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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 76 to 89 out of 89:

  1. Roger, what exactly in the theory of climate that underlies the above that you are objecting to? That, when you add more heat to our climate, global temperatures rise? That CO2 is a greenhouse gas? That greenhouse effect is real? These questions of climate physics are better addressed on other threads. For past climate, it is better to realise that it is primarily where models can be tested and constrained. Phil (also from NZ)
  2. Phil and Doug, Thanks for your answers, please consider the opening statement to the answer of the question on this page. "If there's one thing that all sides of the climate debate can agree on, it's that climate has changed naturally in the past. Long before industrial times, the planet underwent many warming and cooling periods. This has led some to conclude that if global temperatures changed naturally in the past, long before SUVs and plasma TVs, nature must be the cause of current global warming. This conclusion is the opposite of peer-reviewed science has found. Our climate is governed by the following principle: when you add more heat to our climate, global temperatures rise." The above opening statement in the "explanation" as to why there were previous warmings (when there was no anthropogenic CO2) neatly sidesteps the question. The question, which is a very good one, is - "If there are previous warmings, why do we blame this one on CO2?" The answer is "Because an increase in CO2 which is a greenhouse gas, is the cause THIS TIME". So I am saying, where is the empirical proof of this cause. All that is in the explanation is a lot of theory which is not based on anything empirical, in fact like I have mentioned above, the explanations assume that the "Anthropogenic CO2 causes Global warming" hypothesis is fact when in actual fact there is no emperical support whatsoever. In fact previous warmings disprove the hypothesis. Hope you can understand my point. This comment and your answers are posted on for the benefit of my readers. Cheers Roger
    Response: "where is the empirical proof of this cause?"

    There are multiple lines of empirical evidence that CO2 is causing warming. We have a number of different satellites from NASA and Japan finding less infrared radiation escaping to space at CO2 wavelengths (Harries 2001, Griggs 2004, Chen 2007). Surface measurements from thousands of ground based stations are also finding more infrared radiation returning back to the Earth's surface (Wang 2009). A close examination of the infrared spectrum returning back to Earth finds more infrared radiation at CO2 wavelengths (Evans 2006).

    So we have independent measurements finding the same answer - which is consistent with lab measurements and simulations of an increased greenhouse effect caused by rising CO2.

