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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)

At a glance

Just imagine for a moment. You fancy having a picnic tomorrow, or you're a farmer needing a dry day to harvest a ripe crop. So naturally, you tune in for a weather-forecast. But what you get is:

“Here is the weather forecast. There will be weather today and tomorrow. Good morning.”

That's a fat lot of use, isn't it? The same applies to, “the climate's changed before”. It's a useless statement. Why? Because it omits details. It doesn't tell you what happened.

Climate has indeed changed in the past with various impacts depending on the speed and type of that change. Such results have included everything from slow changes to ecosystems over millions of years - through to sudden mass-extinctions. Rapid climate change, of the type we're causing through our enormous carbon dioxide emissions, falls into the very dangerous camp. That's because the faster the change, the harder it is for nature to cope. We are part of nature so if it goes down, it takes us with it.

So anyone who dismissively tells you, “the climate has always changed”, either does not know what they are talking about or they are deliberately trying to mislead you.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further Details

Past changes in climate, for which hard evidence is preserved throughout the geological record, have had a number of drivers usually acting in combination. Plate tectonics and volcanism, perturbations in Earth's slow carbon cycle and cyclic changes in Earth's orbit have all played their part. The orbital changes, described by the Milankovitch Cycles, are sufficient to initiate the flips from glacials (when ice-sheets spread over much of Northern Europe and the North American continent) to interglacials (conditions like the past few thousand years) and back  – but only with assistance from other climate feedbacks.

The key driver that forces the climate from Hothouse to Icehouse and back is instead the slow carbon cycle. The slow carbon cycle can be regarded as Earth's thermostat. It involves the movement of carbon between vast geological reservoirs and Earth's atmosphere. Reservoirs include the fossil fuels (coal/oil/gas) and limestone (made up of calcium carbonate). They can store the carbon safely over tens of millions of years or more. But such storage systems can be disturbed.

Carbon can be released from such geological reservoirs by a variety of processes. If rocks are uplifted to form mountain ranges, erosion occurs and the rocks are broken down. Metamorphism – changes inflicted on rocks due to high temperatures and pressures – causes some minerals to chemically break down. New minerals are formed but the carbon may be released. Plate tectonic movements are also associated with volcanism that releases carbon from deep inside Earth's mantle. Today it is estimated by the U.S. Geological Survey that the world's volcanoes release between 180 and 440 million tonnes of carbon dioxide per year - as opposed to the ~35 billion tonnes we release.

Epic carbon releases in the geological past

An extreme carbon-releasing mechanism can occur when magma invades a sedimentary basin containing extensive deposits of fossil fuels. Fortunately, this is an infrequent phenomenon. But it has nevertheless happened at times, including an episode 250 million years ago at the end of the Permian Period. In what is now known as Siberia, a vast volcanic plumbing-system became established, within a large sedimentary basin. Strata spanning hundreds of millions of years filled that basin, including many large coal, oil, gas and salt deposits. The copious rising magma encountered these deposits and quite literally cooked them (fig. 1).

Fig. 1: schematic cross section though just a part of the Siberian Traps Large Igneous Province, showing what science has determined was going on back then, at the end of the Permian Period.

Now laden with a heavy payload of gases, boiled out of the fossil fuel deposits, some of the magma carried on up to the surface to be erupted on a massive scale. The eruptions – volcanism on a scale Mankind has never witnessed - produced lavas that cover an area hundreds of kilometres across. Known as the Siberian Traps, because of the distinctive stepped landforms produced by the multiple flows, it has been calculated that the eruptions produced at least three million cubic kilometres of volcanic products. Just for a moment think of Mount St Helens and its cataclysmic May 1980 eruption, captured on film. How many cubic kilometres with that one? Less than ten.

Recently, geologists working in this part of Siberia have found and documented numerous masses of part-combusted coal entrapped in the lavas (Elkins-Tanton et al. 2020; fig. 2). In the same district are abundant mineral deposits formed in large pipes of shattered rock as the boiling waters and gases were driven upwards by the heat from the magma.

