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How do we know more CO2 is causing warming?

What the science says...

Select a level... Basic Intermediate Advanced

An enhanced greenhouse effect from CO2 has been confirmed by multiple lines of empirical evidence.

Climate Myth...

Increasing CO2 has little to no effect

"While major green house gas H2O substantially warms the Earth, minor green house gases such as CO2 have little effect.... The 6-fold increase in hydrocarbon use since 1940 has had no noticeable effect on atmospheric temperature ... " (Environmental Effects of Increased Atmospheric Carbon Dioxide)

Predicting the Future

Good scientific theories are said to have ‘predictive power’. In other words, armed only with a theory, we should be able to make predictions about a subject. If the theory’s any good, the predictions will come true.

Here’s an example: when the Table of Elements was proposed, many elements were yet to be discovered. Using the theory behind the Periodic Table, the Russian chemist Dmitri Mendeleev was able to predict the properties of germanium, gallium and scandium, despite the fact they hadn’t been discovered.

The effect of adding man-made CO2 is predicted in the theory of greenhouse gases. This theory was first proposed by Swedish scientist Svante Arrhenius in 1896, based on earlier work by Fourier and Tyndall. Many scientist have refined the theory in the last century. Nearly all have reached the same conclusion: if we increase the amount of greenhouse gases in the atmosphere, the Earth will warm up.

What they don’t agree on is by how much. This issue is called ‘climate sensitivity’, the amount the temperatures will increase if CO2 is doubled from pre-industrial levels. Climate models have predicted the least temperature rise would be on average 1.65°C (2.97°F) , but upper estimates vary a lot, averaging 5.2°C (9.36°F). Current best estimates are for a rise of around 3°C (5.4°F), with a likely maximum of 4.5°C (8.1°F).

What Goes Down…

The greenhouse effect works like this: Energy arrives from the sun in the form of visible light and ultraviolet radiation.  The Earth then emits some of this energy as infrared radiation. Greenhouse gases in the atmosphere 'capture' some of this heat, then re-emit it in all directions - including back to the Earth's surface.

Through this process, CO2 and other greenhouse gases keep the Earth’s surface 33°Celsius (59.4°F) warmer than it would be without them. We have added 42% more CO2, and temperatures have gone up. There should be some evidence that links CO2 to the temperature rise.

So far, the average global temperature has gone up by about 0.8 degrees C (1.4°F):

"According to an ongoing temperature analysis conducted by scientists at NASA’s Goddard Institute for Space Studies (GISS)…the average global temperature on Earth has increased by about 0.8°Celsius (1.4°Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade."

The temperatures are going up, just like the theory predicted. But where’s the connection with CO2, or other greenhouse gases like methane, ozone or nitrous oxide?

The connection can be found in the spectrum of greenhouse radiation. Using high-resolution FTIR spectroscopy, we can measure the exact wavelengths of long-wave (infrared) radiation reaching the ground.


Figure 1: Spectrum of the greenhouse radiation measured at the surface. Greenhouse effect from water vapour is filtered out, showing the contributions of other greenhouse gases (Evans 2006).

Sure enough, we can see that CO2 is adding considerable warming, along with ozone (O3) and methane (CH4). This is called surface radiative forcing, and the measurements are part of the empirical evidence that CO2 is causing the warming.

...Must Go Up

How long has CO2 been contributing to increased warming? According to NASA, “Two-thirds of the warming has occurred since 1975”. Is there a reliable way to identify CO2’s influence on temperatures over that period?

There is: we can measure the wavelengths of long-wave radiation leaving the Earth (upward radiation). Satellites have recorded the Earth's outbound radiation. We can examine the spectrum of upward long-wave radiation in 1970 and 1997 to see if there are changes.


Figure 2: Change in spectrum from 1970 to 1996 due to trace gases. 'Brightness temperature' indicates equivalent blackbody temperature (Harries 2001).

This time, we see that during the period when temperatures increased the most, emissions of upward radiation have decreased through radiative trapping at exactly the same wavenumbers as they increased for downward radiation. The same greenhouse gases are identified: CO2, methane, ozone etc.

The Empirical Evidence

As temperatures started to rise, scientists became more and more interested in the cause. Many theories were proposed. All save one have fallen by the wayside, discarded for lack of evidence. One theory alone has stood the test of time, strengthened by experiments. 

We know CO2 absorbs and re-emits longwave radiation (Tyndall). The theory of greenhouse gases predicts that if we increase the proportion of greenhouse gases, more warming will occur (Arrhenius).

Scientists have measured the influence of CO2 on both incoming solar energy and outgoing long-wave radiation. Less longwave radiation is escaping to space at the specific wavelengths of greenhouse gases. Increased longwave radiation is measured at the surface of the Earth at the same wavelengths.

These data provide empirical evidence for the predicted effect of CO2.

Basic rebuttal written by GPWayne

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 1 August 2015 by MichaelK. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

A good summation of the physics of radiative forcing can be found in V. Ramanathan's Trace-Gas Greenhouse Effect and Global Warming.


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Comments 351 to 400 out of 436:

  1. jessicars - when you do the experiment outside and you want to calculate the effect of your plastic bag of CO2, then you need to consider that column of gas under consideration is 55km tall and you have changed the CO2 content of the bottom few centimeters. Yes, that CO2 will trap IR radiation and re-radiate to the surface. Because that surface is receiving more radiation, it will heat up and the surface will heat the bag.  You note that it is surface under that bag that is heated by back radiation, not the gas in bag. (hence thermometer under bag). The question is how much, and in your setup, yes, it is insignificant. To replicate the atmospheric GHE, you need  a column of gas 55km or so high.

    The experiments we pointed you to isolate other effects and applify the CO2 effect to make it measurable with thermometer. Radiation is radiation whether it is coming from heat lamp or a warm surface.

    If you are looking for empirical evidence of GHE, then that paper on direct measurement is one, but see also our reference especially the CO2 traps heat section with papers from Harries, Evans, Griggs , Philpona, Chen who all compared the calculated radiation at either top of atmosphere or surface of earth and compared it to direct measurements.

