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What does past climate change tell us about global warming?

What the science says...

Select a level... Basic Intermediate

Greenhouse gasses, principally CO2, have controlled most ancient climate changes. This time around humans are the cause, mainly by our CO2 emissions.

Climate Myth...

Climate's changed before
Climate is always changing. We have had ice ages and warmer periods when alligators were found in Spitzbergen. Ice ages have occurred in a hundred thousand year cycle for the last 700 thousand years, and there have been previous periods that appear to have been warmer than the present despite CO2 levels being lower than they are now. More recently, we have had the medieval warm period and the little ice age. (Richard Lindzen)

Greenhouse gasses – mainly CO2, but also methane – were involved in most of the climate changes in Earth’s past. When they were reduced, the global climate became colder. When they were increased, the global climate became warmer. When CO2 levels jumped rapidly, the global warming that resulted was highly disruptive and sometimes caused mass extinctions. Humans today are emitting prodigious quantities of CO2, at a rate faster than even the most destructive climate changes in earth's past.

Abrupt vs slow change.

Life flourished in the Eocene, the Cretaceous and other times of high COin the atmosphere because the greenhouse gasses were in balance with the carbon in the oceans and the weathering of rocks. Life, ocean chemistry, and atmospheric gasses had millions of years to adjust to those levels.

Lush Eocene Arctic 50 million years ago

Lush life in the Arctic during the Eocene, 50 million years ago (original art - Stephen C. Quinn, The American Museum of Natural History, N.Y.C)

But there have been several times in Earth’s past when Earth's temperature jumped abruptly, in much the same way as they are doing today. Those times were caused by large and rapid greenhouse gas emissions, just like humans are causing today.

Those abrupt global warming events were almost always highly destructive for life, causing mass extinctions such as at the end of the PermianTriassic, or even mid-Cambrian periods. The symptoms from those events (a big, rapid jump in global temperatures, rising sea levels, and ocean acidification) are all happening today with human-caused climate change.

So yes, the climate has changed before humans, and in most cases scientists know why. In all cases we see the same association between CO2 levels and global temperatures. And past examples of rapid carbon emissions (just like today) were generally highly destructive to life on Earth.

Last updated on 1 July 2014 by howardlee. View Archives

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Comments 101 to 150 out of 322:

  1. Actually Roger you could learn a lot by just shoving the lawyers' arguments through this site. How about something from a scientist that understand atmospheric physics instead?
  2. Roger,
    Ok how about this: you are correct, technically speaking, no proof of AGW exists. However, this is true for any empirical scientific knowledge, including the theory of gravity or Newton's laws. So saying that AGW is not "proven", is somewhat of a meaningless statement. Here and here are a couple links that go into more detail about what "proof" means to science. Hopefully they will clarify why your usage of the word is somewhat off target.
  3. yocta,

    Its not supposed to be a scientific paper, its looking at the arguments and evidence to see if they stack up from a legal proof point of view.

    Like any lawyer or judge, such a cross examiner does not have to understand the technical side of things, but takes an unbiased view of the evidence and what is presented.


  4. Roger, >Like any lawyer or judge, such a cross examiner ... takes an unbiased view of the evidence and what is presented.

    Cross examinations are biased by definition. They are an examination of your opponents witness, hence the "cross" part. That paper is just a summary of AGW skeptic talking points. If you are going to claim an unbiased view of the evidence, at least listen to what the other side has to say in rebuttal. In any case, science isn't determined by lawyers, it's determined by scientists publishing peer-reviewed research. Take a look around this site and the others linked for you to get a feel for what the science actually has to say.
  5. Roger, if a lawyer or judge does not understand what he's reading or hearing he can be lied to without being aware of it. Inability to discriminate truth from fiction implies that useful judgment is suspended. The conclusions of an ignorant jurist are unreliable even as they are necessarily unbiased.
  6. The legal system is not really a good model for the scientific method.

    Thus, it's perhaps not surprising that I'm very unimpressed by the link Roger provides to a document written by a law professor at the University of Pennsylvania.

