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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 676 to 700 out of 766:

  1. TVC15 @675, "From space. :)" 


    But why stop there? Why not say it originated in the Big Bang. That, too, would be true. But is such a statement in any way meaningful? Not really.

    Your denier used a true statement about the world and then used it to obfuscate about our current problem with CO2 increasing in the atmosphere.

    You are using similar obfuscation by jumping back to the primordial origin of life to talk about the elemental building blocks of all life.

    But the denier wasn't talking about that, he was talking about how life operates here and now: "Did you know that ALL of the carbon atoms in your body (as you are an organic organism) was once CO2?"  

    Do you not accept that the carbon in your body came from the CO2 in the atmosphere?

  2. David Kirtley @676,

    You say of carbon, "Why not say it originated in the Big Bang. That, too, would be true." Actually it wouldn't. Atoms did not form until the universe cooled enough and that would have been at the time the Cosmic Microwave Background radiation appeared. This is some 400,000 years after the big bang. And surely those first atoms were hydrogen and would need to be converted into carbon by nuclear processes within stars, a process requiring a good deal further time.

    As for "ALL of the carbon atoms in your body" being converted from CO2 by plant photosyntheses and then consumed by the animal as food, this would quite a recent process as C3 photosynthesis (the oldest form) didn't begin creating an oxygen atmosphere until perhaps 2 billion years ago. (That a plant does not rely solely on photosynthesis to obtain carbon is a bit too big a pedantic step but worthy of noting.) In the "here & now," that the vast majority of higher animal carbon content is the result of photosynthesis and thus derives from CO2. But ALL the carbon? And if it were, why would that prevent a surplus of CO2 being labelled a "pollutant"? -  that being the point the denialist troll was making.

  3. David@ 676

     No I don't accept that all the Carbon atoms in Carbon based life were once CO2. 

    The Carbon in carbon based life could also come from methane.

    A German-British team led by researchers of the Max Planck Institute for Chemistry in Mainz and the University of Heidelberg, recently discovered that methane in plants is produced from the amino acid methionine, which all living organisms need for the building of proteins.

  4. David@676

    I forgot to link the discovery.

    At the methane source of plants

  5. TVC:

    All carbon in life is fixed by plants via photosynthesis.  A miniscule amount of methane might be incoporated into life but the methane came from carbon dioxide fixed by plants.  This is well known.  

    I suggest you hang your arguments on another point.  There are many clear points where your denier is incorrect.

  6. MA Rodger @677: I stand corrected. I went too far back in time.

    TVC15, the reason I am belaboring this is because if I were one of your friends watching this conversation from the sidelines and I saw you merely declare: "False" in response to the denier's statement which contains at least a nugget of factual information, I would not have been impressed. Most people have a basic understanding that the material in their body comes from the food they eat and that this ultimately comes from plants which get their material from CO2 and water. So most people would have recognized that the denier had made some true statements when he said: "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".  Your denier then makes a false conclusion from these basic facts that CO2 can't be a pollutant: "yet the left has labeled it a 'pollutant'."  You should have shown that this conclusion is false, and doesn't follow from the previous factual information. Instead you attacked the other end of his argument, spinning out irrelevant information about the ultimate origin of elements, or the fact that not ALL (every single atom of carbon) in lifeforms comes from CO2.

    Does any of that information about the origins of carbon or other sources of carbon in lifeforms say anything about the denier's false conclusion about CO2 as a pollutant? No.

    I'm sorry if all of this seems like I'm attacking you. I'm sure you mean well and want to communicate the science well. But too often these online conversations with deniers devolve into shouting matches which don't do any good for the ones listening in on the sidelines.

    All I'm really saying is, ignore the denier and aim past him to get the correct information to those on the sidelines.

  7. @680 & @681
    Thank you both and all points well taken and understood by me.

    I greatly appreciate the feedback of how I handled this denier and the angle I took.

  8. My the denialist is trying to debunk this link I posted.

    "You actually believe that one can parse individual contributions to "climate" change so precisely and then assign (with similar precision) relative contributions from man and "natural" causes?"