    If you could post this answer on your blog, would be much appreciated :-)
  3. Roger - where are you getting this idea from? Besides the papers that John's article points to you (especially Harries and Evans) you might consider your "previous warmings disprove this hypothesis". They do? How? Do you consider that fact that, say, more energy from sun earlier caused a warming as proof that GHG isnt warming us now when there is no extra energy from the sun? If you look at the IPCC WG1, chapter on paleoclimate you will see reference and outputs from numerous models that consider past forcings and compare with past temperature. The physical model that climate change is function of solar, albedo, GHG and aerosol works very well to explain past climate (eg see Benestad & Schmidt 2009) and that model also leads us to conclude that humans, especially through our emissions, are changing climate. Consider the scientific process involved too. A model is derived out of basic physics - at heart it is a heat balance based on conservation of energy. From the model come a lot of predictions about what we should be observing. The match of observations to prediction gives us confidence. We can also apply it to the past to see that previous climate change is accounted for within model (within the very considerable error bounds imposed by the uncertainties in past forcings and observations of climate). Because it is a physical model, not a statistical model, you can compare predictions for say a solar forcing to a GHG forcing (eg and especially stratospheric cooling). All in I would say that gives very considerable support to current climate theory.
  4. Roger, you appear to be missing a lot of important information which I suspect is why you're not connecting the dots here with regard to the order of precedence of discovery leading to present conclusions about climate behavior. Theories and observations originally unrelated in both primary intellectual domain and chronological order led to our ability to understand gross climate behavior and subsequently to the notion of anthropogenic climate change. It's not a matter of imagining that we might change the climate and then hypothesizing mechanisms that might cause such to happen. You've got it quite backwards. I sincerely suggest you temporarily set aside your internally generated hypothesis of how AGW appeared on our collective radar and start from the beginning. Dr. Spencer Weart's Discovery of Global Warming. Weart's book begins from first principles in a number of different scientific domains and spells out pretty comprehensively how what we know of physics and earth sciences leads ineluctably to the conclusion that we can in fact change the climate all by ourselves. Really, you owe it to yourself to read Weart. If you're looking for -actual- gaps in our understanding of climate and how humans may change climate, his book is your best place to start.
  5. Roger writes "All that is in the explanation is a lot of theory which is not based on anything empirical" The explanation in this post describes how satellites have directly measured the change in the earth's outgoing and incoming radiation. This data does not come from models or theories, it comes from physical satellites with physical sensors which detect actual photons emitted from the actual atmosphere. None of this data collection process requires AGW to be true, photons are photons either way. This empirical data shows that CO2 in our atmosphere is absorbing and re-radiating energy just as predicted by AGW and associated theories. It is one of the strongest lines of empirical evidence underlying the theory. On top of this compelling evidence, past climate change is itself empirical evidence supporting the AGW theory. AGW and the theories underlying it predict a specific relationship between the earth's temperature and the various forcings that are theorized to affect it. This relationship can be confirmed or disconfirmed by examing reconstructions of the earth's climate and its various forcings. There are multiple independent methods for arriving at these reconstructions, none of them rely on AGW to be true. In general, the reconstructions depend on basic physical relationships between ambient temperature and various physical processes on earth. The reconstructions are created by observing actual physical evidence taken from the actual physical world, they do not come straight from models or broad theories. These independent methods all converge to the same picture of our climate's past, and are uniquely consistent with the predictions of AGW and associated theories. The same applies to observations of temperatures and forcings made within the past century, which, thanks to modern technology, can now be observed directly.
  6. Rogerthesurf writes: In fact previous warmings disprove the hypothesis. That is a logical fallacy. Does the fact that previous fires were started by lightning disprove the hypothesis that a current fire was started by arson? I agree with the others above who say that you need to be more clear about exactly what it is that you're questioning. Be specific -- and if it's something that's discussed in its own dedicated thread on the site, discuss it there. Do you think CO2 is not a greenhouse gas? Or it is a greenhouse gas, but we're not increasing its concentration in the atmosphere? Or it is a greenhouse gas and we're increasing its concentration in the atmosphere, but negative feedbacks will keep the temperature uniform anyway? Unless you clarify what your question is, it's hard for others to answer it efficiently.
  7. Response, Your reply is faithfully included in my blog. I am not disputing any of the findings that you mention in your answer, although some might, but none of this information proves in any way that anthropogenic CO2 is the root cause. My argument which is simply based on the standard scientific proof of a hypothesis, is not hard to understand, but for your benefit I will explain more. Even in the absence of previous warmings, the earth could be heating up for some other reason. The fact that there are well documented and general agreement that there have been previous warmings, such as the Holocene Maximum, the Minoan Warming, the Roman warming and the Medieval Warm Period, which are recorded in history as well as scientific proxies and the like, make CO2 as the root cause of global warming even less likely. The situation can be likened to the problem that pharmaceutical researchers have. If a patient is ill and you give him some of your new drug, and the patient gets well:- Did he get well because of the drug, or did he get well anyway? Very hard to tell, so as you should be aware, this problem is solved by doing double blind tests on a large sample of patients and doing a statistical analysis of the results. (Double blind because if the patient knows if he is receiving the drug or placebo, it effects his response, as the response is also effected if the person administering knows whether it is the drug or a placebo) To further illustrate the difficulty of proving a hypothesis, I recommend watching the following video. The video has nothing to do with CO2 or global warming, but illustrates well the problems of hypothesis proof. A number of people died when the captain of this aircraft formed a hypothesis of what was wrong with the plane, an incident seemed to support his hypothesis, but in spite of definitive disproof of his hypothesis being readily available, because the hypothesis was incorrect, the aircraft crashed. In fact there are a number of known things which could cause the current warming, and probably a greater number of factors which are unknown. I hope this clarifies things for you and your readers. Please take the time to watch the video. This response is also posted on Cheers Roger
    Response: "The fact that there are well documented and general agreement that there have been previous warmings... make CO2 as the root cause of global warming even less likely"

    The degree and global extent of warming is still debated for certain periods (re the Medieval Warm Period) but putting that aside, we can all agree that there have been many periods in Earth's history when the planet has experienced dramatic changes in temperature.

    Why has climate changed in the past? The primary driver of Earth's climate is and has always been changes in the planet's energy imbalance. If anything causes a change in the energy coming in or going out, that will lead to warming or cooling. This can include the sun getting hotter, more aerosols in the air reflecting incoming sunlight, more CO2 absorbing infrared radiation, etc. CO2 is not the only driver of climate - in the past, various factors have driven Earth's climate. The one constant is that an energy imbalance has driven temperature change.

