Anthropogenic Forcings on Climate

Well, I messed up my post on methane, giving it far greater weight as a contributor to human influences on the climate than does the IPCC.

Since I couldn’t find what I was looking for (a stacked bar chart showing in Column A all positive human contributions and in Column B all negative contributions, I am trying to do it myself.

Radiative forcing has been used as a proxy to express the climate response of different GHGs. It is a hypothetical figure, as it doesn’t include the response of the rest of the climate’s components or natural variability. Increased warmth, for example, has produced a quick response in vegetative cover increase, which should reduce CO2 in the atmosphere, affect precipitation in the immediate region and have an effect on surface albedo as well. None of those is captured by radiative forcing estimates, an indication that physicists have superimposed their concept of the world on us all. All hail our new physicist overlords! (I suspect that biology and chemistry will eventually find their voice.)

My source is IPCC AR4 (I couldn’t find it in AR5), but the physics shouldn’t change that much in a handful of years, right?

So here’s about half the picture in my handmade chart:

IPCC AR4 Greenhouse Gas Forcing

According to the IPCC, human emissions of CO2 comprise 56.6% of the relevant gas emissions.

The total net forcing (subtracting the negative contributions of land use and cloud albedo) is 1.8 Watts per square meter. The total forcing of the elements listed in the chart above are 2.64 Watts per square meter, I think.

Here’s their chart:

figure-2-4

There are a lot of things I don’t understand.

For example, their separate figure for deforestation. Much of the effects of deforestation is the liberation of CO2 from dead trees. Some of it is from the changed albedo of the cleared land. Is the separate figure for deforestation accounting for either, both or something else?

But I guess my major sticking point is black carbon. I’m not sure why they list black carbon is given by the IPCC as a negligible forcing of 0.1 W/m2. In a report by the EPA to Congress, the EPA writes,

“BC influences climate through multiple mechanisms: – Direct effect: BC absorbs both incoming and outgoing radiation of all wavelengths, which contributes to warming of the atmosphere and dimming at the surface. In contrast, GHGs mainly trap outgoing infrared radiation from the Earth’s surface. – Snow/ice albedo effect: BC deposited on snow and ice darkens the surface and decreases reflectivity (albedo), thereby increasing absorption and accelerating melting. GHGs do not directly affect the Earth’s albedo. – Other effects: BC also alters the properties and distribution of clouds, affecting cloud reflectivity and lifetime (“indirect effects”), stability (“semi-direct effect”), and precipitation. These impacts are associated with all ambient particles, but not GHGs. y The direct and snow/ice albedo effects of BC are widely understood to lead to climate warming. Based on the studies surveyed for this report, the direct and snow/ice albedo effects of BC together likely contribute more to current warming than any GHG other than CO2 and methane (CH4).”

The EPA gives the potential forcing of black carbon as “+0.34 to 1.0 W m-2 direct forcing +0.05 W m-2 (snow/ice albedo forcing) ± ? (cloud interactions) Net effect: uncertain, but likely warming.”

Way back in 2001, Mark Jacobson (Yes, him) published a paper in Nature saying “Soot -­ or black carbon ­ may be responsible for 15 to 30 percent of global warming, yet it’s not even considered in any of the discussions about controlling climate change,” says Stanford Professor Mark Z. Jacobson, author of the Feb. 8 Nature study.

Since then, the Guardian has published a story saying “The global warming effect of ‘black carbon’, or soot, has been greatly exaggerated due to mistaken assumptions about the atmospheric altitude at which its particles are concentrated, according to a new study” based on a paper by the Centre for International Climate and Environmental Research-Oslo.

The BBC countered with “Scientists say that particles from diesel engines and wood burning could be having twice as much warming effect as assessed in past estimates. They say it ranks second only to carbon dioxide as the most important climate-warming agent. The research is in the Journal of Geophysical Research-Atmospheres. Black carbon aerosols have been known to warm the atmosphere for many years by absorbing sunlight. They also speed the melting of ice and snow.

This new study concludes the dark particles are having a warming effect approximately two thirds that of carbon dioxide, and greater than methane. “The large conclusion is that forcing due to black carbon in the atmosphere is larger,” lead author Sarah Doherty told BBC News. “The value the IPCC gave in their 4th assessment report in 2007 is half of what we are presenting in this report – it’s a little bit shocking.”

I guess I’m not the only puzzled by all this.

 

34 responses to “Anthropogenic Forcings on Climate

  1. I guess I have to point out all these forcings are mostly offset by temperature. The net energy imbalance over the last decade is about 0.6 watts per m2. Given the current temperatures, it must have fallen in 2014-15-16. If we could get an honest and sophisticated ocean temperature reanalysis (which we don’t have) we may see it’s as low as 0.3 watts per m2.

