

History of Climate Change: Part 1- Learning The Greenhouse Effect




Fourier recognized three ways that a planet could be heated. The first is by incoming sunlight (or solar radiation), which we now know accounts for virtually 100% of the energy Earth receives. The second way is by heat diffusing through the surface from the hot interior of the planet. Fourier reasoned (correctly) that this was too small to play any role in Earth’s surface temperature. Unknown to Fourier, the situation is different on the gaseous planets like Jupiter, where internal heat generated by the gradual compression of the atmosphere (known as Kelvin-Helmholtz contraction) is comparable to the energy they receive from the Sun.

Finally, Fourier thought that heat was communicated to Earth by the general “temperature of space,” which he reasoned was somewhat comparable to the temperature of the Polar winter (perhaps at -100°F). In essence, he thought this was the temperature that any planet would relax to if there were no sunlight. Qualitatively he was correct, but rather than being similar to Polar winter, the “temperature of space” is nearly absolute zero. This misconception was corrected later by Claude Pouillet in 1838, and never again would there be any consideration of the role of “the temperature of space” in climate.

This issue aside, Fourier understood the basic idea that the temperature of Earth, or indeed any planet, is determined by the rate at which it received incoming sunlight vs. the rate at which it loses thermal radiation to space. This thermal radiation (or infrared radiation) is the “heat” that Earth sheds into space in order to equilibrate at a stable temperature. Fourier is also widely credited with coming up with the idea of the greenhouse effect (though he never actually introduced that term); the greenhouse effect is the process by which certain heat trapping gases in the atmosphere keep the surface warmer than it would be without them.

These so-called greenhouse gases are generally transparent (i.e., non-interactive) with incoming energy from the sun, but interact strongly with the outgoing thermal energy of the planet. It would be left to John Tyndall in 1861 to show that the vast majority of our atmosphere did not interact with Earth’s radiation, and only water vapor, CO2, and some other trace compounds (which make up less than 1% of the air) work to keep Earth warm enough to have liquid water. The way the greenhouse effect works was previously described in this article.

The Birth of Modern Climatology

Perhaps the fundamental pioneering contribution to the field of climate came in 1896, when Svante Arrhenius (a Swedish chemist), working with moonlight data and an incomplete theoretical basis, calculated the amount of warming that would occur if the amount of CO2 in the atmosphere were doubled. His estimate was only slightly higher than modern calculations (which range from about 3.5 to 8 degrees Fahrenheit), although he certainly got very lucky along the way.

Arrhenius was primarily motivated not by global warming, but by solving the ice age mystery that challenged scientists at the time. By the late 1800’s, it was recognized that Earth had several times plunged into and out of ice ages, and people were interested in formulating a theory behind it. In fact, Arrhenius did not think it was possible that fossil fuel emissions could elevate atmosphere CO2 so much to be important in the future, and even if they did, he imagined that a bit of warming might be a good thing.

Arrhenius also correctly reasoned that the amount of gaseous water in the air would increase in a warming climate, since the amount of water that can potentially build up in the atmosphere increases rapidly with temperature. Scientists know this rule as the Clausius-Clapeyron law, one of the fundamental governing principles underlying all atmospheres with a condensing substance (on Earth, that is water). Furthermore, since water vapor is also a greenhouse gas, increasing its concentration in response to elevated temperatures would further amplify the CO2-caused warming.

The Opposition

Arrhenius’ idea had plenty of contention however, and could hardly be considered the “mainstream” view. There were at least two popular arguments that likely had a large role in stalling future research on the role of greenhouse gases on climate until the middle of the 1900’s. These were first popularized by Knut Ångström, and then others (this 1901 Monthly Weather Review article following his work warned geologists not to adhere to Arrhenius’ ideas about CO2 changing climate).

Ångström had an assistant measure the passage of infrared radiation through a tube filled with carbon dioxide, whom then reported that adding more of the gas to just small amounts hardly affected how much radiation passed through the tube. In essence, the CO2 was “saturated” and already absorbed all of the infrared radiation from the surface that it could possibly absorb. The second (and related) argument was that water vapor also absorbs so much radiation that there is little left for CO2 to do.