  2. Hi Eclectic,

    > (A) Firstly, there is the empirical evidence from experimentation during the past 150+ years, showing CO2 absorption of (some) Infra-Red radiation. (B) During the past century there is the empirical evidence of the CO2-related global Green House Effect [GHE] : evidence provided by both expensive and (relatively) cheap experimentations & observations. (Admittedly, "greenhouse" is a poorly-named term — but historically we are now stuck with it, and it is now a widely-understood useful label.)

    Your experiment is inappropriate because of its lack of sensitivity and specificity (too many confounding variables in your experimental set-up).

    Not only do you need to address the question of IR absorption by CO2 gas, but secondly you need to address the mechanism of the planetary GHE (a mechanism which is completely unconducive to backyard experimentation, I think).

    What variables? You can't simply make a statement then not substantiate it.

    I am aware of "evidence" of the planet warming or ocean levels rising or ice caps melting, but the climate has always changed naturally. Why assume it is being changed now by human-caused CO2? If you don't know the cause, measuring the effect doesn't prove anything. You really can't realy on any empirical measurements to prove AGW, you are left with the theory alone i.e. what happens when there is more CO2 in the atmosphere?

    I have done the experiment several times. With different levels of CO2. The most I saw last night, at about 20,000 ppm, was an increase of 0.5 degrees. This is a CO2 doubling of over five times, so if this were in the atmosphere, it would be expected to increase by 5 degrees.

    Why is it not possible to do an experiment in a plastic bag to measure a response?

    I have been linked to similar experiments done to prove CO2 where they put CO2 in a fishtank, then shine a heat lamp. I pointed out that in nature, there is no heat lamp or artifiical source of radiation, so that experiment is not indicative of what will happen in reality. Why is it acceptable to do a fishtank + CO2 experiment to try to prove AGW, but not acceptable to do a plastic bag + CO2 experiment to try to disprove it? I'm happy to accept an explanation, but I don't see why, if you understand the reason, you can't simply explain it to me instead of send me to read hundreds of papers (unless you yourself do not understand it).

    Can you also give an explanation - if the correlation shown between CO2 and temperature on the Vostok Ice Core samples is assumed to be causation, with CO2 causing temperature rise - why CO2 would have a linear effect on temperature (~1 degree per 10 ppm), but now we expect a logarithmic effect (i.e. 1 degree per doubling).

    Can you explain what is going on with the molecular activity of the gas that would allow for such an unintuitive behaviour? Do all gases act this way when absorbing IR? Why? At what point do they go from linear to logarithmic and why? Has this been studied? It seems like it is fundamental to knowing whether climate science is accurate or not. How else can you come up with the prediction of 1 degree per doubling?

    My understanding is that they act logarithmically, which would mean that the Vostok Ice Core samples can not be assumed to be that CO2 causes temperature. The 800 year lag, where temperature changes first also would support that. You know what does have a linear relationship though, and could explain the Vostok Ice Core samples? The CO2 solubility of water (oceans) between 0 to ~23 degrees.


    [DB] Please confine comments to the focus of the thread on which you place them.  Thousands of discussion threads exist at Skeptical Science; using the Search function in the Upper Left of every page can help you find them.  Alternatively, you can click on the Arguments Tab to find different listings of topics (like a Taxonomic Listing or by Popularity).  Area experts and knowledgeable individuals will respond to help you increase your understandings, but you must first be on-topic.  Thanks!

  3. jesscars - I explained why you cant do it with a plastic bag - it is not 55km high. You cant complain about science being wrong when the problem is with your understanding of it. You do not appear to have looked at resources posters have offered you.

    You have now raised a whole bunch of long-debunked talking points which are offtopic here. Please use the search button on top left or the "arguments" to find the appropriate myth and comment there, not here.

    eg "Climate has changed before", "Co2 lags temperature". It would seem that with a very large no. of misunderstandings about climate, that a read through the appropriate section the IPCC WG1 to get a grip on the basics. I would also reiterate the Science of Doom. Just for starters, the ice-age cycle is driven by orbital variation which primarily affect earths albedo. Once temperatures change, CO2 changes also from interactions with ocean and eurasian wetlands amplifying the effect. The detail here is huge - if you want to question the science, then please become familiar with the science first.

  4. Also, just to look at what you expect from your experiment, executed perfectly. Assuming you are around mid-latitude and in summer, that you use a jar of CO2 0.5m high, then changing concentration of CO2 from 100ppm to 20,000ppm should change flux from 414.8W/m2 to 415.4 if I have done calcs correctly. Not enough to change temperature by even 0.1C.

  5. Hi MA,

    > jesscars @343,

    The relative strength of CO2 as a GHG is dependent on the logarithmic nature of its forcing. The first doubling will, molecule for molecule, be twice as 'forceful' as the second doubling and a thousand times more 'forceful' than the tenth doubling. So the 'forcefulness' you measure in the High-CO2 bag will be mainly a thousand-times weaker than the CO2 'forcefulness' involved in AGW. And while the ten doublings of CO2 together will provide a very 'forceful' GHG effect at 15 microns, (By-the-way, I note my 12 microns @340 is wrong - it is 15 microns.) this is achieved by stripping all GHG from everywhere else. This one-step-warmer-one-step-cooler effect for the bag world could well explain the non-result although there could be many other contributing reasons.

    I agree with this. I repeated the experiment last night with about 2% CO2 or 20,000 or 5-6 doublings. (I.e. enough to get an effect from CO2 without diluting the effect of H2O.) The bag with CO2 was 0.5 degrees warmer during the night, outside. The difference disappeared in the morning.

    > jesscars @347,

    Your comparison of the 1ºC of warming for double CO2 (without feedbacks) with the Vostok Ice Core temperature/CO2 graph doesn't properly hold. Firstly, the Vostok temperatures will be subject to polar amplification and Ice Ages result from other non-CO2 'forcings' (CH4, ice albedo) and their feedbacks. The direct CO2 contribution (without feedbacks) to the Ice Age cycles (which are globally some 5ºC) is probably something like 0.5ºC, which fits in with the logarithmic relationship. With feedbacks, the CO2 'forcing' is responsible for about a third of the Ice Age wobbles.