    "That is priceless. So I guess the fact that we are in a 50-75 year solar minimum cooling phase is lost to you then? Should we not be concerned about that large burning gas ball in the sky, now that we "know" that the only thing that really matters is CO2?"

  9. TVC - you are wasting your time with this idiot. Your graphic is based on some fundimental physical assumptions, especially the conservation of energy. From this we deduce that changing the radiative balance will change climate. Measuring individual contributions to the radiative balance does indeed yield that diagram. It is possible to construe a possible downward trend in solar, but he thinks a change of 0.1W/m2 is significant then why isnt change of 3.7W/m2 (GHG) even more significant. The claim "that we "know" that the only thing that really matters is CO2?" is strawman. Reading any of the references associated with the diagram shows that all the causes contribute and are accounted for - but that CO2 is the most important for current climate change. He is not interested in examining the evidence. He needs to supply evidence that refutes the methodology or finding of those papers. I doubt you get him to read any of them.

    His comments present not one shred of evidence in reply. It is scoffs from personal incredulity based on wilful ignorance. You will not make any impact on someone who chooses not to understand.

  10. @684 scaddenp

    Thanks scaddenp.  He's the same denier who says CO2 is a basic building block of life. *rolled eyes*

    The other denier I'm dealing with uses odd angles to come at me with.


    "I guess you see only what you want to see.

    Past Century's Global Temperature Change Is Fastest On Record

    Past Century's Global Temperature Change Is Fastest On Record

    It's not the fastest on record.

    24 times in the last 100,000 years, the climate has fluctuated by as much as 20°F in a matter of years or decades.

    78 times in the last 100,000 years, the climate has fluctuated by smaller amounts 4°F-6°F in a matter of years or decades.

    Explain how 1.4°F over 140 years — 14 decades — is faster than that.

    If I had to list every alarmist claim by NASA, or NPR, or National Geographic or the IPCC, I'd be here the rest of my life."

    It's a new form of cherry picking combined with a Gish Gallop.


  11. I have a question about the EPIC ice core data showing that the climate for the seven prior interglacials.  The second denier I'm dealing with is stating:

    "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."


    When I disclosed that the the EPICA ice core data (which covers back to eight previous interglacials) doesn't manage the 4.3°C to 8.3°C relative to today for seven prior interglacials.

    He comes back with this: "Um, those are the temperature changes in the Antarctic, not the average global temperature."

    My understanding of the EPICA Ice Core datas main objective is to obtain full documentation of the climatic and atmospheric record archived in Antarctic ice by drilling and analyzing two ice cores and comparing these with their Greenland counterparts (GRIP and GISP). Evaluation of these records will provide information about the natural climate variability and mechanisms of rapid climatic changes during the last glacial epoch.

    What game is this denier tyring to play with me?


  12. Can you guys tell me where this graph originated from? A denier is trying to use it to claim that there's no correlation between earth's CO2 levels and climate change in either direction (warmer or colder). And that's true over earth's 4+ billion year history.

    Geological Timescale: CO2 Concentration v. Temperature Fluctuations


  13. @TVC15:

    You should pose your question about the source of a graph to the denier who posted it. 

  14. TVC15 - I would say likely it is from here. The graphic itself has the source references for its data. In denier space, this usually goes with arguments that CO2 isnt related temperature - ignoring all the other drivers of climate.

    The NPR article was on the Marcott 2013 paper, extensively discussed here. Put Marcott into the search box on top right. A criticism is that the methodology may not capture high frequency temperature change. The usual denier take is to point major spikes in the NH temperature record (eg Younger Dryas) associated with exit from glacials. There is some evidence of similar, anti-phased events, in SH record. These proxies to indeed indicate very rapid temperature change but I am not aware of evidence for a global temperature change of that speed as opposed to regional change. Mechanism is disputed, but is associated with end of glacial periods so relevance to present climate is doubtful to say least.

  15. @ 688 John,

    I found that this denier took it from wattsupwiththat blog site. (a blog site known for climate denialist propaganda)

    I also found this in searching more about that graph.

    Can we make better graphs of global temperature history?