    So what does past climate change tell us? It tells us that when the planet suffers an energy imbalance, global temperature changes. It doesn't mean CO2 is always the main driver of past climate change. The ice age cycles of the past million years were driven initially by orbital cycles, not CO2 (but CO2 does play a positive feedback role).

    A crucial piece of information we learn from past history is how much climate responds to an energy imbalance. How sensitive is our climate? And what we find is when our planet accumulates heat, there is a net positive feedback response from our climate which amplifies the initial warming. Past climate change reveals a key truth: our climate is sensitive. If you impose an energy imbalance on our planet, positive feedbacks will amplify the initial warming.

    What does this have to do with CO2? We know rising CO2 is causing an energy imbalance because of direct observations (satellites observing less infrared radiation escaping to space and surface measurements of more downward infrared radiation).

    So we have two pieces of information from empirical data:

    1. Direct measurements today find CO2 is imposing an energy imbalance
    2. Past climate change finds the climate is sensitive to an energy imbalance

    Our understanding of climate comes from considering the full body of evidence. You need to consider past climate change in the context of the current energy imbalance imposed by CO2.
  8. Roger, you should add this to your blog because it speaks to the weight of your opinion on this subject: Some scientific conclusions or theories have been so thoroughly examined and tested, and supported by so many independent observations and results, that their likelihood of subsequently being found to be wrong is vanishingly small. Such conclusions and theories are then regarded as settled facts. This is the case for the conclusions that the Earth system is warming and that much of this warming is very likely due to human activities. That's from the National Academy of Sciences. You can find the press release for this just-released report as well as links to the report itself here. What is this "National Academy of Sciences"? You can learn about it here. It's sort of like the UK's Royal Society but with the brand of USA on it. The basic point is, anthropogenic warming is considered to be fact, uncontroversially so in terms of scientific understanding. If you dig into the science you'll find past changes of climate playing the role of evidence in support of this fact.
  9. Doug, Have done, However I expect you to use your brain to discuss my point. I dont give two hoots what the NAS says, unless they can show me how the "Anthropogenic CO2 causes Global Warming" hypothesis is proven. Now that would be not unreasonable to expect from a bunch of scientists right? And it might be news to you but "anthropogenic warming" is not considered to be fact, even in IPCC reports and there is an increasing body of opinion that support what I am questioning. But most importantly, lets not forget this conversation is about whether this blog addresses the question "What does past climate change tell us about global warming?" and I am maintaining that it skirts around the real issue which is what I am raising here. Cheers Roger
  10. Roger, what's to discuss? The National Academy of Sciences says anthropogenic warming is a fact, you say it's not and you're quite unprepared to accept otherwise. I'm a bystander to your argument with the NAS but I have to say, I attach more weight to their conclusion and not yours. Are you surprised, that I'd have to give more credit to the NAS and their conclusion based on a veritable mountain of evidence, as opposed to your personal opinion supported by a Youtube video? What an extraordinary conversation. I've participated in many such yet they still leave my head spinning. Either one must leave the merry-go-round filled with folks who show every sign of technical psychosis or one must jump on and join the endless revolution of repetitions.
  11. Roger - you cannot prove things in science; leave that to mathematics. What you can do is show that observations match the predictions of a theory. For a theory to be replaced, then you did to show either that it makes predictions that are not substantiated by observation within limitations of error, or, better, an alternative theory that explains the observation better. So far, there is a no competitor to the current theory of climate. You asked for empirical evidence,we showed it to you. You assert "he fact that there are well documented and general agreement that there have been previous warmings, such as the Holocene Maximum, the Minoan Warming, the Roman warming and the Medieval Warm Period, which are recorded in history as well as scientific proxies and the like, make CO2 as the root cause of global warming even less likely." This is not true. You plug the known forcings into exactly the same theory of climate and you get the observed warmings within the error for estimating both climate and forcings. Are you aware of the Mann 2009 paper on MCA by the way? You statements on MWP make me suspect otherwise. What we can also observe is that the forcings operating in these past periods are not operating today or even in reverse (eg Milankhovich). Now it is possible that there is some undiscovered energy transfer going on that has somehow eluded us - but that is not the way to bet in a very high stakes game. The empirical observations give us confidence that there is a GHG forcing of the right magnitude to induce current warming. Furthermore, the observations of the upper stratosphere cooling are very hard to reconcile with any other forcing.
