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What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Climate reacts to whatever forces it to change at the time; humans are now the dominant forcing.

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)

A common skeptic argument is that climate has changed naturally in the past, long before SUVs and coal-fired power plants, and this somehow tells us that humans can't be the main cause of the current global warming. Peer-reviewed research and simple logic show this is not the case.

It's important to know there are a number of different forces acting on the Earth’s climate. When the sun gets brighter, the planet receives more energy and warms. When volcanoes erupt, they emit particles into the atmosphere which reflect sunlight, and the planet cools. When there are more greenhouse gases in the atmosphere, the planet warms. It's worth remembering that without some greenhouse gas  the Earth would be a ball of ice.

These forces are called "forcings" because they force changes in the global average temperature.

Looking at the past gives us insight into how our climate responds to such forcings. Using ice cores, for instance, we can work out past temperature changes, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere. Looking at many different periods and timescales including many thousands of years ago we've learned that when the Earth gains heat, glaciers and sea ice melt resulting in a positive feedbacks that amplify the warming. There are other positive feedbacks as well and this is why the planet has experienced such dramatic changes in temperature in the past.

In summary the past reveals our climate is sensitive to small changes in heat. 

What does that mean for today? Over the past 150 years greenhouse gas levels have increased 40 percent mainly from burning of fossil fuels. This additional "forcing" is warming the planet more than it has in thousands of years. From Earth's history, we know that positive feedbacks will amplify this additional warming.

The Earth's climate has changed in the past and ice cores and other measures tell us why. Based on this knowledge, and other types of evidence we know the human emissions of greenhouse gases are warming the climate.

The 'climate changed naturally in the past' argument is a logical fallacy known as non sequitur, in which the conclusion doesn't follow from the arguments.  It's equivalent to seeing a dead body with a knife sticking out the back, then arguing the death must be natural because people died naturally in the past.  It fails to even consider the available evidence.

Last updated on 4 February 2014 by dana1981. View Archives

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Comments 51 to 100 out of 328:

  1. #106: Crustal heat contributes relatively negligible amounts to the system. Certainly not enough to significantly influence ocean currents. In today's Icehouse climate they are primarily driven by Thermohaline circulation, which in itself is driven by the creation of cold saline waters in polar regions.

    I have never heard of any correlation between ENSO and tectonic factors. I'd like to see the data for that. Plus, tectonics doesn't fluctuate on ENSO time scales, nowhere near.

    I don't even know where to start on the last paragraph - not even wrong comes to mind.
  2. Gincko

    There is a weak statistical relationship between volcanic activities and ENSO with an enhanced probability of El Nino-like conditions in the winter following a volcanic eruption. Contemporary interest in this idea comes from a study published in Nature a few years back [*]. More recent research [**,***] supports a weak correlation and indicates that it is only the most vigorous volcanic eruptions that result in ejection of volcanic aerosols into the stratosphere that produce significant effects on ocean circulation.

    Of course this effect has nothing whatsoever to do with the heat from the volcanoes per se! That is just silly. As you say, the geothermal flux is simply too weak, although I believe there is some evidence that undersea crustal heat flow can influence ocean mixing and thus help to draw warmth down to the deeper oceans in a warming world (???). Obviously anyone asserting a contribution of geothermal heating to global warming should provide evidence not that this very weak geothermal flux exists, but that this has increased in line with periods of known global warming (like now!). The advocates of that notion seem reluctant to come up with any such evidence….

    The weak relationship between strong volcanic eruptions and ENSO is due to the aerosolic load and its effects on radiative solar forcing.. I have to say I haven’t read the papers in detail, so the exact mechanism isn’t clear to me. If I have time I’ll have a more detailed look…

    [*]J. B. Adams et al (2003) Proxy evidence for an El Niño-like response to volcanic forcing. Nature 426, 274-278

    abstract: Past studies have suggested a statistical connection between explosive volcanic eruptions and subsequent El Niño climate events1, 2. This connection, however, has remained controversial3, 4, 5. Here we present support for a response of the El Niño/Southern Oscillation (ENSO) phenomenon6, 7 to forcing from explosive volcanism by using two different palaeoclimate reconstructions of El Niño activity8, 9 and two independent, proxy-based chronologies of explosive volcanic activity5 from ad 1649 to the present. We demonstrate a significant, multi-year, El Niño-like response to explosive tropical volcanic forcing over the past several centuries. The results imply roughly a doubling of the probability of an El Niño event occurring in the winter following a volcanic eruption. Our empirical findings shed light on how the tropical Pacific ocean–atmosphere system may respond to exogenous (both natural and anthropogenic) radiative forcing.

