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The empirical evidence that humans are causing global warming

Posted on 30 August 2010 by James Wight

When presented with the overwhelming evidence that the planet is warming, many people react by asking "but how can we be sure that we’re causing the warming?" It turns out that the observed global warming has a distinct human fingerprint on it.

In climatology, as in any other science, establishing causation is more complicated than merely establishing an effect. However, there are a number of lines of evidence that have helped to convince climate scientists that the current global warming can be attributed to human greenhouse gas emissions (in particular CO2). Here are just some of them:

10 Indicators of a Human Fingerprint on Climate Change

The first four pieces of evidence show that humans are raising CO2 levels:

  1. Humans are currently emitting around 30 billion tonnes of CO2 into the atmosphere.
  2. Oxygen levels are falling as if carbon is being burned to create carbon dioxide.
  3. Fossil carbon is building up in the atmosphere. (We know this because the two types of carbon have different chemical properties.)
  4. Corals show that fossil carbon has recently risen sharply.

Another two observations show that CO2 is trapping more heat:

  1. Satellites measure less heat escaping to space at the precise wavelengths which CO2 absorbs.
  2. Surface measurements find this heat is returning to Earth to warm the surface.

The last four indicators show that the observed pattern of warming is consistent with what is predicted to occur during greenhouse warming:

  1. An increased greenhouse effect would make nights warm faster than days, and this is what has been observed.
  2. If the warming is due to solar activity, then the upper atmosphere (the stratosphere) should warm along with the rest of the atmosphere. But if the warming is due to the greenhouse effect, the stratosphere should cool because of the heat being trapped in the lower atmosphere (the troposphere). Satellite measurements show that the stratosphere is cooling.
  3. This combination of a warming troposphere and cooling stratosphere should cause the tropopause, which separates them, to rise. This has also been observed.
  4. It was predicted that the ionosphere would shrink, and it is indeed shrinking.

(References for all of these findings can be found here.)

Often one hears claims that the attribution of climate change is based on modeling, and that nobody can really know its causes. But here we have a series of empirical observations, all of which point to the conclusion that humans are causing the planet to warm.

This post is the Basic version (written by James Wight) of the skeptic argument "It's not us". We're currently writing plain English versions of all the skeptic rebuttals. If you're interested in helping with this effort, please contact me.  

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Comments 1 to 43:

  1. Thanks James, this was really helpful. I am trying to follow the peer reviewed literature on these issues which sometimes is difficult because not all these papers are publicly available without cost - althoug I have some kind of access to a library service...

    What I am missing is an open discussion on the effects which Svensmark discovered (Starry influence on cloud creation due to cosmic ray control thus increasing or decreasing the albedo). I recently read his book (published in 2007 - together with Calder) and it looks as if most of his arguments have strong weight ... So a combination of greenhouse effect which nobody negates and the cosmic ray effects might be a way to consider the causes of climate change ...
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  2. kampmannpeine,

    You might be interested in reading this post on cosmic rays. Current evidence strongly suggests that cosmic rays are unlikely to be responsible for warming in the past 30 years.
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  3. I think this needs clarification

    "7. An increased greenhouse effect would make nights warm faster than days, and this is what has been observed."

    I'm not sure under what circumstances "nights warm faster than days". Nights tend to cool down and days tend to warm up.
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  4. I'm not sure under what circumstances "nights warm faster than days". Nights tend to cool down and days tend to warm up.

    Yes, but nights in the 2000s are warmer than nights in the 1990s, which were warmer than nights in the 1980s, which in turn were warmer than nights in the 1970s. That is nighttime warming.

    Predictions suggest that this process should happen faster than the similar warming of daytime temperatures, and observations confirm this.
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  5. Perhaps it would be better to say that increased CO2 hinders night-time cooling.

    Also: 4.Corals show that fossil carbon has recently risen sharply. Perhaps better to say, 'Corals show greater amounts/proportions of carbon/ carbonates/
    calcium carbonates/ thought to/likely to originate in fossil fuel.' At the risk of pedantry, we don't actually know the specific origin of any individual carbon atom no matter what the isotope in any given coral.

    A brief statement explaining that corals are animals which produce an outer skeleton made out of calcium carbonate would prevent excessive dumbing down.

