What would the temperature of the Earth be without CO2 in the Atmosphere?


Here is my take on the issue.  Please feel free to provide any input you have on this topic.

The question I asked of everyone was what would the temperature of the Earth be if everything else was held constant except there was no CO2 in the atmosphere.

So questions of albedo and clouds must be ignored. Another thread can discuss the legitimacy of such feedbacks, but the question I want answered by everyone is what would the Earth’s temperature be if there was no CO2.

My approach was to determine the total net energy that is transferred from the surface to the atmosphere. I used Kiehl-Trenberth 1997 and 2008 and others. While slight differences existed the overall result is that there is 120 W/m^2 of energy transferred to the atmosphere by the Earth’s surface. This is 71% of the total energy that is absorbed by the surface from the Sun.

I then broke down each transfer mechanism. Here is the end result as shown in my book.

Evaporation: 80.0 W/m^2
Water vapor (GHG): 18.1 W/m^2
Convection: 17.0 W/m^2
CO2 (GHG): 3.3 W/m^2
Ozone (GHG): 1.0 W/m^2
Other (GHG): 0.7 W/m^2

The Inconvenient Skeptic

The 6 main components of the Earth's Greenhouse Effect. The total energy for them is the 120 W/m2. GHG is energy absorbed by specific greenhouse gases.

This total energy transfer is consistent with the daily temperature cycle that exists in the atmosphere. I can provide more details on that if anyone is interested.

Since the accepted value of the total GHE is 33 °C, I used each proportion of energy to the 33 °C. The result was as follows:

Evaporation: 22.0 °C
Water vapor (GHG): 5.0 °C
Convection: 4.7 °C
CO2 (GHG): 0.9 °C
Ozone (GHG): 0.3 °C
Other (GHG): 0.2 °C

If CO2 were removed, the change in energy transfer would be 3.3 W/m^2 which is 2.75% of the total. That change corresponds to a total change to the GHE of 0.9 °C which I will consider 1 °C as the ozone transfer really takes place in the stratosphere.

Since the Earth’s temperature is ~287K, the temperature of the Earth without CO2 would be ~286K.

Posted in Energy Balance by inconvenientskeptic on August 15th, 2012 at 2:57 pm.

14 comments

This post has 14 comments

  1. Richard111 Aug 19th 2012

    Baffled layman comment. Each and every CO2 molecule in the atmosphere is a unique black body that absorbs or emits radiation at 2.7, 4.3 and 15 microns. Wein’s Law tells us the peak temperature of a standard black body for each one of those bands. Radiation at 2.7 and 4.3 microns is not emitted from anywhere on the earth’s surface. 15 micron radiation is emitted from all the earth’s surface. A cool black body can only warm up if it can absorb radiation of a higher frequency/shorter wavelength than its current peak temperature. CO2 molecules are incapable of absorbing any radiation above the 15 micron band from the earth’s surface. Peak temperature for the 15 micron band is 193.2K (call it -80C). All CO2 molecules in the atmosphere are warmed to local air temperature by collision induced conduction to above this temperature. CO2 molecules can radiate 15 micron photons and do so to cool the atmosphere. CO2 can only absorb a small statistical amount of upwelling 15 micron radiation from the surface.
    To answer your question: removal of CO2 from the atmosphere will result in warming.

  2. Go Canucks!! Aug 19th 2012

    Your assumption is that removing CO2 would have no affect on the other components.
    The theory as I understand is that without the first 100 or so ppmv of CO2, all of the water vapour would precipitate from the atmosphere, there would be no lapse rate and the temperature would be isothermal.

  3. To quote the great Wolfgang Ernst Pauli, this is not even wrong.

    I think a few people might misinterpret this to mean that CO2 is only driving a 1K influence on temperature, but the whole thing is just speculative nonsense to begin with. How can you hold water vapour constant while examining a reduction in temperature? If you remove CO2, the resulting decline in temperature will cause a decline in water vapour, which would drive temps down further than 1K.

    How much of your book qualifies as non-fiction?

  4. inconvenientskeptic Aug 20th 2012

    I have seen the proposed theory that it is CO2 that keeps water vapor in the atmosphere, but that is only a theory and not a very good one.

    I am working on a longer article about why energy is energy in the atmosphere.

    There is nothing special about the energy that is absorbed by CO2. The idea that it is somehow different is one of the most bizarre idea’s to develop recently.

  5. Go Canucks!! Aug 20th 2012

    Perhaps you will find this of interest. It’s from Dr. Spencer’s blog.

