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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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How sensitive is our climate?

What the science says...

Select a level... Basic Intermediate Advanced

Net positive feedback is confirmed by many different lines of evidence.

Climate Myth...

Climate sensitivity is low
"His [Dr Spencer's] latest research demonstrates that – in the short term, at any rate – the temperature feedbacks that the IPCC imagines will greatly amplify any initial warming caused by CO2 are net-negative, attenuating the warming they are supposed to enhance. His best estimate is that the warming in response to a doubling of CO2 concentration, which may happen this century unless the usual suspects get away with shutting down the economies of the West, will be a harmless 1 Fahrenheit degree, not the 6 F predicted by the IPCC." (Christopher Monckton)

 

Climate sensitivity is the estimate of how much the earth's climate will warm in response to the increased greenhouse effect if we double the amount of carbon dioxide in the atmosphere.  This includes feedbacks which can either amplify or dampen that warming.  This is very important because if it is low, as some climate 'skeptics' argue, then the planet will warm slowly and we will have more time to react and adapt.  If sensitivity is high, then we could be in for a very bad time indeed.

There are two ways of working out what climate sensitivity is. The first method is by modelling:

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).

The second method calculates climate sensitivity directly from physical evidence, by looking at climate changes in the distant past:

adapted fig 3a

Various paleoclimate-based equilibrium climate sensitivity estimates from a range of geologic eras.  Adapted from PALEOSENS (2012) Figure 3a by John Cook.

These calculations use data from sources like ice cores to work out how much additional heat the doubling of greenhouse gases will produce.  These estimates are very consistent, finding between 2 and 4.5°C global surface warming in response to doubled carbon dioxide.

It’s all a matter of degree

All the models and evidence confirm a minimum warming close to 2°C for a doubling of atmospheric CO2 with a most likely value of 3°C and the potential to warm 4.5°C or even more. Even such a small rise would signal many damaging and highly disruptive changes to the environment. In this light, the arguments against reducing greenhouse gas emissions because of climate sensitivity are a form of gambling. A minority claim the climate is less sensitive than we think, the implication being we don’t need to do anything much about it. Others suggest that because we can't tell for sure, we should wait and see.

In truth, nobody knows for sure quite how much the temperature will rise, but rise it will. Inaction or complacency heightens risk, gambling with the entire ecology of the planet, and the welfare of everyone on it.

Basic rebuttal written by GPWayne

Last updated on 1 August 2013 by gpwayne. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

Related Arguments

Further reading

Tamino posts a useful article Uncertain Sensitivity that looks at how positive feedbacks are calculated, explaining why the probability distribution of climate sensitivity has such a long tail.

There have been a number of critiques of Schwartz' paper:

Comments

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Comments 251 to 300 out of 307:

  1. 249, Eric,

    Q1: My opinion only, but no, I don't think a return to 285 is necessary, just desirable (but impossible). I do think a return to 350 is required, but also impossible at the current rate of action (meaning that by the time we start, we'll be lucky to hold it to 500 at this point, and as I described, I think getting it down once its up will be almost impossible).

    Q2: How do you propose that the carbon get into the deep ocean? There are natural processes that work on huge, huge ("global") scales, but not nearly so quickly as to naturally drawn down both atmospheric and ocean CO2 levels to a reasonable degree (although I could be wrong on this... this is where an ocean expert like Doug Mackie should step in. Perhaps he knows better. But otherwise, how does someone suck all of that carbon out of the air and oceans and put it in a form that will sink to the bottom and stay there?

    It is interesting to note two things. The first is that the 300+ gigatonnes of carbon that man has burned in fossil fuels so far (and we're still not done) took nature hundreds of millions of years to sequester underground. It took a mere 100 years to release it, but there is no reasonable way to match nature's feat and put it back. It can go into the atmosphere, ocean or biomass, but not very easily back into the ground.

    The second point is that I recently did a back of the envelope calculation, trying to figure out how much land would be needed to plant giant sequoia redwoods that could suck up the carbon and turn it into biomatter (trees). The answer, with some very optimistic fudging, was that 75% of the arable and agricultural land on earth needed to be covered with redwoods in order to drawn atmospheric CO2 back down to 285 ppm in the course of 100 years from today, assuming we planted those trees right now and also instantly stopped burning more fossil fuels.


