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Welcome to Skeptical Science

Posted on 29 April 2021 by John Cook, BaerbelW



Skeptical Science is based on the notion that science by its very nature is skeptical. So what is skepticism? Skepticism is not doubt! Skepticism is the open-minded consideration of something based on the evidence. A skeptic doesn't have a preference for what the truth is, a preferred answer. They want to discover what the truth is based on the balance of all evidence. You look at all the facts before coming to a conclusion. In the case of climate science, our understanding of climate  comes from considering the full body of evidence and being 'skeptical' for well over a century.

In contrast, climate denialism is closed minded. It thinks it knows the truth and wants to interpret the evidence to suit that. It has a preferred answer and wants to look at everything in that light. So it looks at small pieces of the puzzle while neglecting the full picture. Climate 'skeptics' vigorously attack any evidence for man-made global warming yet uncritically embrace any argument, op-ed, blog or study that supposedly refutes global warming. If you began with a position of climate 'skepticism' then cherry pick the data that supports your view while fighting tooth and nail against any evidence that contradicts that position, that's not genuine scientific skepticism.

If 99 pieces of evidence support an idea and 1 doesn't, a skeptic says 'that idea is probably true'. A denier says 'Ahah, that idea is false'.

Skepticism is a process, denial is a position.

So the approach of Skeptical Science is as follows. It looks at the many climate myths, exposes the techniques and fallacies used to distort the science and then puts them in their proper context by presenting the full picture. The climate myths are listed by popularity (eg - how often each argument appears in online articles) or with fixed numbers you can use for permanent references. For the more organised mind, they're also sorted into taxonomic categories.

Good starting points for newbies

If you're new to the climate debate (or are of the mind that there's no evidence for man-made global warming), a good starting point is Warming Indicators which lays out the evidence that warming is happening and the follow-up article, 10 Human Fingerprints on Climate Change which lays out the evidence that humans are the cause. More detail is available in empirical evidence that humans are causing global warming. Contrary to what you may have heard, the case for man-made global warming doesn't hang on models or theory - it's built on direct measurements of many different parts of the climate, past and present, all pointing to a single, coherent answer.

Another good starting point is the SkS climate graphics page, with each graphic featuring links to informative SkS material. Good introductions to climate science can be found at Global Warming in a Nutshell and The History of Climate Science. You could lose yourself for hours in those pages!

Smart Phone Apps

Note (December 2019)Our apps are currently "out of order" as they unfortunately are no longer maintained. They may still work if already installed but have vanished from the app stores. We are looking into options to make them available again. Please directly use the list of most used climate myths instead for the time being or download PDF versions via zip-files provided here. Thanks!

For smart phone users, the rebuttals to all the skeptic arguments are also available on a number of mobile platforms. The first Skeptical Science app was an iPhone app, released in February 2010. This is updated regularly with the latest content from the website and very accessible in a beautifully designed interface by Shine Technologies. Shine Tech then went on to create a similar Android app which has some extra features missing from the iPhone version. A Nokia app was also created by Jean-François Barsoum (this was one of the 10 finalists in the Calling All Innovators competition).

As well as the list of rebuttals, Skeptical Science also has a blog where the latest research and developments are examined and discussed. Comments are welcome and the level of discussion is of a fairly high quality thanks to a fairly strict Comments Policy. You need to register a user account to post comments. One thing many regulars are not aware of is you can edit your user account details (to get to this page, click on your username in the left margin).

Keep up to date by email, RSS, Facebook, Twitter or - since Nov 2022 - Mastodon

To keep up to date on latest additions to the website, sign up to receive new blog posts by email. There's an RSS feed for blog posts and for the engaged commenter, a feed for new user comments. We recommend you follow Skeptical Science on Twitter to keep up with the latest blog posts and other interesting climate links. In November 2022 we also set up a presence on Mastodon. Blog posts from Skeptical Science and relevant articles from many other reliable sources are also shared in a steady stream via our Facebook page.

About John Cook

For those wondering about who runs Skeptical Science, the website was founded by John Cook, Senior Research Fellow with the Melbourne Centre for Behaviour Change at the University of Melbourne and adjunct faculty at George Mason University. John originally obtained a Bachelor of Science at the University of Queensland, achieving First Class Honours with a major in physics.

John is the author of a number of books and scientific papers including being lead-author of the paper Quantifying the Consensus on anthropogenic global warming in the scientific literature, which was tweeted by President Obama and was awarded the best paper published in Environmental Research Letters in 2013. In 2014, John won an award for Best Australian Science Writing, published by the University of New South Wales. In the summer of 2016 John finished his PhD in cognitive psychology, researching how people think about climate change.

The SkS Team

There are many more who make invaluable contributions to Skeptical Science with a number of authors who write blog posts, rebuttals and other articles. They contribute by moderating the comments sections, editing and proofreading posts, sharing information with visitors, responding to emails, and providing technical support. There are also many regular commenters whose feedback has helped to improve and hone the website's content. Translators from all over the world have translated selected content into 20 different languages.

In 2011, Skeptical Science won the Australian Museum Eureka Prize for Advancement of Climate Change Knowledge. In May 2016 Skeptical Science received the "Friend of the Planet" award from the National Center of Science Education (NCSE).

Operational expenses to maintain the website and the funds to support our projects are currently (May 2023) still covered by a combination of internal funding provided by team members as well as some regular small-scale reader contributions. John Cook has no affiliations with any organisations or political groups other than academic institutions such as Melbourne University. Find more details on our "about us" page.