    [**] Emile-Geay J et al. (2008) Volcanoes and ENSO over the past millennium. J. Climate 21, 3134-3148.

    abstract: The controversial claim that El Nino events might be partially caused by radiative forcing due to volcanic aerosols is reassessed. Building on the work of Mann et al., estimates of volcanic forcing over the past millennium and a climate model of intermediate complexity are used to draw a diagram of El Nino likelihood as a function of the intensity of volcanic forcing. It is shown that in the context of this model, only eruptions larger than that of Mt. Pinatubo ( 1991, peak dimming of about 3.7Wm(-2)) can shift the likelihood and amplitude of an El Nino event above the level of the model's internal variability. Explosive volcanism cannot be said to trigger El Nino events per se, but it is found to raise their likelihood by 50% on average, also favoring higher amplitudes. This reconciles, on one hand, the demonstration by Adams et al. of a statistical relationship between explosive volcanism and El Nino and, on the other hand, the ability to predict El Ni no events of the last 148 yr without knowledge of volcanic forcing.
    The authors then focus on the strongest eruption of the millennium (A. D. 1258), and show that it is likely to have favored the occurrence of a moderate-to-strong El Nino event in the midst of prevailing La Nino-like conditions induced by increased solar activity during the well-documented Medieval Climate Anomaly. Compiling paleoclimate data from a wide array of sources, a number of important hydroclimatic consequences for neighboring areas is documented. The authors propose, in particular, that the event briefly interrupted a solar-induced megadrought in the southwestern United States. Most of the time, however, volcanic eruptions are found to be too small to significantly affect ENSO statistics.

    [***]Christiansen B (2008) Volcanic eruptions, large-scale modes in the Northern Hemisphere, and the El Nino-southern oscillation. J. Climate 21, 910-922 .

    abstract: The author analyzes the impact of 13 major stratospheric aerosol producing volcanic eruptions since 1870 on the large-scale variability modes of sea level pressure in the Northern Hemisphere winter. The paper focuses on the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) to address the question about the physical nature of these modes. The hypothesis that the phase of the El Nino-Southern Oscillation (ENSO) may control the geographical extent of the dominant mode in the Northern Hemisphere is also investigated, as well as the related possibility that the impact of the eruptions may be different according to the phase of ENSO.
    The author finds that both the AO and the NAO are excited in the first winter after the eruptions with statistical significance at the 95% level. Both the signal and the significance are larger for the NAO than for the AO. The excitation of the AO and the NAO is connected with the excitation of a secondary mode, which resembles an augmented Pacific-North American pattern. This mode has opposite polarity in the Atlantic and the Pacific and interferes negatively with the AO in the Pacific and positively in the Atlantic in the first winter after the eruptions, giving the superposition a strong NAO resemblance.

    Some evidence is found that the correlations between the Atlantic and the Pacific are stronger in the negative ENSO phase than in the positive phase, although this difference is not statistically significant when all data since 1870 are considered. The author does not find any evidence that the impact of the volcanic eruptions is more hemispheric in the negative than in the positive ENSO phase.
  3. Thanks for your response, Chris

    I don't have an issue with significant changes in volcanic activity influencing climate - the correlation is quite obvious. However, Quietman's #106 post (para. 3) seemed to imply that it is the heat released into water that substantially drives climate by altering ocean currents.

    There's a difference between the influence on climate that subaerial volcanic gas emissions can have (effectively altering the total amount of solar energy in the system), and that of heat out of the earth's interior. The references you cite only focus on the former, but Quietman is mainly arguing direct and indirect influences from the latter.