    Also, the presence of increased carbonates of fossil origin seems unreferenced in the original post (though this might be an oversight on my part). Perhaps this
    leads onto the question of oceanic sequestration of carbon though maybe this could be dealt with in another post.
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  6. Jaydee, greenhouse gases slow the rate at which heat escapes the atmosphere. As you say, nights tend to cool down... because heat is escaping and no more is coming in from sunlight to replace it. However, as the concentration of greenhouse gases in the atmosphere increases the rate at which heat escapes decreases... and nights cool down more slowly... which causes the average night time temperature to be higher... which is why "nights warm faster than days" under greenhouse warming.
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  7. Re; Jaydee #3.
    Recently the 'average' daily temperatures in Houston have been so high that we will see the hottest August (for that matter the hottest month) ever recorded. This is due significantly to the extremely hotter nights. Yes the nights cool but they cool less and therefore the averages are higher. There, the nights are staying warmer, thus warming faster than the days. Our daily high temperatures are high but not much above the averages. Our nights are much higher than average. Hope this makes sense somewhat.
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  8. For all this "empirical -circumstantial evidence" there is still no experimental data and test that prove that the "greenhouse gas effect " exists. Much of the "empirical evidence " has been shown to be from other causes ,no relationship to CO2 period. The fantasy work of John Cook and the AGW fanatics.
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    Response: The direct observational evidence of a CO2 greenhouse effect is outlined here, giving several independent lines of evidence. The direct observational evidence of an increasing greenhouse effect due to increasing CO2 levels is given above in points 5 and 6 but also fleshed out in more detail here.
  9. factfinder, the greenhouse gas effect was first proposed by Joseph Fourier in 1824, proven to exist by John Tyndall in 1858, and quantified by Svante Arrhenius in 1896.

    Anyone who tells you that it doesn't exist is simply ignorant. It has been unquestioned science for well over a century.
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  10. Another two observations show that CO2 is trapping more heat:

    1. Satellites measure less heat escaping to space at the precise wavelengths which CO2 absorbs.
    2. Surface measurements find this heat is returning to Earth to warm the surface.

    A little cherry picking here. Water vapor is the biggest blocker of radiation to space. There is a notch in that block around the temperatures we need for life. CO2 is a very small block at the bottom of that notch. As temperatures rise the emitted IR wavelength becomes shorter and starts to miss the CO2 block. If temperatures rise enough the effect of CO2 becomes minimal.

    The whole focus on CO2 while disregarding H2O is cherry picking. While temperature is rising at one rate according to the measurements presented here, the global dew point is rising faster.
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  11. TOP - You might want to look at the discussion on Water vapor is the most powerful greenhouse gas. Water vapor is more powerful as a greenhouse gas, but changes in water vapor have a lifespan in days or weeks, while CO2 has a lifespan on the order of centuries. Hence the changes in water vapor are feedbacks/reactions to the temperature changes from CO2, the current forcing driver.

    Secondly, the CO2 and H2O spectra (as seen here), while separable, are quite interlaced. If you remove some of the CO2 spectra by heating then you're removing H2O effects as well. And note that the thermal spectra of the Earth's surface would have to heat up a LOT to no longer involve CO2 and H2O - not quite to plasma levels, but well beyond anything predicted by any greenhouse effect.

    Paying attention to the reduced emissivity of the atmosphere due to CO2 is by no means cherry picking. It's a core detail of how our climate is changing.
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  12. TOP, you apparently agree that water vapor is a positive feedback, increasing w/warming and multiplying the primary effect of additional C02 in the atmosphere, as predicted?

    Dai, HadCRUH, Barry & Kent specific humidity 1970-.
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  13. KR at 03:12 AM, the residence time of water vapour is a red herring, what is relevant of course is the volume of water vapour in the atmosphere at any one time and how this changes over time.

    The relating of CO2 to night time temperatures also applies to clouds which have the same effects both in the short term and over the longer term.
    It is no coincidence that when looking at periods of long term drought as against periods where above average rains occur in the drought flooding rain cycle, frosts tend to be more frequent, and more severe during the drought cycle because of the generally lower cloud cover.

    With regards to the absorption spectra, one needs to decide whether the H2O spectra is determined by the properties of H2O that enables it to change state at fixed points or not, and whether it is coincidence or not that the conditions that allow life on earth as we know it just happens to be within that H2O band of high emissivity.
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  14. TOP #10, a hundred years ago actual skeptics argued that the IR absorption spectrum of H20 completely overlapped that of CO2 and thus CO2 caused no additional warming. However, this was proven incorrect both in that better instrumentation has allowed us to identify bands where the two do not overlap (as you note) but also because CO2 is found higher in the atmosphere than H20 and thus would continue to have a warming effect even if its absorption spectra WERE completely overlapped by H20.