Fig. 2: an end-Permian smoking gun? One of countless masses of part-combusted coal enclosed by basalt of the Siberian Traps. Photo: Scott Simper, courtesy of Lindy Elkins-Tanton.

It has been calculated that as a consequence of the Siberian Traps eruptions, between ten trillion and one hundred trillion tons of carbon dioxide were released to the atmosphere over just a few tens of thousands of years. The estimated CO2 emission-rate ranges between 500 and 5000 billion tonnes per century. Pollution from the Siberian Traps eruptions caused rapid global warming and the greatest mass-extinction in the fossil record (Burgess et al, 2017). There are multiple lines of hard geological evidence to support that statement.

We simply break into those ancient carbon reservoirs via opencast or underground mines and oil/gas wells. Through such infrastructure, the ancient carbon is extracted and burned. At what rate? Our current carbon dioxide emissions are not dissimilar to the estimated range for the Siberian Traps eruptions, at more than 3,000 billion tons per century. The warning could not be more clear. Those telling you the climate's changed before are omitting the critical bit – the details. And when you look at the details, it's not always a pretty sight.

Last updated on 14 February 2023 by John Mason. View Archives

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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 701 to 725 out of 898:

  1. @ 699 MA Rodger,

    What is a discal projection?

  2. Hi MA Rodgers,

    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.

    I'm a bit confused. What do you mean by where did the other 110ppm come from?

  3. TVC15 @700. Re. CO2 levels in the distant past, see this rebuttal: Do high levels of CO2 in the past contradict the warming effect of CO2?

  4. I need your help again guys!  I posted this statement: In July 2007, a survey of hurricanes in the North Atlantic over the past century noted an increase in the number of observed...

    A denier who many on the sidelines thinks is brilliant and who I suspect is being paid to spout what he spouts responded with this.

    "The operand is "observed."

    You have the technology to observe both tornadoes and hurricanes that you were never able to observe in the past.

    And that's the recent past, outside of the last 50 years.

    There's no science behind "climate change." It's all political and socio-economic-based:

    German economist and Intergovernmental Panel on Climate Change (IPCC) official Ottmar Eddenhofer, explained prior to the Cancun conference in an interview with the Global Warming Policy Foundation (Potter 2010): First of all, developed countries have basically expropriated the atmosphere of the world community. But one must say clearly that we redistribute de facto the world's wealth by climate policy. Obviously, the owners of coal and oil will not be enthusiastic about this. One has to free oneself from the illusion that international climate policy is environmental policy. This has almost nothing to do with environmental policy anymore, with problems such as deforestation or the ozone hole...Basically it's a big mistake to discuss climate policy separately from the major themes of globalization.

    In a paper prepared for the Cancun conference Professor Kevin Anderson, Director of the Tyndall Centre for Climate Change Research, said the only way to reduce global emissions enough, while allowing the poor nations to continue to grow, is to halt economic growth in the rich world over the next twenty years.He called for World War II-type rationing of electricity in order to force people to conserve (Gray 2010)



  5. @703 David Kirtley thank you so much. Odd that did not come up when I searched for Ordovician-Silurian.

  6. This is more motivated reasoning. Well obviously there is science behind it - the whole IPCC WG1 is nothing but science. However, solving it is political and economic and the argument he is trying is that there is a nefarious plot by scientists who want everyone including themselves to suffer massive economic damage for no good reason except... But people which view the world through ideological glasses seem to believe this.

    There is also the IPCC WG3 on ... solutions. In there you can see the published opinion from the many that have studied the issue instead of the opinions (misrepresented at that) of carefully chosen few.  I wonder how well Ottmar Eddenhofer feels his views were represented by the Global Warming Policy Foundation.

  7. I would also say this is totally off-topic. PLease put your comments in an appropriate thread.

  8. TVC15 @701,

    The sun illuminated the disc of the Earth with an intensity measured by TSI. The disc has an area of πr^2. But this energy is spread out, not over a disc but over a globe with area 4πr^2. So TSI requires dividing by 4 to give the average solar climatic impact.