  12. scaddenp, I am awaiting some answer from the owner of this blog, However I will comment on "You plug the known forcings into exactly the same theory of climate and you get the observed warmings within the error for estimating both climate and forcings" Are you telling me you can do this for previous warm periods (when there was no anthropogenic CO2) as well and get an intelligible result? Did you watch the video and do some thinking then? Cheers Roger
    Response: Sorry, what am I responding to? I must've missed a direct question somewhere but perhaps if you just email me a direct question, I can respond to you directly.
  13. "Are you telling me you can do this for previous warm periods (when there was no anthropogenic CO2) as well and get an intelligible result?" Yes. See the paleoclimate chapter 6, IPCC WG1 for graphs and references to papers that do this. Not one effort but many. As stated earlier, our theory of climate involves solar, aerosol, and albedo as well as GHG. Did you not look at the Benestad & Schmidt paper I referenced above? As for video - what the? This problem is the everyday reality for every scientist - that the value of peer review and why you want the person most likely to be upset by your findings to review them. We certainly see alternative hypotheses published - they just dont stand up to scrutiny.
  14. Response, Yes expecting a reply to Comment 82. Rather do it on this forum if thats OK Cheers Roger
  15. Roger, off-topic but I've visited your archive of failed conversations and find it quite interesting. You refer to it as "My Other Blog where I record conversations that Global Warming Protagonists put in the "too hard basket", an ironically accurate description from my perspective. It is indeed too hard, impossible really to have a productive conversation when one's conversational partner refuses to address evidence that is accepted by what is arguably one of the premier scientific bodies as uncontroversial. You say of the NAS report I mention earlier "...I expect you to use your brain to discuss my point. I dont give two hoots what the NAS says, unless they can show me how the "Anthropogenic CO2 causes Global Warming" hypothesis is proven. Now that would be not unreasonable to expect from a bunch of scientists right? I'd suggest that as you are the person making an assertion that flies in the face of facts, the onus is on you to provide a detailed rebuttal to the NAS report. You should do so in a way leading a reasonable person to conclude that "a bunch of scientists" practicing in domains directly related to climate science as opposed to economics are lacking in the insight necessary to conclude as they do that "Some scientific conclusions or theories have been so thoroughly examined and tested, and supported by so many independent observations and results, that their likelihood of subsequently being found to be wrong is vanishingly small. Such conclusions and theories are then regarded as settled facts. This is the case for the conclusions that the Earth system is warming and that much of this warming is very likely due to human activities." Failing that, I'd say you've invited yourself into another conversation that is "too hard", too hard for you. But perhaps raw pugilism without hope of victory is your main objective. I can't say.
  16. Roger > "Are you telling me you can do this for previous warm periods (when there was no anthropogenic CO2) as well and get an intelligible result?" Yes! You seem to be under the misconception that current theories of climate include only CO2 and nothing else. This is not the case. As scaddenp pointed out, current theories of climate take into account all known forcings, not just GHG's. As for how we can have warming in the past when CO2 is low, and warming now that can be attributed to CO2, imagine a room with two heaters: Let's call them heater 1 and heater 2 (since I'm not very creative). Now let's say I told you that if I turn up heater 2 without changing heater 1, the temperature in the room will increase. Hopefully it is pretty self-evident that this is true. What you are arguing is that the room was warmer in the past, and heater 2 was set low, therefore heater 2 could not possibly have a warming affect on the room. I hope you can see the mistake in that line of thought. Clearly, it is possible that heater 1 was set high at a time when heater 2 was stable, thus leading to warmer temperatures in the past. This does not preclude the fact that heater 2 can have a warming effect right now. In this analogy, think of heater 2 as greenhouse gasses and heater 1 as solar irradiance (or any other non-GHG forcing). When the earth was warmer in the past while CO2 was low, other forcings were responsible for the warming (such as the earth being generally closer to the sun due to cyclical changes in our orbit). Scientists know this because they can reconstruct the historical levels of forcings and global temperatures, and analyse the relationships between the two. What they conclude is that man-made CO2 was the primary driver of warming in the past 30 years. This is reason why past climate change acts as evidence for AGW, which is the point of this post. One final note: dozens of climate models have been developed that can accurately recreate both past and present temperature trends. Out of all these, none have been able to recreate real world temperature trends without confirming that CO2 was the primary driver of warming in the past 30 years. Is this all just a coincidence?
  17. Support, Thanks for your answer. My response is rather lengthy so I have posted it at You are welcome to comment there further, as is anyone provided they can keep to the point and avoid ad hominem remarks etc. Cheers Roger