    You are thus recycling an actual reasonable skeptic argument... from 1908. Unfortunately, as KR points out, you add an additional layer of error in the claim that IR emissions will shift to exclude the 'CO2 only' absorption bands... we'd all be dead LONG before that could happen, but as noted above the CO2 higher in the atmosphere would STILL induce warming even at the wavelengths where H20 overlaps.
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  15. johnd - Residence time for H2O is anything but a red herring. The short residence time makes H2O extremely responsive to temperature changes induced by other forcings - H2O level is a feedback, not a forcing.

    As to clouds - I'd have to say that CBDunkerson's comment is right on the money. We've had satellite observations of cloud cover and water vapor levels for decades, and the forcing from cloud cover is so small that there's no agreement on whether it's positive or negative. It certainly does not match or override the CO2 forcing in magnitude. At this point the science indicates that cloud feedbacks are essentially irrelevant.

    John Cook/moderators - I've been seeing the skeptic argument that 'the clouds are a huge negative feedback' for some time; from the Lindzen 'iris' effect to JoNova's web site, etc. This is essentially a "It won't happen" argument regarding AGW. Should we have a topic to discuss that here on SkepticalScience?
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  16. johnd, as regards to the H2O spectra - What we need to do is pay attention to what the various GHG spectra are, not philosophize on the anthropogenic principle. The various spectra are what they are; discussing whether or not we would exist in alternate universes is a completely separate (although interesting, over sufficient high quality beer) discussion.
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  17. KR there is a place here suitable for cloud discussions but it does seem as though a specific "Clouds will save us" topic would be a good thing. Comes up time and again.

    The albedo effect.

    Related to this I'm interested in current efforts to reprocess old Nimbus tapes to extend ice trends farther back. Follow that link and you can see the stunning results available via reprocessing. The same methods ought to work w/longitudinal cloud cover as well, something that's not well quantified now.
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  18. breaking new

    InterAcademy Council - Review of the Processes and Procedures of the IPCC

    "authors reported high confidence in some statements for which there is little evidence. Furthermore, by making vague statements that were difficult to refute, authors were able to attach “high confidence” to the statements. The Working Group II Summary for Policy Makers contains many such statements that are not supported sufficiently in the literature, not put into perspective, or not expressed clearly."
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  19. Wow, quote-miners going to work on the IPCC review w/pick and shovel. Amazingly brazen omission in pursuit of impressionism, mscavazz. How fortunate that the IPCC does not follow such degenerate techniques.

    Those looking for context might start w/the complete executive summary: Climate Change Assessments Review of the Processes and Procedures of the IPCC

    Meanwhile, notice that mscavazz' plucked cherry was from WGII. Notice from the topic heading here, this thread is about scientific evidence of climate change itself, not the subject of WGII.

    Find an appropriate thread mscavazz. Try plugging "IPCC" into the search box at upper left, pick an appropriate thread, go there w/further comments on the InterAcademy Review.
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  20. doug_bostrom, what brazen omission are you talking about ?
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  21. I find the "less heat escaping to space" label in the figure to be rather confusing and it could potentially be used to discredit the effort. I looked at it and cringed a bit until I saw that this label refers to the spectral signature of the TOA emission. At equilibrium, the amount of heat escaping to space has to be the same has what is coming in. If you are talking about the current imbalance due to lagging ocean warming, then I think you have to tell a different story. Maybe the label should be "emission fingerprint" but that might be too complicated still.
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  22. factfinder:
    "For all this "empirical -circumstantial evidence" there is still no experimental data and test that prove that the "greenhouse gas effect " exists."

    Well Roy Spencer is happy with it:

    So why aren't you?

    It's based on fundamental science used as a basis of thermal imaging, in chemistry and other areas of engineering and science.
    eg. infrared spectrography, quantum physics.

    Some teenagers do an experiment:

    However such experiments don't demonstrate the lapse rate.
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  23. Unrecovered - Yes, "At equilibrium, the amount of heat escaping to space has to be the same has what is coming in". However, when increasing GHG's change the emissivity spectra, reducing the amount of radiation emitted at a particular temperature, the equilibrium temperature for equal energy is higher - things get hotter.

