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The Scientific Guide to Global Warming Skepticism

Posted on 8 December 2010 by John Cook

Note: Please be aware that the Scientific Guide to Skepticism was first published in December 2010 and that the information presented is therefore - at least in some places - no longer completely current. As a rewrite and update of the guide (not to mention its many translations!) is not really feasible, please check the links provided further down on this page leading to additional and more up to date information.

Scientific skepticism is healthy. In fact, science by its very nature is skeptical. Genuine skepticism means considering the full body of evidence before coming to a conclusion. However, when you take a close look at arguments expressing climate ‘skepticism’, what you often observe is cherry picking of pieces of evidence while rejecting any data that don’t fit the desired picture. This isn’t skepticism. It is ignoring facts and the science.

The Scientific Guide to Global Warming Skepticism looks at both the evidence that human activity is causing global warming and the ways that climate ‘skeptic’ arguments can mislead by presenting only small pieces of the puzzle rather than the full picture. 


The Guide explains the science in brief, plain language without getting too technical. For those who wish to dig deeper into the science, more detailed treatments can be found at the following pages (often presented with varying levels of complexity from Basic to Advanced):

How people are using the Guide

The Guide is being used by teacher associations, museums, websites, student groups and other organisations. Read some of the examples of how the Guide is being used.


Since its initial publication, The Guide has been translated into the languages shown below, but no further translations are planned, due to the content being based on information from 2010 and earlier (see green box at the top). If you are interested in helping with other translations, please check this blog post explaining active translation activities as of February 2022.

Czech translation of Scientific Guide to Global Warming Skepticism
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Comments 1 to 50 out of 68:

  1. Great Work Everyone and in Particular John! Thanks for all the time you've put in John!
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    Response: I forgot to mention in the post that a big word of thanks is owed to the many scientists and Skeptical Science contributors who scrutinised the Guide and offered comments. In particular, the Skeptical Science authors nitpicked and critiqued with an enthusiasm that would make any skeptic proud!
  2. Incredible work John! Congratulations, this is a professional document that is crammed with important and pertinent information. Consequently, it is going to be a great resource for lay people wanting to learn more about climate science and anthropogenic climate change (climate disruption). Again, a job well done and thanks to all those experts who offered their valuable time and expertise. And most of all, a sincere thanks to John Cook-- he is a true champion of science and the epitome of pedagogy. PS: Is there anyway people will be able to view the document's content on their iPhones?
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    Response: The Guide is essentially a compilation of content from the various rebuttals and blog posts throughout the Skeptical Science website, simplifying the text to make it more accessible to the average person, then showed to a number of scientists to ensure all the science is accurately portrayed. So generally speaking, most of the content from the Guide can be found in the iPhone app.

    Sorry, that's the best I can do at the moment :-)
  3. It's Christmas come early! Thanks, John!
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  4. A really clear document. I assumne there's no restrictions ( apart from correctly attributing the material) if I print off and give away a few copies
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    Response: The Guide has a Creative Commons licence (see the second page of the PDF) so you're welcome to copy the material and distribute.
  5. Absolutely fantastic. Certainly a lot of work but absolutely fantastic. Bob
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    Response: Bob, if we do an extended version, we will of course have to explain why greenhouse warming causes the stratosphere to cool. Fortunately you've softened that subject up for us :-)
  6. Thunderbirds Are Go Push it out there people. G
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  7. Brilliant!
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  8. [standing ovation for John's work] Already blogged on my site: Doc alert: The Scientific Guide to Global Warming Skepticism
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    Response: Thanks Lou, the post is much appreciated (but for the record, I am definitely defatigable).
  9. This guide is simply superlative. Excellent work John & contributors!
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  10. @ Albatross: I have an iphone 3Gs and it comes through fine as PDF via the Safari viewer, not sure about 3G, but most people should be able to see it without problem..
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  11. This is a great summary and presentation of the data. You have done a terrific job of putting it all together. I like the clean look and easy to read summaries.
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  12. I like the fact that it has lots of graphics.
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  13. Folks, I have a technical question related to the guide. I don't mean to say that the guide is incomplete; it's just that I would like more information for myself. The guide, as is, is perfect. For some reason, I'm having trouble really understanding why nights warm faster than days and winters warm faster than summers. For some reason, understanding this is eluding me. Thanks, Bob
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    Response: I am intentionally brief about those fingerprints in the Guide, acutely aware that you can't fit everything into a single guide without it bloating to unwieldy proportions. Fortunately, I have a blog to flesh out the details and in anticipation of these kinds of issues, I'd even already gone into more detail about the daily and annual cycle (my original plan was to have blog posts about all the human fingerprints before the Guide came out but well, I'm just not that well organised):