    OK, so you are saying that the effect of CO2 on the temperature is only minor. If so, then what explains the correlation? Why would the other factors that contribute to temperature change move/fall at the same time as CO2? This is obviously not chance, so whatever affects the CO2 must also affect those other factors in order to get that correlation. Has this been proven by empirical research?

    (Also, what is the cause of historic atmospheric CO2 change? I've heard several contradictory answers I.e. Milankovitch Effect or volcanoes. Why does CO2 change over time i.e. where does it come from, where does it go?)


    [DB] Please confine comments to the focus of the thread on which you place them.  Thousands of discussion threads exist at Skeptical Science; using the Search function in the Upper Left of every page can help you find them.  Alternatively, you can click on the Arguments Tab to find different listings of topics (like a Taxonomic Listing or by Popularity).  Area experts and knowledgeable individuals will respond to help you increase your understandings, but you must first be on-topic.  Thanks!

  6. Jesscars, I rather suspect you have been pulling my leg with your story of your plastic bag experiments.   Perhaps you just used that as an entry point for your argumentative disagreement with mainstream science.

    As Scaddenp has said, you really need to educate yourself on basic science before you can seriously start to question things.   Otherwise . . . you embarrass yourself with a Dunning-Kruger performance.

    But fear not — there is time to redeem yourself.   Why not try the intellectually-stimulating exercise of learning some genuine climate science from the articles, videos, etcetera found here at SkepticalScience & similar reputable sites.   Or if you find your dour & angry mood persisting, then try the very entertaining Potholer54 video series I mentioned — all are amusing as well as informative about real science.

    The more you learn, the more you understand reality.   It is not a coincidence that all real scientists are in consensus agreement about AGW !!

  7. jesscars - I have responded on a more appropriate thread here. Any discussion of past climate should go there.

  8. jesscars @355,

    The Ice Age cycles are strange beasts. They are triggered by changes in the solar warming of the Northern Hemisphere (the Milankovitch Cycles) but the climate has to be primed and in an a-stable state for the trigger to work.

    And while the trigger is quite a gentle shove to climate, the triggered 'impacts' are big enough to raise global temperatures some 5ºC. The 'impacts' are technically feedbacks forced by the Milankovitch Cycles but it is these feedbacks that do all the work.

    Simplistically, the main instability is the polar Ice Age ice caps that begin to melt out, this raising temperatures and destabalising further ice caps. And on the back of this warming, the level of atmospheric CO2 and CH4 will rise.

    In the case of CO2, the carbon cycle requires oceans and biosphere to be in equilibrium with the atmosphere. With warming ocean waters, less CO2 can be carried by the warmer water, raising atmospheric CO2 levels which in-turn adds to the warming process. And the frozen biosphere also releases captured CO2 as it melts. (These processes will be at work today under AGW but with only 1ºC of warming in less than a century, the impact of the warming CO2 feedbacks is much less than the 100ppm CO2 Ice Age effect that resulted from much more warming over 8,000 years.) In very simple terms, that answers "Why does CO2 change over time i.e. where does it come from, where does it go?" Volcanoes do emit CO2 but it is only very exceptionally (within the billion year planet's history) that volcanism has elevated atmospheric CO2 by anything of significance.

  9. "warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade". More specifically and quite interestingly:

    +0.165 degrees / decade: La Nina years 1967-2012
    +0.165 degrees / decade: ENSO-neutral years 1970-2013
    +0.20 degrees / decade: El Nino years 1966-1990
    +0.23 degrees / decade: El Nino years 1990-2013 (sparse data though)

    El Ninos are "pulling away".

  10. The link to Puckrin 2004 is broken

  11. I think I understand the spectrum graphs and the role of CO2 in the outer layers and the sensitivity to the CO2 concentration relative to the base level in the simple model. My question is: as the global mean temp rises, and water vapor rises, and polar ice cap coverage decreases, a number of things change. Surface reflection changes, ice reflects whereas open ocean absorbs; water vapor convection and absorption change. Is there an equation equivalent to the 5.35 ln (C/C_0) equation with additional terms for these effects? Or is that equation already based on a models which already have these additional feedback effects? Thanks.

  12. PS I noticed you folks are typing quite lengthy responses and spending a lot of time answering a lot of (some quite silly) people with much more patience than I would have with such people. A simple link to read a paper or two would be fine. Math and statistics is not a problem, these are my fields of education, but I have not read much climate science and would like to. Just need a good place to start and I can follow bibiliographies from there. Thanks again.

  13. ebelba - doubling CO2 by itself gives an extra 4W/m2 (your equation) to surface of the earth and that corresponds to ~1.1C increase in global temperature. All of the rest of temperature increase is due to feedbacks as you outlined which is why climate models are so complex and why the range of climate sensitivity estimates is so large.

    The IPCC WG1 report, starting with the technical summary, is quite definitely the best place to start getting an education because you can go from technical summary to full report and from there down into the referenced papers.

    The 1984 "Climate Sensitivity: Analysis of feedback mechanisms" is now dated but not a bad starting point as well. Check out the more recent Proistosescu and Huybers though.

  14. I've read the 1984 paper and the Proistesescu paper and subsequently a bunch of abstracts of papers on the feedback roles of land cover and land use, albedo, etc. It appears that one area causing a dispersion of uncertainty is the role of cloud cover albedo feedback. Is there a single source you would recommend which puts confidence intervals around each of the remaining sources of uncertainty as well as ranks the robustness of the existing models in each area, such as climate+land use, climate+vegetative cover, climate+cloud cover albedo, etc.?

    thanks for your prior links, they were good starts.

  15. ebelba - sorry for delay - no internet over weekend. Clouds are indeed one tough issue for feedback predictions. Clouds are both a positive and negative feedback depending on whether high or low. This is not well captured in climate models (cell size in models is too large for the processes involved) so figuring out how that would change with increasing water vapour is challenging. I am not aware that uncertainties for individual components have changed significantly since those published in Fig SPM.5 (see text for sources) of IPCC WG1 or table 8.6 in the main text. Chpt 8 has the main coverage of this. There has been a focus recently on trying to establish empirical constraints via paleoclimate archives and direct observations. For recent work, see for example Dessler and Forster 2018. For paleo, see say Hansen & Sato 2012. Their model/observation fit for a sensitivity around 3 impressed me.