    Perhaps the statement should be "Less energy escaping to space at any given temperature [due to reduced emissivity]"? A bit wordy, but I think correct?
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  24. The amount of energy escaping is the same. Not sure if emissivity helps much here.
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  25. Unrecovered - Actually, it's not the same amount of energy escaping. Reducing the emission spectra at a particular temperature directly reduces the amount of energy radiated at that temperature.

    The difference is the radiative forcing induced by changing amounts of greenhouse gases, accumulating energy here on Earth until the temperature rises, the emission spectra scales up accordingly, and the summed energy escaping matches the energy coming in - equilibrium.

    The various feedbacks and energy accumulation take a bit of time - even if we were to stop changing CO2 levels right now warming would still continue for decades, until that sum energy emitted matches the amount coming in.
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  26. KR at 05:06 AM, the change of state that allows water vapour to enter the atmosphere is due entirely to conditions that occur at the immediate surface of the earth where the reservoir of H2O resides in either it's liquid or solid state.
    The process extracts heat from the surface which is then carried into the atmosphere being liberated through various levels until finally all is exhausted at the highest levels at which clouds form.
    The rate at which water vapour enters the atmosphere is therefore dependent primarily on the amount of solar radiation and water that is available at the immediate earths surface, and the rate at which the change of state takes place to enable the hydrological cycle to complete is dependent on being able to liberate heat into an environment where there is a ongoing process of nett heat loss out of the system.
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  27. KR at 05:16 AM, there is no philosophizing necessary, the H2O spectra moves from high absorption to high emissivity then to high absorption within a range that provides a window of opportunity for conditions conducive to the existence of life, that range being due to the unique properties of H2O.
    CO2 might be able to alter to some degree the factors that drive the closing of the emission window on one side, but that doesn't change the fact the properties of H2O alone would have closed that same window, all be it after a greater loss of heat from the system than what CO2 would close that same window of emissivity.
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  28. KR. Yes certainly, when you referring to the transient state. I guess my point is that, I don't think we have direct measured evidence of this imbalance. The current estimated imbalance (models) of 0.9 Wm-2 at the TOA is beyond our current capabilities to measure from satellite. What we have, and I think what you are referring to, is evidence is that the emission spectrum at the TOA has changed in the way we would expect it to from increases in various green house gases. That's useful information but doesn't quite amount to evidence that: "less heat escapes to space". Of course I haven't made a better suggestion yet.
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  29. Suggested correction to point (3):

    (We know this because the two types of carbon have different chemical properties.)

    Err, no. They have the same chemical properties. They have different physical properties, specifically different 13C : 12C ratios.
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  30. Johnd - The rate at which water vapour enters the atmosphere is surely dependent on the surface temperature - dependent on the radiation from both the sun AND from the atmosphere (ie the GHG effect).
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  31. factfinder and mscavazz, I suggest you review the Comments Policy as your post are inflammatory in one case and off-topic in the other.
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  32. re: the label 'less heat escaping to space'.

    Would it be more accurate to say that the 'heat is delayed from escaping to space'?

    As was pointed out by others, even if you add more GHGs eventually an equilibrium is reached and just as much heat as before escapes!

    The only alternative is that the missing energy is emitted at a different frequency which balances the in/out equation, or is that what is implied?

    If you consider extra insulation of a home, you have to reduce the energy input to maintain the same temperature as you had before, because the insulation causes a delay.
    If you turn off the heating then eventually the energy will escape. The time between turning off the heating and the house temperature reaching the same temperature as outside is the delay. The more insulation the longer that delay or 'gradient'.

    Sorry about the analogy!
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  33. Unrecovered - Exactly, I was talking about the transient state. However, given the thermal inertia of ocean warming, that transient can last for a long time...

    The 0.9 W/m^2 is on the edge of measurement tech right now, but the difference in emission spectra is measurable and clear. And, very importantly, indicates that conditions on Earth have to change in order to radiate the same amount of energy as before that spectral change (reduction), primarily by warming up.
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  34. Czy korale, gąbki , mówią prawdę o byłych stężenie CO2

    Opublikowanym niedawno artykule : 13C efekt Suess w scleractinian korale lustro zmian w inwentaryzacji antropogenicznych emisji CO2 z powierzchni oceanów , et Swart al. 2010

    W zawiera na poniższym rysunku. . Oczywiście, dane te są identyczne z rdzeni lodowych - pokazują one, praktycznie stał się stały wzrost CO2 w XX wieku , zwłaszcza .
    Autorzy piszą: " Z tych zapisów, 64% wykazuje istotne statystycznie (p < 0,05) spadek D13c do dnia dzisiejszego (23 z 37). Spadek ten wynika z dodatkiem CO2 pochodzenia antropogeniczną ( 13C efekt Suess ) do atmosfery. [...]"