Update April 2021 - An interactive version of The Story of Skeptical Science

For the 2020 Fall Meeting of the American Geophysical Union (AGU) John Cook and Bärbel Winkler submited an abstract to session SY043 - Communication of Science - Practice, Research and Reflection convened by Heidi Roop, Priyanka Kushwaha, Kristin Timm and Erin Leckey. It seemed a good fit to submit "The Story of Skeptical Science" to, something we had also done earlier in 2020 for a comparable session at the European Geosciences Union (virtual) meeting. The EGU-presentation consisted of a "display" - basically a PDF created from a PPTX-presentation accompanied by a live chat-session. At AGU it was an "eLightning" session, which was a combination of a 3 minute talk and an interactive "iPoster". So, while the content is basically the same, the format of the presentation is completely different. You can check it out yourself here or by clicking on the poster's screenshot. If the iPoster doesn't load, you can try this "mock up" PPSX-version instead.


As the presentation shows, Skeptical Science has evolved from a small blog into a community of intelligent, engaged people with a commitment to science and our climate since its creation in 2007. Many of the contributors are working scientists who have many published scientific papers to their name. All the work is done as volunteers and a running joke among the author community is that we are being paid peanuts and they haven't even been delivered yet!

In August 2017 we published a series of posts to highlight SkS' 10th birthday. This series of short articles gives a good overview of how SkS evolved from a one-author-blog to the global volunteer effort it is today.

Note: to access the earlier version of this post and to read the comments posted until April 2015 please check out Newcomers start here

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Comments 1 to 50 out of 124:

  1. I'm looking for some links. Hopefully someone here can help me.

    1. I'm hearing a lot of fuss about satelite data diverging from other climate data sets. ( I'm assuming that these are public data sets. Can someone point me to where I could download them? I'm assuming they're a few hundred gigs or so of text when uncompressed?

    2. I've also heard that there was a recent change of normalization procedures that deniers are saying increased warming, but this site seems to claim made no difference. Can someone point me to data sets that I can examine and decide? A few pointers of where to start looking would be appreciated too.

    3. There's been a lot of study of the sun, the oceans, and glaciers. Is anybody aware of a study quantifying the amount of heat contained in the Earth's core? Hypothetically speaking, how big of a fizzure would need to open in the ocean floor to warm the oceans 1 degree farenheit over 100 years? Is there even enough energy in the earth's core to do that? My gut says that someone's thought of this and studied it ad-nauseum. I'm just curious what they found. Can someone point me to their research?

    Thank you!

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    Moderator Response:

    [Rob P] - The oceans are warming from the top down - see the image below adapted from the IPCC AR5. Granted not a lot of readers understand oceanography, but geothermal heating as a possible cause would require some crazy kind of physics to match the observations - buoyancy considerations for instance.


    [TD] In addition to the link One Planet Only Forever gave you regarding satellite data, see climate statistician Tamino's recent post of balloon data, "Desperate for a Pause."

    For the "recent change of normalization" see the SkS post "What You Need to Know About the NOAA Global Warming Faux Pause Paper."

    See "Underground Temperatures Control Climate."

  2. Hi vesuvian and welcome to skeptical science.

    Please allow me to be frank: You're not going to be able to figure out 1 and 2 by yourself even with the data (which is pretty easy to find at the GHCN and RSS websites).

    If you're keen to learn more about climate science, here is a really good place to start, it contains a good primer on temperature data (incl adjustments and raw data) and adresses heat coming from the earth's interior.

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  3. versuvian7 @1.

    I have a response to your third question on a more appropriate thread here.

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  4. I've done two calculations to determine the contribution to atmospheric CO2 from wildfires, compared with burning fossil fuels.  I did not include Volcanoes or other natural CO2 sources.  When I estimated forest density, I came up with wildfires producing 88 times fossil fuel CO2 production.  When I found pre-computed numbers, I found that wildfires and fossil fuel burning are comparable.

    Assuming that forest fires produce the same amount of atmospheric CO2 as burning fossil fuels, and the half-life of atmospheric CO2 being 500 years, even if the entire WORLD shut down all fossil fuel burning (impossible!), the reduction in atmospheric CO2 would take centuries. And, since making more than a 25 cut in global fossil fuel use is unlikely, we are in this mess for the long haul.  So, my questions to you are:

    1. What do you propose to realistically cut CO2 significantly?

    2. How long will it take to reduce CO2 levels to pre-industrial age amounts?

    Thank you in advance,


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    Moderator Response:

    [RH] Changed all-caps to italics. Please avoid all-caps, per commenting policies.

    [edit] Also, please show us your calculations that estimate forest fires produce 88 times the CO2 as FF emissions. 

  5. Since you dont supply link for forest fire Co2 release nor show us your calculation, I cant comment except that your numbers seem at odds with other sources. The isotopic composition of excess CO2 in our atmosphere is consistant with FF (which have no C14 whereas forest do).

    Forest fires dont produce long term change in CO2 concentration unless the forest is not replanted in something with similar carbon capture rates. Land use changes are an issue of course and you will see the accounting for that in IPCC reports.

    Cutting CO2 emissions significantly means switching energy use to non-carbon sources. Using less also helps. The best way to make the cut is simply to ban building new power stations that emit CO2 - let the market figure out the best replacement technology as FF stations age out. That doesnt go well with right-wing "govm't restricting freedom" types so second best way is Friedmann economics and impose cost on the externality (the effect of CO2 emissions). In practise this is some sort of carbon trading or carbon tax which prices FF-generated power more expensively than non-carbon sources.

    You dont need to reduce CO2 to pre-industrial age. You only need to slow climate change to a rate at which economic and human systems can adjust.