    I picked one area with which I am somewhat familiar (sea level rise, discussed on pp. 65-68) and examined it. Unfortunately, it turns out to be exactly what one would expect from someone trained in the adversarial legal system rather than in the scientific method -- he is making a case rather than skeptically evaluating the evidence. (Roger, do you understand the actual meaning of the word "skepticism"?) It also seems to have been heavily influenced by a recent error-riddled paper on sea level rise by Madhav Khandekar in Energy & Environment, which might explain some of Johnston's problems.

    Bottom line, I would file Johnston's paper in the recycling bin. If there are any valid points in there, they're obscured by a lot of obvious garbage. There are much better resources out there for understanding climate change.
  7. Ned wrote :

    Thus, it's perhaps not surprising that I'm very unimpressed by the link Roger provides to a document written by a law professor at the University of Pennsylvania.

    You're not the only one.
    Not only does the author of that piece start off by thanking McKitrick, Lindzen and Pielke Jnr for their assistance, but the use of terms like "group of activist scientists" and "faith in the climate establishment" give a good flavour of the author's pre-conceived views.

    Also, the first foot-noted link goes to the American Enterprise Institute for Public Policy Research, which has an article using academic papers which have been countered (e.g. Lindzen & Choi, 2009; Mclean, de Freitas & Carter, 2009); attempts to discredit the peer-review process; accepts the views of the Wegman Report with regard to 'tribalism' in climate science, and uses examples from the leaked CRU emails.

    Only the committed so-called skeptic would advance that paper as 'evidence' for anything other than his/her personal preference.
  8. Upon further investigation, the "recycling" here is kind of fascinating. Johnston's document relies heavily on a 2007 paper by Lindzen in E&E (yes, another E&E paper ... Johnston is looking worse and worse).

    That E&E paper was recycled by Lindzen in a 2009 blog post.

    That blog post by Lindzen, in turn ... is the very same "skeptic argument" quoted by John Cook and then debunked at the top of this thread!

    In other words, we've come full circle ...
  9. It never seems to occur to the people who make the 'climate has changed before over the last 700,000 years ' argument that almost no-one was around at those times to suffer the consequences. The few that were around ( about 5 million, ten thousand years ago according to NOAA) ) could move to follow the climate that suited them anyway. Before a few 100,000 years ago Homo Sapiens didn't even exist in any case.
  10. Firstly I would like to thank you and your website for generating valuable discussion on AGW.

    Secondly, I would like to say that I don't think it is impossible for humans to change the climate, but that the change we bring about through AGW will be less significant than claimed by your article. In other words, my research has shown that our climate isn't as sensitive to CO2 as most AGW proponents claim.

    In your article, you claim that "we" can calculate that a doubling of CO2 will result in approximately 3 degrees centigrade. I hope you can enlighten me on the methodology of this calculation. The empirical evidence does not support your conclusions.

    You can take any era from history, but I will take the Jurassic and Triassic to make my point. The raw data is taken from encyclopedia Britannica 11'th edition. During the Jurassic Period CO2 concentration was 1950ppm (7 times greater than preindustrial levels of 250 ppm). You claim that for every doubling of CO2 temp increases by 3 degrees centigrade. With that logic, the Jurassic period should have been warmer by 9 degrees. It was only warmer by 3 degrees. Triassic period had CO2 concentrations of 1750ppm and was also only hotter by 3 degrees. I understand that other variables were different during that period as well. But, if you look anywhere on the geological timescale you will have a hard time proving that a doubling of CO2 directly results in a 3 degrees increase in temp.

    Thank you for the article!
    Response: Thanks for the kind comments. Climate sensitivity is essentially the change in temperature in response to a change in the planet's energy balance. So to calculate climate sensitivity, you need to work out how much global temperature has changed in the past and the changes in the planet's energy balance at the time. So if we can obtain records that give temperature (eg - from ice cores) and couple that with records that give changes in solar activity, atmospheric composition and volcanic activity, it's possible to calculate climate sensitivity empirically.

