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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 176 to 200 out of 420:

  1. #174: would it be like these 60-ish year and non-significant fluctuations, discussed by Tamino? There's a good discussion of periodicity and the detection of cycles within. People can pretend that the world's climate is driven by something nicely uncontrollable like planetary movements (climastrology?), but back in the real world, it's the radiative forcings that dominate, and the biggest forcing factor is indeed 'controlled' by humans.
  2. 176 - skywatcher... "climastrology" :-D Tamino should add that to this discussion. Anyway, I have the strong suspicion that 174 is spam... but if you get a reply, it's probably because Mars is exerting a strong influence.
  3. 176, skywatcher, 177, les, Climastrology I like it. It's actually better than mathturbation, and more appropriate (in that mathturbation is clearly an important "skill" needed by climastrologists, but doesn't describe the overall, full version of alchemy in which they indulge). I'd personally like to recommend that we begin using the word where ever it applies... today's post by Dana on climastrologist Syun-Ichi Akasofu being a perfect case.
  4. Turns out I'm not first with the word (bah!) - a google search on 'climastrology' comes up with all sorts of nasty anti-Gore, anti-science stuff. But I would certainly say it fits very well for people who think they can predict climate using some flavour or combination of 'cycles' rather than the well-understood and well-verified radiative physics, just like your example Sphaerica.
  5. Climatologist sighting on the Akasofu thread!
  6. Yes, well if climatologists are anti-science (lets say) than what better term to use to describe the sighting in 180?
  7. What I don't understan is why Mr. Cotton didn't post on the Akasofu thread to protest that his epicycles are more true then those epicycles. I mean, they can't both be right, surely? Without physical reality as the final arbitrator, it should be a good bit of sophistry.
  8. Sorry, I meant climastrologist sighting, not climatologist sighting.
  9. Yes, climate has changed before. When grapes were grown near the Scotish border in Roman times it was probably warmer than when I was there this time last year (in summer) experiencing winds so strong I could hardly open the car door. My arguments are far too detailed to repeat here - see them at and at least note just two things ... (a) Consider the sound physical proof given there that solar insolation contributes a mean of less than 10 degrees whereas over 280 degrees K comes from heat coming through the surface from the core and the crust which warms the lower atmosphere we live in from absolute zero to above 280 deg.K, even at night. So the IPCC "theory" has only those 10 degrees to play with for a start. (b) All the available photons from the sun are already captured each day by water vapour and CO2 etc and there is surplus vapour and CO2 left over. Even what heat goes into the ground is lost again that night. (For example, hot sand on a beach cools at night.) You cannot create energy. Speaking as one who teaches Physics and has marked university assignments, I can assure you that the IPCC argument about this feedback leading to more warming each year is totally incorrect. All feedback only leads to temporary warming and I don't care if 70 odd "scientists" mostly in other disciplines seem to think energy can be created by extra CO2. It can't be. And it isn't. Equilibrium will be established at the level dictated (at least 96%) by the heat flow from the Earth which has natural long-term cyclic variations regulated by the planets by at least three mechanisms explained on my site. THAT is the reason there has been no increase in mean temperatures from Jan 2003 to July 2011 despite increased CO2. Get up to date here: I welcome ANY discussion via my email address on the site, provided you indicate that you have read all that is there.
  10. I would like to see some of our resident deniers comment on DougCotton @184.
  11. #184, how do you quantified the gravitational energy that you claim to be 200,000 times greater than solar energy? What units and what conversions?
  12. Tom@186: Thankfully, I didn't miss this one. I just havvve to read this. Thank you.
  13. DougCotton, it looks like your featured evidence for "global cooling", comparing 2003 to 2011 is cherry-picked. For example in your chart you show that 'the mean for the first half of 2011 was less than the mean for the first half of 2003" and "the mean for the second half of 2010 was less than the mean for the second half of 2003". In your graph linked above there is more support for saying "the mean for the first half of 2010 was significantly higher than the mean for the first half of 2003 and considering that those were both El Nino years, it suggests warming". Your comparison of 2011 to 2003 is not useful since 2003 was El Nino and 2011 was La Nina. You use AMSU sea surface temperatures which are only representative of part of the planet (missing all land) and heavily reflect SST which fluctuates due to ENSO. In fact the AMSU sensor that you use tracks closely to the ICOADS values of actual SST measurements, see figure 1.
  14. Wow, Doug #184 I would like to see one of your physics classes if that is what you teach! It sounds like you are suggesting that planet Earth would be pretty much just fine without the Sun, among other things. Yours is a great comment for any resident skeptics to debunk (good start Eric), as I think they could safely do it without causing damage to their own understandings of the climate system, even if they are not too close to the truth about climate. A starter for 10 - how does Doug's hypothesis account for the poles being markedly cooler than the equator, if most heat comes from within Earth? I might even have to come up with a new term for DougCotton's understanding of climate!
  15. Oddly enough, the theory that most heat comes from within the earth does not contradict GH theory since outgoing LW would still be absorbed by GHGs.
  16. Doug, the heat flux through the earth is of enormous importance to the oil industry since it is a critical component for calculating when sediments with an organic components will produce oil and gas. As a result, it is measured. The heat flux from the core around 0.04W/m2 - 0.06W/m2. Compare this with 300+/W/m2 from sun.
  17. Skywatcher at #189: "Wow, Doug #184 I would like to see one of your physics classes if that is what you teach!" He doesn't- he claims a 4 year degree in physics, and "Extensive subsequent private research and post-graduate studies in Economics, IT, Accounting, Business Administration, Marketing, Climate Change, Nutrition and Natural Medicine". He started something called the "Natural Medicine Research Centre". That doesn't sound promising. He is not a physics teacher, he's an internet scientist.
  18. I come to this debate as a philosopher and science layman. The thing that strikes me is that we have descended into a debate about the truth of facts. Without absolute verification possible in some instances of these facts we can only posit, as all good science eventually does, the most probable circumstance. If this depends on a consensus of scientific opinion, then authority rests with those with sufficient knowledge to debate what is the most probable scenario. In other words, whatever the layman thinks, the expert is the only one with real knowledge. But then another problem arises, endemic to this particular debate. We are talking about scientific theories about systems, not individual facts. The truth of this debate hinges on probabilities about complex totalities, and no consensus can be reached on such contentious grounds. If authority cannot be given to cognoscenti when the very object is too complex to predict or prejudge, then the argument must rest on faith. That is why this issue has sparked so much division and opinion-mongering. In which case, I side with Pascal and his wager. Not knowing the real truth, the total picture with absolute certainty, and having to rest content with mere probabilities about complex systems, it is better to err on the side of caution. If the worst case scenario is no habitable planet then we should opt for a sustainable future.
  19. But kropotkin, consensus has been reached, and the predictions to date have proven accurate.
  20. Tom, To what consensus are you referring? If you mean that temperature have risen globally or that atmospheric CO2 has increased, then yes. But, if you are referring to how much CO2 has contributed to the observed warming, and how much warming we can expect in the future, then I am afraid we have a long way to go to reach a consensus. Predictions have been all over the board, however as any fortune teller or stock broker will say, "make enough predictions, and some will come true."
    Response: [Dikran Marsupial] Actually the world climatologists are in pretty good agreement about the contribution of the CO2 to the observed warming etc. You may disagree with this, however it is for you to provide evidence to back up your opinion.