    TVC15 @702,

    The denialist is quoted @695 saying "Is man made CO2 not 5% of atmospheric CO2?" With 410ppm CO2 in the atmosphere, 5% would be 20ppm. But since pre-industrial times CO2 has rise from 280ppm, a rise of 130ppm. If mankind is responsible for only 20ppm of this, where did the other 110ppm come from? Perhaps the denialist is believing that this extra 110ppm is down to the shape-shifting lizards, or perhaps all the unicorns he sees inhabiting the world.

  9. MA Rodger @708

    Thank you for the clarifications! 

    scaddenp @ 706,707

    Ops sorry to step off topic but I appreciate the insights. I read some interesting information about Eddenhofer on Desmog.

  10. Hi Again,

    I'm not sure how to respond to these types of denalist claims.

    So how does one parse out the individual influences of the sun, CO2, water, and now "sulphate aerosols"?

  11. The assertion of the author can be countered with many examples. The subject of longterm climate patterns is so complex and beyond current human understanding that any assertions are highly suspect.


    [PS] Argument from personal incredularity. I suggest you take time to inform yourself of the science and respond with research to back your assertion.

  12. Warend @711 ,

    over less than one hour, you have made 4 comments in 4 separate threads here at SkS.   Each comment was distinctly fatuous.   So the readers can only draw the conclusion you are not a bot.    ;-)

    Warend, you are posting on the wrong website.   This website here is for rational skeptics.   Your comments would have a much better fit at WhatsUpWithThat ~ a website where misery loves company.    ;-)   

  13. All these arguments are irrelevant as mankind is destroying the wildlife and environments of earth.

    Unless mankind changes immediately Man will be extinct before 2400

    The earth does not need mankind!

    Stop polluting the land and seas, stop cutting down the trees, and stop and feed the poor!

    Educate the population so that the population falls. 

    You don't have a choice!


  14. "Unless mankind changes immediately Man will be extinct before 2400"

    Probably earlier?

    “The IPCC report that the Paris agreement based its projections on considered over 1,000 possible scenarios. Of those, only 116 (about 10%) limited warming below 2C. Of those, only 6 kept global warming below 2C without using negative emissions. So roughly 1% of the IPCC’s projected scenarios kept warming below 2C without using negative emissions technology like BECCS. And Kevin Anderson, former head of the Tyndall Centre for Climate Change Research, has pointed out that those 6 lone scenarios showed global carbon emissions peaking in 2010. Which obviously hasn’t happened.
    So from the IPCC’s own report in 2014, we basically have a 1% chance of staying below 2C global warming if we now invent time travel and go back to 2010 to peak our global emissions. And again, you have to stop all growth and go into decline to do that. And long term feedbacks the IPCC largely blows off were ongoing back then too.”

    “ The level of fossil fuel consumption globally is now roughly five times higher than in the 1950s, and one-and-half times higher than in the 1980s, when the science of global warming was confirmed and governments accepted the need to act on it. This is a central feature of the “great acceleration” of human impacts on the natural world. . . .
    CO2 emissions are 55% higher today than in 1990. Despite 20 international conferences on fossil fuel use reduction and an international treaty that entered into force in 1994, man made greenhouse gases have risen inexorably.”

  15. I've come across another climate change denier who stated these things.

    If you read the peer-reviewed scientific articles, you will see that in every Inter-Glacial Period going back 800,000 years the sea level rose 3 meters to as much as 14 meters.

    Sea levels during MIS-7 and MIS-9 were 10 meters to 14 meters higher than present.

    What did you just say?

    You said CO2 levels haven't exceed 300 ppm CO2 in 1 Million years.

    So, what exactly is the point?

    Who was burning fossil fuels in any of the previous Inter-Glacial Periods?

    No one, yet sea levels still rose 3 meters to 14 meters.

    In fact, CO2 levels ranged from 260 ppm to 280 ppm CO2.

    So, the reality is that it doesn't matter if your CO2 level is 270 ppm or 470 ppm, because your sea level is going to increase 3 meters to 14 meters and neither you, nor anyone living, dead or who will ever live can stop it.