    Climate sensitivity is around 3 degrees warming for a doubling of CO2. A more technically correct definition is 3 degrees warming for a radiative forcing of 2.7 watts per square metre (which is the radiative forcing from a doubling of CO2). So if you want to look at the planet's energy imbalance over past periods, you need to include other variables which affect the planet's energy balance. Specifically, we find that as you go further in the past, the sun is less bright. So you need to consider the combined effect of a dimmer sun with higher CO2 in past periods. When we do that, we find a close correlation between the net radiative forcing and climate.
  11. Svettypoo - I'm afraid your analysis is rather simplistic, for instance you fail to account for reduced solar luminosity further back in time, and also new analysis is casting some doubt on the extremely high CO2 levels once thought to have existed.

    Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100

    Furthermore, how exactly do you think the estimates for climate sensitivity came about, if not from the study of Earth's previous climates?
  12. OK, I'll make this short and quick. CO2 levels are about 380 per million here. They are about 965,000 per million in the Venetian atmosphere. Ya think that about .04% of the same concentration is going to throw us way out of whack? The big dog, which no one wants to talk about when it comes to greenhouse gases is water vapor. It goes from about nil when we are in the depths of an Ice age to a worldwide average of 2% during recovery and the following times. THAT is our basic greenhouse gas. CO2 is a bit player. You drop CO2 levels to under 1% on Venus and that place would turn into an iceball without water vapor.

    Yes climate just keeps on changing. We are in a period where the temperature has fluctuated, sometimes rather quickly, within a 4C range over the last 10,000 years. We are near the middle of that range now.

    Sun activity is relatively high, higher than it has been for the last 2,000 years. The long range trend has been up since about 1500.

    We have seen temperatures rise about 0.5C since 1900. Yawn, I hate to say it but a rise of about 3C in about 100-200 years was seen about 8,000 years ago. That's a quick warm-up.

    BTW, it has been warmer than this about half the time since we snapped out of our last ice age. At least 4 times it was 1C warmer than now and once it was 2C warmer.

    Bottom line. Climate changes and I am not alarmed.
  13. cruzn246 wrote : "Bottom line. Climate changes and I am not alarmed.

    Bottom line is assertions and beliefs are worth nothing. If you have any linkable evidence for even half of the figures you posted concerning temperatures, please let us see them.
  14. Look up the stuff for Venus and the earth yourself. It's easy to find. I derived my temp and sun activity from easy to access sites. Here you go. The temp data was derived from ice cores. I took the temp graph and blew it up to capture the Holocene maximum and other features.

    Here is the page for the solar activities
  15. The basic stuff about changing Venus' atmosphere is just common sense stuff I derived from taking meteorology. Yes, I took a class. The 2% worldwide average is from the same place. I know in any spot on earth it ranges from near zero to 4%. I just averaged it. It could be 0.5 either way, but it would still be at least 37 times more by mass than CO2(0.04%) at lowest average values (1.5%).
  16. Well Christ man it is a continuation of a discussion. Where do I have to go to discuss electromagnetic absorption? I guess you just want to split up everything so there is no real big linking pool of info.
    Response: The big list of Arguments is the linking pool of info. There is also a "Newcomers Start Here" page linked in the left side of this page.
  17. cruzn246 wrote : "Here is the page for the solar activities"

    As well as looking at the picture, how about reading the relevant WIKIPEDIA page for context :

    The scientific consensus is that solar variations do not play a major role in determining present-day observed climate change.

    Also, the increase of temperature is a little more than you suggest :

    The updated 100-year linear trend (1906 to 2005) of 0.74°C [0.56°C to 0.92°C] is therefore larger than the corresponding trend for 1901 to 2000 given in the TAR of 0.6°C [0.4°C to 0.8°C]. The linear warming trend over the last 50 years (0.13°C [0.10°C to 0.16°C] per decade) is nearly twice that for the last 100 years. The total temperature increase from 1850–1899 to 2001–2005 is 0.76°C [0.57°C to 0.95°C].
    Summary for Policymakers

    Finally, this picture (also from WIKIPEDIA) seems to disagree with your assertion about temperatures since we "snapped out of our last ice age" :

    Holocene Temperature Variations
  18. I commented a little more than a week ago and I received some kind responses. Sorry I haven't answered yet, I've been camping in beautiful British Columbia with the family.