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  6. Bobbi @4, if you don't mind my saying so, you have made two of the classic errors of AGW denialism.  The first is that you assume existing rates of a natural process represent the change in rates of the natural process.  That is important in that we are trying to explain not the long term stable background concentration of CO2 (280 ppmv) but the recent rapid increase of the CO2 concentration by 120 ppmv.  Background rates of processes in the CO2 cycle clearly cannot change the current rapid rise, for if they did there would also have been a rapid rise at similar rates over the whole of the holocene.  It follows any background emissions of CO2 from wild fire are matched by background sequestration of CO2 so that the net longterm change in CO2 concentration in the atmosphere is zero.  So, before taking your argument any further, you need to indentify the increase in CO2 emissions due to wildfire relative to background rates.  As wildfire and controlled burnoffs due to Land Use Change (LUC) are already included as anthropogenic emissions in IPCC calculations, you also need to specifically identify how much of the increase in wildfire is not due to LUC. 

    The second classic error is to ignore the fact that any biological emissions of CO2, including by wildfire, comes from CO2 originally drawn down from the atmosphere by photosynthesis.  That does not mean automatically that an increase in wildfire will not result in an increase in atmospheric CO2.  Such an increase, with no matching increase in photosynthesis and with no matching decrease in respiration (either by animals eating the plant matter, or through natural decay of plant matter) could result in a decrease in carbon stored in plant matter and a consequent increase in CO2 in the atmosphere.  But because of the close connection between photosynthesis and combustion, you need to look at the relative rates of each (and respiration) to determine what the net effect is.

    As it happens, combustion of plant material from all sources including as a fuel, only accounts for about 2.4 PgC/yr emissions.  Further, not only has the combined emissions of combustion of plant material plus respiration increased, but so also has photsynthesis by a larger amount (see chart below):

    As a result the combined effect of photosynthesis plus respiration/combustion is to take 2.6 PgC/yr out of the atmosphere if we ignore LUC (ie, the natural effects only), or 1.5 PgC/yr including anthropogenic LUC.  Both are a relatively small fraction of the 7.8 PgC per year from industrial emissions (fossil fuels pluc Cement) or 8.9 PgC/yr from all anthropogenic sources.

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  7. Ok I don’t know where to post these questions so I’m trying here.

    I have made a few posts and have gotten very good answers that explain a lot. But I am still having difficulty finding the answers to these because the IPCC website is difficult for me to navigate.

    Is the CMIP5 Ensemble mean the average of all the different RCP models or an average of something different?

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  8. Hank @7, the CMIP5 ensemble mean, in IPCC usage, is the mean of the values of one run from each model that performed a given experiment in the Coupled Model Intercomparison Project 5 (CMIP5).  The runs for each Representative Concentration Pathway (RCP) each represents a seperate experiment, so there is a CMIP5 ensemble mean for RCP 2.6, and a distinct one for RCP 4.5, for RCP 6, and for RCP 8.5.  The RCPs are not the only experiments that have been done with CMIP5 models, but they are the main ones.

    It is important to realize that not all CMIP5 models have performed model runs for all experiments (not even all RCP experiments), while some models have performed multiple runs in some experiments.  The IPCC restricts the ensemble mean to one representative per model so that those models are not given undue weight, but in some usages that restriction is not applied.  Typically, in those usages the paper reporting the results will specify the models runing the experiment, and how many runs were performed with each experiment.

    Finally, the outcomes of the CMIP5 RCP experiments can be found at the KNMI climate exporer, with all runs performed for each CMIP5 model performing a run.  If you make use of the data, just remember that to obtain the same results as the IPCC you need to select the data for "one member per model" in any category.  Otherwise you will obtain multiple runs for some models.

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  9. Thank you Tom. What I’m trying to understand is what I’m looking at in your reply to me in comment #3 in the “ Tracking the 2 C limit – February 2016” post. It shows the CMIP5 Ensemble mean along with the actual temperature data from several originations. What was used to make that CMIP5 graph?

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  10. Hank @9, one of the model experiments is the historical forcings up to about 2002.  If you look at the KNMI data, you will see several models have a "historical" run.  However, when running any of the RCP experiments, the model will be run with the historical forcings first before switching over to the RCP forcings about 2002.  Because the RCP forcings do not vary significantly from each other for the first decade, and because of the thermal inertia of the models, the temperature response for all scenarios is approximately the same to about 2020-2030.  Consequently what you are seeing is the ensemble mean for one run per model for the historical forcings to the end of that data, and one of the rcp scenarios (often rcp 4.5) thereafter.  Which precise rcp scenario was used in Tracking the 2 C limit, I could not say.

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  11. Correction to my @10, the graphs I posted from real climate are specified as forcing adjusted, so they will have used historical forcings for the entire period, but the research was post the IPCC AR5 process, and so I do not know which models were used.  The paper from which the graph originated does not specify in the body of the text, only referring to the CMIP5 ensemble.  That should mean they have used one run only from each of the models used in the CMIP5 project, or almost all of them.  If you want to confirm that, however, you will need to send an email to the lead author, Gavin Schmidt.

    The graph from Zeke Hausfather is definitely stated to use the RCP4.5 extension on the historical forcings.

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  12. Thanks Tom, that helps a lot. 

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  13. I am having trouble finding support for the contention that most CO2 which enters the ocean gets there through the action of falling rain.  

    can you point me in the right direction or otherwise advise me?

    Thank you.


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  14. Just a point of interest; and I realise this question has probably been answered previously, is there a consensus view on the possible cause(s) of the average global temp spike during the early 1940's?

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    Moderator Response:

    [TD] Tom Curtis gave an explanation in a comment.

    [PS] See also IPCC Ar5 report, pg 887 ("Early 20th Century Warming").

  15. tommyb86 @14, the comment of mine linked to by the moderator (TD) is actually a comment about the spike in temperatures in the contiguous USA in the 1930s.  Given that the contiguous USA represents approx 2% of global surface area, that is not a major factor in the 1940s spike in global temperatures to which I think you refer.