There were some issues with Ångström’s experimental setup, but more importantly, the conclusions were wrong on a number of fundamental grounds. First, more sophisticated measurements of the radiation absorption properties of CO2 (that were not available until after WW2) showed that CO2 was nowhere near saturated at Earthlike conditions. Even Venus, with some 300,000 times more CO2 than Earth is not “saturated.” Note that even when the “peak” of the absorption band of CO2 is filled up, there is much more absorption that can happen in the far edges (or “wings”) that are weaker, but still very important for Earth’s temperature.  The following image shows the wave numbers of light where CO2 absorbs strongly (i.e., a specific region throughout the entire spectrum of light, one can also use wavelengths or frequencies to describe light). The vertical axis is just an absorption coefficient that increases going upward, indicating stronger absorption. There are two dashed lines- everything above the 300 part per million (ppm) line indicates the wave numbers of light that would be strongly absorbed at that concentration (marked out by the green box); everything above the 1200 ppm line is where CO2 strongly absorbs at that concentration.  The extent of this region is marked out by the orange box, and you can see that some absorption increases in the “wings” (away from the center). This is the extra amount of energy that cannot exit to space as freely as it would have at the lower CO2 concentration, forcing the planet to warm.

Absorption Co-efficient vs. Wavenumber for the Carbon Dioxide molecule. Shows the regions in the spectrum of light where CO2 impacts Earth

Ångström’s logic was even more flawed than this, since even if the whole atmosphere were “saturated” in the sense he thought, adding more CO2 could still cause warming.  The reason is that the greenhouse effect is not like a single glass pane composed of absorbing gases stuck in the atmosphere (though even a lot of modern textbooks teach it this way). In reality, air gradually gets colder and thinner as you move upward into the atmosphere. Eventually it reaches a point where it is so thin that it simply transitions into outer space. If you could follow the history of a “particle of energy” (which we can call a photon) emitted by Earth’s surface traveling out to space, you would find that there is a very small chance that it escapes directly to space due to the presence of intervening greenhouse gases. Most of it would be absorbed at some point in the atmosphere, upon which a photon would be re-emitted and sent in a random direction. The “greenhouse effect” is therefore like a pinball effect, with energy cascading up and down throughout the atmosphere, with various fates along the way. Some of that energy would gradually find its way up into the upper atmosphere. Once the photon reached a layer that was so thin that there was little chance of a greenhouse molecule absorbing it, it could escape to space. Even if the lower atmosphere were saturated in Ångström’s sense, increasing CO2 could always increase the greenhouse effect in these upper atmospheric layers. Because these layers are colder than the surface, and emission of energy decreases at lower temperatures, adding more greenhouse gas can always reduce the amount of energy leaving the planet. This forces the planet to heat up as explained in the last article.

By the middle of the century, computer power and radiative transfer data had advanced to the point where the saturation myth could be dispelled, and where more sophisticated calculations of how the atmosphere absorbs and emits infrared radiation could be done. It could also be shown that CO2 was strongly absorbing in certain regions that water vapor was not so much, reducing the competition between the two gases. Furthermore, there is little water vapor in the dry upper atmosphere, so CO2 has a profound impact on the energy balance of the planet.

Another landmark paper on this came in 1956, when Gilbert Plass helped revived interest concerning the effects of doubling the CO2 content of the atmosphere. Plass did an excellent job detailing the influence of CO2 band on the upward and downward infrared radiation flux at different heights in the atmosphere. Though, in translating his results into changes in surface temperature, Plass got caught up in another fallacy (one which is routinely cited in some popular descriptions of the greenhouse effect even today).

The erroneous Surface Energy Budget perspective

In many internet descriptions of the greenhouse effect, the impact of adding CO2 to the atmosphere allegedly arises by holding the atmospheric temperature fixed and supposing that the air becomes a better emitter of infrared radiation downward to the surface. In other words, when you increase the greenhouse gas concentration, more radiation is absorbed in the lower atmosphere and is then re-emitted to the surface, which then supposedly heats the surface further.