    The OP was nice enough to leave me a comment. I have to first respond that there are no records of solar activity that go back more than 1000 years (and even those are unreliable) There aren't even available proxies we can use to estimate solar activity. You must be refering to the young dim sun hypothesis... As explained earlier, this would make it impossible to find 3 degrees of warming through a doubling of CO2 "empirically." Proving something empirically means that you would have to prove it through records or experimentation. There is no empirical way to show any trends in the sun's history. Perhaps the dim sun hypothesis is correct and the sun has been warming (I believe this is probable although uncertain) even then CO2 doesn't tell doesn't even come close to telling the rest of the story.

    The solar irridiance has to make some pretty funky and unscientific loops to make CO2 be strongly correlated with temperature in the long term. Perhaps in the short term there is a strong correlation between CO2 and temp but I believe the 800 year lag weakens a CO2 - temp causation. I would like to know where you find estimates of detailed solar irridiance in the past. Furthermore I am even more curious of the methodology of how you combine these "guesstimates" with CO2 proxies to find a close correlation with temp.

    Lastly, I couldn't access your first link. I'm not sure if its broken or I am trying to open it wrongly. I am new to this site.

    Thank you
  19. To Dappledwater:

    Sadly your link was broken and I couldn't open it.

    To quote you, "Furthermore, how exactly do you think the estimates for climate sensitivity came about, if not from the study of Earth's previous climates?" You try and mock me with this statement... but I couldn't agree with you more. I only wish estimates for climate sensitivity came from the Earth's previous climate. This however, isn't the case. Today's climate sensitivity and models (at least issued by the IPCC) place an unprecedented emphasis on CO2, which simply isn't supported by the empirical record.
  20. Beautiful blazing BC, burning bark and beetles.

    Today's climate sensitivity and models (at least issued by the IPCC) place an unprecedented emphasis on CO2, which simply isn't supported by the empirical record.

    Levels of C02 unprecedented since ~15 million years ago when global temperatures were several degrees higher, is that the missing empirical evidence you're talking about, svettypoo?

    I suppose we can dodge forming a conclusion by sticking with an appropriate definition of "empirical evidence."
  21. doug_bostrom,

    I hope you are not trying to argue paleoclimatic analysis with forest fire and beetle phenomena of the last several decades. I don't mean to be rude but please stay on topic.

    Secondly, I don't think you completed your thought in the third paragraph. You wrote "Levels of C02 unprecedented since ~15 million years ago when global temperatures were several degrees higher, is that the missing empirical evidence you're talking about, svettypoo?" I am going to assume you mean current levels of CO2 are unprecedented since ~15 mil years ago when global temperatures were several degrees higher. The logical question is if the CO2 is the major climate driver and ppm was matched 15 mil years ago and the average temp was several degrees warmer, why isn't it several degrees warmer now? I have not confirmed your statements anywhere but if they are true, they would only strengthen a AGW sceptic argument... I will give you a chance to explain what you meant with no judgement...

    I did form a conclusion. Did you not read my previous post? If I wasn't clear enough i will state it now. I concluded that CO2 has never been empirically shown with statistical significance to be the driver of climate and yet the IPCC models place it in that very position. I would also like to address my emphasis on empirical evidence. One can not claim to have a record of solar activity for the past 500 million years when such a record doesn't exist. If you would have kept on reading my post you would have read that even if we were to use the dim young sun hypothesized irridiation and combine it with the CO2 proxies as the major climate drivers we would not be able to explain prove causation of CO2 driven temperature.

    Lastly, I have tried to be as clear as possible in describing my argument and conclusion. Perhaps you could share some of your conclusions?