  16. Berner authored those first graphics at the RC link.  Here's the same image, with his comments about the overall correlation between atmospheric carbon dioxide and global temperatures over geologic time:



    Of course, the Royer graphic also corrects for the Faint Young Sun and ocean pH changes over the same geologic timeframe, with the result of strengthening the correlation between those CO2 levels and global temperatures over geologic time:


  17. @691 Daniel


  18. @689 scaddenp

    Much appreciated!

  19. TVC15:

    Generally speaking, when a climate science denier is shoveling pseudo-science poppycock, always aggressively demand that they document the source(s). WUWT itself is not an acceptable source. 

  20. This is the craziest Gish Gallop I've ever seen. Yes it's one of the deniers I deal with.

    Please refute the facts, instead of simply launching emotional diatribes.

    1. Is CO2 not .04% of atmospheric gases?

    2. Is man made CO2 not 5% of atmospheric CO2?

    3. Does water vapor not absorb IR energy over bandwidths 30X that of CO2?

    4. Is water vapor not .4-1% of atmospheric gases?

    5. Can one accurately compare over time temperature measurements estimated or measured by four different methods?

    6. Why don't the "temperature plots vs time" show the error bars for the methods used for temp measurement? (comparing "proxy temps" to digital, satellite proxies, and mercury thermometer measurements should immediately disqualify any scientific comparison).

    7. Why did temps not fall in the Great Depression when CO2 production fell 60%? (atmospheric CO2 has a half life of 3 years, not the very long periods suggested)

    8. Why did temps fall in ww2? Was the Battle of the Bulge and Stalingrad fought in tropical climates?

    9. How can the 1930s be the hottest decade on record when the AGW crowd says temps have continually increased since then?

    10. Why has Miami and New York not flooded?

    11. Why has there not been worldwide droughts?

    12. What happened to the "times without snow"? Tell that to everyone in the US this year.

    13. Why are temps falling?

    14. Are we not at the beginning of a prolonged solar minimum, similar to the Mauder minimum?

    15. Why did the earth not end and temps reach the boiling point of water when CO2 levels were 10X what they are now?

    16. What is the contribution of solar activity and sun spots to temps?

    17. What is the contribution of the orbit of the earth around the sun?

    18. What is the contribution of volcanic activity?

    19 If the "warming" models from 20 years ago are wrong, why are they correct now?

    20 How did they measure multiple temp points at remote areas of the ocean and polar regions 200 years ago?

    21. Have all the locations of temps measured over time been consistent geographic points? (Of course not- there has not been one consistent data point until the last twenty years).

    22. Why were temps warmer during the Roman Empire when CO2 levels were half what they are today?

    CO2 provides all the carbon that is the building blocks for ALL ORGANIC LIFE on this planet. Every carbon atom in your body that makes up all of the carbon compounds in your body were once CO2. It is not surprising that the death cult of AGW would seek to reduce or eliminate a molecule equally important as water or oxygen for life on earth.

    The "optimal" CO2 for plant growth is 900-1100 ppm. We need a lot MORE CO2, not less. Due to higher CO2 levels, plant life has increased over the last 30 years, providing a greening of the planet and higher crop production. Do you want to reduce plant life and cause famines?

  21. Since it looks to me like all the above are readily answerable and mostly from our myths section, I would assume that your denier has not the slightest interest in the correct answer and very much doubt they would take the time to read it anyway. Aside from the strawmen like "what happened to time without snow" -sure sign someone has never opened IPCC report.

    I'd repeat, you cant reason someone out of something they werent reasoned into. If this is an online public argument, then post links to the answers here (we can help if you cant find them), so observers can see he is an idiot, but be assured that reply wont change the mind of someone who's position is based on identity. If it is someone you know, then I would recommend Katherine Hayhoe TED talk for more effective way to talk, but I suspect you are way past point where person is capable of hearing anything you say.

  22. TVC15 , welcome to the world of crazy Gish Gallops.  Don't bother to reply on every point ~ just select a few, e.g. :-

    1.  On your skin, a very thin smear of suncream chemicals causes a major reduction in sunburn.  A big change, from a very small dose.