    With respect to the peak in global temperatures, there are three long term trends contributing to global warming from the early to mid-twentieth century.  First, the rise in CO2, and anthropogenic forcings generally continued at a fairly steady pace until the mid 1960s, after which it accelerated significantly.  This is likely to have contributed about a third of the warming.  Second, following Krakatoa (1883) and a series of smaller volcanic eruptions in the late 19th and very early twentieth century, Earth had no large tropical euruptions until the eruption of Augung (1963-64).  This is possibly the largest single factor in the early twentieth century trend (but note the differences in the reconstructed forcing histories).


    Thirdly, there was a appreciable trend in solar activity from about 1910 to the peak in 1955.

    These three together with ENSO may be sufficient to account for the temperature peak in the 1940s, although the data does not match models based on these forcings plus ENSO alone perfectly over this interval (example).  That may be due to insufficient weight attached to Black Carbon as a forcing (with the BC forcing being calculated for its effects on snow, but not for its overall effects in an interval where those effects were in some regions sufficient to allow the Peppered Moth to switch almost completely from a light to a dark form).  It may be due to some residual effect from ocean variability not covered by ENSO.  Or it may (and I think this is most likely) be due to errors in the temperature data.  In particular, SST data showed a great reduction in the proportion of temperatures collected by buckets (as in most commercial ships) to those collected by engine manifolds (as in most military ships) in the 1940s, with a concurent significant change in the regions most frequently travelled (and hence for which we have temperature data):

    It needs only a slight error in one of the adjustments to create a large artifact in the warming in the 1940s.  That possibility is ably argued here.

    The upshot is that the peak in 1940s temperatures is at least partly understood just from basic forcings, but we still have some way to go before we understand it fully.  Further, given what we know, the possibility that the specific 1940s peak (as opposed to the 1910s-1960s trend) is an artifact relating to the great changes in temperature collection methods during WW2, but possibly also due to some unknown or under appreciated climate forcing, or form of internal variability.

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  16. tommyb86

    Further to Tom's last graph, that big change during world war 2 has been identified quite clearly. Most SST records were taken by UK & US ships in the early period of the record. The UK used mainly the bucket method while the US used engine inlets. During WWII the proportion of ships contributing SST records switched to mainly US ships. The transition out of that has been narrowed down to Aug 1945.

    Additionally, there does seem to be indications that there was a general warming in higher latitudes during the 20's & 30's. So the spike is quite likely to be a mix of several factors including climate and instrumentation.

    Contrast the different latitude bands from GISS:

    Why the bigger spike in the tropics/southern extratropics? That is mainly ocean, and the biggest part of that ocean is the Pacific. The big stomping ground of the US Navy in WWII.

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  17. Apathy and inaction are our greatest enemies. To quote Rachel Carson:

    “We stand now where two roads diverge. But unlike the roads in Robert Frost’s familiar poem, they are not equally fair. The road we have long been traveling is deceptively easy, a smooth superhighway on which we progress with great speed, but at its end lies disaster. The other fork of the road—the one “less traveled by”—offers our last, our only chance to reach a destination that assures the preservation of the earth.”

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  18. I am brand new to this site.  
    Here are some observations from the current literature, as I understand them, and questions:

    1. Average global temperatures are predicted to rise by 2100 by from 1.1 to 5.4 deg C. (Is this accurate?)

    2. Once CO2 gets into the atmosphere it stays there for a long time (How long?), and presumably continues to contribute to rising temperatures while it is there.

    3. To set a lower boundary on the problem, let’s say that ALL new human-produced CO2 and methane added to the atmosphere is reduced to ZERO starting tomorrow. Using current models, what is then the predicted change in average global temperature in 2100?

    4. Are my statements/assumptions accurate?

    5. Has anyone run the simulation I describe in (3)?

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  19. Richard @18:

    1)  In the words of the IPCC AR5:

    "Global mean temperatures will continue to rise over the 21st century if greenhouse gas (GHG) emissions continue unabated.  Under the assumptions of the concentration-driven RCPs, global mean surface temperatures for 2081–2100, relative to 1986–2005 will likely1 be in the 5 to 95% range of the CMIP5 models; 0.3°C to 1.7°C (RCP2.6), 1.1°C to 2.6°C (RCP4.5), 1.4°C to 3.1°C (RCP6.0), 2.6°C to
    4.8°C (RCP8.5)."

    So, the projection is for the average over the two final decades of the century, and depends on assumptions about future changes in forcings.  For the scenario which has the best claim to be a BAU scenario (RCP 8.5) the projected temperature increase is 2.6 to 4.8 C, but depending no how robustly we reduce emissions it may be a lot less than that.

    2)  David Archer has said that as a rule of thumb, ""The lifetime of fossil fuel CO2 in the atmosphere is a few centuries, plus 25 percent that lasts essentially forever."  The processes are illustrated by this graphic showing the draw down from the addition of a large quantity of CO2 in one pulse:


    The "few centuries" is represented by the blue shaded portion of the graph, after which comes the long, slow drawn down (extending to about a million years or so to get rid of the last few ppmv increase).  The 25% is a rough figure, and depends on how much we emit in total.  The greater the amount the greater that value, with a full fledged BAU scenario pushing the value up closer to a third.

    3)  If we eliminate all anthropogenic emissions, the slow increase of temperature to equilibrium approximately matches in pace the slow draw down in CO2 concentration, with the consequences that temperatures remain approximately at the value to which they had risen when you eliminated all emissions.  This is an approximate projection, with mismatches in the paces possibly resulting in small fluctuations on either side of that, and overall uncertatinty meaning it may be a slow rise or slow fall overall.  This has been shown in simulations (to anwer your fifth question), but I cannot remember the relevant links at the moment, for which I apologize.  Your question (4) also appears redundant. 