  22. Just so I'm clear on your position, svettypoo, what would you consider evidence of CO2 being the primary driver of the currently-occurring climate change? What would that evidence be? What would make you say, "Aha! Ok, I see it now"? Or do you think it's fundamentally impossible to provide, no matter what the conditions?
  23. svettypoo - CO2 has, in the paleo record, been a component of climate change. In warming, as CO2 is forced out of warmer waters, it's been a positive feedback. When CO2 weathers into newly exposed rocks, dropping temperatures, it's been a forcing.

    Currently we're changing CO2 levels at 100x any paleo recorded rate. That makes CO2 the first to change, and thus it's the forcing on the climate. Doubling CO2 causes ~1°C, and with the various water vapor and other feedbacks, an estimated 3°C warming.

    As to solar activity - we have quite literally millions (billions?) of data points as to the evolution of stars of our sun's mass - via astronomy. Not to mention the various paleo proxies. We know that stars of our sun's type evolve warming over time. Unless you have solid evidence indicating basic astronomy and stellar lifetimes are wrong?

    As to your graph - You have quite clearly not incorporated the 'warming sun' into it. The evidence others have presented indicate that CO2 levels and solar forcing together match quite well to temperature.
  24. Svettypoo I'm guessing you're pretty new to this topic, that or you're practicing some form of impressionism by ignoring important features of this topic.

    Notice that we've been adding C02 to the atmosphere in significant quantities only for the past 150 years, reaching close to 400ppm only in the past couple of decades. This means atmospheric temperature has not come close to equilibrating to the temperature it can be expected to reach at the present concentration, let alone where it'll eventually settle assuming we end up in the 800-1000ppm level where my intuition (cynicism?) suggests we'll sit given our indolence, complacency and proclivity to believe in comforting fairy tales.

    As to your loner perspective on solar evolution, yes I did read to the end of your version of "I doubt it" and found that part unpersuasive.

    Start here w/Spencer Weart's informative book on the topic of global warming to get caught up, if indeed you're fresh.
  25. I do not have a loner perspective on solar evolution doug_bostrom and KR, just like you I think that the young dim sun hypothesis is likely true. To quote myself "Perhaps the dim sun hypothesis is correct and the sun has been warming,I believe this is probable" Please don't commit a straw man. I stated it wasn't empirical because there is no record of it, which is also true. Which one of my points do you disagree with? The only reason why I mentioned it was not empirically proven was because the OP claimed that CO2 effect on the climate can be proven empirically.

    KR, there is a statistical reason why i wanted to leave out the warming sun. Its the whole point of the argument. Here is the statistical explanation. Radiative forcing hypothesis claims CO2 combined with solar irridiance to provide the closest correlation with temperature proxies. statistically speaking, this would mean that both CO2 and solar irridiance should be positively correlated with temp proxies when calculated alone. I however agree 100% that solar irridiance is heavily correlated with temperature proxies. I wanted to show the lack of correlation that CO2 had with temperature proxies in paleoclimate. This makes perfect sense statistically and in the context of the argument. Please try and understand the argument and the post before making a rebuttal.

    KR, Sadly, those graphs that you posted do not show temperature on any axis. So I don't know how you can claim that "the evidence others have presented indicate that CO2 levels and solar forcing together match quite well to temperature." I am beginning to think that you post first and think later. Actually, simply by looking at the graph you can see the holes in the solar forcing combined with CO2 argument. The Ordovician, Devonian, early Carboniferous, and Permian ice ages are not correlated with troughs in the graph.(the Permian ice age happens on a mini crest, look closely) Thats 4 out of six ice ages... This blows a pretty gaping hole in the argument... Also, the interglacial between the 4th and 5th ice ages makes absolutely no sense at the level of radiative forcing at that moment.
  26. Svettypoo @119, I'll try again - Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100
  27. Svettypoo at 10:04 AM on 29 August, 2010

    I’m not sure where your chart originates, but the temperature schematic is from Scotese, from around ten years ago. It is disheartening to see this schematic repeatedly being wheeled out on skeptical websites and venerated like the bones of some long dead saint, despite more than a decade of painstaking research since which makes it quite obsolete. It is a schematic only, meant to show very approximate periods of relative warmth and cold. The composite d18O proxy data used to estimate paleo-temperature variations, which has been gathered over many years is far more complex. I have charts if anyone is interested. Anyway, keeping it simple, the most recent chart showing Phanerozoic temperature variations estimated from updated d18O records compared with those which would result from (updated) paleo-CO2 data I have seen is from Royer 2009.