    Pozycji, jednak i takie zdania : " Niewielki wzrost stawki fotosyntezy, związane z wzrostem natężenia światła , wydaje się zwiększenie D13c szkieletu , natomiast zmniejsza się w świetle spowodowałaby spadek wartości D13c w szkielecie [ Weber, 1970] . Sugerowano, że różnice w D13c szkielet może być również związane ze zmianami tempa wzrostu , nasłonecznienie i inne czynniki wpływające na symbiotyczny związek między korali i ich zooxanthellae . Oprócz rocznej różnicy w D13c , zauważył kilku pracowników, którzy na długoterminowych tendencji w kierunku niższych wartości D13c w szkielety koralowców i przypisać te spadki do 13C Suess efekt [ Druffel i Benavides , 1986 ]. Pierwszy papier do tej obserwacji w szkieletów koralowców [ Nozaki et al. , 1978 ] stwierdził, zbliżenie 0,4 ‰ zmniejszenie D13c 1900 / 50 , o takiej samej wysokości, zostały zachowane w pierścieniach drzew [ Damon in. , 1978 ]. Mimo, że wnioski z Nozaki et al. [1978] , zostały podważone [ Weil et al. , 1981 ], długoterminowe zmniejszenie D13c korala szkielety są dobrze udokumentowane ... [ dostarcza informacji na temat źródeł ]

    Jeśli jednak tylko Weil i jego zespół patrz niezgodności : ziemi - ocean ?

    Korale : Konsekwencje korali wzrostu stawek, Juillet , Leclerc i Reynaud , 2009 :
    "To eksperyment , który pozwolił na wyodrębnienie efektów świetlnych i temperatury na rafy , wskazały na znaczące wpływy na światło zarówno szkieletowych _18O i _13C . wysoki rozrzut _18O między kolonii obserwowano w jednym miejscu, może wynikać z różnic w reakcji fotosyntezy glonów symbiotycznych zespołów . Odpowiedzi _13C może być również związane z różnych dystrybucji glonów w różnych częściach układu kostnego . "," Istnieje wiele skutków tych danych dla paleoklimatycznych rekonstrukcje z udziałem korali .

    "Mimo, że od wartości δ13C morskich węglanów dostarczyć cennych informacji na temat ostatnich zmian w obiegu węgla , w wyniku odpowiedzi na lądowych i biomasy nie może bezpośrednio wynika z tych wartości [ fizjologia , degradacji mikrobiologicznej i ] diagenezy skał. W celu uzyskania pełniejszego obrazu tych ostatnich zmian w obiegu węgla , naziemnych pochodzenia atmosferycznego wartości δ13CCO2 następnie potrzebne. " Patrz tutaj .

    Atmosferyczne δ 13 CO 2 i jego stosunku do p CO 2 i głęboko ocean δ 13 C w późnym plejstocenie, Köhler et al. , 2010 . " te , które występują w terminach krótszych niż tysiąclecia nie są wykrywalne w δ 13 CO 2 z powodu równowagi wymiany gazowej z powierzchni oceanu ... "
    chciałbym mieć (znowu) dodaje się do niezwykle aktywny CO2 - woda ...

    Poza tym, Swart et al. 2010 roku. nie obejmuje okresów wcześniejszych, i nie może być inaczej:

    klimatu i wody Antarktyki Średnio sprzęgło w późnym holocenie , Euler i Ninnemann 2010 roku. : " Poniżej przedstawiamy pierwszy subdecadally próbą rekonstrukcji zmienność w południowo-wschodniej upper-intermediate Pacyfiku od ca. AD 0-1300 pomocą otwornic [bez korali i gąbek ] izotopów tlenu i węgla rekordy . Nasze wyniki wykazały dużą różnorodność powierzchni oceanu zarówno właściwości fizycznych i dekadowej stulecie skale czasu na południowym wschodzie Pacyfiku aż 3 ° C lub więcej w ciągu zaledwie o 50 yr .
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  35. “terrestrial-derived atmospheric δ13CCO2 values are then needed.”