    I dont think there is any escaping the problem that governments need to set policy despite stubborn uncertainties in the values of ECS; but need to do this on basis of a best estimates being close to 3.

  16. I have a couple of questions re. the historic vs future predicted relationship between CO2 and temperature:

    If you look at the Vostok Ice Core Records, the relationship between CO2 and temperature is linear, and is approximately 1 degree change per 10 ppm change.[1]

    1) Why is this not the expected predicted relationship of CO2 to temperature? Why does it go from 1 degree per 10 ppm to 1 degree per doubling, the first doubling being 300 ppm (then 600, 1200, etc.)? Why does the sensitivity of the earth's temperature to CO2 change so severely to have only 1/30th the sensitivity? What is the reason for this reduction in sensitivity?

    2) Why does the relationship change from linear to logarithmic? There is a steady and consistent linear relationship of 1 degree for 10 ppm - why should this change to a logarithmic relationship of  degree per doubling i.e. instead of 1 degree per 10 ppm, we now have 1 degree per 300 ppm, then per 600 ppm, then per 1200 ppm, and so on. What is the cause of the change of the nature of this relationship?

    It seems to me that the "skeptics'" explanation - which assumes temperature is causal in the observed temperature-CO2 correlation - does not involve such erratic and unexplained behaviour.

    N.B. The linear 1 degree per 10 ppm can be explained by the linear relationship of CO2 solubility in ocean water (at temperatures below 23 degrees, see link [2]).

    As the temperature changes (measured by the atmospheric temperature), this causes the ocean temperature to change. Within the temperature range seen on the graph in link [2] i.e. below about 23 degrees, you would expect a similar amount of CO2 to be released or absorbed, per unit or degree of change, per volume of water, resulting in a linear atmospheric temp-CO2 relationship.

    The Vostok Ice Core records also show an 800-year lag where temperature changes before CO2 does. This indicates that temperature is causing CO2 to change, not vice-versa. (The Shakun study only attempts to provide an explanation for this for the last deglaciation, not the entire duration of the Vostok samples (400,000 years), so really is inadequate.) This can be explained by the fact that the oceans take so long to heat or cool. So it takes hundreds of years for the warming or cooling to have an effect on the CO2 levels, as this has to happen via the oceans.

    2) The causal mechanism to explain the temperature-CO2 correlation is explained by:  natural causes (e.g. Milankovitch cycles, sun radiation cycles, circumpolar jet-streams, etc.)  to be caused by ocean absorption of CO2, is expected 




    [PS] Just a quick note that icecore data is indeed used as a way to constrain to climate sensitivity. Try for instance Hansen & Sato 2012 which does it properly. Also see here for Co2 lags question

  17. Please ignore that last point "2)".

  18. Jesscars - just a comment about the log relationship. My intuition is as follows: imagine a completely dense wall of CO2 completely blocking all of the parts of the infrared spectrum that CO2 is known to block. That is the maximum theoretical contribution. As you create gaps by halving that wall, you allow infrared to escape. We are coming at it from below, doubling. It has to be something almost asymptotic to that wall. A log has the right shape - as a practical matter its not really a log, because the total amount of CO2 that could be put in the atmosphere from all stored forms is finite. So a log is a good approximation to the asymptotic relationship as we get to higher levels. At very low starting values close to zero, it could easily be linear (or more).

  19. I think there is Jesscars is a little confused about what the science actually states. There is a log relationship between concentration of CO2 and the surface irradation. (not temperature). ie, increase in CO2 since pre-industrial has caused average of 4W/m2 increase in surface radiation. To get another 4W/m2 of irradiation, then you have to double concentration again. (ie go to 800ppm). The relationship is always logarithmic, never linear. As to why, well it falls out of the radiative transfer equations but it is anything but straightforward. More recent work on it here.

    There is no simple relationship between increase in CO2 and surface temperature, because of all the feedbacks that cut in on different timescales. eg water vapour response is near instant; albedo is complex time scale because of dynamics of ice melt; GHG feedback (eg methane from tundra, CO2 from ocean) are on millenial scales. The Equilibrium Climate Sensitivity (ECS) tries to estimate this and best guess is 2.8-3C for doubling of CO2 but with wide bounds.

  20. What is the response to this article[ ] reasoning that climate models do not correctly recognise the effects of increasing CO2 conentrations and that CO2 is not the main driver of climate changes?

  21. Sorry - first post :-) didn't insert as link..


  22. Penguin,

    Your article claims that the concern about AGW started with Al Gore's movie An Inconvienent Truth in 2006.  He apparently missed James Hansen's Senate testimony in 1989 that AGW was an incoming disaster.  Lindon Johnson asked the National Academy of Science if AGW was a problem in 1965 and they replied that it would be a problem in 40 years or so.  The first IPCC report was written in 1990!

    The article claims that the CO2 absorbtion band is saturated.  The probem here is the writer does not understand how the greenhouse effect works.  At the surface the absorbtion band is saturated, everyone knows that.  That does not matter.  About 10 km up in the sky (30,000 feet) is the important area.  At this height there is no water, only CO2.  This is the escape altitude.  Increased CO2 increases the escape altitude which warms the Earth.  Read the OP for more information.

    This dribble has been debunked many times.  The author admits his ignorance when he claims no-one cared about AGW before 2006.  The first IPCC report was written in 1990!!

  23. Penguin @370,
    Adding more detail to michael sweet @372, you are asking about a 6,000 word article from 2018 entitled "CO2 is Not Driving Global Warming" written by...

    Well we do not learn the name of the "NARTE certified electromagnetic compliance engineer with more than 30 years practical experience" who is also "a systems engineer with plenty of experience in software design and development" with the "lifetime fascination with astronomy and cosmology." That is never a good sign - to flaunt your qualifications without naming yourself.
    Whoever he is, it took him from 2006 (the Al Gore flim) until 2018 to decide to present this grand revelation to the world, even though he had "alarm bells ringing" in 2006. A second bad sign.
    And he asserts that the theory underpinning AGW is no more that a CO2/GlobalTemperature correlation which is nonsense. A third bad sign.