    This includes recently revised (2009) paleosol CO2 estimates from Breecker 2010 but we must remember it is a compressed overview (each pixel is bigger than our entire ice core record). Over recent years, we have been able to address many gaps, uncertainties and lack of detail in our knowledge of paleo-CO2 data, from the Neogene to the Ordovician. Though much work is still to be done, as each new piece in the jigsaw is added, the link between carbon cycle and climate is strengthened. For those interested in more detail I have tried to find some free links to some good recent work, see: Seki 2010 (and see Seki 2010 supplementary data), Young 2010, Tripati 2009 (and see Tripati 2009 supplementary data).

    Incidentally, for some longer term solar irradiance proxy data (9300 years) try
    Steinhilber 2009, and on the NOAA paleo website there are much longer reconstructions based on the 10Be records from ice cores, though these should also be interpreted with a little care.
  28. Lung cancer existed before cigarettes were invented too.
    Does that fact invalidate cigarette induced lung cancer?
  29. bobconsole, actually many of the 'think tanks' (i.e. propaganda units) disputing global warming also insisted that cigarettes do NOT cause lung cancer. Go figure.
  30. Thanks for the post Peter.

    To say the least, Scotese chart shows the lack of correlation between low CO2 troughs and glaciation periods and CO2 crests inter-glaciation periods. It is meant to represent averages through different periods. The chart you found in Royer's 2009 paaper is actually from 2004. Its referenced right on the paper. So its not too long after Scotese. She doesn't show CO2 and Solar variation separately on the graph, just combined as radiative forcing.

    Also, on a side note, please see this response to Royer's temperature sensitivity assumptions. Detailed Response to Royer et al.’s letter
    “CO2 as a primary driver of Phanerozoic Climate”

    Here is a more detailed (than Scotese) temperature reconstruction from Veizer, and CO2 reconstruction from Antarctic ice cores, Pagani and geocarb. Solar variation is left out to show CO2-temperature correlation only.

    I hope to post raw data for everyone when I find some time. And I'll try to respond to the other comments later tonight.
  31. svettypoo at 11:57 AM on 1 September, 2010

    Thanks. I am aware of the correspondance between Vezier and Royer, and there is a chain that goes beyond your reference. The temperature data from Royer 2009 is indeed from work in 2004, and Vezier acknowledges that to correct for pH (as Royer did) is valid. The Vezier T curve looks similar (as the d18O raw data will not be very different). However the CO2 data from Royer 2009 is very up to date (late 2009 corrections, please have a look at the references), most of the CO2 data you show (the output of model, GeoCarb) is not. We have proxy data from much recent work, and some of this is summarised in Royer 2009 and the later GeoCarbsulf(volc) model output). You should also read more widely on this, Pagani, Retallack, Zachos and Zeebe spring to mind, but then look at the recent references I linked above. On sea level, I will have to look at Schutter again, but there is the small matter of completely different continental configurations over this period...
  32. You know how everyone is talking about if climate change is natural or man made, in both cases (or even in the combination of both) don't we need to adapt?
    Because isn't that what our ancestors (most of them) did when the climate changed?
    Response: See the Argument "It's Not Bad."
  33. "Using ice cores, for instance, we can work out the degree of past temperature change, the level of solar activity, and the amount of greenhouse gases and volcanic dust in the atmosphere."

    Ice-cores are worthless, since CO2 sublimates above -70C, and thus esapes to newer parts of the ice; and there's NO place on Earth where temps remain below -70C, and so ice can't provide a reliable record since it simply escapes upward whenever the temperature's above this, giving the false impression of an increasign carbon-levels in the atmosphere.
  34. The CO2 is in a solid state? Can't be found unless it's solidified? Have you looked in a mirror recently, Captain Skywalker? Noticed any snow coming out of your nostrils?
  35. KirkSkywalker - It's not CO2 ice, it's CO2 gas trapped as bubbles in water ice; a physical sequestration (think ice gas tanks).