    This of course presumes that all of humanity moves to deserts and other places of the earth so that we can exclusively grow food crops on the remaining agricultural/arable land. Of course, since that represents only 25% of the total, we must also assume that food production will drop by 75%. This implies that the population of the earth (currently 7 billion) must also drop as a consequence -- so that "solution" implies:

    1) Plant sequoias immediately on 75% of the arable land on earth (completely ignoring the fact that sequoias will not grow just anywhere, and in fact could only grow in very specific environments)

    2) Move the entire human population off of such land

    3) 5 billion people must die (because there won't be enough land to produce enough food to feed 7 billion, but instead only 2 billion).
  2. (Redirected from the Cloud Feedback thread here)

    RW1 - Quite frankly, this issue on total sensitivity has been explained to you, at length, in multiple threads here. You have yet to demonstrate any tendencies to incorporate the science you have been shown.

    For new readers: A doubling of CO2 would add 3.7 W/m^2 to the top of atmosphere (TOA) forcing of the climate. This should by all measures (and by that, I mean spectroscopic effects as integrated through the depth of the atmosphere - very basic physics) result in ~1.1°C warming directly.

    That works out to ~0.3°C/W/m^2. The 3°C warming estimated from numerous estimates is in the range of roughly 2-4.5°C, most likely estimate of 3°C, indicating a TOA forcing of roughly 10 W/m^2. That's an additional 6.3 W/m^2 forcing from feedbacks.

    CO2 represents roughly 1/3 of the current greenhouse effect - increases in water vapor will easily (well within the uncertainty ranges) account for the additional 2/3. In regards to cloud feedback (the change in forcing with temperature, not the initial value as RW1 emphasises), please read the opening post on that thread. The best estimates, best data, on that topic indicate that cloud feedback with temperature is slightly positive, with a range of uncertainty that does include (at low probability given the data) very slightly negative. Certainly not enough to overwhelm the increase in CO2 and temperature dependent absolute humidity.
  3. KR,

    You're very good at 'explaining' things to me and making declarations I'm wrong, but this is not offering anything to the discussion here or on the other thread.
    Response:

    [DB] Actually, KR and others have more than amply explained things to you, including the specific points where you stray from accepted understandings into error. 

    Thus, it is your intransigence (amounting to agenda) that is standing in the way of the discussions.

  4. RW1 - I don't think anyone knows how to help you. People go so far and then you seem to point blank refuse to get it. "I dont understand". Left to a 14 year girl to do your homework IIRC at one point. It seems you believe one thing and when an argument takes you to the point when that belief is challenged, then you shut down. It still seems to me that you are stuck in the "back radiation cant warm the surface" mindset, and discussion cant go forward till you get that.
  5. RW1 - Two items.

    First: The appropriate numbers for TOA forcing with feedbacks given a 3°C climate sensitivity is ~10 W/m^2, resulting in the aforementioned 3°C rise in surface temperatures due to changes in total Earth emissivity and the surface temperature required to emit another 10 W/m^2 at TOA. Your numbers are wrong.

    Second: I wrote my most recent post for the general public, the readers of this thread. You have not shown any indications that you recognize evidence contrary to your preconceptions. As per the Debunking Handbook, Worldview Backfire , "...outreaches should be directed towards the undecided majority rather than the unswayable minority."
  6. KR,

    "Your numbers are wrong."

    Are you trying to say the surface does not have to receive +16.6 W/m^2 in order to warm by 3C?
  7. RW1 - You continue to mix TOA forcings with surface flux. Please note that an effective TOA emissivity of ~0.612, as measured and calculated, means that a TOA forcing of ~10 W/m^2 leads to 1/0.612 = ~1.64, or a required ~16.4 W/m^2 increase at the surface to increase emissions by ~10 W/m^2 at TOA to eliminate the imbalance. And that is strictly due to the emissivity of the Earth wrt. a blackbody.

    Your posts continue to interchange TOA with surface forcings, neglecting the effective emissivity to space (as per multiple threads), continue to invoke inappropriate "halving" of absorptions, and IMO represent errors. Nonsense statements such as "+6 W/m^2 (+1.1C) from 2xCO2 (3.7 W/m^2 directly from the CO2 'forcing' and the remaining 2.3 W/m^2 from the current average opacity of the atmosphere" do not aid your position (I have absolutely no idea where you got 2.3 from, for example). Your insistence on these issues demonstrate either (a) a lack of comprehension, or (b) an unwillingness to let data influence your position.

    Enough said. You have repeatedly demonstrated either a lack of knowledge or unwillingness to examine the evidence.