    The entirety is un-referenced which is fine when it is discussing widely understood subjects but when it begins to dip into fantasy, the lack of referencing becomes entirely unscientific and fatal for the presented thesis. Thus CO2 contributes roughly 16% to the greenhouse effect and would unassisted provide 25% of the greenhouse effect. I can say that un-referenced without much controversy.  But within an un-referencing article, the assertion that CO2 is "responsible for more than 2.8% of greenhouse gas warming" is the beginning of the end for this grand thesis.

    A few paragraphs later he asserts that CO2 absorbtion is IR is multiply-counted (a bit like double-counted but many more times) thus "cumulatively contributing to atmospheric warming." Such an idea is nonsensical. And nobody has spotted this alleged eggregious error? That would require some very good explanation. (The assertion "CO2 will not radiate more infrared energy than it absorbs if it’s at the same temperature as its surroundings" appears fundamental to the poor understanding of the author. It is precisely because it is the gas temperture that defines the CO2 IR emissions (and thus not the levels of absorbed-IR as he asserts) which creates the power of the CO2 greenhouse effect. Thus the comment "Increasing CO2 concentrations ... would mean that the greenhouse effect of CO2 will be concentrated at lower altitudes" is back-to-front.)

    The guts of his unsupported assertions run:-

    "[CO2] is plainly saturated. Adding more CO2 to the system will not result in any less energy being radiated into space at those frequencies"
    "The other misstatement in this [AGW] argument is that, “... it is the layers from which radiation does escape that determine the planet’s heat balance.” This is incorrect. The temperature of the upper layers of the atmosphere has no effect on the IR radiation if that atmosphere is transparent to the IR radiation. If the transmissivity of the atmosphere is at or near one, the IR radiation will simply pass through it with no interaction. If it were otherwise, then IR radiation simply wouldn’t propagate through the atmosphere at all. Since there is little to no water vapor at high altitudes where the atmospheric temperature are claimed to be a factor, the atmosphere is completely transparent to IR radiation across most of the spectrum." [My bold]

    He is effectively saying 'Once the IR has a clear shot at space, the temperature of the atmosphere it is passing through doesn't matter.' The fool (and he is surely that) misinterprets "the layers from which" for "the layers through which". It is the temperature of gas from where the IR is shot into space that is crutial to the amount of IR energy cooling the planet.


  24. I'm looking at the comments and wondering about what I think are obvious things.

    1.  The 800 year CO2 lag should indicate that CO2 isn't driving temperature.

    2.  If increased CO2 raises temperature, what is causing the subsequent temperature crashes since CO2 is still elevated?

    3.  If you can't measure greenhouse gas effects with 'back yard' science experiments, what makes anyone think there is an effect in the first place?  Yes, CO2 is a 'greenhouse gas' where people add over 1000 ppm of CO2 to help the plants grow.  Apparently that much additional CO2 isn't noticably changing the inside temperature, so why would a 100 ppm change in the atmosphere have any measurable change in planetary surface temperatures?

    4.  There is another reason why surface temperatures can increase, specifically, reductions in surface wind speeds, which is occuring.  Here is a report complaining about it.

  25. @youjaes @374

    OK, I will take the bait.

    You clearly are not very well informed on climate science and you have not spent anytime thinking about the points you make. Let me give you some ideas to think about. If you have more questions there are plenty of knowledgeable people who will (sincerely) help if you ask in good faith.

    1. The CO2 may not be driving the initial temperature rise but there is no reason to discount it in subsequent rises.

    2. Is CO2 still elevated? What events are you talking about? I would guess Milkanovich cycles may answer your question.

    3. Who says you cannot measure greenhouse effects with "backyard" experiments? Why do they have to be "backyard"? Are "backyard" experiments somehow more convincing than frontyard experiments? I suggest you read something about the greenhouse effect as you do not understand it.

    4. Um. Yes, wind can reduce/increase local temperatures. What has that got to do with global warming?

  26. @JohnSeers @375

    Okay, I'll bite you back.

    1.  If CO2 isn't driving the initial temperaturte rise, then what reason is there to cite it in subsequent rises?

    2.  Did you forget about the ice core data?  Temperature goes up, then temperature goes down before yhe CO2 does.  Were you not paying attention?

    3.  Go ahead, do some.

    4.  Do you normally contradict yourself?  Decreasing surface wind speeds is associated with increasing surface temperatures.  Decreasing global surface wind speeds means what, no global surface temperature change?

    Do pay attention.


    [DB]  This is a moderated forum.  Please comport your comments to comply with this site's Comments Policy.  

    From the depths of the Last Glacial Maximum 20,000 years ago, CO2 levels increased due to warming from Milankovitch forcings, which then triggered an immense increase in atmospheric CO2, which drove the bulk of the temperature increase needed to drive the world from full glacial phase into the full interglacial world of today.

    In short, the initial warming was indeed triggered by the Milankovitch cycles, and that small amount of orbital cycle-caused warming triggered the CO2 release from the Southern Oceans, which caused most of the glacial-interglacial warming.  CO2 led and was the primary driver behind most of the glacial-interglacial warming.

    From Parrenin et al, we see that temperatures and CO2 levels in Antarctica rose synchronously, with no lag in either measurement.

    According to the Shakun et al data, we see that increase in atmospheric CO2 led the increase in global temperatures for the remainder of the globe.

    Shakun 2012

    Inflammatory rhetoric snipped.

  27. Youjaes @376 , LOL but please do not bite me   ;-)

    1.    . . . was expressed rather ambiguously.   For each rise (or fall) of temperature in glaciation/de-glaciation, the first 10% is caused by slight variation in "insolation" and the subsequent 90% is caused by change in CO2 level (i.e. change in GreenHouse Effect).   Rough figures, of course.

    So your comment #1 was 90% wrong.  Ah, if only you had read the Original Post and subsequent comments!    ;-)

    2.  Ice core data conforms with the 10% / 90% description (above). 

    No problemo !

    3.  The so-called (but poorly-named) GreenHouse Effect [ = GHE ] has already been shown with data from satellites.   Long ago.   ( But half the crazies at WhatsUpWithThat blog . . . are still in full denial about it all !  . . . even though the good Mr Watts occasionally whispers that they're wrong to deny it. )

    No need for backyards or front yards being involved.