    There is some movement while additional snow/ice packs on top, which depending on the ice core is why a single layer is a running average of perhaps several decades - but sublimation isn't an issue.
  36. What an enormous pity that this level of debate is not centre stage. One would think that given the urgency of the matter it would be possible to get a permaneant link printed on all newspaper title boxes directing those interested in the topic to this site. I have been interested in global warming for many years, yet have only happened on this site today by pure fluke.

    Please keep up the good work.
  37. KirkSkywalker, to expand on the comments by KR and doug... you have essentially shown that CO2 cannot be a solid at the temperatures found in ice cores. Instead, it must be a gas. Of course... that is exactly what studies of ice core samples have stated all along. That they are examining the amount of CO2 gas found in air bubbles. Since those air bubbles date back to when the ice was formed this allows us to determine the CO2 content of the atmosphere at various points in the past.

    The website you reference in another post and its argument which you repeat here make no sense whatsoever. Indeed, if the CO2 were in solid form it would be much more difficult to isolate it and determine past atmospheric concentrations. Even making such an argument shows a complete lack of understanding of the underlying science.
  38. I have one simple question that I hope someone can asnwer.
    In that film 'The great global warming hoax' I think that is the name of it. Def something like that, it said that the huge graph which Al Gore used to demonstrate the history of warming on our planet (by showing the direct corellation between CO2 and warming), failed to tell us that on closer inspection, the temperature rose first and then the CO2 because the ocean was releasing the CO2 as it warmed and not the other way round. Is this true or false?
  39. @flanerz: check out the response to the CO2 Lags Temperatures argument.
  40. Re: flanerz (138)

    In addition to archiesteel's nice link at 139, please see "What does CO2 lagging temperature mean?" for a good explanation of what Gore said in his movie and what it means.

    RealClimate does a nice deconstruction of Gore's An Inconvenient Truth here, where they talk about what he got right with the science and what he got wrong.

    One of the more knowledgable commenters at RealClimate, Patrick 027, offers up a dissection of forcings, ice ages and milankovitch cycles here.

    I have not seen the film you name in your comment, so I couldn't characterize what they said that Gore said (he said, she said revisited).

    Hope that helps,

    The Yooper
  41. Sorry, this is a repeat of a post today, which I should have included with this topic, but placed under stratospheric cooling. My first blog--I haven't found such an interesting site before.

    I have reviewed some old posts and found one under "climate's changed before" with a question that I have also wondered, from jebjones42. It did not seem to have been addressed in any subsequent posts.

    "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?"

    I am also interested in this question. Is it sun cycles and precession/sun obliquity, and is the prevailing thought that we will overwhelm these historical cyclical temp. changes ?
  42. Re: reluctant skeptic (141)

    I've posted the answers to your questions over here where I first saw them.

    To make things easier, when you have questions, please use the search feature in the upper left portion of any page here. This will give you a narrowed choice of where to post your question. Just pick the one that seems most appropriate & post it there. If multiple questions, follow this procedure for each.

    It'll get easier the more you do it.

    The Yooper
  43. Try this page . Some good stuff to start you off and some links that might help.
    Response: Indeed, that is probably the best place for any further discussion of positive feedbacks and "runaway" warming.
  44. To look at the chart below and claim we are a primary driver of climate is nonsense. The next time the climate turns cooler - are we supposed to retool again to produce massive emissions of CO2?
  45. Re: averageguy (144)

    Welcome to Skeptical Science, wherein we debunk crap climate science, on both sides of the aisle. If you have an open mind and are here to learn (why else would you be here?), then Enter! This Door is always open.

    One thing I draw from your linked graphic is that it is from Alley's Central Greenland core. Thus, a timeline for a singular or regional location. It is considered an apples-to-oranges (i.e., "cherry picking") comparison to conflate localized data into global.

    The next thing to understand is that temperature variations over time from cores run the gamut over hundreds of millennia; it is rather unwise to focus on such a small window of time as presented in your graphic.