    Readers - if you wish to follow these conversations further, I would suggest the Climate Sensitivity or Lindzen and Choi threads, where this issue is discussed at great length. Personally, I feel no desire to rehash these topics...
  8. RW1 - Well, then, my apologies, I had not found that clear from your posts, which is probably my mistake. Mea culpa.

    So: a 10 W/m^2 TOA forcing results in a ~16.4 W/m^2 surface change. Of that 10 W/m^2 3.7 W/m^2 is direct CO2 forcing (assuming a CO2 doubling), and the remaining 6.3 W/m^2 is (as predicted by a 3°C sensitivity, with caveats due to uncertainties - 2-4.5°C) due to feedbacks.

    I would suggest viewing the detailed discussions at Water Vapor vs CO2 as a “Greenhouse” Gas and in particular Clouds and Water Vapor – Part Four by Science of Doom. Note that models of outgoing longwave radiation (OLR) match very well with observations, indicating that the models are pretty accurate.

    Water vapor represents ~2/3 of the greenhouse effect (in conjunction with clouds), and since water vapor is temperature dependent, it is a feedback, not a forcing.

    In addition, see Philipona et al 2005 ("...enhancing the forcing and temperature rise by about a factor of three") and others - water vapor is a strong positive feedback, as shown by the data.
    Response:

    [DB] Please note that RW1 has never retracted this statement:

    I appreciate that you seem to be interested in helping me, but I'm not really interested in being helped per say. I'm a staunch skeptic of AGW, so my purpose here is to present contradictory evidence and logic that disputes the theory. That's what I'm doing.

    By his own admission he is here to not learn.

  9. Skywater @261 I believe that is the starting point in understanding how energenic the atmosphere realy is And without the van allen belts to protect us from the solar winds and cosmic rays (charged partical) life how we see it would not exist. That said it's my belief that what we are seeing regarding man made climate change is a result of or com's and detecting that use electromagnetic radiation from the ground and space
    http://missionscience.nasa.gov/ems/02_anatomy.html
    and is very sensitive to this process and would create changes and hot spots through processes like this.
    http://www.ips.gov.au/Category/Educational/Other%20Topics/Radio%20Communication/Transequatorial.pdf There's a picture halfway down that shows hot spots expanssion and a bulging at the equator that is interesting. And as you know heat and preasure differences drive the weather Just putting it together to for a bigger picture
  10. DB, you should probably tack that comment on to every post that RW1 makes, so that no one makes the mistake of engaging him/her in discussion. It will also act as a standing demonstration of exactly what denialism is--a one-way street where the denialist presents the Truth and refuses to admit error.

    I've asked "wrongologist" Kathryn Schulz to target the global warming issue through interviews with a number of opinion-makers and scientists. I hope she ends up doing so. It's a very rich area for her--not just in the exploration of what happens when people who are committed to alternative theories come up against hard evidence against them, but also in statisticians' and scientists' relationship with modeling, in people who are paid to be publicly wrong, and in how scientists deal with being wrong.
  11. For the record, the 16.6 W/m^2 RW1 keeps throwing around is from his own entirely incorrect logic that there is a direct relationship between the radiation leaving the surface and the radiation emitted at TOA, and that this requires a linear "gain" and therefore the creation of non-existent energy.

    It basically comes from a completely flawed understanding of the system, I think because he is trying to translate it entirely into his own misapplied EE concepts of "gain," "feedback" and control theory rather than by understanding climate science and the actual system under discussion.

    The clearest (convoluted) path to understanding his logic is here, but in a nutshell, 16.6 W/m2 is a ridiculous constraint of his own devising, and there is no arguing with it, because he can't get past the mumbled incantations and heavy incense needed for his magical spells.
  12. I love Kathryn Schulz! Her talks aren't as good as her book though.
  13. jmorpuss, none of those links give any hint of any way by which the phenomena discussed could have any material effect on climate - by orders of magnitude. As such I cannot see how you can link this in any way to the idea that climate sensitivity is low.
  14. John Russell at 04:50 AM on 16 December, 2011:

    I certainly did not feel like I was being banned.

    I am moving to this thread so as to not be off topic.

    The warming since 1950 has been around 1 degree F or .55 degrees C.

    But how much of that is due to CO2?

    I read 75% in one article and 50% in another.

    Lets say 75% of the warming from 1950 is due to CO2 and the rest is due to land use changes, black carbon on snow, methane, etc.

    So .75 degrees F seems like a fair estimate of the warming from 1950 caused by CO2.

    First off - does that seem about right to you?

    I am not a climate scientist - so what I see from this data is that we seem to be on target for about the amount of warming you would expect from physics - but just the direct warming - no amplification effect.