    4.   As global warming has proceeded, wind speeds have slowed very slightly, I am told.   But WUWT has made a mountain out of a molehill, on that.   Kind of a nothingburger.   Strange, since WUWT is usually trying to make molehills out of mountains !    ;-)     ;-)     ;-)

  28. "1. If CO2 isn't driving the initial temperaturte rise, then what reason is there to cite it in subsequent rises?"

    Ah... because that's the difference between a forcing and a feedback.

    Without that CO2 feedback the initial orbital forcing would only produce a very small change in temperature. The resulting feedback is what gives us glacial/interglacial cycles.

    Regardless, the effect is the same. CO2 is a gas with radiative properties. Adding CO2 to the atmosphere will cause the planet to warm. Add lots of CO2 and the planet will warm a lot.

  29. I am not a scientist but would somebody explain to me how a gas that consists of 400 parts per million is going to heat the other 9600 parts per million in any significant way and why would one of the other green house gases water vapor not have a much greater effect.  

  30. Firstly let me say how much I have enjoyed reading this topic, oh and I had better add I have no doubt that mans activity is warming the planet, but I am a little at odds with the how....

    I must confess that I am more than a little surprised that in everything I have read there is no mention of the heat component thats mans activity is adding to global warming?

    I we take the ocean for instance a throw a few thousand ships in it pouring billions of Kw of heat in to the ocean for say the last 70 odd years, and more than 1 or 2 reactors in subs spewing heat in to the oceans.  The ocean is not infinite, so all of this hot water must go somewhere, right?.  Where are the calculations that determine what percent of the oceans warming is by the heat released by mans "industry"?

    And again if we take the worlds population and distribute it evenly over the globe for the sake of back of the napkin math, tabulate the daily fuel burn, heat released by reactors, exothermic process in industry, heat released by electrical appliances driven by wind and hydro, (some fair guesses can be made here) and apply it to our 1 square km model.  Throw a bit more water vapor in to the atmosphere, as after we are burning fossile fuels, stand a coloum of air on the top of this heat source about the dimensions of the atmosphere with a large heatsink at the other end and you come up with some really interesting numbers.  Certainly they are big enough to be, well not nothing.....

    My back of the napkin math suggests that the heat being produced by mans industry at the very least needs to be incorporated in to any greenhouse model, and the sun is not the only significant source of heat.  I suspect that greenhouse gases are not nearly as efficient at trapping heat as we give them credit for and the petawatts of heat being liberated in to the atmosphere by man are a much bigger part of the "full" picture, especially when the wavelength of wate heat is considered....

    Is it just me or has this work been done already?  Or am I simply wrong?


    [PS] Please see the "its waste heat" myth and post any further comments on that thread please, not here.

  31. Dukester @380,

    My back of fag packet calculation puts the energy used by shipping at roughly (300Mt/year x 43 GJ/t / (8766 x 3600) = 400 GW. That is certainly billions of kWh/year. But as a global forcing it comes to 400e9W / 510e14m = 0.0008Wm^-2. As of last year NOAA AGGI puts the forcing from CO2 at 2.044Wm^-2 with a total positive GHG forcing of 3.1Wm^-2. Burning fossil fuels does result in much energy release but, depending on the fuel, the resulting increase in atmospheric CO2 will be heating the planet by the same amount over the following 9 to 18 months, and again for following periods of that length. The combustion energy release thus quickly becomes a trivial value relative to the GHG forcing.


    [PS] no more comments about this on this thread please. Take it to the waste heat thread.

  32. Recently many scientist start to doubt on such theories about man made climate changes, specially those from other background like me. I am a phisicist. For me it is difficult to give credit to a mere conference paper as the one you cite as main reference. Is there any other reference to address the full sun spectrum and compare with the presented one? Also I am in doubt of the name you used to describe the FTIR spectrum. It is not a " greenhouse radiation spectrum" as you claim, it is just an FTIR of the atmosphere. Have the authors accounted for the emissions from the Earth and subtracted them? You can use a simple fit with a black body radiation with an emissivity also called as brown body. Another issue is the water spectrum being ommited. Why? Is not the water contributing to warm Earth's surface? In resume I do believe in the possibility of warming, my main criticism is that experimental procedure seems to be incorrect. Also to a cientist it is not enough saying that many people believe in something or that you're the majority of them. This is not the way scientific evidence is validated. If there is ANY inconsistency in ANY theory it does not turn it completely false immediately but it put the model in serious doubt. Number of scientist that agree to a flaw evidence is useless here. I rather know how do you conduct your research and how do you reach your conclusion. So tell me some measurements made from a standard labs like the NREL of the sun radiation. Because to compare data taken from distinct instruments one decades after the other in distinct times of the year or even the day and also without absolute power calibration cannot be accounted as serious science. Forgive me by being skeptical but that is my job and I am giving you an opportunity to show me more arguments of your claim.
  33. Rero @382 ,

    What a happy co-incidence that you have posted here!  I am delighted to find another fellow phisicist.  There are so very few of us, and our scientific field of specialty is so very new, that it has not yet even been incorporated into the Oxford English Dictionary (but I have hopes it will be so, in February).

    More to the point, Rero, you have unfortunately been extremely vague in your commentary ~ amounting to little more than semantic nihilism.

    Best if you start from the beginning, and provide some names of well-qualified & well-informed scientists who have recently (say in the last 100 years) developed a credible doubt about the mainstream physics of climate.

    More importantly, you should specify the plausible (and preferably peer-reviewed) evidence which justifies their doubt.  Because we phisicists abhor empty words, do we not?

  34. Eclectic @383,

    I fear you fail to spot the linguistic limitations within the comment of Rero @382 who doesn't sound like a native English speaker. And I do not see Rero @382 saying there are "well-qualified & well-informed scientists who have recently developed a credible doubt about the mainstream physics of climate." Rather it is "recently many scientist start to doubt" (my bold). There is no mention of "credible doubt."

  35. Rero @382,

    Picking up on some of your comment, I would echo the view @383 that if you do mention their existence you should give some indication of who these 'recently doubting scientists' are.