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  20. Hello,

    Its been a few years since I posted here.  I used to teach Physics of the Environment at the University of Connecticut, and upon retirement decided to learn the nuts and bolts of computing the CO2 no feedback climate sensitivity. I did this using Spectral Calc, combined with the Schwartzchild Equations  and got good agreement with the U. Chicago Modtran website.

      Now I am trying to compute my own transmittances, using the HCG approximationfor computing the transmittance of isolated lines, coupled with the random overlap approximation.  I get good agreement with the graph on page 233 of Pierrehumbert's Text on Principles of Planetary Climate for the 575 to 600 wn band but only if I remove the Hitran lines in that band with intensities less than 10 to the minus two molecules  per square centimeters.       It would seem reasonable to me that the intense bands are far enough apart in that band to allow the assumption that they are approximated by a random distribution, but that this might not hold if one included tha much larger number of weaker lines. But there is nothing about only using the more intense lines includeded in the text. 

    Can anyone help me with this?


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  21. Sorry,

    I meant ten to the minus 22 not ten to the minus 2 for the cutoff intensity in the above comment.


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  22. curiousd @20, that question is a tad too technical for me, and (I suspect), most regular commentors on SkS.  If we are to help at all, you will need to identify equations used by equation number in the text, and ideally show a plot of your result, with and without the the low intensity lines.  As an alternative, contacting Science of Doom or Real Climate, or Gavin Schmidt or Chris Colose, or Raymond Pierrehumbert himself mored directly is likely to be more fruitful. 

    For those who may want to have a crack at answering the question, the figure can be found in the Google books version of Pierrehumbert's text book (just scroll down), but unfortunately critical discussion from the preceding two pages is missing.

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  23. Thank you Tom Curtis for the helpful response. I used to know how to post graphs here and can learn that again.  In the meantime:

    1. The equivalent width of a Lorentz line in the strong approximation is given by W = 2 x square root of (Smass gamma Ls) .  Gamma is the width of the line at surface pressure. Ls is the "strong path" and is plotted on the horizontal axis in P-H Fig. 4:13.  Smass is the intensity one obtains by converting from the moles per cm squared (wn) in HITRAN to kg per meter squared (wn). Since the plot is in terms of Ls the expression used  to obtain Ls is not part of the present discussion.

    2.  Let Wj be the equivalent width of line j.  Goody's random overlap approximation states that approximately the total averaged transmission is given by  T = e to the power ( - (Sum over j of Wj)/delta) where delta is the band width;  this is 25 wave numbers in this problem. Goody's random overlap approximation was subsequently improved by others, especially Malkmus. 

      On page 232 of P-H it states the following: "...the strong line transmission function in eq. 4.69 fits the calculated transmission in the 575 - 600 wn band almost exactly throughout the range of paths displayed, when used with the random overlap modification in equation 4.7."  If I include all the HITRAN lines in this interval and the associated line widths, I get transmittances that are too small. But there is a set of intense lines in the band that really stand out, and can be separated from the weaker lines without one being at all subjective.   These have magnitudes of ~ 10 to the minus 21 power as opposed to many more lines of magnitudes of 10 to the minus 23 or 24 power. If I remove all lines less that ten to the minus 21 the fit is really good; keeping also 10 to the minus 22 lines gives a pretty good fit, and there is no fit if all the lines are included. 

    This theory uses only surface pressures, and assumes a constant temperature equal to the surface temperature. HITRAN uses Voigt lines, but I believe these approach the Lorentz lines assumed by the theory as one approaches the full atmospheric pressure at the earth's surface.



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  24. Again a stumble ....Smass is what one obtains by converting  from a cross section in cm squared  per molecule in HITRAN (times w n) to meter squared per Kg (times w n) .  The path Ls is in kg/meter squared. Then the equivalent width has units of wave number and thecombination of equivalent width divided by the band width delta in wave numbers is dimensionless.  Since the sum of equivalent widths divided by band width is an exponent it must be dimensionless. And it is.  


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  25. curiousd, on page 228, Pierrehumbert gives a formula for a double integration that yields the mean transmission (Formula 4.63), and then writes:

    "The argument of the exponential is just the optical thickness of the layer between p1 and p2, and to keep the notation simple we will assume the integral to be taken in the sense that makes it positive. The double integral and the nonlinearity of the exponential make this a hard beast to work with, but there are two limits in which the result becomes simple. When the layer of atmosphere between p1 and p2 is optically thin even at the center of the line, where absorption is strongest, the line is said to be in the weak line regime. All lines are in this regime in the limit p2 → p1, though if the line is very narrow or the intensity is very large, the atmospheric layer might have to be made exceedingly small before the weak line limit is approached. For weak lines the exponential can be approximated as exp(−δτ ) ≈ 1 − δτ, ..."

    He then give equation 4.64, which won't copy and paste, so I will leave interested readers to look it up.

    He then discusses formulas for the weak line regime, including informing us (just after formula 4.65) that W ≡ S(To)

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  26. curiosd, my original post @25 was much longer, although probably not much more useful.  Essentially, I suggest you plot the weak line fit and formula 63 in addition to the strong line and Malkmus model fits.  As I understand the text, all four should be close approximations so that if you have an outlier, you will have identified that you implimentation of the outlier will contain a mathematical error.  Failing that, you have to alternatives.  If you print a plot of your output, some other of the regular commentators here may be able to identify the error.  However, better would be to seek advise directly from one of the three individuals named @22.  Finally, here is an alternative version of the text of Principles of Planetary Climate.  The page numbers of the relevant section are about 30 less than in the printed version.  It may be that some small difference in wording in the alternative may give you a clue.  I doubt that this is particularly helpful, but I am afraid it is the best I can do on this topic.