    Here's a bigger snapshot of time, showing the coupled relationship between temperatures and CO2 over the ice core record periods. You'll see that there are ample times one could focus on that would be markedly different from others:

    Returning now to the time period covered by your Alley graphic, look at this graphic showing the "sweet spot" of temperatures that has allowed mankind to develop a stable civilization (well, fairly stable):

    The interesting thing about the CO2/temperature record from ice cores (usually referred to as the paleo record) is that (as you refer to) natural variations, which are well-understood, were the dominant factor in climate change.

    However, the thing differing today is the massive slug of CO2 mankind has re-introduced into the carbon cycle. As a non-condensible GHG, CO2 is the Control Knob of Temperatures, capable of acting as feedback and forcing. In modern times, this means CO2 is driving temperatures up (with about a 40-year lag due to the thermal inertia of the oceans):

    We've pretty much eviscerated any chance of returning to glacial conditions for millennia. Indeed, there's these quotes from Dr Toby Tyrrell of the University of Southampton's School of Ocean and Earth Science at the National Oceanography Centre, Southampton, appearing in Science Daily:
    "Our research shows why atmospheric CO2 will not return to pre-industrial levels after we stop burning fossil fuels. It shows that it if we use up all known fossil fuels it doesn't matter at what rate we burn them. The result would be the same if we burned them at present rates or at more moderate rates; we would still get the same eventual ice-age-prevention result."
    "Burning all recoverable fossil fuels could lead to avoidance of the next five ice ages."
    The Yooper
  46. New NASA computer model shows plants slow warming by 0.3C-0.6C when CO2 is doubled against the predicted 1.94C globally.

    No mention of atmospheric sulfur (a source of particulates which help form rain) having declined from a peak in 1970 to 100-year lows in 2000. Don't you love it when they use data that stops 10 years ago in a current article?

    Far too much data is left out of models to assure accuracy, IMHO.
    Worse still, there is no mention of missing/incomplete data, only mention of major consensus.

    'Greener' Climate Prediction Shows Plants Slow Warming

    A new NASA computer modeling effort has found that additional growth of plants and trees in a world with doubled atmospheric carbon dioxide levels would create a new negative feedback – a cooling effect – in the Earth's climate system that could work to reduce future global warming.

    The cooling effect would be -0.3 degrees Celsius (C) (-0.5 Fahrenheit (F)) globally and -0.6 degrees C (-1.1 F) over land, compared to simulations where the feedback was not included, said Lahouari Bounoua, of Goddard Space Flight Center, Greenbelt, Md. Bounoua is lead author on a paper detailing the results that will be published Dec. 7 in the journal Geophysical Research Letters.

    Without the negative feedback included, the model found a warming of 1.94 degrees C globally when carbon dioxide was doubled.

    Bounoua stressed that while the model's results showed a negative feedback, it is not a strong enough response to alter the global warming trend that is expected. In fact, the present work is an example of how, over time, scientists will create more sophisticated models that will chip away at the uncertainty range of climate change and allow more accurate projections of future climate.

    "This feedback slows but does not alleviate the projected warming," Bounoua said.
  47. Re: tobyw (146)

    There has been some discussion of the Bounoua et al study on another thread, specifically comments 15-24 located here.

    But thanks for the heads-up!

    The Yooper
  48. @tobyw: interesting study, but right now we haven't seen any increase in vegetation due to additional CO2 in the atmosphere (so far, it's been the opposite), so I'm a bit skeptical about this expected negative feedback.
  49. Hasn't climate also changed, (warming) on other planets and moons at the same time as the earth? Plenty of studies seem to show that to be true. AGW believers then search for any reason they can find to say "yes, but it's happening at the same time for different reasons"... what a coincidence!
    Response: [Daniel Bailey] Then you should have no difficulty providing links to those peer-reviewed studies then. We're waiting... And respond on the more appropriate thread "Mars is warming," after reading that post.
  50. Please refer to argument #31. Then refer to argument #1 because "other planets are warming" is just an indirect way of saying "it's the sun".

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