    Doesn't that imply about 1.5 degrees F of warming to 2100 (or about .83C) from just CO2. Of course, there would be temperature increase also due to the other 25% non-carbon causes.

    If you just extend the trend line - doesn't it look like we will get about 1.2 degrees C by 2100?

    When I look at the data, I see the direct warming from CO2 - but no indirect warming from CO2.

    That is my main problem with a CS of 3 degrees C - it just doesn't add up for me.
  15. Richard Arrett, among many other problems, you're ignoring the possibility that more than 100% of the warming since 1950 is due to CO2. Impossible! I hear you cry. But not, actually, as it is quite likely that aerosols are offsetting the non-CO2 warming effects and some of the CO2 warming effects. It will be "interesting" in a Chinese curse sort of a way, when China and India sort out their pollution issues.

    Another issue is you keep discussing equilibrium sensitivity values when you should be discussing transient sensitivity values, which are closer to 2C per doubling. We don't expect to see equilibrium sensitivity-sized changes instantaneously.
  16. Richard#265: "The warming since 1950... "

    Let's set the record straight. Warming of ~0.7 C since 1970; approx 0.18 C per decade.



    CO2 in 1970 = ~325 ppm, now = 395 ppm (see Mauna Loa). The 'percentage caused by CO2' is a meaningless hairsplit at this cursory level of analysis; it's a system of forcings and feedbacks. But if you want more detail, you can find it here.

    The sensitivity of 3C per doubling of CO2 is a straightforward calculation; you can find it many places here or even on wikipedia (search 'radiative forcing'). But in very rough terms, if a 22% increase in CO2 results in 0.7 degrees; four 1/2 times that in CO2 gets you in the ballpark of 3C.

    The point is this: A 2 or 3 C increase in global temperature has effects that are not what you should want to risk.
  17. A question to all - is it really necessary to rehash the previous discussion on the Lindzen and Choi thread, where RW1 spent considerable time pushing the same hypotheses, and where he was pointed at the same facts that he's being pointed at (and ignoring) now?

    RW1 - the same objections to your unbased claims still hold. What's the term? Debunked a thousand times (DATT)?

    Readers - Take a look at the Lindzen and Choi "Working out climate sensitivity from satellite measurements" thread if you have any questions about this discussion. Personally, I don't have the patience to discuss this again, as RW1 has stated:

    "I appreciate that you seem to be interested in helping me, but I'm not really interested in being helped per say. I'm a staunch skeptic of AGW, so my purpose here is to present contradictory evidence and logic that disputes the theory. That's what I'm doing."

    Those are not the words of someone willing to discuss the data, the facts. Rather, the words of someone who just wants to argue. DNFTT - Do Not Feed The Troll.
    Response:

    [DB] "What's the term? Debunked a thousand times (DATT)?"

    Very close.  PRATT - Point Refuted A Thousand Times.  Silver Star to you, circle gets the square.

    Edit:

    A large number of off-topic comments by RW1 and responses to him were deleted after this, as they belonged more properly on the 2nd law of thermodynamics contradicts greenhouse theory thread (or others) and were thus off-topic here.

  18. RW1, clearly you do not understand.

    What determines the strength of the greenhouse effect is the difference in the energy as it is radiated to space from energy radiated from the atmosphere, and the energy that would have been radiated from the surface in the same spectral band with no atmosphere. Therefore, the thing which determines the strength of the greenhouse effect is the temperature of the gas or cloud top which radiates to space relative to surface temperature, not the temperature of any intervening cloud top or gas which may absorb IR radiation in the same spectral band.

    The consequence of this is that in the band of strongest absorption (and emission by CO2), it contributes almost all of the greenhouse effect when compared to low lying cloud or water vapour. It will still contribute most of the greenhouse effect over medium level cloud. Over high cloud, the effect will be similar, depending on the cloud.

    Consider the spectrum below taken over the Sahara. It was taken on a day with high humidity as can be seen by the strong H20 signal in the spectrum. From the temperature difference between the black body curve of the surface (320 K) and the water vapour bands (280 K) we can tell that the effective altitude of emission to space from water vapour was about 6 Km, approximately the boundary layer between midlevel (alto) clouds and high level (cirrus) clouds. The effective altitude of emission to space of the CO2 is approximately 15 km is this case, which is also approximately the altitude of the tropopause.