    I've never seen any data on the effect of ocean basin heat on the global ocean current conveyor belt. It is generally accepted that this is mostly driven by Thermohaline circulation in our Icehouse climate (dominated by the polar ice caps), which probably overwhelms most other influences on larger scales. Surface current changes (which can influence upwelling) can be caused by changes in atmospheric circulation, but again, this is not influenced by heat released from the earth.

    It's interesting to note that during a Greenhouse climate (e.g. Cretaceous) the global circulation tends to be driven by Halothermal circulation (dominated by evaporation at the equator), which is much weaker and can easily lead to stagnant oceans.
  4. ginckgo
    Sorry, that was posted for Patrick who was up to speed on vulcanism. The Volcanos thread has the argument presented with links to recent articles explaining the background. I am missing one reference about ENSO and I can't find it again to post a link. When I do it will also be posted in the Volcano thread. John wants us to keep the subject relevance when we can. From your statement I think you have some reading to catch up on. :)
  5. ps
    Volcanos actually causing ENSO is far fetched and yes a bit silly. It's what happens on the ocean floor near the subduction zone where the driver for ENSO resides.
  6. Chris
    Your examples are results of modern education just like these:
    "This finding has opened new doors in dinosaur research on this part of the continent: "It established that dinosaurs were nesting at this high latitude," said Miyashita. "
    Science Daily or Live Science
    "Some dinosaurs (warm-blooded, perhaps) were surprisingly good at withstanding near-freezing temperatures, they say. Witness the team's latest find, a diverse stash of dinosaur fossils laid down just a few million years before the big impact, along what's now the Kakanaut River of northeastern Russia. Even accounting for continental drift, the dinos lived at more than 70 degrees of latitude north, well above the Arctic Circle. "

    There is no excuse for this poor education. This started in the late 1960s with the long hairs and just went downwards since then.
  7. Here is something that you should know already:
    The Paleogene Period of the Cenozoic Era: 65.5 to 23.0 million years ago
    The Paleocene (“ancient recent life”) epoch marks the beginning of the Paleogene Period and the Cenozoic era. The sea-level fell to expose dry land in much of inland North America, Africa, and Australia. South America however was cut adrift with its own unique evolving “ark” of birds, mammals, and reptiles.
    The Paleocene Epoch of the Paleogene Period: 65.5 to 55.8 million years ago
    The rifting of the North Atlantic cut off North America from Europe, and South America lost links with Antarctica. India and Scotland were home to mountain-building episodes. The sea-level rose and seas invaded much of Africa, Australia, and Siberia.
    Climates were generally warm or mild worldwide. Tropical palms flourished as far north as the London Basin. The unusual mixture of tropical and subtropical elements in the northern latitudes in the Eocene suggests that the mean annual temperature of these regions was not as high as in the present tropics, but that the flora was maintained by a greater rainfall than occurs in these northern latitudes today, with no pronounced seasonality in its distribution, and by the absence of winter frost.
    The Eocene Epoch of the Paleogene Period: 38-54 million years ago
    There was an increase in volcanic activity, and plate tectonic movement, as India collided with Asia. The last remnant of the supercontinent of Gondwanaland broke up as Australia and South America both separated from Antarctica
    The Oligocene also marked the start of a generalized cooling, with glaciers forming in Antarctica for the first time during the Cenozoic. The increase in ice sheets led to a fall in sea level. The tropics diminished, giving way to cooler woodlands and grasslands. Although there was a slight warming period in the late Oligocene, the overall cooling trend was to continue, culminating in the Ice Ages of the Pleistocene.
    The Oligocene Epoch of the Paleogene Period: 33.9 to 23.0 million years ago
    Source: Palæos
  8. Burning books, and scientific publications, is necessarily banned due to the carbon emissions this would engender. We are therefore left with Dr. Michael Mann and his statistics to erase the following. And soon!