    “But what many people don’t realize is that the 33 deg. C of surface warming is not actually a measure of the greenhouse warming – it represents the balance between TWO competing effects: a greenhouse warming effect of about 60 deg. C (the so-called “pure radiative equilibrium” case), and a convective cooling effect of about 30 deg. C. When these two are combined, we get the real-world observed “radiative-convective equilibrium” case.

    This has been known since at least 1964 (Manabe and Strickler, 1964). It was also discussed in Dick Lindzen’s 1990 paper, Some Coolness Regarding Global Warming, which is when I became aware of its significance.”

  6. Proposed theory? What is it about the relationship between water vapour and temperature that you dispute?

    If you reduce temperature by 1K by removing CO2, there will be a decline in atmospheric water vapour due to the reduced temperature. Do you not accept that H2O is a greenhouse gas and influences temperature, or that the atmospheric concentration is temperature dependant; or both?

  7. inconvenientskeptic Aug 27th 2012

    The basis for water vapor being dependent on CO2 is the Clausius Clapeyron relation. That is completely worthless for the situation of the Earth’s atmosphere because most evaporation takes place in the Tropics where the temperature would not drop at all if there was no CO2.

    Saturated air usually only happens in the early morning hours when air has cooled. Once the sun rises and the dew evaporates, the air is no longer saturated. In no way would the loss of CO2 alter any of that.

    Water vapor is the key gas, CO2 is not.

  8. That is some seriously flawed logic. Is there no evaporation other than in the tropics? Anywhere CO2 does influence temperature there will be an increase in evaporative loss through its presence. If removing CO2 won’t change temp in the tropics, your estimated 1K reduction must be spread across the higher latitudes rather than evenly across the globe. So that is an even greater influence on evaporation in higher latitudes than your initial argument implied. How much will water vapour be reduced and what will be the resulting effect on temperature?

    As you said, water vapour is the key gas so there is no getting around the fact that a 1k reduction in average temps would drive a decrease in atmospheric H2O. It looks like you are unwilling to accept that your oversimplified estimate is actually meaningless.

  9. inconvenientskeptic Aug 28th 2012

    Sigh. A theory is a theory until proven otherwise.

    There is no convincing data to support the idea that CO2 level regulates atmospheric water vapor concentration. There is a theory about that, but no evidence.

    Computer models are not evidence.

    Just like the theory at CO2 regulates ocean pH levels, there is a shocking lack of evidence that such things actually happen, just an unsupported theory that looks nice on paper, but no evidence that it makes a difference.

  10. Richard111 Aug 31st 2012

    The UK has just experienced the coldest August night since records began. The wife will be putting washing on the line shortly. Only some light strato-cumulus overhead. Almost no wind. Not the best drying day, but dry it will. The point being that water will evaporate into the atmosphere at any temperature. Even ice sublimates at below zero C. Its all relative you know. :-)

  11. Um, hang on we are talking about temperature. You are disputing that a decrease in temperature will influence H2O concentrations. The role CO2 plays in the Clausius–Clapeyron relation is through temperature. You have already stated that your modelling (which as you stated is not evidence) indicates that removing ALL the atmospheric CO2 would reduce global temps by 1K. What would a 1K reduction do to water vapour?

    Also do you have any evidence that CO2 does not influence temperature in the tropics? I’m not sure what the basis for that opinion is either.

    PS you might want to check a dictionary for the definition of the word “theory”. You are sounding a bit like a creationist mate…

  12. inconvenientskeptic Sep 2nd 2012

    Name calling is not constructive commentary.

    Usually it is the responsibility of those presenting a new theory (such as one that CO2 regulates water vapor) before it is accepted. This one is assumed, but has never been proven.

    Much like the idea that atmospheric CO2 level contributes to ocean acid levels. There is a nice basic chemistry theory behind, but no evidence to support it.

  13. No name calling here, just stating a fact that you seem to be confused about what a theory is and that I have often heard creationists refer to evolution as “just a theory”.

    I’m pretty sure the relationship between water vapour concentration and temperature is not a “new theory”. But it looks like you are only interested in giving me the run around on this so I suppose there is also no point in continuing the discussion, let alone asking for evidence to support your assertion that CO2 does not affect temperature in the tropics?

  14. inconvenientskeptic Sep 4th 2012

    Old or new is irrelevant to the quality of the theory. Creationism has acceptance with many because it is an old theory, but that is no indicator for the quality of the theory.

    Water vapor enters the air regardless of the temperature of the air. It is the temperature of the water that determines the evaporation rate.

    Oceans absorb solar energy at ~95% or so because of their low albedo. Oceans will always warm because of that. Nowhere in there does the temperature of the air enter into the equation.

    There has never been anything that has ever shown the amount of water vapor in the atmosphere is dependent on the CO2 concentration. Until there is, there is only the hypothesis that CO2 regulates water vapor concentration.

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