    Once you accept that scientific reality, the best thing to do is let the Free Market handle it, instead of ramming useless laws down people's throats that will do nothing except screw people over.

    I this he's cherry picking and misrepresenting.  

    My questions are:

    1. Is it an accurate claim that in every Inter-Glacial Period going back 800,000 years the sea level rose 3 meters to as much as 14 meters?
    2. Is it accurate to state that it doesn't matter if your CO2 level is 270 ppm or 470 ppm, because your sea level is going to increase 3 meters to 14 meters and neither you, nor anyone living, dead or who will ever live can stop it?


  16. I meant to state that I think he's cherry picking and misrepresenting. 

  17. TVC15 @715,

    The claim that "in every Inter-Glacial Period going back 800,000 years the sea level rose 3 meters to as much as 14 meters" is garbled nonsense, as is the comment about MIS-7 & MIS-9. The 'rise' presumably refers to SLR exceeding today's levels and the "3 meters" is probably referring to MIS-5 (although it is usually given as a little higher) which was the last interglacial 100,000 years ago while the "14 meters" is probably referring to MIS-11 400,000 years ago. (MIS-7 & MIS-9 were the interglacials inbetween these two.)

    Reconstructing a SLR record over recent ice-ages is not as simple as the equivalent CO2 & polar temperature record. So it is not impossible that wildy contrardictory evidence exists and I'm not aware that a definitive source for ice-age SLR actually exists yet. Our good friend Google provides the graphic below although it requires signing-up to get a proper sight of the data it is based upon.

    SLR over 800,000 years

    As for CO2 being below 300ppm during those previous interglacials, it was the planet's orbital configuration that allowed that extra ice-melt back then, the whole amplified by reduced albedo due to lower ice cover. Today those orbital configurations do not exist so without mankind's GHGs the planet would now be slipping into an ice-age and sea level would have been dropping. Our extra GHGs is more than preventing that and CO2 levels of 470ppm (not sure why that particular value is stated) will melt out Greenland (as happened in MIS-5) and a fair bit of Antarctica as well. So 14m SLR would be on the cards, although the melting is expected to take some millennia if you managed to stop at 470ppm.

  18. MA Rodgers @ 717 

    Thank you once again for educating me so I can educate others!

    With respect to the state of this planet and human activity I now see that's it too late to undo what human activity is doing to our climate.

    I apologize if I come across as a "Debbie downer" but from all that I've learned thus appears that this earth cannot overcome human caused destruction until we destroy ourselves.

    I am not saying we should simply stop trying but when I look around the globe it's pretty evident that what we've unleashed on this earth is not stoppable even if fossil fuel use ceased 100% today.

  19. @TVC15,

    Don't be so sure about that. While humans have huge destructive capacity, we also have tremendous creative capacity too.

    You are right about just dropping emissions to zero won't be enough. That's been in the IPCC models all along. But the carbon cycle is just that...a cycle. There are two sides to balance. While reducing emissions can't work alone, the other side of the carbon cycle is sequestration. And it only takes about a 10% improvement on the natural carbon cycle sequestration side worldwide to offset emissions. 

    So while it is controversial still, we actually do have the capacity to improve the long term sequestration side of the carbon cycle at the same time as we reduce emissions. That means we actually can get to a drawdown scenario and it is not yet too late.

    I wrote this up to show how:

    Can we reverse global warming?

    That gets us back to the IPCC scenario that stabilizes the climate! So no. It is not too late.

    And there are more details regarding the emissions side of a drawdown scenario here:



    And more information on how to properly set up a carbon market to facilitate both emissions and sequestration here:

    Farming a climate solution.


    Emissions is straight forward in a fee and dividend system. You put a fee on fossil fuel sources. That makes people search for low carbom alternatives, which are abundantly available already. The fee just makes them relatively cheaper. But then we take the dividend and use it to pay for measured verified carbon sink increases (rising SOC), and the two together can get us to a net negative.

    There are still a few people quibbling over nonsense like which sector should take the heavier load. Should energy take 50% and agriculture the other 50% on the path to a drawdown scenario? Or should it be 80%/20%? Or maybe even 20%/80%? It really doesn't matter as long as in the end we get to a net negative atmospheric carbon flux.