    F. Engelbeen criticizing the Beck papers publishes data on "sea" delta 13C and comments like this:
    “That is a very fast one: from the base line in 1936 at around 330 ppmv (historical) to 430 ppmv in 1943.” on the latest Beck figure (2010) we have, however, (after smoothing filter), only circa 40 ppmv ... Let us dispense with, however, this "minor" inaccuracy.

    “Again, there is no sign of anything happening around 1943, even if the d13C records have a high resolution of 2-4 years around that period and the accuracy is fine enough to detect an extra addition/uptake of 1 GtC (0.5 ppmv) from/by vegetation or 4 GtC (2 ppmv) from the (deep) oceans.

    Thus all we can say is that other (proxy) methods, even with high resolution, don't show any abnormal variation around 1943.”

    Really, nothing unusual happens, the sharp in the 40's?

    Reconstruction of the history of anthropogenic CO 2 concentrations in the ocean. Khatiwala et al. 2009.:
    “Our results also suggest that the terrestrial biosphere was a source of CO 2 until the 1940s, subsequently turning into a sink.”

    ... and let's look at this graph:
    by “Global and European temperature (CSI 012) - Assessment published Jun 2010”
    Shocking, is not it (!?) Change (decrease) in temperature from 1940 to 1950 in Europe - comparable (increase) from 1950 to 2009! 10 years = 60 years!

    Rapid change in 1940-1950 can be found throughout NH - naturanych main source of CO2 emissions.

    ... And land d.13 C?

    Here, of course, I will quote my favorite graph: A bi-proxy reconstruction of Fontainebleau (France) growing season temperature from AD 1596 to 2000, Etien et al. 2008.: Fig. 2 - there is a “severe” proxy delta - δ13C - The data d. 13C for the period under discussion (194? -5?) are slightly lower than for the late twentieth century, their decline as rapidly as in Beck and temperatures in Europe ...

    Even the stomata do not want to show as beads and so wants to F. Engelbeen.
    In this figure (Kouwenberg, 2005.) but you can see a clear "hump" in the middle of the twentieth century.

    Also loving CO2 coccolith Phytoplankton Calcification in a High-CO2 World, Iglesias-Rodriguez et. al, 2008., indicate its mass, peak - fall - similar to that in Beck, but quite different in the case of d. 13C corals and sponges.
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  36. naturanych = natural - sorry
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  37. Arkadiusz - Your postings are often long, with multiple references, and clearly show that you are doing some research and digging into sources.

    However, here, as in many previous postings, I find myself unable to determine what your point is.

    It's something about mid-century records of carbon and temperature, but are you asserting that there are (a) problems with one or more of the records, (b) issues with isotope methods, (c) anomalous temperature swings not congruent with current theories, or (d) something else entirely? I cannot tell!

    It would be very helpful if you could summarize or otherwise clearly state what your concern is in these postings.
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  38. I recently attended a seminar where the presenter stated that overwhelming proof exists for industrial humans contributing to the increase of atmospheric CO2. One proof was based upon atmospheric ratios of C12, C13 and C14. Recall that all living systems incorporate C14 into their tissues, and that C14 has a half-life of 5,730 years, and that fossil fuels are so old that they contain virtually zero C14. This means that burning massive amounts of fossil fuels will result in much lower C14 in the atmosphere than the amount placed there by current/recent living processes (which also includes other stuff like burning wood, slash and burn farming practices, etc.)

    Apparently economic records exist for all fossil fuels sold since 1960 (on a country-by-country basis). These records can be used to compare fossil burning against the carbon isotope ratio for the same time period. Scientists can see the resultant dilution of C14.
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  39. @neilrieck

    - high solar activity also reduces the number of 14C atoms and because of the nuclear explosions, we do not have data for recent decades. Until then, the activity of the Sun definitely growing. Effect Suess can be determined only by the delta 13C.
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  40. What I am missing in this explanation is how much it is warming, and how good the different models are at predicting the measured warming over time. The way to disprove a model (which is a theory) is to show that it cannot predict observations, so one has to show that the models actually make accurate predictions.
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  41. svdwal, have you read both basic and intermediate versions of this?
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  42. Re 1: There is little doubt about the contribution of anthropogenic CO2 emissions. But our understanding of the natural CO2 cycles is insufficient to estimate the size of its contribution. We don’t know, for instance, the size of CO2 outgassing from the deep sea into the atmosphere and the return flux (order of magnitude: 100 – 150 GtC/y). The statement as such bears no relevance to an expected enhanced greenhouse effect by CO2. It is only suggestive, circumstantial evidence.