    The human fingerprint in the daily cycle
    During the day, the sun warms the Earth's surface. At nighttime, the surface cools by radiating its heat out to space. Greenhouse gases slow down this cooling process. This is why deserts cool so much at night. Water vapour is a strong greenhouse gas and the dry desert air traps much less heat than more humid areas. A more extreme example is the moon which has no atmosphere. At nighttime, there are no greenhouse gases to trap the outgoing heat. Consequently, the difference between day and night is more extreme with daytime temperatures getting up to around 118°C and nighttime temperatures falling below -168°C. In other words, the stronger the greenhouse effect, the smaller the difference between daytime and nighttime temperatures.

    The human fingerprint in the seasons
    During summer, a region receives more sunlight and warms. During winter, the region receives less sunlight and cools by radiating heat to space. Greenhouse gases stop some of this heat from escaping to space so an increased greenhouse effect slows down the winter cooling. Consequently, if greenhouse gases are causing global warming, we expect to see winters warming faster than summer.
  14. Thanks. I've been working on the issue for several years but probably reaching the wrong audience, online newspaper readers, most of whom are repetitive ideologically-driven trolls. Fortunately, your document is clear enough that perhaps even the politicians might understand and they are my current target. I won't try to convince the MP for my riding in Canada, John Baird who is probably the worst possible choice for the job in our parliament. At the COP15 in Bali when he had the substantive role rather than the current "temporary" one, he left a high-level meeting and was seen minutes later drinking a cocktail at a party. There is no way that he's getting my vote. But it appears very likely that votes alone won't help us to deal with the issue. I guess that it's time to "get in their faces".
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  15. Oops. Not "online newspaper readers" but "online newspaper commentators".
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  16. For some reason, I'm having trouble really understanding why nights warm faster
    Thinking about it as why nights cool more slowly helps, maybe, since the cooling all takes place through the radiation of LWIR?
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  17. For the next edition, I would also add Human Fingerprint #8: Decreasing atmospheric O2, caused by the burning of fossil carbon. If the increase in CO2 had come from natural sources, O2 would not be decreasing by similar amounts. Langenfelds et. al. (1999), GRL 26:13, 1897-1900.
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    Response: That is mentioned in passing on Page 1 on the 'Human Fingerprints on Climate Change' graphic but there were only so many green box Human Fingerprints I could fit into the rest of the Guide. If we ever do an "extended edition", I'll get the opportunity to flesh out more fingerprints.
  18. Bob Guercio @13- This is a laypersons understanding of the night/winter issue, so please excuse and correct any misstatements or misconceptions, but I'll give a try at explaining my understanding as maybe we are on a similar level scientifically. Think about daytime being when the earth absorbs heat from the sun and nighttime as when heat is radiated back out through the atmosphere. That's why it's almost always coldest in the early morning just before dawn after an entire night of losing heat. The warming effect of CO2 is related to how it interferes with the heat radiating back out through the atmosphere. Since there is more radiating of heat during the night it is the nighttime temperatures that will be most affected by the increasing CO2. Although I'm sure there is some radiation of heat occurring during the daytime, I imagine it must be less because the gradient in the temps between the earth and the atmosphere is less than at night. Also the temperature moderation during the daytime from radiating heat would be relatively small compared to the temp moderation driven by heat absorption. With regards to winter temps I think the concept would be the same since you have less insolation, longer nights etc during the winter so the effect of the CO2 would show up more. One question that occurs to me from writing this up is why doesn't CO2 have an equal effect in blocking the heat coming into the earth as it does on blocking the heat leaving? My guess is it has to do with the radiation coming in (sunlight) being of different wavelengths compared to the heat radiation going out.
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  19. Great job John but ... there's a mistake in the figure on page 8 where the captions at the top "Likely" and "Very Likely" are the wrong way round :-( I'd vote for "Its frigging cold" being included in the next edition, if only because where I am, it is - at the moment. And whilst I'm on the subject - any plans for a blog post on this "WACCo"(Warm Arctic, Cold Continent) weather modeling ?
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    Response: No, the captions for Likely and Very Likely are correct (I checked now just to be sure). The shorter thicker bar (off the top of my head) means there is a greater than 66% chance that climate sensitivity falls within that bar. The longer, thinner bar means there is a greater than 90% chance climate sensitivity falls within that range. When you think about it, it makes sense that there is a greater chance (eg - very likely) that climate sensitivity falls within the wider range of values.
  20. Bob Guercio @13 Though not highly technical, this might help. I pay attention to night time dew, because it can effect my work. What I have observed is that there is less dew on overcast or cloudy nights. On clear nights, heat radiates out into space faster, causing more dew. Similarly, greenhouse gases slow the radiative cooling at night, hence warmer night time temps. If the sun was the cause of warming, you would expect to see more daytime warming, when the sun is out. But instead, night temps are rising faster than day temps. Bacisally the same idea for summer / winter. Now I'm wondering if the overcast nights being warmer has more to do with mixing between layers of the atmosphere, in which case, the analogy is not as good. Anyone?
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  21. Moderator @19 Dang yes you're right. I think there's something about the sequence "Most Likely", "Likely", "Very Likely" that looks wrong, but yes when you think about it more ... Sorry for the false alarm
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  22. Geo77 -18 I think what you are saying makes sense. To paraphrase, the earth warms up during the day and cools off at night. So it seems logical that there would be more outgoing radiation after it has heated up and outgoing radiation is what is blocked. Regarding your comment about heat coming into the earth - Infrared does not come in from the sun; at least nothing appreciable if anything at all. Ultraviolet comes in, impacts and warms the ground and the ground radiates the Infrared. sailrick - 20 You got me thinking. It seems to me that because of the warmth of the day, you will have more moisture in the air than you would at night. Water vapor is a greenhouse gas. CO2 would be more appreciable with less water vapor. During the day, for the sake of argument only because I have no idea what the numbers are, CO2 may represent 20% of the greenhouse gases while at night it may represent 80% Is this what you are saying? Also, I suppose whatever argument we come up with for the night/day issue is going to apply to the winter/summer issue. Bob Guercio
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    Response: "Ultraviolet comes in, impacts and warms the ground and the ground radiates the Infrared."