    You also mention the figure in the OP of Spectrum of Greenhouse Radiation described in the OP as measurement of FTIR spectroscopy. This is clarified in the paper referenced which states "The measurements have been obtained using commercial Fourier-transform infrared (FTIR) spectrometers." You ask for a more substantial reference than Evans & Puckrin (2006) 'Measurements of the Radiative Surface Forcing of Climate' which is a conference paper. The figure is not controversial so I am not sure why further reference is required. The same result can be obtained using the UoC MODTRAN model (with Water Vapor set to zero, altitude to zero and looking up). But if you insist on a peer-reviewed published paper, perhaps Ellingson & Warren (1996) would be what you are looking for.

    Your following statements are not entirely clear. When you state "my main criticism is that experimental procedure seems to be incorrect," this seems to be separate from the criticism of using consensus to define the science (which is not a valid crticism. The consensus rests on science, not the other way round). If your "main criticism is that experimental procedure seems to be incorrect" and if this is separate from your consensus consideration, please set on why you consider the "experimental procedure seems to be incorrect".

  36. MAR @384 , your comment is doubtless kindly meant.  There were numerous indications (including the first sentence of #382) that it was a case of "non-native English".   And no-one should object to grammatical and spelling trespasses, where the underlying meaning is obvious enough.   Just as each of us would hope to be forgiven our own trespasses.   (And I am very happy for posters to post comments in their native tongue . . . although often it would be prudent for them to provide a rough translation into English, for the benefit of the majority readership.)

    Nevertheless, to borrow a non-English word, there was in #382 a considerable chutzpah  in making an improper spelling of physicist , while criticizing/berating the mainstream scientists for inattention to proper detail.   The irony was amusing.

    MAR, you have a formidable depth of knowledge of climate matters, and I find it hard to believe that you could find it credible that Rero would come up with anything to back up his statement that "many scientists were starting to doubt".   That's why I asked Rero to name some scientists & supply a modicum of the evidence on which any true scientist could base his "increasing doubt".   Of course, a real scientist is only wishing to entertain credible doubt [my phrasing, not Rero's].

  37. Figure 2 is wrong. This was pointed out more than 10 years ago @1 by HumanityRules. The caption for Figure 2 says "Change in spectrum from 1970 to 1996...", but Figure 2 is a copy of the Harries 2001 1c graph, a simulated spectrum, i.e. a purely theoretical graph, something never measured at all, which is why all the values are below zero Kelvin. This article should be using a copy of the Harries 1b graph instead: the actual measured spectrum difference between 1970 (IMG satellite) and 1996 (IRIS satellite). In the the 1b graph there are large portions above the zero line, e.g. between 750 - 1100. This is what @HumanityRules was asking about: why so much positive energy at these frequencies? @2 provides an explanation from the Harries paper itself about "residual small ice crystal effects". However, I believe this explanation is wrong. The real reason for a <b>net positive</b> energy difference between 1996 and 1970 is that the earth was warmer in 1996 than it was in 1970. The Stefan Boltzman law requires that a hotter earth emits more heat. Since CO2 and CH4 and other trace GHGs are blocking parts of the emitted IR spectrum, then other parts of the spectrum must make up for this. The Harries 1b graph simply confirms that earth was warmer in 1996. In contrast, Figure 2 implies that the earth was cooler in 1996 than in 1970.

  38. If greenhouse gases such as CO2 are absorbing the sun's radiation and emitting it as long wave infrared radiation as the post suggests, why would an increase in atmospheric CO2 translate to an increase in downward longwave emissions but a decrease in upwards longwave emissions attributed to CO2 as measured via Satelite? Again, as the post suggests, greenhouse gases absorb the sun's radiation and then these same gases emit that radiation in all directions (not favoring up or down). Wouldnt an increase in atmospheric CO2 (and O3, CH4) result in an increase in both upward and downward longwave emissions for their respective greenhouse gases? 

  39. unsure @388,

    The essential characteristic of GHGs is that they do not absorb sunlight. They do absorb (and re-emit) the long wave infrared. With an increase in CO2, there isn't directly an increase in the 'intensity' of this long wave infrared, be that up, down or sideways. That is, there are more CO2 molecules emitting, but there are also more CO2 molecules absorbing. The extra absorption means the higher number of emitted infrared photons have a reduced pathlength. So at any point, the surface say, the infrared recieved is unchanged by simply adding CO2. Something else has to happen to increase the infrared 'intensity'.

    What does cause this increase in infrared (up, down and sideways) is an increase in global temperature. The temperature rises because the extra CO2 increases the height in the atmosphere at which the CO2-emitted infrared has a clear shot at space. This means the CO2 molecules shooting out to space are in a higher colder part of the atmosphere. Cold gases emit less than warm gases, so to balance the global energy equation the planet has to warm, thus boosting the infrared emissions into space, from all sources, not just CO2. Note that because the temperature boost to infrared is across all sources and this is to balance the reduced infrared from CO2 alone, there will still be less CO2 emissions out into space when the balance is restored.

  40. Unsure @388 , I will add in some extra food for thought.

    The "greenhouse" planet-warming effect of the GHG [GreenHouse Gasses] molecules is not simply explained in a single sentence (or three).  But once you get your head around how it works, you will see that it is a straightforward basic mechanism.

    You will need to do some more of reading & thinking it through.  Several points to keep in mind :-

    (A)  InfraRed photons are emitted in all directions by the CO2 molecules ~ when each molecule has enough energy to emit an IR photon.  Emission rate depends on local air temperature.

    (B)  The energy (to produce an IR photon) for each CO2 molecule ~ is gained from collision with neighbouring "air" molecules (almost all of which are nitrogen and oxygen).   Likewise, when a CO2 molecule receives/gains an IR-photon's worth of energy, the CO2 molecule immediately distributes energy to neighbouring "air" molecules, by collision.   In other words, a CO2 molecule can warm the neighbouring nitrogens/oxygens when it receives an IR photon . . . or it can (by emitting an IR photon) cool its neighbouring nitrogens/oxygens.

    (C)  Each layer of air is receiving and radiating IR  from/to the layers above and below . . . except for the uppermost layer, where the CO2 is so "thin" that some of the radiated IR photons can escape to outer space, through the "gaps" between the nearby CO2 molecules.   (Lower layers with denser concentrations of CO2, in effect have "no gaps".)