In most cases however, the balance of energy by the planet at the top of the atmosphere (between incoming sunlight and outgoing radiation) has a greater influence on the surface temperature than the forcing directly at the surface. Moreover, the reason the downward infrared flux increases to the surface has more to do with the increase in temperature than the direct increase in CO2, and the other surface energy exchange mechanisms (like evaporation) also change in a new climate. The atmosphere itself must adjust its own outgoing energy to changes in temperature, and most outgoing energy by the planet originates in the upper atmosphere, due to how strongly absorbing it is. It may seem odd that what is happening so high in the atmosphere can have such a profound impact on surface temperature, but this perspective would need to adopted from the 1960’s onward in more advanced treatments of planetary temperature.

The first article to resurrect this “top of the atmosphere” perspective, but also to simulate many key physical processes at the computer calculation level of sophistication was the 1967 work of Manabe and Wetherald (here), which is probably the first fully sound estimate of the temperature increase from a doubling of CO2. This was also the first attempt to add convection in a comprehensive manner to the “radiation only” perspective discussed so far. Since the surface is heated strongly by sunlight, an unstable situation is set up where heat must be transported from the surface to the overlying atmosphere. This forces the atmospheric temperature structure to relax into one that cools with height at about 30 degrees Fahrenheit per mile going upwards (and often less than that depending on moisture content, due to the heat released when vapor condenses into clouds).

Stay tuned…

This article described some of the history behind the “first principle” physics underlying global warming. In Part 2 of this series, I’ll talk about some of the history of attempts to measure global temperature, CO2 concentration, etc and the efforts to build knowledge into comprehensive coupled models of the climate system.

Chris Colose

11 Responses

  1. R Harding says:

    You said “there is little water vapor in the dry upper atmosphere, so CO2 has a profound impact on the energy balance of the planet”. I wonder why there would be little water vapor since the H2O molecule is lighter than CO2? I guess I just picture things floating up like little balloons. But then I suppose we wouldn’t have any H2 in the atmosphere if this were true. Thanks for your article.

  2. Chris Colose says:

    The reason most of the water is lower down has to do with temperature (remember in the article I mention that it gets colder the higher you go, and by the Clausius-Clapeyron relation also mentioned, the colder air cannot support much water vapor). Water has a rather short residence time in the atmosphere (days to weeks) so if you were following a parcel of water traveling around the air you’d find most of it would rain out by the time it gets to high altitudes (or latitudes). But, the little water that is in the high, upper atmosphere still has a very profound impact on Earth’s radiation budget by the same reasoning discussed in this post. If you replace the surface emission of infrared energy with very cold (and feeble) emission aloft, the net effect is that the whole planet is losing less energy than before.

    As for your other point, there is very little separation by molecular weight throughout most of the atmosphere, which is well stirred by turbulent motions, so most of the atmosphere (N2, O2, Argon, CO2, etc) is well-mixed vertically. There are some exceptions- a lot of the ozone is high up in the stratosphere as a result of chemical reactions and the availability of energetic sunlight.

  3. Gabriel Atega says:

    It should be considered that evaporation takes place all over the Earth on one hand, while precipitation does not. Rainfall are concentrated in some areas while other areas are having droughts. This could mean that the volume of moisture that is being added into the atmosphere by evaporation is not matched by a corresponding amount of precipitation. If the additions are greater than the reductions, then the amount of moisture in the atmosphere is increasing.

    If as shown, the polar caps have been melting and the ice sheets retreating from since the last Ice Age, it means that there is a continuing adding of moisture in the atmosphere, and that there is more moisture today in the atmosphere that there was in the past. Or that there is more moisture today in the atmosphere than what there was during the last Ice Age. And it would be safe to assume that as the ice sheets from the last Ice Age retreated, the forests correspondingly increased in areas covered and mitigated the amount of waters that should have gone up into the atmosphere following the retreat of the ice sheets.