    Secondly the projections have not been "all over the board"; the uncertainties of the projections are high; that is not the same thing.

    Now this part of the thread seems to be heading to a point where no progress is likely to be made, and posts become indistiguishable from trolling. So unless you want to provide an evidence based argument with references to sources backing up your position, I suggest we all move onto a more substantive issue.
  21. This is somewhat off topic but it seems that whenever the scientific consensus on AGW comes up the reaction of skeptics is to show that there are some outliers that disagree, thus there is no consensus. Consensus does not require 100% agreement. con·sen·sus    1. majority of opinion: The consensus of the group was that they should meet twice a month. 2.general agreement or concord; harmony.
  22. I've recently come across a number of arguments suggesting that the ice core CO2 measurements are inaccurate as they can be contaminated or only show CO2 concentrations in one location etc. Is there any charts that show the data of the various ice core datasets laid over each other to demonstrate that they are in agreement with each other as you wouldn't expect the same problems to occur at exactly the same time periods at different locations around the world. Cheers
  23. Fitz, there is an IPCC graph which shows different records overlapping. However, demonstrating that they align wasn't its intended purpose so the resolution is low and the records aren't all identified. The red is atmospheric, the green looks like it is probably Law Dome, and the purple must be Vostok. In any case, see the How reliable are CO2 measurements? page for more info.

    [DB] There is this one; I'll look for others:

    Ice Core CO2


    This one, showing the departure from the natural range of CO2, is a jaw-dropper:



    To paraphrase the Bard:  The Rate's the Thing...

  24. Good grief, DB, where did you get the second graph? I don't recall having seen it. That is almost painful.

    [DB] I collect 'em, like Imelda Marcos does shoes...

  25. That's one heck of a 'natural cycle!' And for those who accept that increasing temperature is necessary for increasing CO2 (the Salby effect), the 'its cooling' meme is blown.

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