    Re2: Agreed. It would be surprising if this CO2 was not present. But see comment under 1 and its conclusion: The statement as such bears no relevance to an expected enhanced greenhouse effect by CO2. It is only suggestive, circumstantial evidence.

    Re 3: Of course, fossil fuel burning will use oxygen from the atmosphere. But again: The statement as such bears no relevance to an expected enhanced greenhouse effect by CO2. It is only suggestive, circumstantial evidence.

    Re 4: This is to be expected as under 2. But again: The statement as such bears no relevance to an expected enhanced greenhouse effect by CO2. It is only suggestive, circumstantial evidence.

    Intermediate general conclusion: Wight’s reasoning is so far exclusively based on circumstantial evidence. Not a single proof is presented that CO2 can affect the natural greenhouse effect. But we have to take a closer look at his additional arguments.

    Re 5: This observation is incorrect. Satellite measurements have shown that more total radiation energy has been transported into space.

    Re 6: It is, of course, to be expected that with increasing CO2 in the atmosphere, more radiation from it contributes to downward radiation at its specific wavelength. But that is no proof that it contributes to additional warming because the authors who claim such an effect, are insufficiently aware of physical forces other than radiation, which remove heat from the atmosphere (e.g., evaporation and forced convection).

    Re 8. This has nothing to do with the greenhouse effect in the troposphere. CO2 is a gas that goes higher up in the atmosphere than water vapour. Consequently, it facilitates the radiation out into space.

    Re 9: The altitude of the tropopause differs depending on latitude. It is low at the poles and high at the equator. It is determined by the vertical convection. When it rises, it is a sign of warming at the surface – not that this warming is caused by CO2.

    Re 10: The underlying reference states: ‘The increase in global surface air temperature during the 20th century has been attributed mainly to the increasing atmospheric concentrations of greenhouse gases.’ It states that it is ‘attributed’ to greenhouse gasses of which water is the most important one – not that CO2 is the cause.

    The AGW hypothesis is still exclusively based on the fact that CO2 is absorbing and emitting infrared radiation in a narrow band and the expectation that this will enhance the greenhouse effect.

    Point 5 is not correct. The outgoing radiation increased by 2.6 per cent or 6 W/m^2.

    Points 6 to 10 can be explained today without attributing an enhanced greenhouse effect to CO2.

    Written by Arthur Rörsch
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  43. T2000 - regarding your comments on these 10 points:

    1) We know the amount of CO2 we're generating. The enhanced amount of CO2 in the atmosphere is found through direct measurements, and indicates that ~half the human generated CO2 amount remains in the atmosphere. That limits ocean exchanges.

    2) Supporting point for 1, see comments for 1.

    3) Known, measured increases in CO2, from 280 around 1850 to 380 now.

    3) Supporting evidence related to 1, 2, etc., your comment on 'circumstantial' is incorrect.

    5) The key is "at the precise wavelengths which CO2 absorbs", which your comment doesn't include. Decreased energy at CO2 wavelengths, along with increased energy elsewhere (from higher surface temperatures), is exactly what is expected with greenhouse heating.

    6) Known and measured downward radiation, exactly as expected due to the physics involved, and with measured temperature increases from multiple data sets and independent instruments.

    8) Actually, CO2 traps energy, meaning that stratospheric cooling is just what is expected - and measured. The mean CO2 radiation altitude is only 6km.

    9) Warming troposphere means expanding troposphere, increasing tropopause height. It's a sign of warming no matter what the cause, but when tied to stratospheric cooling it's a fingerprint of greenhouse gas heating.

    10) Your relevance in this comment? Ionospheric shrinkage is congruent with CO2 heating.

    All of these observed signs accompanying global warming are consistent with increased CO2 leading to an enhanced greenhouse effect.

    If you feel that some other cause is responsible for the warming trend over the last 150 years, in particular the last 35, then by all means I would love to hear your suggestion. However, you would need to supply both a different cause matching these fingerprints AND some reason why the CO2 enhanced greenhouse effect due to measured CO2 levels is NOT happening.

    So - two new things to believe in (one of which, CO2 not having an effect, is contrary to physics), versus one known change having predicted effects? I think I'll stay with the CO2 hypothesis...
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