    Now since we have only during the last two centuries have begun to loss the forests, are we not now having more moisture in the atmosphere equivalent to what should have been kept on the ground by the forests that we have lost?

  4. Chris Colose says:


    I wouldn’t think of ice sheets melting as a contributor to the long term global hydrologic cycle in the sense you are describing, since the oceans always act as essentially an infinite supply of water to the atmosphere anyway. Most of that water from the melting ice is going to become ocean water, and the regular cycle of evaporation, cloud formation, rain, etc will proceed as usual, with the rate of these processes determined by the base climate state (largely temperature). Certainly they are important locally- in order to have an ice sheet at all you need snow that can accumulate faster than it melts in the summer, and of course ice sheets are very important for global sea level.

    In the climate mean, global evaporation is well balanced by precipitation, and both go up slightly in a global warming scenario. Though, the amount of water stored in the atmosphere is actually expected to go up much faster than the precip/evaporation increases (~7% per degree Celsius warming for water vapor concentration vs. 2-3% for precip/evaporation). This situation implies that rate of transport of moisture from the lower atmosphere (the boundary layer) to higher levels where it rains out must go down, something that seems to be observed and simulated across most models.

    You can think of increases in moisture over recent decades as primarily a consequence of changes in temperature (rather than deforestation or ice sheet changes). As for deforestation, I don’t know if they have huge contributions globally, but certainly there are a lot of regional hydrology changes that happen when you replace canopy with desert soil. Most studies that see what happens when you deforest the Amazon for example agree that deforestation causes a local reduction in precipitation, evaporation, and moisture convergence in the region, although with minimal impact on the global hydroclimate. I don’t follow the literature on that very well though, so there could have been more recent advances I am unaware of..

  5. SoundOff says:


    Are there actual laboratory experiments that show how much temperature increases given a certain increase in water vapor, similar to the ones that show that doubling the concentration of CO2 increases temperature about 1.2 deg C? It doesn’t seem like such an experiment would be too difficult to do.

    I’m guessing (from rough calculations) that an increase of 1.2 deg C would result in 8% more water vapor, which would add a further 1.8 deg C to temperatures. An actual laboratory experiment showing 8% equates to 1.8 deg C would make me more confident.

  6. Chris Colose says:


    Keep in mind that the radiative transfer problem is quite sensitive to the vertical distribution of the water vapor. A little bit more water near the top of the atmosphere means more than putting a bunch of extra water closer to the surface (in terms of warming effect) because you need cold air aloft to generate a greenhouse effect. Theoretically, I see no problem with satisfying the Clausius-Clapeyron equation while simultaneously failing to generate an enhanced water vapor greenhouse effect, but this is not seen in any observations or models, and at this point the magnitude of the WV feedback is fairly well constrained (see Dessler and Sherwood’s Science article on this, but there are plenty of others (Brian Soden has some good work on this). Though, this makes the problem a bit more complicated than for CO2, which is well-mixed throughout the atmosphere. You also have to get the temperature structure of the atmosphere right; a large chunk of the planet tends to stay on a moist adiabatic lapse rate which goes down in a warmer world, reducing the temperature contrast between the surface and upper atmosphere, reducing the greenhouse effect and offsetting a portion of the water vapor response.

    The 1.2 C for a doubling of CO2 that you mention is taken by calculating with spectroscopy the reduction in longwave energy at the top of the atmosphere that occurs when you increase CO2, and then making use of that number in the Planck function (which relates emission to temperature). Once you get past the line by line radiative transfer results (see Myhre et al 1998 for CO2 and other GHGs) it is a simple back of the envelope calculation, but keep in mind that it doesn’t include any feedback processes (including water vapor increases once you double the CO2, but also any changes in albedo or lapse rates)

  7. Craig says:

    Chris, I would just like to thank you for the articles that you post. I spend a good deal of time trying to debate many people on many different subjects using verifiable information. You have done an excellent job on this very subject and I would just like to encourage you to keep it up. Thank you

  8. Chris Colose says:

    Thanks Craig, let me know if you want any specific points covered eventually…

  9. Pete Ridley says:

    Hi Chris, may I first thank you for your recent participation in the E-mail exchanges discussing Roger Taguchi’s comments on back radiation. I look forward to reading Roger’s response. You also provided a link to this blog and I’ve read a few of the threads – very interesting, especially the comments.