    We live today in the Holocene Epoch, or the last 11,500 years since we melted out way out of the Wisconsin ice age. Just like we melted our way out of the previous 7 ice ages dating back to the Mid Pleistocene Transition (where we went from the 100,000 year ice age/interglacial cycle [which matches the eccentricity cycle in our orbit] to the 41,000 year cycle [which matches the obliquity cycle in our orbit]). At 11,500 years old, this places the Holocene at precisely one half of a precessional cycle (23k years). All 6 interglacials dating back to the MPT have lasted roughly one half of a precessional cycles). This is also the interglacial in which all of human civilization has occurred, only cave paintings being found in the "written" record prior to 10k years ago.

    At the Holocene Climate Optimum, between 7000 and 6000 years ago, sea levels were a mere 6 meters higher than today. This was the time period when the Egyptian civilization erupted onto the scene.

    According to the National Research Council (NRC, 2002), half of the melting which brought us out of the Wisconsin ice age occurred in less than a decade. Sea level swings between the post MPT ice ages and interglacials result in typical sea level changes of only 400 feet.

    The previous interglacial, the Eemian or penultimate, also known for the first occurrence of fossils of the species Homo sapiens, ran for about 10,000-10,800 years, or almost half of a precessional cycle. It ended with a LEAP (Late Eemian Arid Pulse). Stable platform sites record at least 3 sea level highstands within the Eemian that were higher than present-day sea level. About 20 meters (~65 feet) is known from the Grand Caymans, 52 meters (~170 feet) is reported from a site in Siberia. Sea levels can and do occur at different relative elevations in different parts of the world at the same time.

    The Eemian ended in a series of pulses, the LEAP being one of them. It lasted 468 years, with dust storms, aridity, bushfires and a decline of thermophilous trees with the onset of glaciation. The LEAP occurred at a 65o north insolation of 416Wm-2, close to the 2005 value of 428 Wm-2, which may be relevant in terms of understanding present climate variability. The onset of the Leap occurred in less than two decades. It ended roughly 117-118k years ago with the Last Glacial Inception (LGI), the beginning of the Wisconsin ice age (NA nomenclature).

    During the Wisconsin, 24 Dansgaard-Oeshger events lie well recorded in the Greenland ice cores. These run from 1,000 to 4,000 years long, averaging 1,500 years. They have the same sawtooth shape as the major transitions characterized by on average 8C-10C warmings that occur from years to just a few decades (outliers ranging to 16C), floowed by a very rocky gradual descent to ice age conditions. All distinct pulses that are gradually being verified by sediment cores from ocean deep drilling projects. Evidence for D-O events extends in the sedimentary record as far back as 680 million years. Something, we do not well understand, causes these events.

    We are left to ponder what anthropogenic effects will, or are, to be overlain on this tapestry. The verdict cannot be said yet given such a AGW signal to the noise of natural, frequent, abrupt and seemingly reliable climate change. But it cannot be discounted quite that easily. Read, and save (in my case), thousands of treatments of this subject from literally all fields of paleoclimatology and what we seem to know for sure is that the shift between the two natural states of climate (cold and warm) seem to be responses far out of proportion to whatever forcing seems the most probable. Meaning that doubling CO2 from less than one tenth of a percent to still less than one-tenth of a percent in s few hundred years could very well release some sort of instability, given climate's real sensitivity.

    One should not discount the fact that as far as the paleoclimate record is concerned, GHGs may not have triggered these events, ice age cold or nearly instant interglacial. There is strong evidence that they may have amplified, perhaps even dramatically, whatever triggered the sudden increase in temperature.

    Some orbital models predict that of the next 4,000 years the climate will be in a state of sensitive variability, followed by 55,000 years of interglacial style 65oN insolation. No interglacial for the past 5 million years has lasted near so long. And in the past 3 million years hominid braincases went from an average of 500cc to 2,500cc, which, upon considerable research, you may prize out that frequently, researchers cite significant climate change events as a probable cause. During that 5 million years it is estimated from proxy data, that the earth was in its cold state 90% of the time.

    If, at the end of this half precessional cycle, the tendency may be towards resumption of our cold state, then GHGs, from paleoclimate studies anyway, may actually be needed, as it does seem that their lingering slows eventual descent into the glacial maximums. On the other hand, we know that for a given known input, climate response can be triggered rather suddenly into its other state.