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  27. I want to back off to something more basic, and if this also is considered too technical for Skeptical Science than I would feel better about contacting someone like Gavin Schmidt.  What is the formula that relates the HITRAN tabulated cross section I will call STAB to the corresponding mass absorption coefficient I call SMASS? Here is how I do this.

    1. multiply STAB (cm2/molecule) by 10-4 m2/cmto give STAB in m2/molecule.

    2. PV = NkT where k is Boltzmann's constant. And so N/V = P/kT.

    Then multiply equation 1 by P/kT so that (m2/molecule) x (molecules/m3)

    gives SLIN, the linear absorption coefficient in reciprocal meters.

    3. Now one has SLIN = STAB x 10-4 x P/kT ; units m-1

    4. One now needs SMASS = SLIN/mass density of atmosphere

    5. PV = nRT where n is the gas constant and n is the number of moles per cubic meter. I next divide by n/V = P/RT to obtain

    6. STAB x 10-4 x (P/kT)/(P/RT); the Ps and Ts cancel to yield

    7. STAB x 10-4 (R/k) x (1/n) where n is the number of moles per cubic meter.

    8. The mass of gas per mole is 0.029 kg.

    Then n (moles/cubic meter) x 0.029 (kg/ mole) = kg / cubic meter

    9. SMASS = STAB x 10-4 x (R/k) x (1/0.029)  (m2 / kg)

    The most intense line in the CO2 bending mode part of the IR spectrum is close to 

    STAB = 3 x 10-19 cm2/ molecule . Inserted into equation 9 above I get something between 600 and 700 m2 /  kg.  I think this may be  somewhat too small looking at Fig. 4.12 in Pierrehumbert.

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  28. I believe I am correct with the above expression for SMASS, but that somehow the data published in Fig. 4.7 of P-H is as if it were at higher resolution than what I get from the Spectral Calc version of HITRAN. Except for the sharp fundamental around 670 wn, the other features I get agree with P-H pretty well, agreement which yields a check on my expression for SMASS. 

    A few years back, someone on this site told me how to make graphs and publish them cheaply or maybe free with an associated URL. There is some website that does this.  Could someone remind me how this works?

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  29. curiousd @27 and 28, I am fairly sure the formula you are using is incorrect.  Unfortunately I am not sure as to the correct formula.  The HITRAN database gives Sij and γair for each line, where Sij and γair are illustrated by this diagram:

    The values given are for a reference temperature of 296 K, and 1 atmosphere pressure.  S varies based on temperature, and γ based on temperature and pressure.  As a result both Pierrehumbert in Principles of Planetary Climate (PoPC) and HITRAN give formulas for making the appropriate adjustment.  For adjusting γ you use PoPC formula 4.61 and HITRAN formula 6.  For adjusting S you use PoPC formula 4.62 and HITRAN formula 4.  At least, that is as best I understand it.  However, these formulas differ, probably based on assumptions about the shape of absorption pattern (shaded area above), which is not strictly known.  There is a brief discussion of this in PoPC pages 227 and 228.

    The actual absorption coefficient in each spectral line is not determined by S alone, but by S and γ as per formula 4.63 (PoPC) and HITRAN formula 10.

    Even if I have misunderstood this, I am certain your formula is incorrect in not taking account of doppler and pressure broadening, which I understand to be very important.

    At this stage I am again going to recommend you consult somebody with significant experience with these formulas. 

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  30. Thank you Tom,


    Attempting to contact Chris Colose. 


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  31. Hi Tom Curtis,

    I have attempted to contact everyone on your list except Dr. Pierrehumbert and either get no response or find that the listed e mail address does not work. I am not on Facebook nor Twitter!  Do you know of a more recent e mail address for Gavin Schmidt?  I would prefer to check with another expert before contacting Dr. Pierrehumbert.



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  32. curiousd@31, apparently Chris Colose joined NASA GISS just this month, and consequently has a new email address.  For that he deserves congratulations.  For the rest, I am not a correspondent with any of the people listed, and am finding the email addresses by google search.  If I were you, and if the email address you have is current, I would make Dr Pierrehumbert the first point of contact.  My experience in contacting scientists is that so long as you remember that any help they provide you is a courtesy by them, not a right of yours; they tend to bend over backwards to help honest enquirers.  Given that all three of the people I recommended, and SOD, have a history of trying to help explain AGW, I very much doubt that they would be different in this regard; and Dr Pierrehumbert would be acknowledged by the three others as the most expert on this topic, not to mention best informed about what he meant when he wrote his text book.  Here is a more recent email address for him.  

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  33. New member, with a question probably not suitable for this thread and/or already addressed elsewhere, so will make it brief:  I get that the full-spectrum absorption of 12C16O2 is essentially saturated even at pre-industrial CO2 levels, but am curious about minor isotopomers 13C16O2, 12C18O16O, and 12C16O17O (which should have populations about 11 ppt, 4 ppt, 1 ppt respectively vs 984 ppt for 12C16O16O, rounded to nearest ppt).  Won't these minor isotopomers have significant but unsaturated absorption?  Or perhaps their absorption bands ride so close to 12C16O16O bands as to be effectively saturated already?  But then how about 12C18O16O and 12C17O16O (together comprising ca. 5 ppt of CO2), won't they have pure rotational absorption bands not present in 12C16O16O, and wouldn't that absorption have some greenhouse effect?

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    Moderator Response:

    [PS] I really think any discussion of this should happen on this thread. And David, you have opened with a mistaken assumption, so please read the article there.

  34. We should probably start with your initial assumption here: "I get that the full-spectrum absorption of 12C16O2 is essentially saturated even at pre-industrial CO2 levels..."