  18. Roger, I am somewhat disappointed by your post on your blog. I think it would be have better to continue the discussion here, clearing up misconceptions one at a time rather than posting a public essay with a number of incorrect assertions. Lets see if I tackle the main points. "it is difficult to understand why we did not experience excessive heat (such as enough to make the world uninhabitable) during say the Holocene Maximum where the climate was significantly warmer than today.". Well watch for new papers on this, but Holecene maximium was a/ similar to today and b/ at time when most of humanity was hunter-gatherers. The worry about AGW is mostly about RATE of change and also that the last time we had atmospheric Co2 at 450ppm was in the Pliocene when humanity didnt exist let alone have developed sophisticated civilizations based on settled agriculture. The question indeed is "is it the driver of current warming?". I dont think you have understood the intent nor the conclusions of Harries, Griggs, Philipona, etc. Firstly, lets deal with water vapor. Clouds<> water vapour. They occur when vapour condenses. The do however complicate the measurement that these papers are trying to make. The reason for lack interest is the water vapour that it is a function of temperature. It is always a feedback not a forcing. It doesnt matter what the forcing is, GHG, solar, aerosols - if the temperature changes then so does water vapour. see water vapour is the most powerful greenhouse gas for more detail. Since we are interested in the FORCING not the feedback, water is deliberately filtered out. Now here is the condensed basis of the those papers: Hypothesis - the forcing is GHG. Prediction: if the GHG is the forcing, then we can (for a cloudless sky anyway), predict the spectrum of detected radiation, filtered for water. (incoming for Philipona, Evans, Weng; outgoing for Harries, Grigg, Chen). This the "modelled result" in the papers, but please note this "model" is the GHG equations from fundimental physics, not the output of a GCM. Next you measure the actual radiation, filter for water vapour and compare results. Observation confirms prediction - there isnt a placebo effect, statistical uncertainty, and skeptics can examine the data themselves at leisure, no need for double-blind. The results can also determine how much energy is from the increased GHG - roughly 4x the radiation difference from solar minimum to solar maximum. The paper is written for scientists in the field. They dont need to discount the sun because the sun does not emit radiation in this part of the spectrum. (see for example of The sun and Max Planck agree. For more on why its not the sun see, Its the sun. Especially, explain upper stratospheric cooling - increased CO2 is the only theory going so far that can explain this. And by the way, we have no way of measuring what the outgoing radiation was in holocene. Despite being told explicitly earlier in the thread about accounting for past climate change, you state "There is no attempt in your analysis to identify and then rule out the reasons why the earth has warmed in previous epochs. (I agree that it would be a very tough project)". This is patently false. Why do you continue to assert this? You also assert without proof: " Neither have you have not taken into account, so far as I can see, of the negative logarithmic relationship that CO2 has with its greenhouse properties," Where on earth did you get this fanciful idea? Or perhaps it is better to ask why do you believe this? The mathematics used in the code is published and the GCM code is online. Given other comments on your site, I suspect you knowledge of climate "science" comes mostly from sites like WWUT and Climate audit, rather than from climate scientists (especially Instead of making assertions about what science does or does not say, how about actaully reading it IPCC WG1 ? Then we all start on the same page and have a sensible discussion but please respond in the appropriate sections of this blog.
  19. scaddenp, Thanks for your comment. First of all I make no apologies for the length of my reply as it is in response to the answer I received from the owner of this blog for comment #82. I understand the intentions and content of the papers and abstracts I carefully read, thanks for your concern. It appears however that you do not or refuse to understand the relevant points, I suggest you read again and give it some deep thought. The fact you refer me to any IPCC publication where the AGW hypothesis (Anthropogenic CO2 causes Global Warming) is assumed to be valid, and every thing is based on it, shows me that you have not yet understood what my assertions are about, let alone appreciated the difficulty in arriving at a sufficient standard of proof that will justify the sacrifices expected of us. Some comment though: I'm surprised you haven't heard of the negative logrithmic properties of CO2 and it's greenhouse properties. Try googling the subject. Its even described in that "epitome of authority" Wikipedia " "it is difficult to understand why we did not experience excessive heat (such as enough to make the world uninhabitable) during say the Holocene Maximum where the climate was significantly warmer than today.". " This is in response to the feed back theory mentioned in the above answer. "And by the way, we have no way of measuring what the outgoing radiation was in holocene." Correct and this is a problem when trying to prove the AGW hypothesis. You are welcome to continue this discussion on my site where there is no chance of having reasonable comments spammed. However comments containing Ad Hominem comments and the like. will not be published. Cheers Roger