    We are therefore left to ponder how best to manage. Given the disparity between 3rd world resource demand, and "American Plush", and the ever-consuming desire to achieve that lifestyle (witness the largest population group aspiring, China), we need to rethink the root of the problem. And that is growth. And not just population growth. Growth itself.

    Resources on Spaceship Earth are not unlimited. With better extraction, purification and manufacturing technologies, there is only so much naturally occurring and accessible such resources. We may have to not only retool, but our economic models of ever increasing profits may need to be modified. Especially at American Plush resource consumption, growth either entails more consumers of resources at the same rate, or ever greater levels of resources consumption by a static population of consumers. It would be sensible to conclude that neither is really sustainable in the long term.

    We must therefore work out what is feasible related to reliable, abrupt and seemingly unavoidable natural climate change, which we can reasonably guess to occur, while also paying attention to the fact of outsized forcings from what could be several sources, including GHGs.

    Pondering this, we must eventually face the connection between resources and population. In order to sustain our current level of civilization will require both resources and energy to sustain even a static population. Perhaps we should spend some time thinking about fusion. It has, afterall, powered the known universe since its beginning, and provided all 92 naturally occurring elements. It has the potential to provide some of the answer.

    Meanwhile, enjoy the interglacial!
  9. Everyone is talking about GGs and other "causes" of GW. I am a service tech for an electrical company and have learned that you can either fix the problem, or fix the symptoms. From what I have read, there is evidence that GG's are indeed caused by GW, which would make them a symptom, much like a fever to a viral infection. Has any research been done to determine what caused the sudden and dramatic reversals in temperatures in the past? If so, where are we in relation to the trigger(s) today? Are we doing any good what so ever by treating the symptoms, or are we actually doing harm?
    Response: CO2 is both the symptom and the cause. We are emitting CO2 into the atmosphere, which warms the temperature, which causes the warming ocean to outgas more CO2. This is the feedback loop which caused the dramatic warmings in the past that took the planet out of the ice ages into interglacial periods. Eg - warming in the Southern Ocean (due to changes in the Earth's orbit) led to outgassing of CO2 which amplified the warming and spread it through the rest of the planet as the CO2 mixed through the atmosphere. Your question is addressed in detail at the CO2 lags temperature page.
  10. sentient

    Well said and something to ponder. The more important most ignored point is where the source of CO2 and why is it called a feedback. It's life itself IMO.

    In the age chest phase of an ice age things die, not an extinction event or might but volume of life takes a nose drive. We see in H4 the extant human species nearly goes extinct. We were able to recover, neandertal did not.

    Not so much as cold as it is food. The climate decreases the available sources including food. Plants that do not die are just surviving, not producing O2 much but still produce CO2 in the process of just existing. This means no new growth to replace what dies. What not deads goes dormant. Bottom line, no food. No food, life forms not capable of going dormant dies. Populations at the top of the food chain decreases.

    Bottom line, no production of CO2.

    When it warms up, plants no longer dormant, produces new growth, and food at the bottom step of the food chain. This follows by fauna and repopulates the earth and we seen the growing of all the GHGs acting as as feedback and helps it to defrost.

    No rocket science, just common sense.
  11. "When it comes to climate, the early Paleogene period (~65-34 mya), at the start of the Cenozoic Era, had one of the most Eden like climates of the Phanerozoic. As the Cenozoic progressed a cooling trend set in leading up to the formation of permanent ice caps and the Pleistocene Ice Age we are still experiencing. But before the world started to ice up our planet underwent one of the most dramatic bouts of global warming known to science—the Paleocene Eocene Thermal Maximum or PETM. Recently, global warming activists have tried to liken human CO2 emissions to the cause of the PETM, 55 million years ago. Is it true, that our actions may trigger a sudden sharp rise in global temperature?