    Where do you get the idea that IR absorption is saturated for any specific isotopic variation of CO2?

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  35. Posting answer to "where do you get.." on the suggested thread.  Appreciate the response -

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  36. Hello,

    1. In regards to post 32 above I am now certain that my formula for the SMASS is correct for the constant temperature case at surface conditions of temperature and pressure. Now I have another question.

    2. If one looks at a satellite determined plot of absorption versus wave number , then right at the large dip in detected radiation near 667 wn, the peak of the CO2 bending mode absorption, there is always a small sharp upward peak. If you run MODTRAN U. Chicago at, say 20 km you do not see this, and  I believe that peak has to do with narrow absorption due to the small doppler broadening in  the upper atmosphere. I have a feeling that this effect was discussed elsewhere on Sk. Sc. some years ago? Can anyone tell me where that peak comes from?

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  37. curiousd @36:

    1)  Did you in fact consult with an expert source as I suggested, which source agreed with you?  Or is your renewed confidence simply a question of your having convinced yourself?

    2)  The central spike in the CO2 absorption/emission band seen in emission spectrum results from the fact that the average altitude of emission to space at that wavenumber is in the stratosphere.  Because the stratosphere is warmer than the tropopause, that spike consequently shows a higher brightness temperature.

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  38. Thank you Tom Curtis,

    1. No one contacted me (I emailed Dr. Pierrehumbert at the address you gave me and the message went through). I understand he is busy and may receive many inquiries from crackpot people. Chris Colose contacted me to say he too is presently busy and I understand that as well. But I found old work by Crisp, Fels, and Schwarzkopf, J. Geophys. Res. 91, 11, pp. 851 - 866. Their figures 3 and 4 are consistent with the SMASS of the most intense CO2 line at seal level and 296 degrees K, at 667 wn { with HITRAN STAB of  3 E (-19) [cm^2/molecule]x (wave number)^-1} having an SMASS with upper limit 810 m^2/kg (cm^-1) and lower limit of 130 m^2/kg (cm ^-1). I get SMASS of 620 m^2/kg (cm^-1) which is quite consistent with the Figs 3 and 4 of Crisp, et al.

    For the H-C-G approximation, all you need is the value of SMASS at one atmosphere and a standard temperature such as the HITRAN default 296 degrees K, and your answer will give correctly (within the approximation that the fixed temperature assumed in H-C-G introduces only a relatively small error) both the strong and weak limits if you use for your average pressure between ground and your highest altitude point Zmax the average obtained from the massweighted average, namely (Pground  + Pzmax)/2.  

    2. Thank you for the excellent explanation of the central spike in the CO2 emission.

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  39. There is a URL which works to access the article by Crisp, et al for free without access to a research library. That URL is

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    Moderator Response:

    [BW] tried to fix the link as it seems to break the page-format

  40. Hi,

    I've been trying to understand more about climate change, as well as the impacts it will have on the planet. I feel like I reasonably understand, but I do have concern over the future predictions. I know that they are not certain, but I have seen claims that "3-5 billion people will die" or of "imment collapse of civilization". Are these sensationalised, or do they have some truth to them?


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  41. Redfa1 @40, if we burnt nearly all available reserves of fossil fuels, or if climate sensitivity is towards the high end of the estimated range, an increase in Global Mean Surface Temperature (GMST) of 10 to 12 degrees is likely.  With such an increase, for significant parts of the year hotter weather patterns will lift the wet bulb temperature above 35oC.  If that happens for about six hours of the day, all large mammals that cannot find refuge in water or airconditioning will die.  That includes humans.  Smaller mammals (which have more efficient cooling and higher basal temperatures) and cold blooded animals will survive to higher temperatures.  The following map shows in mauve the areas likely to experience those sorts of temperaratures regularly at least durring the local summer months:

    In those circumstances, those areas would have to be evacuated durring summer of nearly all humans, along with their live stock and domestic pets every summer.  In the yellow areas heat fatalaties would be common but not ubiquitous.  When you consider the areas involved (all of India, large portions of China, the Eastern Seaboard of the USA, Spain) the economic impact of this circumstance would be extreme, and the shere number of environmental refugees created could well overwhelm our capacity to deal with.  It is plausible that such a circumstance, therefore, could so overwhelm the economic system as to cause an almost complete breakdown of the system of trade.  That in turn would result in the effective technological levels of our economy plummiting, along with our capacity to provide food for the population.  So, in this scenario our civilization (ie, the technological trade based society that dominates the world) would likely collapse, and with it several billion people would die.

    Let me emphasize this is not the only climate based stressor that could result in that outcome.  There are several others which could, in themselves cause an effective collapse of trade; and all of these will be acting concurrently so that their combined effect is even more likely to do so.  Further, lack of food or stress from an excess of refugees could well cause instigation of large scale, potentially nuclear wars.

    So, in short, those estimates do have some truth in them, but as worse case scenarios in situations in which we do not take effective action against global warming.  Even the inadequate methods agreed to todate would likely prevent such outcomes.  If such measures are significantly wound back, as is likely under President Trump, the more extreme scenarios come back into play.

    Finally, it should be noted that any scenario involving the death of multiple billions will most likely result from a situation where we destroy ourselves (through inadequate responses to crises, or through war) rather than changes in climate itself directly killing us (although that may well result in the deaths of tens, or even hundreds of millions with inadequate mitigation and adaption).

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  42. Redfa:

    Predictions are hard, especially about the future.

    According to this NPR Article, about 634 million people live within 10 meters of sea level.  If you imagine their population would otherwise rise, how many would be "killed" by sea level rise of 10 meters over say 300 years?  About 11 million people are within 2 meters of sea level in Forida (not to mention the rest of the USA) and might lose their cities by 2100.  