    To be precise, it's primarily visible light that warms the Earth's surface. UV light is mostly absorbed by the ozone layer.
  23. Geo77 @18: why doesn't CO2 have an equal effect in blocking the heat coming into the earth as it does on blocking the heat leaving? Your guess is correct: the sun, being a black body at ~5000 K, radiates mostly in the "visible" region, with a peak near 500 nm. The earth, also a black body, but at ~290 K, radiates in the infra-red, with a peak near 10,000 nm (10 um). Nice graphics here and here. Greenhouse gases (CO2, H2O, CH4, etc) are transparent in the visible region, so absorb very little radiation from the sun. However, they do absorb strongly in several regions of the infra-red. Another nice graph there.
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  24. Great work, John. Will make sure everyone I know knows about it... BTW, have you sent out press releases to the various media organisations? Might be worth it to get the guide a bit more widely disseminated.
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    Response: Scott Mandia (the guy who suggested doing the Guide in the first place) has notified major media outlets and his extensive list of media contacts.
  25. Great stuff John. Many thanks to the contributors as well. I've made mention in my "usual" spot. Your usage of the "Human Fingerprint" in one of your replies leads me to reflect that it certainly is not the planet that is broken but rather humanity itself. The planet is quite capable of taking care of itself, and will on geologic time scales (say roughly another ~250Myr).
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  26. The content of the guide is excellent, but perhaps as important for the general public, it just looks damn good. A consequence of John's considerable graphic arts skills.
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    Response: Wendy did the heavy lifting in the graphic arts department. She's the right brain part of our partnership.