    The mid-Cretaceous (~125-85 million years ago) and the early Paleogene are among the best known ancient “greenhouse” climate intervals—times when Earth's average temperature was significantly higher than they are today. During the Cenozoic (the last 65 million years) the global climate has cooled substantially, up to a main cooling step at the Eocene-Oligocene transition (~34 mya), which included the development of the first glaciation at a continental scale in Antarctica. Another main cooling step occurred in middle Miocene (14 mya) and was a significant step in the development of the Antarctic continental glaciation."
    FROM: Could Human CO2 Emissions Cause Another PETM?
    Read the rest, It's an interesting view.
  12. Thanks QM; an interesting article. I shall have to go and revisit clathrate physical/chemical properties. From what I recall, they only form under extreme pressure/low temperature conditions ( which is why they are mostly found in very deep water).
  13. Global Warming: Scientists' Best Predictions May Be Wrong
    ScienceDaily (July 15, 2009)

    No one knows exactly how much Earth's climate will warm due to carbon emissions, but a new study suggests scientists' best predictions about global warming might be incorrect. ...

    The study, which appears in Nature Geoscience, found that climate models explain only about half of the heating that occurred during a well-documented period of rapid global warming in Earth's ancient past. The study, which was published online July 13, contains an analysis of published records from a period of rapid climatic warming about 55 million years ago known as the Palaeocene-Eocene thermal maximum, or PETM.

    "In a nutshell, theoretical models cannot explain what we observe in the geological record," said oceanographer Gerald Dickens, a co-author of the study and professor of Earth science at Rice University. "There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models."
    Read the rest, Interesting.
  14. I'm curious. Do we know what caused the reversal in past warm periods in the Earth's history? What made it get cool again? Clearly, despite CO2 having a positive feedback loop, we didn't get runaway warming. We're not living on Venus.

    Even if we're headed for higher temps, rising sea levels, drought, mass extinctions, catastrophic loss of human life, etc. At some point won't it top out an head back to another ice age?

    What's prevented a runaway greenhouse effect in the past?
  15. Right; there are positive feedbacks, but they are not boundless. Water vapour can only be added into the atmosphere up to saturation point, counterbalanced by a tendency to rain more the more there is. Greenhouse gasses trapped under permafrost, ice, in the ocean and wherever else can only be released once, and there's only so much ice to melt to diminish Earth's reflectivity. One of the things that can counteract an excess of CO2 is excess growth/adaption of plants, and IIRC this is what eventually causes the atmosphere to bounce back and temperatures with it.
  16. Quietman. Even if we ignore the impact of past climate change on animals, look what slower-less extreme-warming events had on human civilizations. Two come quickly to mind-the Anasazi & The Khmer Empire both died out because they failed to adapt to a relatively small warming of the planet during the Medieval Warm Period.
    Another thing-the feedbacks may not be boundless, but evidence of past climate suggests the situation could get very bad if we let it. Throughout much of the pre-Quaternary period, the planet was a good 4-8 degrees warmer than what it was at any point in the Quaternary period. Is it mere coincidence that this higher temperature was at a time when CO2 levels were 10 times higher than today? I seriously doubt it.
  17. As a total layman I can follow the arguments in my simple way to the point where I see that GHGs amplify warming and cooling periods, so more co2 in the atmosphere increases amplification.

    But when I look to see what the science says about what initiated pre-industrial inter-glacial warm and cool periods i get a bit stuck in debates about solar activity, a plethora of weather oscillations between negative and positive and now feeback loops and planet earth knowing and adjusting its own temperature because it is conscious of an energy imbalance. Global warming doesn't get any easier to understand.
    Response: Hang tight, I'm at this moment working on a post on the whole ice age/interglacial mechanism, the emphasis on making it easy to understand. Hopefully online within a day or two.
  18. The initial statement says Natural climate change in the past proves that climate is sensitive to an energy imbalance. If the planet accumulates heat, global temperatures will go up." This is false: If the planet accumulates heat then it will be hotter and hence will radiate more heat out until it returns to equilibrium per the gray body Stefan- Boltzmann Law.
    The planet goes from warming in the morning to cooling in the evening as the amount of absorbed energy increases and decreases. It passes through equilibrium temperature exactly twice every day. The concept that the planet could accumulate heat and be out of equilibrium for any extended length of time is just not possible. The computer model however assume this. They are wrong.
  19. If the forcing is transient then the temperature will return to its original equilibrium, yes.