    (D)  All of the above, also applies to IR emission/absorption by other GHG's e.g. methane, water vapor ~ but for each of these other compounds, the corresponding "uppermost thin layer" is at a different altitude (than CO2's "Top Of Atmosphere" emitting layer).   O3 is rather a special case, being mostly in the stratosphere.

    And I will stop at that point, since the consequence of all this is the higher heat concentration at the planet's surface i.e. the so-called (and poorly named) GreenHouse Effect.

  41. I have found Chris Colose's explanation very useful, particularly the last diagram on effective height.

  42. Ok. I am new to this thread. I wonder if someone could help me with a CO2 concentration problem? I was researching CO2 levels on other planets to compare those to Earth along with surface temperature and atmospheric pressure so I can understand how they all interact. The CO2 concentration on Earth is .041%; the average temperature is 59F; and the atmospheric pressure is 14.7psi. Lets go to Venus now: CO2-96.5%;average temp+864F; atmosperic pressure-1363psi. And lastly Mars:CO2-95%;Temp- -81F; atmospheric pressure-.088psi. Can someone explain how Mars and Venus have basically the exact CO2 concentrations that are magnitudes above ours; and have drastically different temperatures?  Thanks if anyone can explain this to me.

  43. Responding to the question posed @392 (not being sure if the commenter is still 'with us', but the question remains),

    The point of a greenhouse effect is that it elevates the temperature of the planet above the temperature it would be without a greenhouse effect. Thus (and apologies for using SI units here) the start point is the actual surface temperature of the different planets minus their blackbody temperature. And it is not the percentage of CO2 but the volume of CO2 that should be considered because 100% of naff-all is still naff-all.

    (Note this is an overly simplistic analysis as a greenhouse effect can be reliant-on or boosted-by the presence of other gases. For instance, on Earth the greenhouse effect would be 25% of current values if the CO2 warming wasn't boosted mainly by water vapour and clouds for the remainder. And it is not just greenhouse gases that can play a role.)

    From this Venus fact sheet & this Mars fact sheet:-

                                              Venus         Mars          Earth

    Surface teperature                737K        210K         288K

    Blackbody temperature         226K        210K         254K

    Greenhouse effect                 515K            0K          33K

    Atmospheric pressure             92bar  0.006bar       1bar

    CO2 (by weight)                      96%         96%        0.06%

    CO2 content                           88bar   0.006bar    0.0006bar

    So the answer to the question "how Mars and Venus have basically the exact CO2 concentrations that are magnitudes above ours; and have drastically different temperatures?" is that the strength of the greenhouse effect is reliant (simplistically) on CO2 content and not CO2 concentrations. The table presented here simplistically sets out why Mars and Venus have "drastically different temperatures". The Mars/Earth difference is another (and more complex) story.


    [DB] The user account to which you were responding is a sock puppet account of the same name as the user which ceded their commenting privileges previously.  This new iteration of the account had its commenting privileges accordingly suspended.  As will all future iterations.

  44. (Checking to see if my post uploads successfully to SkS)

    Thank you, MA Rodger.   Mr Dakota was quite off-target in trying to picture things in relative CO2 concentrations such as 0.041% or 410 parts per million.

    As you say, the presence of water vapor adds a large complication ~ except for Mars.   Adjustments also for albedo or reflectiveness at non-visual wavelengths . . . plus or minus reflectiveness of sulfate aerosols from industrial and/or volcanic origin.   Other adjustments for Earth's tilt or seasons, and for clouds at different heights & latitudes.

    The climate scientists certainly have their work cut out for them, to get a handle on it all.   Mr Dakota is probably tempted to think it's much easier just to be a science-denier, and firmly close one's eyes to reality !

  45. Correlation does not confirm a theory, it leads to a mechanism . There is not enough CO2 in the atmos to account for global sea temperature rise. Temperature rise is caused by the tremendous Heat emanating from Coastal cities. This Heat goes into water ( sewers, streams, sheet water) into rivers into the Sea. Civilization cause water sources to become Turbid, there is not enough water treatment to prevent Turbidity levels. Heat and Turbidity cause anoxic regions to proliferate. Warm coastal water causes storms and polar melting of ice. Civilization itself causes Global warming not levels of Carbon dioxide.

  46. pettman - Waste heat is _not_ the problem; the forcing changes from waste heat in our climate system are 100x smaller than the CO2 forcing. See Greenhouse warming 100 times greater than waste heat, where you can check the numbers. 

    The data does not support your assertion. 

  47. Pettman says "Correlation does not confirm a theory, it leads to a mechanism." You got this exactly wrong. The mechanism is identified by physics and does not depend at all on the correlation. Correlation is in fact more important when there is not a known physical process, hence the vacuity of the null hypothesis problem advanced by some so-called skpetics. Furthermore, the correlation does not lead to a mechanism, it only shows the possible existence of causation, which then must be identified separately. Then the mechanism of why something causes something else should be investigated. That is, of course, in cases where only statistical data is available initially to investigate a phenomenon. Fortunately, in the case of climate change, the correlation was predicted beforehand by physics, and its later appearance in the data was an expectation.

  48. @pettman @395

    Some interesting ideas there. You have obviously done considerable research to come up with those thoughts. Could you please give some of the key references that you have used to come to your conclusions. They would make very interesting reading. 

  49. What is this? It appears to pop up on the denier blogs these days.

  50. SDK @399,

    You provide the link to Allmendinger (2017) 'The Refutation of the Climate Greenhouse Theory and a Proposal for a Hopeful Alternative' and say it is featuring on denialst sites. This should not be a great surprise as Allmendinger (2017) is a pack of nonsense, pretty-much like the rest of the content of denialist websites. There is a post about this particular pack of nonsense at …and Then There's Physics. Apparently Allmendinger paid $519 for his vanity publication.

    Another grand work from the same author was 'published' a few months later, 'The Real Cause of Global Warming and its Implications', and a further work with a similar title is also listed in his biog but appears to have disappeared with a defunked website. Other works are listed here. I would suggest the only reason for examining them would be to gain a better insight into the mind of a lunatic obsessive.

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