  20. Thank you RedBaron @ 719

    To be honesty I have no faith in the human species. Overpopulation leading to humans crowding out and forcing other animal and plant species into extinction on top of the GHG emissions and all the other human activities that's destroying life on this earth is why I have bleak outlook on the human species. 

    I sometimes wish I did not know of all the mass destruction humans are causing. Climate change is just one in many things humans are contributing to.

    I digress.

  21. Don't digress because one is just a symptom of the other, and fixing one fixes both. And more importantly to your lack of faith, please remember. Science is about evidence not faith.

    Soil Carbon Sequestration Potential for “Grain for Green” Project in Loess Plateau, China

    Sure that paper just discusses potential. But in fact the project did go forward and has indeed suceeded in already restoring ecosystem function to vast acreage and is even now sequestering approximately 25% of China's emissions. The effect is so profound and widespread it can be seen from space.

    Human Activity in China and India Dominates the Greening of Earth, NASA Study Shows

    So you see? Where the highest human population density on the planet is also the most improvement in ecosystem restoration, which is actually already making significant strides in restoring ecosystem function over vast areas...

    Now is not the time to give up with dispare. Now is the time to tighten your belts and get to work! We have a lot of work to do and pouting around with gloom and doom is not helping one bit.

    We can do it. Get er done!

  22. Hi RedBaron @ 721,

    Trust me I am a scientist and I know science is based in evidence not faith.

    In thinking about your first response to me with respect to the quibbling over which sector should take the heavier you really think either one is going to simply agree to taking the heavier load? I don't. These two sectors have tons of money to buy any lobbyist or politician they want in order to fight against taking any load. And I'm certain there will be resistance from both sides.  Thus this leads me back to it's too late to turn back now.

    Just look at the current heat wave hitting India with those crazy high temps!  Even with this news you still see the deniers in the US and around the globe.

    I am not a doom and gloom type gal, just a realist.

  23. @ RedBaron 721

    Those are two truly encouraging links you posted about China and India dominating greening the earth! 

    Thanks for sharing this!

  24. TVC15 @724,

    There were of course "EXTREME" climate processes prior to mankind arriving on the scene. These can perhaps be classified into two different groups.

    The first can include really big changes but they occur very slowly, although sudden on a geological time-scale. So the end of the last ice age saw a rise of perhaps 6ºC in global temperature over 8,000 years or 55 million years ago the PETM which saw similar temperature rises over 40,000 years (long enough for, for instance, horses to adapt to the temperature increases by slowly evolving from pony-size into the size of large dogs).

    The second group are far more sudden, the suddenness often obvious. A big volcanic eruption (Mt Toba 74,000 years ago), a meteor strike, or a sudden influx of fresh water that destabilises ocean currents (as per Dansgaard–Oeschger events). This second group can still have very very big local effects but obvious causes that soon dissipate (althugh D-O events can take 2,000 years to return to the prior climate).

    But in all this, I'm not sure what a denialist is trying to argue. If we wait long enough there will eventually be a mega-volcano blow its top, or a big meteor will eventually strike the Earth. (There isn't enough ice about for a D-O event to occur without an ice-age.) So is the denialist suggesting we set about creating our own climatic disaster to allow us to practise for how to respond to the real thing? Or does he want an explanation for every wobbly bit of paleoclimate before he will accept the blindingly obvious fact that it is humanity driving todays warming climate and it will not end well if we don't do something about it?

  25. I accidently deleted the following comment. My bad.


    TVC15 at 19:59 PM on 4 June 2019 

    Is there an easy answser for this question being asked by a climate denier?

    And as you know, nature's impact on climate can and has been EXTREME prior to man, and man's industrialization. How do you account for that?

    So far from what I've learned from you guys is Earth's orbit, solar output, the sun being cooler, greater volcanic activity, rock weathering, surface ice albedo, massive amounts of Dinosaur gas? (sorry guys I had to toss that in for grins)

    Are there other factors I missed?


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