    The important regions of the chart for this discussion are the yellow and green areas. The yellow area is approximately the area of overlap between the absorption/emission spectrum of the water vapour and the CO2. The absorption band of water vapour weakens in that area, so that in the absence of cloud and CO2 the H2O absorption/emission band would in fact slope up to 320 K within the yellow area, so that the yellow area overstates the greenhouse effect of water vapour in the area of overlap. Of course, solid cloud tops of that temperature would result in a spectrum following the 280 K black body line except for a trough in the green area, and an ozone peak from the stratosphere.

    Importantly, that means that in either case, the green area represents a contribution to the greenhouse effect which exists regardless of the presence or absence of H2O, either as water vapour or clouds. More importantly, in the complete absence of water vapour or clouds, the CO2 trough would have occupied almost the entire area of both the yellow and green zones. In this situation, the most accurate description is that in the area of overlap, CO2 contributes the entire greenhouse effect, as CO2 would have contributed all of that effect regardless of whether H2O was present or not.

    There are circumstances in which CO2 actually counters the greenhouse effect of very high clouds. There are also circumstances in the Antarctic winter in which CO2 contributes an anti-greenhouse warming effect. Consequently it is wrong to assume that the globally averaged effect of CO2 with water vapour present is the same as its globally averaged effect without water vapour present. But none-the-less, CO2 contributes a substantial part of the greenhouse effect in the spectral band where CO2 and H2O emissions overlap, and therefore best estimates place the contribution of CO2 to the greenhouse effect at about 20%, with a further 5% coming from other well mixed green house gases (O3, CH4, NO2, etc). Therefore your persistent claim that CO2 contributes 10% or less of the greenhouse effect is just false.

    Finally, I note on rereading your posts that you continually claim that half of absorbed radiation is emitted upward to space, while half is emitted downward to Earth. For a layer of atmosphere thin enough to have approximately the same temperature through its entire thickness, this is true, but it is not true of the atmosphere as a whole as can be easily determined by looking at the diagram @273. That you should think so suggests you continue to use a single slab model of the atmosphere to guide your thinking. Such models are false representations of the atmosphere,and only used in climate science as instructional tools to introduce more complex models with (in typical cases) around 20 layers. Using a single slab model reduces the atmosphere to a 2 dimensional shell, making my comment @275 exactly correct. Please take due note of the Trenberth et al diagram, and of the explanation above, and allow some reality into your model of the atmosphere.
    Response:

    [DB] Note:  This comment was inadvertently deleted and has been reinstated.  Apologies.

  19. Hello
    First of all, hats off to this website for its clarity and ease-of use. It has been a great source of information for me.

    I am developing a high-school physics chapter where I show the back-and-forth debate on AGW.

    Here is a skeptic's graph that they say shows that observed temps/CO2 levels of the last 100+ years indicate a climate sensitivity of about 1.85. Can you please tell me how the skeptics have their data/graph/conclusions wrong? (please remember that the audience is going to be high-schoolers).

    the graph can be seen more clearly at http://img152.imageshack.us/img152/6972/zoominco2logwarmingwp3.png

    I am not here to debate the issue, just to get information and to move on to the next topic.

    I thank you in advance.

  20. 269, SirNubWub,

    First, for a high school text I suggest you use log2 rather than natural logs. If you do so, then your constants will actually be the climate sensitivity (3, 1.85 instead of 4.7, 2.73).

    For the discrepancy, the short answers:

    1) The model as described is far too simplistic. For instance, it presumes that the only influence on climate in the past 100 years has been CO2. More specifically, it ignores the opposing anthropogenic negative forcing of aerosols. Unfortunately, as we work for cleaner air we are reducing the aerosols without reducing CO2 emissions. And if we were to stop abruptly, the added aerosols would quickly fall out of the atmosphere while the CO2 would stay active for hundreds/thousands of years.

    See this page of the IPCC AR4 report and more specifically this diagram.

    2) The model presented only measures transient, not equilibrium climate sensitivity. The first is what you get from fairly fast feedbacks, while the latter is what you get if you wait long enough for the system to stabilize (which includes all ice sheet melting, ocean warming, ecosystem transitions, permafrost methane releases, etc.). Transient climate sensitivity is estimated to be about 2˚C per doubling, and equilibrium sensitivity about 3˚C, so your 1.85˚C/doubling number is pretty close, especially after you consider the negative influence of aerosols.

    Sadly, the ice on Earth is far from finished melting, the carbon cycle is far from equalizing, and the oceans are far from absorbing as much heat as they can.