    If the forcing persists for thousands of years (like CO2 in the atmosphere) then the planet's temperature will reach a new and higher equilibrium while that forcing persists.
  20. "What does past climate change tell us about global warming?"

    In case you dont know it, your explanation uses the AGW theory to explain the question when the question is really asking for some proof of the AGW theory.


  21. Rogerthesurf, you'd do better to explain yourself. Failing that, presumably you won't care if your post is deleted?
  22. He probably just wants to "enlighten" us with a link to his own blog.

    Anyway, a large part of the discussion is about PETM and AGW (with the link to resilient earth). A lot of it sounds like, if we extrapolate our CO2 emissions it would take forever to reach PETM concentrations, and PETM wasn't even caused by CO2 alone, so PETM cannot be used as an indication for the effect of CO2, so AGW does not exist. All the individual statements above are probably correct, except the conclusion. Think about it, have we seen any projections from IPCC showing a 6 -9 C global temperature rise? No.

    Oh, BTW it can also be found on that website that models can not fully reproduce PETM even if we use the CO2 concentrations at PETM, so models are WRONG! (It is understood why, because GCMs currently use bandwidth parametrisation instead of line-by-line CO2 absorption schemes (because of limited computer power) and will thus deviate if brought very far from their original (~300 ppm) state. This probably introduces a large error when going to extremely large (2000 ppm) CO2 concentrations.

    This PETM event can (in "skeptical" reasoning) even be used to say "look, even if we get a 3 C global temperature, it is all natural! Because in the near past of the Earth's history it has been 9 C warmer, and humans were not yet around!" And, using this reasoning and the paleo record, all climate variation will always be natural...
  23. The mistake on the part of environmentalists has been to talk about "saving the planet". This leads directly to the sceptics' argument that the planet has changed in the past, and done just fine. Quite true. But we're not really interested in the planet, we're interested in our own welfare. A dramatic change in the climate would, first and foremost, affect our civilisation. Our cities, farmland and economies are far more vulnerable than the planet itself, which will no doubt continue to adapt.

    To win the global warming argument politically, we need to underline the threat to ourselves from climate change, rather than talking about ice sheets, polar bears and barrier reefs (important as those things might be).
  24. "71.Rogerthesurf at 12:52 PM on 8 April, 2010
    "What does past climate change tell us about global warming?"

    In case you dont know it, your explanation uses the AGW theory to explain the question when the question is really asking for some proof of the AGW theory.


    72.doug_bostrom at 13:53 PM on 8 April, 2010
    Rogerthesurf, you'd do better to explain yourself. Failing that, presumably you won't care if your post is deleted? "

    Sorry your reply did not show up on my "My Comments" page.

    Thank you for editing my comment (not)

    However my point is simple.

    Correct me if I am wrong, but at no point does your explanation discuss the validity of the "Anthropogenic CO2 causes Global Warming" hypothesis.

    Instead your host of explanations which are all based on the assumption that it (the above hypothesis) is fact, which actually it is not fact but as yet simply an unproven hypothesis.

    Therefore all your explanations are no better than this unproven hypothesis.

    I trust that is clear.



    I also always post my comments and replies on my other site where my readers can evaluate my questions and your answers. Check under your url and post title.
  25. Roger, I'm not spotting the tautology. Which part of the physics do you disagree with?
  26. 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)
  27. 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.


    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 :-)
  28. 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.
  29. 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.
  30. 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.
  31. 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.
  32. 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


    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.
  33. 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.
  34. 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.


  35. 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.
  36. 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.
  37. 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?


    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.
  38. "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.
  39. Response,

    Yes expecting a reply to Comment 82.

    Rather do it on this forum if thats OK


  40. 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.
  41. 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?"


    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?
  42. 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.


  43. 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.
  44. 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.


  45. 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.
  46. 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.
  47. 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.


  48. 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.
  49. 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.
  50. "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
    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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