asinine antics of the eloquent Lord Monckton ~ quite amusing to see the "error-prone Viscount" [unquote] shoot himself in the foot repeatedly.

  20. Hi Electric @669,

    Yes a agree it's a pointless point but that denier keep trying to use it to prove CO2 is good for the planet which of course it's true, but only when the balance is not offset.

    Most of this deniers tactics are what both you and David pointed out...they are sprinkled with some facts but the conclusion he draws from these facts is misleading which is what I try to point out to the bystanders reading his chest beating comments.

  21. @669,

    Forgot to mention that yes I've enjoyed Potholer54! Thanks for informing me about his videos.

  22. TVC15 @668: "No CO2 is not a basic building block of life."

    Is Carbon a basic building block of life?

  23. David @672

    I think you must have misread what I posted. The denier I battle is the one who keeps trying to claim the CO2 is a basic building block of life. Thus why I pointed out to him the 6 known elements that are the building blocks of life. Recall I asked him if he's ever heard of CHNOPS?

  24. TVC15 @673 So, where does the carbon in all life forms come from?

  25. David @674

    From space. :)

    Delivery of carbon, nitrogen, and sulfur to the silicate Earth by a giant impact

    Where Did Carbon Come From For Life on Earth?

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