    But it is true, her work looks damn good. :-)
  27. Thanks for the hard work. I will be sure to politely share this as much as possible.
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  28. Great work John, thanks.
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  29. Great job on the "Guide." I hope you can do an expanded version and get it in bookstores so the general public will have access and you can generate some income.
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  30. I LOVE it! Very useful. And... has anyone worked out a daily-life example for the statistical probability that all these ominous numbers are random, perhaps in terms of poker? Such a thing could be a vwonderful grand finale for your list. For example, see Larry Gonick and Woollcott Smith's immortal book, The Cartoon Guide to Statistics? They open the chapter on testing hypotheses with a legal example about racial bias... I'm skipping the calculations here... in which the cartoon lawyer concludes triumphantly that the chances of getting an 80-person jury panel with only 4 African Americans work out to about .0000000000000000014. "Is that a small number or a big number?" says the judge. The lawyer explains, It's less than the chances of getting three consecutive royal flushes in poker. So the judge rejects the hypothesis of random selection, confiding to the reader, "If I was in that poker game, I'd a started shootin' after the second royal flush..." Yeah. Keep up the good work. Elise
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  31. Superb work John, thankyou for this excellent resource. I'd perhaps have added a mention to Tyndall and Fourier, highlighting the depth of time that we have understood CO2 causing warming, but that is a trivial point in an otherwise lovely readable and informative resource. I'd like to secong Phil's request for an article on the "Warm Arctic, cold continents" weather pattern. Cold weather is rapidly becoming the latest denier meme in the UK as we face our second (or third, depending on your location) really severe winter in a row. There are some interesting research articles around on WACCo (like the acronym Phil!) and on the hypothesis of reduced autumnal sea ice causing cold mid-latitude winter conditions, see for example the Arctric Report Card 2009 - Atmosphere or Petoukhov and Semenov 2010. But additionally some suggest that the remarkably low solar activity may be the cause, e.g. Lockwood et al 2010, at least for Europe. Given the Russian winter of 2005-06 (a focus of the Petoukhov paper) and the widespread nature of the 2009-2010 cold, maybe the Lockwood example doesn't work hemispherically? I know it seems strange to ask an Aussie about Pommie weather, especially during the Ashes :), but this is the best site on the Web for resources linked to debunking false skeptic arguments, or providing links to the good science.
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    Response: You had to bring up the Ashes, didn't you? As an Aussie and a (very) passionate cricket fan, that's an intenseful painful subject right now. If we win the 3rd Test in Perth, I may consider including WACCo in the next edition of the Guide.
  32. Sorry John! But everything goes in cycles, doesn't it? (yikes! :) ) Well, cricket perhaps, though I'd never write off any Aussie cricket team. I wasn't meaning WACCo for the next edition of the Guide, but as a future article on SkepticalScience, unless of course the pattern verifies so strongly in the next few years that there is little argument about its anthropogenic cause! At present, I think I'd just class it as an hypothesis that needs more data to be verified, but maybe there are some folk out there with a better grasp of atmospheric circulation that might be able to shed some light on it. Best of luck for Perth!
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  33. "Psst skywatcher, dooon't mennntion theeeee ashhhhhessssss"
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  34. John: Kudos to you and your colleagues on a job well done! I recommend that you switch the color of the primary text from blue to black. I just printed the document and the blue text is not easy to read. In addition, it would be less costly for everyone to print the docuemnt if the primary text were black.
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  35. Everyone: I'm now posting the following note on comment threads to media articles that address climate change and encourage you to do follow suit. "All of the anti-AGW poppycock posted on this comment thread is thoroughly debunked on the SkepticalScience website: "
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  36. #35 Badgersouth, such a comment on capitalweathergroup (a DC area site now owned by the Washington Post) brought me here. As a result I have refined my arguments so that they are no longer so easy to debunk. But I do honestly appreciate the feedback I get here, especially negative feedback. I happen to like negative feedback.
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  37. @36 Eric(skeptic): "To each his own."
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  38. @36 Eric(skeptic) Interesting concept Eric! That you 'refine' your arguments to make them harder to debunk. Surely the point of 'debunking' in this context is to illustrate faulty logic,reasoning and evidence, not just less artful 'arguments'. Since we are discussing physical phenomena in the real world, 'refinements to the argument' won't tip the physics in or against your favour. This isn't a debating club where we 'win' if our sophistry is cleverer. This is the real world.
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  39. Glenn Tamblyn, "refine" sounds a little too sophisticated. What I actually do is look up my argument in the long list of contradicted skeptic arguments, and I don't use it if it is there. Then I present my own theories on the cosmic ray thread for example. The ability of posters here to quickly point out flaws is exceptional. If my flaw is repetitious or obvious then someone will point that out also. If those theories seem to cohere with everything else I read, then I use those. (N.B. I am not trying to "avoid" CO2 warming theory, just imminent catastrophic CO2 warming theory). In the solutions threads in particular, the real world takes top priority and I agree with the consensus opinion in those threads. I think the difference is that it is much easier in the real world to test a solution than to test a model.