    13.  Thermometer readings vary slightly from year to year, but the Earth is still warming because excess heat is still coming in (through the excess Greenhouse effect) and the oceans are still building up heat since they absorb around 93% of the excess incoming heat ~ that's why the world's ice is continuing to melt.  No cooling and no pause in melting!

    14.  If it does ever happen to come, a prolonged solar minimum (just like the Maunder Minimum) will cause a cooling of about 0.3 degreesC [ about 0.5 degreesF ].  Since the world's warming is continuing at approx 0.15 degreesC per decade, that means it will take only 20 years of Greehouse warming to cancel the effect of the solar minimum (if it comes at all).  And then the warming will just continue to get worse.  Nope, there's no hope to be gotten from a grand solar minimum.  

    15.  In the distant past, when CO2 was much higher, the sun's radiation level was significantly LOWER. (Over the long term, our sun gets 1% hotter per every 150 million years approx.).  If you want to see oceans boil, come back in a few bilion years' time!

    22.  All else being the same, more CO2 is helpful to most plants ~ but in the real world, more CO2 leads to more droughts, more floods, and hotter & more prolonged heat waves : so plants suffer damage and produce less crop-yield.  Not good for humans.

    TVC15 , tell 'im to go away and educate himself and not spout the rubbish he's been giving us.

  23. @696 scaddenp @697 Eclectic

    You guys are great!  I see most of his silly Gish Gallops can be addressed from the Myth Section here on Skeptical Science.   

    Thank you both so much for all the wonderful information you provide me with in order to debunk these deniers. I have learned so much from you all and I am honored to be able to interact with people who know what they're talking about! 

  24. TVC15 @695,

    Correcting someone who refuses to be corrected is a bit of an up-hill struggle. I'm sure we have been over his (2) before (although @652 it was 4%). Why would the denialist consider that just 5% of atmospheric CO2 is down to anthropogenic causes? That would be just 20ppm. Where did the other 110ppm come from? That's 860Gt of CO2 so the source should be quite evident.

    And his (7), the poor fool appears to be confusing the average length-of-stay of an individual CO2 molecule in the atmosphere with the length-of-stay of an increased CO2 concentration. On the latter, the 'half-life' is perhaps 100 years but there is a long tail in that the last fifth will remain in the atmosphere for many thousands of years. After just three years, an injection of CO2 into the atmosphere would have reduced by less than 5%. (When we consider this, we talk of the Atmospheric Fraction, the amount CO2 rises each year relative to the anthropogenic emissions. The Af is roughly 45% but implying 55% has been sequestrated into oceans/biosphere. But the 55% is actually the sum of all those tiny percentage reductions for all the years since human emissions began as a percentage of just one year's emissions.)

    And back upthread @683, you quote presumably the same denialist source insisting that "the fact that we are in a 50-75 year solar minimum cooling phase". I did a quick 11-year averaging of TSI data which stretches back to 1976. The weak Sunspot Cycle has resulted in TSI dropping by 0.25Wm^-2 which needs converting from a discal projection to a global value and adjusted for albedo, yielding 0.04Wm^-2. That is about the same as one year of AGW so if there is a full Maunder Minimum on the way, its impact is yet to show up in the TSI data.

  25. @ 699 MA Rodger,

    Indeed it's been a huge up-hill struggle in my attempts to find a way around deniers.

    I appreciate all the new insights I'm gaining from this site.  I am so thankful this site exits!

    Here is another poor fool making these claims and trying to tell me I'm wrong for stating that analysis of past climates shows that greenhouse gasses, principally CO2, have controlled most ancient climate changes.

    "Proof that CO2 does not drive climate change is to be found during the Ordovician-Silurian and the Jurassic-Cretaceous periods (approx 450 and 150 million years ago, respectively) when CO2 levels were greater than 4,000 ppm and about 2,000 ppm, respectively. If the IPCC AGW/ACC theory is correct, there should have been runaway greenhouse gas-induced global warming during those periods but instead there was glaciation.

    Current CO2 level is slightly more than 400 ppm. Compare at will."

    I'm not sure how to respond as I came up with nothing when I search for Ordovician-Silurian on this site.

    Thank you for the great responses!


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