    • I forgot to add: because the NET imbalance is so low, a change in methane emissions could lead to lower methane concentrations, which coupled with a slight temperature increase MIGHT just stabilize temperatures as long as the other feedbacks don’t kick in too strong. This is a what if scenario, but it’s a viable outcome. Given the recent flattening of CO2 emissions and the high probability that fossil fuel prices will rise fairly fast in the future, a push for intelligent nuclear and some sort of better battery would solve the problem.

  2. Tom,

    According to AR5, Table 8.2, the forcing from CO2 increased from 1.66 W/m^2 in 2005 (essentially AR4) to 1.81 W/m^2 in 2011. So I suppose it is now somewhere between 1.9 and 2.0.

    The same table gives the rest of the well-mixed gases as having increased only from 0.98 to 1.01 W/m^2. That is due to HCFC’s replacing CFC’s and CH4 leveling out (although I think I saw somewhere that it has started to go up again).

    So CO2 is increasing in relative importance. That is a natural result of CO2 being determined largely by the integral of all emissions to date while things like CH4 and HCFC’s are controlled by recent emissions only. The effect is even stronger for total net forcing since the negative forcing is from particles, which have a short lifetime. IPCC expects the relative importance of CO2 will keep increasing, with the difference between CO2 forcing and net forcing remaining constant, within the uncertainty of the projections.

    I might have to look into what is going on with black carbon. If memory serves, 25 years ago people thought that the positive forcing from black carbon and the negative forcing from light scattering by particles might be nearly a wash. Then they realized that black carbon was a much smaller fraction of particulates than they had thought, so that the negative forcing dominates. I don’t know if the numbers you cite are people pulling up old estimates, or if there is a good reason to revise the black carbon numbers upward.

  3. Tom,

    “None of those is captured by radiative forcing estimates, an indication that physicists have superimposed their concept of the world on us all.”

    Well, those things are incorporated into feedbacks. There are good reasons for the distinction, although in some gray areas they can be a bit arbitrary. That has nothing to do with imposing anything on the rest of us; it is just part of the the standard reductionist-constructionist method used by physicists to try to understand complex phenomena.

  4. Kinda like that cartoon floating around, innit? Put stuff in a black box and parameterise it. I kinda have my doubts about it, mostly due to reading what Freeman Dyson has said.

  5. Thank you for having the integrity to be transparent on this topic. My recent research into this shows a bizarre perspective that gas been worked into the conversation as an assumption. That misleading assumption us that human inputs are the greatest part of the global budget. That’s a recent assumption. “Biomass burning” that is actually misleading because the majority of that is from natural forest fires. Also, on at least most graphs. Animal methane seems to be credited to human causes by the climate obsessed. That is oxymoronic on their part. If you are going to work up a graphic display of this, perhaps it should be global, putting the human industrial contributions into a global context.

    • Hunter,

      You are misinformed.

      “That misleading assumption us that human inputs are the greatest part of the global budget.”

      No such assumption. The budgets are what they are. For some things, like methane, human inputs are the largest part and for other things, like CO2, they are not.

      ““Biomass burning” that is actually misleading because the majority of that is from natural forest fires. Also, on at least most graphs. Animal methane seems to be credited to human causes by the climate obsessed.”

      Forcings are not budgets. Forcings are determined from the change in atmospheric concentrations due to anthropogenic causes.

      Natural forest fires do not cause a change in forcing since the CO2 released is balanced by the CO2 taken up by regrowth. But burning a forest to convert the land to, say, grazing is a forcing since the CO2 is released but not taken up by regrowth. Methane from domestic animals is quite properly credited to humans, unlike methane from wild bovines. Similarly, methane from rice paddies is credited to humans while methane from natural wetlands is not.

      • Mike M. You did not actually address my points. It is as if you are on a sort of reflexive mode.

      • Hunter,

        Then I have no idea what your point was.

      • catweazle666

        Mike M. | March 20, 2016 at 8:58 am | Reply
        “Hunter,

        You are misinformed.”

        LOL, you’re funny!

        Have you considered a career in stand-up comedy?

  6. Tom
    One of the big factors in the rating of methane by the IPCC charts is that the forcing factor absorption is in a dry atmosphere – an artificial construct which you can only find out about if you read the very fine print. The narrow bands of methane are almost totally overlain by water. In a typical humidity, there is very little effect.

    • chrism56,

      I am curious as to where I can find this “fine print”. It has struck me as odd that what I have seen on forcing by methane has said nothing about interaction with water vapor.

      • catweazle666

        “It has struck me as odd that what I have seen on forcing by methane has said nothing about interaction with water vapor.”

        That’s because the statement “the narrow bands of methane are almost totally overlain by water” hasn’t anything whatsoever to do with any form of interaction between methane and water vapour.

        Now go right ahead and start with the personal abuse – that’s what you usually do when you are shown to be wrong, isn’t it?