    From Florida they can all move to Kansas, but the 17 million in Bangladesh displaced by 1.5 meters of rise have no-where to go.  Perhaps they can also go to Kansas, although I doubt Trump would think that is a good idea.  More likely it will go the Syria route and they will be killed in war.

    For RCP 8.5 in 2013 experts thought sea level rise of 1-2 meters by 2100 could be expected (Real climate post), IPCC projections are less.  Since then expectations of sea level rise have gone up (they always go up with time).  The best farmland in the world is often in river deltas that will be the first to go with sea level rise.  Speculations of new farm land in Alaska are unrealistic.  How will populaitons be fed after the farmland is under the sea? The problems with heat Tom points out are in addition.  

    While your 3-5 billion is probably a worst case (over what time period was that?  Do wars caused by climate change count?) a realistic evaluation of 50 years from now with BAU does not look pleasant.  Since the deaths are additive, over 200 years 3-5 billion is not so high.  

    The high end danger is collapse of civilization.  That is not considered a likely risk but if there is a 1% chance it would mean the human population could drop to less than one billion.  How much risk can you tolerate?  If there was a 1% chance your house would burn down would you take action to lower the risk?  I would.  What if the action reduced pollution and made us all healthier?

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  43. Hello All,

    I used to know how to post figures and graphs. There was some web site that lets you post small images which have a URL,  I think. I may be needing to do this in the section on Modtran Infrared Light in the Atmosphere. Could someone refresh my memory on how to post images in  Skeptical Science posts?


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  44. curiousd:

    Images have to be located on a web-accessible server somewhere, not on your local hard drive. Then switch to the Insert tab and click on the picture of the tree (on the left). Enter the URL for the image (hence the web-accessible restriction) and complete the form. Try to make sure the image isn't too wide (500 pixels).

    More hints are available on the Comments Policy page (link in red just above the Post a Comment box...)

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  45. Good day, all.  I've been following Skeptical Science for a couple of years and consider you the Go-To folks on climate change. 

    I've run into a book that I have not yet seen addressed in this forum: "Inconvenient Facts: The science that Al Gore doesn't want you to know" by Greg Wrightstone.  I would not have paid much attention to it except that it's come up in a blog of an engineering group (ASCE).  If anyone here knows something about it, I would like to hear.

    Many thanks and keep up the good work.

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  46. IowaCorn: I can't find any serious reviews of Wrightstone's book. Judging from his web site, my guess is that nobody has bothered because his claims are all the usual, incorrect ones. For example, the first and third items in his book excerpts section of his site is the old CO2 is plant food one, which you can find rebutted here at SkS by searching for that phrase in the Search field at the top left of the page, or by clicking View All Arguments at the bottom of the Most Used Climate Myths list below the Search field. Note that many posts here have Basic, Intermediate, and Advanced tabs.

    He goes on a bit about warming being good. Please see the rebuttal to the myth It's Not Bad.

    He's also got a graph of central England temperature, which is not especially relevant to the topic of global warming. My guess is that he's showing that together with a CO2 level graph to imply that the curve shapes don't match, therefore CO2 can't cause warming. But he is wrong.

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  47. Tom:  Thank you.  I suspected as much when an Internet search brought up the usual denier web sites.  I'm saddened that folks in my line of work (engineering), folks who supposedly studied science and learned the scientific process, are not using it.

    Thank you again.

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  48. IowaCorn:  I had occasion to see Gregory Wrightstone present on his book at the Lebanon 9/12 Project meeting this past Dec. 21 in Lebanon County PA.  I asked some tough questions he wasn't able to answer adequately, and later purchased a copy of his book through his website (promo code 1776) — mainly so I can use it in my freshman-level "People & the Planet" course at Lebanon Valley College as a kind of "information literacy" assignment — the students' task will be to select one or more of Wrightstone's 60 "inconvenient facts" and hold it up to the scientific light-of-day by investigating the claim (and, I hope, amply demonstrating why it's bogus or misleading).  Wrightstone is a longtime Republican activist in Central PA and a paid consultant for the oil & gas industry, and has only recently turned his attention to climate change issues.  I wrote a scathing letter to the local paper (Lebanon Daily News) on his presentation, characterizing his book as "junk science," and the editor of the book, a local guy in a nearby township, wrote a rebuttal letter calling my letter a "smear".  Anyway the book is only recently published and I hope that by April or so I'll have a bunch of student papers debunking at least some of Wrightstone's fallacious claims.  Hope that helps. 

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    Moderator Response:

    [TD] Perhaps you and your students could collaborate in writing a Skeptical Science post about that? It would be a nice way to cap that project for them, and force them to cope with having to summarize a lot of info for a particular audience.

  49. Thanks, Climate Change is real I believe. Now what can we do about it or what have we done to make it worst. I don't think it matters we need to invent a better Mouse Trap or we want be able to do anything about it. The real truth is if Fossil Fuel has made the Climae change worst than we have to replace it with something Better or we want be able to make any differents. If we have to go back to Horses we would have more Gas poluting the air than now as everyone would have to have a Horse. Plus the problem with Poop building up Mountains of Poop every where.

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  50. Using the abbreviation"FF" is confusing. It could be forest fires or fossil fuel. 

    Fossil fuel is also confusing since hydrocarbons are now considered to be naturally produced by chemical reactions under high pressures and temperatures inside the earth and not by decay of plants and animals. Hydrocarbons would then be renewable.

    Except for transmutation and arrivals from space, we are a closed system. Many processes interact, emerge, and disappear over time. We are intellectually incompetent to imagine what might happen or actually did happen. We would be advised to not do anything lest we make everything worse which is the only history we actually know.

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