    You may recall our exchanges back in 2009 on your “Richard Alley at AGU 2009: The Biggest Control Knob” thread ( about the validity of the ice sheet record. The discussion was unfortunately ruined by several trouble-makers butting in and pretending to be other contributors, which caused you to close the thread. (I have since been able to find out who two of them are and hope that they’ll stay away from your new blog.)

    Since our exchanges I took up the issue of preferential fractionation of CO2 out of the air “trapped” in ice for decades, Centuries and millennia in E-mail exchanges with Professors Richard Alley, Michael Bender, Jeff Severinghaus, Hartmut Frank, Zbiniew Jaworowski, Eric Wolff, Euan Nisbett and others and these are underway at the moment. If you are interested I can include you in the circulation.

    I was having excellent exchanges with Professor Wolff (British Antarctic Survey) on the University of Cambridge’s The Naked Scientists on my thread “Another Hockey Stick Illusion?” ( but the thread was closed prematurely by the moderator. That individual hides behind the false name yor_on and is a staunch supporter of the Catastrophic Anthropogenic Climate Change (CACC) hypothesis. The Naked Scientists had been unable to respond to my simple question “ .. “why do paleo-climatologists use collision diameter in preference to kinetic diameter when considering the migration of air molecules through firn and ice”? .. ” so I managed to persuade Professor Wolff to participate. It didn’t take yor_on long to jump in and close down the discussion. He obviously hates to hear the sceptical argument. (I have my suspicions that the University of Cambridge’s Naked Scientist project funding was also a major factor and I’m in the process of researching that using Freedom of Information and Data Protection legislation, but that’s another story).

    I see that Professor Alley’s 2009 AGU presentation “The Biggest Control Knob: Carbon Dioxide in Earth’s Climate History” ( is mentioned on this blog by Robert Grumbine (I’m tempted to add him to the circulation too). You picked up on one of Professor Alley’s comments in that presentation – the one comparing the cause/effect relationship debt/interest with temperature/CO2. you said ( “ .. Debt causes interest, so clearly interest can´t put you further in debt… I have issues with such logic .. ”. I know how impressed you are with Alley but initially I was rather surprised that you’d brought economics into a discussion on a blog that you claimed you would spend some time on “ .. discussing the underlying physics of planetary temperature and the greenhouse effect, the evidence that humans are changing the climate, and some future projections .. ” (

    You made no mention of bringing in economics or for that matter politics, but then I came across your comment “ .. Arrhenius .. calculated the amount of warming that would occur if the amount of CO2 in the atmosphere were doubled. His estimate was only slightly higher than modern calculations (which range from about 3.5 to 8 degrees Fahrenheit) .. ” ( That figure of “3.5 to 8 degrees Fahrenheit” for a doubling of CO2 from guesstimated 1750 levels was widely reported in the media as being a conclusion presented in the IPCC’s 2nd Feb. 2007 AR4 SPM (e.g. see although I have not been able to find it in the SPM available presently on the IPCC web-site (I see that Alley is the firast of the listed “Draughtuing Authors –

    You don’t get a more politicised version of science than in the IPCC’s reports, especially the SPMs, which in 2007 was published before the report itself was agreed.

    As I understand it (and I’m not a scientist) this figure is arrived at by making unsubstantiated assumptions about feedback effects, which you discus in “Understanding Global Warming: Feedbacks, and how Carbon Dioxide helps control Earth’s Temperature” ( You said “ .. If the globe gets warmer, more water vapor can build up in the atmosphere, and force it to get warmer still. Similarly, if the globe were to get colder, for example by reducing CO2 concentrations or dimming the sun, the air would support less water vapor and this would amplify the cooling. This is an example of a positive feedback system. .. ”. With your profound understanding of the processes and drivers of the different global climates perhaps you can explain to an aged layman why it is that, if water vapour provides positive feedback, past increases in global temperature haven’t caused a catastrophic runaway effect without the help of anthropogenically generated CO2?