  20. Roger -you persist with this idea that science "assumes AGW". Either you havent read IPCC WG1 or you didnt understand it. WG2 and WG3 DO assume AGW because they ask the questions about what will happen. I state again - here is how the process you work. You say IF, IF, the hypothesis is true, then what would I expect to observe. If you the observation match prediction, that is support (but not proof) of the theory. ALL SCIENCE IS DONE THIS WAY. This is not somehow "assuming AGW is true". I dont see how anyone could read IPCC WG1 and come away with idea. Roger, read more carefully what I have written. I and the whole of science is well aware of logrithmic relationship. What I am asking is WHY you believe that the science doesnt take it into account. It does - demonstrably - but somehow you believe it doesnt? AGW support is mostly based in physics not paleoclimate. Paleoclimate is an area dogged with uncertainties so its happy hunting ground for deniers. Since you started this discussion on this blog, it would be imappropriate to move it yours. I will not respond there.However, if you prefer to correspond on this by email, feel free.
  21. Roger, With all due respect, you demonstrate some profound misunderstandings about the nature of climate science, the IPCC report, and the scientific method in general. It is ill advised to be commenting on the nature of something you clearly haven't read or understood. If you want to argue in good faith, I strongly suggest you spend some time learning what climate scientists actually have to say rather than relying on the strawman depicted by climate denial blogs. A good source would be the IPCC WG1 as linked above, or one of it's summary reports. Another interesting read is the epa response to comments on their findings on greenhouse gasses. This site's own list of skeptic arguments is also a great overview of common skeptic points. The Discovery of Global Warming is great for getting some perspective on the history of climate science, and understanding that AGW did not leap spontaneously from the minds of scientists and some in the blog-o-sphere would have you think. Finally you can find a host of great links here. In any case, if you have any specific questions or points, please place them in the appropriate post, as this post is focused on the significance of past climate change specifically and this discussion has veered off-topic.
  22. Scaddenp Thanks for your comments, I have copied them to my page at where I will comment on your answers for the benefit of my readers. I would remind you though that I have made no assertions of any sort in any part of this discussion, I have only asked for reasonable proof of the "anthropogenic CO2 causes global warming" hypothesis and explained why I believe a good standard proof is required. I reiterate that no such proof appears in any IPCC publications. Measurements of global warming of any sort do not constitute proof because we are looking for the cause of the warming. You are too proud to watch the video I suggested and your insistance that the proof is found in IPCC publications shows you don't actually understand my question. PS. Check out this report from the University of Pennsylvania. It appears their conclusions are similar to mine except they have taken a different route. I hope I will get a proper answer from the owner of this blog. Cheers Roger
  23. Roger, As has already been explained, there is no such thing as proof in science. There is only evidence in support of or in contradiction to theories. Your request therefore is invalid and meaningless. If you have any issues with specific lines of evidence, please post them in the appropriate thread.
  24. RE#97 Rogerthesurf That PDF is 82 pages of non-peer reviewed work. It comes from a non-scientist (legal professor) at the University and is uploaded freely to the SSRN (Social Science Research Network). The author does not appear to understand very much about climate science. It reads more like an essay than of anything with any scientific rigor and I don't think it adds any value to the discussion. I for one would not spend my time reading it unless it has passed a peer review.
  25. "I reiterate that no such proof appears in any IPCC publications." This is dealt with exhaustively in chapter 9 of WG1. What you are looking for is called "attribution". Read the chapter then take up the argument piece at a time. (in the appropriate thread - this is about past climate change). See also an excellent article at On Attribution. "You are too proud to watch the video I suggested". I watched - more case of teach your grandmother to suck eggs. I frankly resent the implication that this contains lessons that scientists didnt know. "you don't actually understand my question." Of this I agree. In part because it keeps changing. You asked for empirical evidence but it seems there is trouble understanding why this is empirical evidence. Trouble understanding the nature of scientific proof, trouble understanding past climate change. We are trying to help. The reason climate science has confidence that anthropogenic gases is causing change is based on multiple supporting lines of evidence. See ch 9. Look, consider instead an alternative hypothesis. eg. the sun causes most of the warming. Run the model and make some predictions. These would include: There should be more energy from sun reaching TOA. Tropics (closer to sun) should be hotter Warming should be more pronounced in daytime rather than night. Stratospheric should be warming etc. Check this against reality - whoops. Next hypothesis. See how it works? Increasing GHGs is the one that matches our reality. As to your link. How about some skepticism of this to match that of your skepticism of scientists? As far as I can see, its motley collection of long-debunked denialist talking points without a look at the real evidence at all.

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