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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

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Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Past

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


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Comments 626 to 650 out of 883:

  1. 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.

  2. 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).

  3. "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.

  4. 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.

  5. 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.

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

  7. "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.

  8. 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?

  9. 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. 

  10. 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.

  11. 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.

  12. 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?

  13. 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.

  14. 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.

  15. "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.

  16. 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.

  17. 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?

  18. 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)

  19. 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?

  20. 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.

  21. 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

  22. 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]

  23. 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.

  24. MA Rodger and others interested:

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

  25. 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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