  7. hunter
    Here is the IPCC way of determining the greenhouse effect of each gas https://www.ipcc.ch/ipccreports/far/wg_I/ipcc_far_wg_I_chapter_02.pdf. Note that the effect of each gas is considered in isolation.
    However, if you look at this graph, which is produced at numerous sites, https://commons.wikimedia.org/wiki/File:Atmospheric_Transmission.png The methane spectrum is almost totally within that of water vapour. Look at the Total Absoption spectrum in the IR band – which is the methane peak?Methane only has an effect on IR absorption if there is no water vapour present.

    • chrism56,

      OK, you say that if they are doing the calculation the way you think they do it, then it is being done wrong. I am willing to believe that. The question then is whether they are wrong or whether your understanding is wrong.

      You wrote: “Here is the IPCC way of determining the greenhouse effect of each gas”.
      I am sorry, but I don’t see that anywhere in your 25 year old source. There are no details whatever, only an overview of concepts and results.

      “Note that the effect of each gas is considered in isolation.”
      Really? Where does it say that? It seems to say just the opposite on page 9, in the paragraph beginning “These considerations are complicated …” and ending “… A molecule able to absorb in such a transparent spectral
      region is able to have a far larger effect”.

      I think it likely that the people who know what they are doing are right, and you are wrong.

    • chrism56 –
      The standard reference for ghg forcing is Myhre et al. 1998. I’m on my phone atm, so unable to supply a link, but I mentioned it on another thread within the last couple of days. Or you can find it on Google Scholar. As I recall, they accounted for humidity.

      • HaroldW and chrism56,

        Gunnar Myrhe et al., “New estimates of radiative forcing due to well mixed greenhouse gases”, GEOPHYSICAL RESEARCH LETTERS, VOL. 25,NO.14, PAGES 2715-2718, JULY 15, 1998.

        I don’t see anything explicit about water vapor, but they do account for clouds. Most of the details seem to be in earlier papers.

  8. OK, back on a real computer, so here are two links:
    Myhre et al., (1998)
    Myhre & Stordal, “Role of spatial and temporal variations in the computation of radiative forcing and GWP”, J Geophys. Res. (1997)

    From the former paper: “The absorption of solar radiation in the troposphere yields a positive radiative forcing at the tropopause. This effect is however weak due to overlap with water vapour and a high reference concentration of CO2.”

    In the latter paper, the abstract says, “Spatial and temporal variation in the radiative forcing due to variations in temperature, humidity and cloudiness has been taken into account on the basis of observed data.”

    Those statements lead me to believe that H2O has not been ignored in the analysis.

  9. Mike and Harold
    The numbers used in the IPCC report I earlier referenced are still essentially the same as the current ones so the science hasn’t changed.
    In 2.2.2 there is a sentence about the overlap between methane and nitrous oxides. This is also shown in the table 2.3. Further down in that table, they assign an arbitrary 0.3 overlap for water / methane but that is only in the stratosphere where water concentration is very low. What about the Troposphere where it is 1% or more. In 2.2.6, they talk of only stratospheric water vapour, yet discuss the troposphere for other gases. Why the exclusion?
    On a first principles basis, the main band for methane absorption is about 8 micron. Water vapour has near 100% absorption at this wavelength. If there is water vapour in the atmosphere taking all of the IR radiation, what can the methane do?

    • chrism56,

      Think about what you are saying. You are looking at a brief, non-technical summary of what the experts did and from that drawing a conclusion that the experts got important details wrong. Do you really think that is reasonable? It is reasonable to assume that the experts know what they are doing. It is also reasonable to decide that you won’t trust what they did just on the basis authority. But in that case, if you want to criticize what the experts did you should dig into the details so that you actually know what they did.

      HaroldW points out that although the absorption by H2O is large at the methane lines, it is not 100%. But that is absorption of radiation emitted by the surface. Vertical energy transfer in the lower atmosphere is mainly by convection, not radiation. Most of the emission to space is from the upper troposphere. There is much less water vapor once you get above 1-2 km, so the absorption by water vapor is much weaker in the upper troposphere. So although water vapor reduces the effect that methane might have, it by no means eliminates it.

  10. chrism56: “On a first principles basis, the main band for methane absorption is about 8 micron. Water vapour has near 100% absorption at this wavelength.”
    This post on the other recent methane thread shows that H2O is not near 100% absorption at the ~7.8 um wavelength where CH4 and N2O have strong lines.

    Look, you seem to be suggesting that Myhre & co-authors did not take H2O into account in their calculations. I recommend sending them an email, asking specifically if H2O lines in the troposphere were included in those papers. [As that seems to be your primary concern.] My experience with sending brief, polite questions to scientists has been on the whole quite positive.