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  40. Why climate change is a big freaking deal! “Climate Scientist Warns World of Widespread Suffering If Further Climate Change Is Not Forestalled” “ScienceDaily (Dec. 8, 2010) — One of the world's foremost experts on climate change is warning that if humans don't moderate their use of fossil fuels, there is a real possibility that we will face the environmental, societal and economic consequences of climate change faster than we can adapt to them.” In this case, the foremost expert is Lonnie Thompson, distinguished university professor in the School of Earth Sciences at Ohio State University. Kudos to Dr. Thompson for telling it like it is!
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  41. NASA GISS has a new page about the record high November global temperature and cold weather anomaly in Europe. 2010 - Global Temperature and Europe's Frigid Air
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    Moderator Response: Fixed broken link
  42. #41: The map in that page is stunning and well worth showing, but I will put it in the 'extreme weather' thread.
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  43. Johns book is already being used by some educational institution. John's Book
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  44. 39, Eric: If you're interested in finding out the truth, you have to argue TO THE POINT, not just to avoid the point. Looking for a causal basis for global warming in cosmic rays is a lost cause.
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  45. nealjking, I'm not looking for alternative causes for global warming, but I am trying to identify the factors involved in the amplification of CO2 warming. Cosmic rays seem to be one of those factors but there are others.
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  46. #45: "Cosmic rays seem to be one of those factors" Eric, I'd love for you to fully explain how that actually works (not how it could work or might work). But it belongs here.
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  47. John- great book! I've got one request, which is to have the next edition available as a single column instead of/as well as two columns. With a lot more people reading on the screen and on e-readers, two columns are a pain as you have to go to the bottom of a page, then scroll back up to the top, then back down again. A single column allows you to make the best use of the available screen space (i.e. half the page isn't taken up with stuff you shouldn't be reading yet).
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    Response: That's an interesting question. I'll have to investigate the specs of ebooks and how one would put together an ebook version for readers like Kindle and iBooks, both of which I use on the iPad (so I welcome any technical tips from those wise in the ways of ebooks - please feel free to contact me).
  48. I was going to print the guide out to give to a skeptical friend, but now I am hesitating because of several confusion black spots (rather than actual errors) which I see it containing. I know he will be alert to these because, although he is not fully abreast of climate change science (who is anyway?), he is clever and knows enough science to spot problems straight off. Sadly there are plenty. I’m going to point to just two now: (a) the figure showing an example of a positive feedback on page 3 and (b) the figure showing build-up of Earth's total heat content on page 4. They immediately raise questions. I wouldn't be concerned so much if it was easy to find answers to these questions by searching the site. Unfortunately that's not the case. (a) The example of positive feedback on page 3 has a caption saying “Warming causes oceans to give up more CO2”. Elsewhere we are told that the oceans are getting more acidic - i.e. more dissolved CO2. So which it? Is CO2 in the ocean going up or down or both? Is it different in different places? Is one from the deep sea and the other not? Why is it so paradoxical, if so? (b) The graph of Build-up in Earth’s total heat content. My problem here is a bit harder to explain. I’m fascinated by that graph of increasing ocean heat energy. I’m also confused by its seeming variability. Why is it going up in such a stagger? Where is the heat going when it seems to level off every decade or so? So I look at the reference at the back and I see it is from Murphy et al in 2009. Hmmm. 2009 that’s good - recent. But wait. Hang on. It says: “Figure redrawn on data from paper supplied by Murphy.” Hmmm. It would be better to get a graph taken from an actual paper. So I check around the site here doing searches for ocean heat content and I can’t find this graph or anything similar. I know it used to be here somewhere. Has it disappeared? All I can find are rebuttals of claims that the ocean cooled during the last decade. Not quite the same thing, though, is it? Why isn’t there more information on this graph? How reliable is it given that ocean temperature data are supposedly so vexatious and that reliable temperature measurements, we are told, are almost non-existent until recently? How is heat content calculated, roughly? Does it include the whole ocean or is it just a part? I really feel that this graph needs more explanation. It is probably the most interesting graph I’ve seen illustrating global warming. If it is reliable, why isn’t it shown more often? You can see how suspicions arise in the mind just following this line of thought. I would really appreciate it if someone could provide satisfactory answers to these questions for me - pointing elsewhere if necessary. I would be even more delighted if my queries give rise to improvements to the clarity of the site and the guide too. Please keep up the good work, it is greatly appreciated.
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    Response: "Is CO2 in the ocean going up or down or both?"