    While you’re at it, can you also explain why, if we stop using fossil fuels in order to reduce global warming this will not trigger a sudden descent into a catastrophic “snowball earth” condition? If you can’t explain it then maybe we should heed the advice of Stephen Schneider back in 1978 when discussing the worry at that time, global cooling, in the “In Search of .. the coming ice age” broadcast, Part 3. Schneider said “Can we do these things? Yes. But will they make things better? I’m not sure. We can’t predict with any certainty what’s happening to our own climatic future. How can we come along and intervene then in that ignorance?” ( at 06:10 minutes).

    Also, in 2009, when ridiculing the book “Heaven and Earth” by CACC sceptic Professor Ian Plimer, his fellow Adelaide University Professor Barry Brook said “ .. There are a lot of uncertainties in science, and it is indeed likely that the current consensus on some points of climate science is wrong, or at least sufficiently uncertain that we don’t know anything much useful about processes or drivers. .. ” ( but please read his full statement as Professor Brook gets upset when I only quote what I regard as his most significant words).

    You have said “Part of the purpose of this blog is educational, so any other reader trying to get information out of these comments is simply in a position to trust one of us .. ” ( I don’t think I am alone in being very wary of what politicians do or say and the scientists appointed to contribute to the IPCC reports are chosen by politicians. I also understand that the reports that it produces are scrutinised by political appointees before approval is given for publication so can the reports produced by the IPCC be trusted? All of those IPCC-gates suggest to the contrary.

    Do we not disregard those words of Schneider and of Brook at our peril? Who should the layperson trust Chris, you, or brook, or Plimer, or Ball, or Spencer, or etc. etc. etc? How can we know how much your own political motivations influence the presentation of your version of climate science?

    Best regards, Pete Ridley.

  10. Gary says:

    Pete, you wrote: “How can we know how much your own political motivations influence the presentation of your version of climate science?”

    One thing that I have found helpful in this setting is to try to see if the people presenting the science have evidence of avowedly political motivations or not. Recent quotes from Spencer indicate that he feels his scientific job has a political purpose, for example. Ian Plimer, I believe, also works for libertarian think tanks…Chris, and as far as I know, other climate scientists, don’t feel that their work has a political purpose.

    Hope that is helpful, Gary

  11. Mike Flynn says:


    I posted a comment on your old blog at WordPress. I didn’t realise it had been retired.

    I hope to can help me to understand a problem I have with your explanation of the greenhouse effect. I have cut and pasted the relevant part of your post; –

    “For example, if 10x units of solar radiation hit the surface, then

    10x solar in, 10x infrared out establishes radiative equilibrium

    Now suppose that the solar is 10x to the surface, but only 6x of infrared escapes to space, and 4x is absorbed by the atmosphere. Of that 4x, 2x is re-radiated back to the surface, and 2x radiated back out to space.

    12x in the surface
    8x back out to space


    Now my problem is that if 6 x leaves the surface, the surface temperature will drop by 6/10 of the increase caused by the 10x in. Obviously, the temperature cannot rise, nor can it remain the same if the surface is emitting infrared. Now if 2x is reradiated back to the surface, then the temperature is raised by 1/3 of the drop which occurred when the 6x left.

    In no case can the surface temperature be higher than that caused by the radiant energy absorbed from the Sun. The atmosphere as you have stated acts as a fairly poor insulator, which retards the escape of heat from the surface, and retards the absorption of radiation from the Sun.

    This would explain why the max day temp on the Earth’s surface is lower than that on the Moon (same distance from the Sun as the Earth, on average) and why the min night temp on the Earth is higher than that on the Moon.

    I have seen other explanations of the greenhouse effect, and all of them seem to overlook the fact fact that the temperature of a body losing heat actually drops.

    Thank you in advance.

    Mike Flynn