  11. I think what we can see clearly is that methane is not the key to a runaway climate effect. Like all other aspects of what the climate imperialists have promoted regarding an imminent apocalypse, they have been wrong. Whether bad science, bad reporting on science, political profiteers or the ancient human soft spot for apocalyptic stories, it ain’t happening. They have about 30 years of failed predictions and historical rewrites. This is a social movement and a social dispute, not a scientific issue.

  12. Mike/ Harold
    From your responses, I gather that your/ IPCC’s contention is that it is only in the stratosphere that the IR radiation is absorbed by water vapour. This is in contradiction with Weubbles and Hayhoe that state:
    “Like other greenhouse gases, methane absorbs infrared radiation (also called longwave or terrestrial radiation) emitted by the relatively warm planetary surface and emits radiation to space at the colder atmospheric temperatures, leading to a net trapping of infrared radiation within the atmosphere. This is called the greenhouse effect. The balance between the absorbed solar radiation and the emitted infrared radiation determines the net radiative forcing on climate.”
    Now which is correct? Is water vapour not a greenhouse gas or is it that the science not settled?

    • chrism56,

      You wrote: “From your responses, I gather that your/ IPCC’s contention is that it is only in the stratosphere that the IR radiation is absorbed by water vapour.”

      Neither I nor Harold nor IPCC said anything that could possibly be interpreted that way. Indeed, we have all explicitly said otherwise. So I must conclude that you are an intentional idiot, who is proud of your ignorance and stupidity.

  13. Mike
    From this and other posts, name calling seems to be your go to stance – nice guy.
    Myrhe was referenced as the go to paper for the IPCC paper. Read the last sentence on Page 11,181. that is to what I was referring. Myhre describes the method used to look at methane overlap but does not actually do it, so the reference is not correct.

    • chrism56 –
      Are you referring to the paragraph in Myhre & Stordal [1997] which spans the end of page 11,182 & the start of page 11,183? “The overlap … between CH4 and water vapor applies transmission for water vapor described by Rodgers and Walshaw [1966].” Why do you say that the authors did not do as they describe? (And if that’s not the correct sentence, please provide the words to which you refer.)

    • chrism,

      I only resort to insults when reason appears to have failed.

      • catweazle666

        Mike M: “I only resort to insults when reason appears to have failed.”

        When you have been trounced in the debate, you mean.

  14. No hunter, the sentence on 11181 as I identified is “There is also large variation in the way clouds are represented in radiative forcing calculations and even whether clouds are represented at all.”.
    I tried finding the Rodgers paper, but only got contemporary references to it.
    According to AR4, Collins et al (2006) is now the referenced paper for radiative forcing of methane, but that seems to be all clear sky model based comparisons of various codes (and proving they fit the hockey stick) and not a comparison between the model and the actual data..
    However, AR4 also makes this comment which I am still trying to work through “Collins et al. (2006) confirmed that line-by-line models agree extremely well for the calculation of clear-sky instantaneous RF from CH4 and N2O when the same atmospheric background profile is used. However, GCM radiation schemes were found to be in poor agreement with the line-by-line models, and errors of over 50% were possible for CH4, N2O and the CFCs. In addition, a small effect from the absorption of solar radiation was found with the line-by-line models, which the GCMs did not include

    • chrism56 –
      Thanks for the reference to Collins et al. [2006], which may be found here among other places. But I wouldn’t call it “the referenced paper for radiative forcing of methane”; Collins compares GCM implementations, which are necessarily simplified for efficiency, to more precise (LBL) methods.

      I’m still left wondering why you connect the given statement in Myhre & Stordal [1997] to your claim that Myhre does not follow its process description. The sentence emphasizes that predecessor methods vary as to what is evaluated and under what circumstances. It is intended to motivate the M&S approach as taking all relevant circumstances into account. There’s nothing in that sentence to back up the contention that “Myhre describes the method used to look at methane overlap but does not actually do it, so the reference is not correct.”

  15. Sorry, the first line was supposed to be Harold not hunter.

  16. Harold (I got it right this time), my comments about Myhre not being the correct reference were that the original statements by me were the to do with the forcing factors of methane. You stated that Myhre was the reference for determining forcing factors. I was looking at the 97 paper, not the 98 one We were talking about different papers.
    With regard to AR4, I took the line “Collins et al. (2006) confirmed that line-by-line models agree extremely well for the calculation of clear-sky instantaneous RF from CH4 and N2O when the same atmospheric background profile is used.” to mean that Collins was the reference for RF number for Methane, but on rereading, I am not sure. There seems to be a circular referencing going on and no footnotes to indicate where the number 0.48W/m-2 in the table 2.1 originally comes from. Myhre (98) has the number for methane as 0.5 to 0.578 in cloudy skies and 0.625 to 0.702 in clear skies which indicates it is not the source.

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