    CO2 in the ocean is going up. The ocean is building up CO2 because it's absorbing much of the CO2 we're emitting. But as the ocean warms, it's ability to absorb CO2 is lessening. So we are seeing more of our CO2 emissions remain in the atmosphere each year (the airborne fraction). The trend in the airborne fraction is slight, teetering on statistical significance.

    "I’m fascinated by that graph of increasing ocean heat energy. I’m also confused by its seeming variability. Why is it going up in such a stagger?"

    I haven't discussed this with Dan Murphy, author of the paper where that graph came from, but my speculation is the variability in the ocean heat graph is because he calculates total ocean heat from the upper ocean heat content. Upper ocean heat shows more variability compared to the total ocean heat calculated to greater depths because the upper ocean exchanges heat with the deeper layers. This is why when you see graphs of heat over 0 to 700 metres, the heat content jumps up and down while graphs of heat down to 2000 metres deep show a more monotonic increase in heat.

    To calculate ocean heat back to 1950, Murphy had to use ocean data calculated from measurements of the upper ocean. To extrapolate this to deeper waters, he used studies that found the heat accumulating in the deep ocean was around 30% of the heat accumulating in the upper ocean. Thus if he'd have had access to direct ocean heat measurements down to the abyssal depths, I'm guessing the ocean heat graph would've shown less year to year variability. That's just speculation on my part.
  49. Paul Barry, my explanation for (b) is that like most parts of the climate system, ocean heat storage is not a nice monolithic, even process. The graph in the guide is crude. But looking at the ENSO numbers here it shows that whenever there is strong El Nino (ocean releasing heat) there is a leveling off or dip in the OHC chart (e.g. early 80's, early 90's, 1998). So basically the ocean is storing heat over the long run but the rate of storage can fluctuate based on weather-related ENSO cycles in the Pacific.
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  50. Paul Barry @ 48 - The example of positive feedback on page 3 has a caption saying “Warming causes oceans to give up more CO2”. Elsewhere we are told that the oceans are getting more acidic - i.e. more dissolved CO2. So which it? Is CO2 in the ocean going up or down or both? Is it different in different places? Is one from the deep sea and the other not? Why is it so paradoxical, if so? The following graphic from NOAA gives an idea of John what is talking about: A simplified version is that CO2 is less soluble in the oceans at higher temperatures. You can see the band of CO2 flux to the atmosphere around the tropical regions, where water temperatures are higher, and the absorption of CO2 in cooler waters (Note the obvious warming around Antarctica & flux of CO2 to the atmosphere). So you can see that both absorption and release of CO2 from the oceans can occur at the same time, it's a matter of temperature, the net effect at the moment is seeing CO2 build up in the ocean, as also evidenced by increasing ocean acidification measurements and declines in carbonate saturation states. So there's no contradiction. Now as the oceans continue to absorb more heat their ability to store CO2 will diminish, and we'll see the red regions in the graphic start to rise.
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