    3) The model presumes that warming is instantaneous. Honestly, very few times in the history of the earth has a forcing of this magnitude been applied this quickly. It is very hard to predict how long it will take for the forcing imbalance to raise the planet to new equilibrium temperatures, even without considering the slow (equilibrium) feedbacks.
  21. It should also be pointed out that the IPCC quotes 3C/doubling as the most likely sensitivity. The value of 3.25 used above is a slight misrepresentation that overstates the mismatch. It is the average of the upper and lower extremes (2 and 4.5 respectively) cited by the IPCC, but the probability distribution is not symmetrical between these extremes.
  22. Stephen,

    I didn't even notice that the graph had upped it to 3.25.

    SirNubWub, I'd almost think you were a denier-in-disguise, playing hard-to-notice tricks with your audience.

    The number is 3 (or better yet, the range between 2 and 4.5). And transient sensitivity is around 2.

    And there is absolutely nothing at all behind any such denial argument (and please don't call them skeptics, because they aren't, if they were skeptical they would have researched the issue well enough to figure this out for themselves and not bother to make such a specious argument).
  23. SirNubWub @269, that is a strange graph. In addition to the errors noted by Stephen Baines and Sphaerica, I notice that the line marked "Global Warming Models" is almost certainly mislabeled. I draw your attention to the comparison of actual temperatures (HadCRUT3) and model results from the IPCC AR4 below:



    As you can see, the model results for actual forcings (Red line, graph a) very closely follow the observations (black line). Therefore in a graph such as you show, the model results would be shown by a scatter plot that overlapped with the observed data through out its entire range, and which had nearly the same mean for most of it.

    Fairly obviously the line labelled "Model Range"is therefore not the model range at all. Rather it is a simple plot based on a projected response function of temperature to CO2 of 3 degrees per doubling. As noted by Sphaerica, that response function is not the climate sensitivity. I note, however, that the IPCC definition of Transient Climate Response states:

    "The transient climate response is the change in the global surface temperature, averaged over a 20-year period, centred at the time of atmospheric carbon dioxide doubling, that is, at year 70 in a 1% yr–1 compound carbon dioxide increase experiment with a global coupled climate model. It is a measure of the strength and rapidity of the surface temperature response to greenhouse gas forcing."


    In other words, the Transient Climate Response is not the immediate response of temperature in the year of the change of CO2 concentration. As such, and contrary to Sphaerica, the graph plotted is not a graph of the Transient Climate Response. To plot that you would need to plot CO2 concentration against lagged temperature. Even then you would still face confounding factors in the effects of other Green House Gases, increases in solar radiation, and most particularly, changes in Aerosol Optical Depth. It is dubious, therefore, that such a plot will give anything better than a vague approximation of the Transient Climate Response.

    However, if you were to plot the IPCC TCR on the graph for comparison, the IPCC AR4 value for the TCR for a doubling of CO2 is between 1 and 3 degrees C:
    "Agreement among models for projected transient climate change has also improved since the TAR. The range of transient climate responses (defined as the global average surface air temperature averaged over a 20-year period centred at the time of CO2 doubling in a 1% yr–1 increase experiment) among models is smaller than the range in the equilibrium climate sensitivity. This parameter is now better constrained by multi-model ensembles and comparisons with observations; it is very likely to be greater than 1°C and very unlikely to be greater than 3°C. The transient climate response is related to sensitivity in a nonlinear way such that high sensitivities are not immediately manifested in the short-term response. Transient climate response is strongly affected by the rate of ocean heat uptake. Although the ocean models have improved, systematic model biases and limited ocean temperature data to evaluate transient ocean heat uptake affect the accuracy of current estimates. {8.3, 8.6, 9.4, 9.6, 10.5}"

    (Note, this quote is from the Working Group 1 technical summary. The numbers at the end are relevant section of the WG1 report for further details.)

    In looking at the graph I noticed that the measurement range of CO2 was from 287.50 - 388 ppmv. The temperature range was 0.8 degrees C. That strongly suggests the temperature data was taken from Gisstemp, and that the time interval of the graph was from 1880 to approx 2009. This information, and the information about who produced the graph should always be included in any graph used for teaching (or science in general).

    I also notice from the large number of temperature values at the lowest CO2 value that the plot was made against the most recent ice core value of CO2 concentration prior to the availability of Mauna Loa data. Using that method instead of plotting against a smoothed value introduces further inaccuracies to the graph. There is some possibility that values other than ice core values where used prior to 1959. If so, that should be specified, and great care taken as many CO2 measurements prior to 1958 are strongly distorted by local sources and sinks of CO2 (factories, roads, forests).

    In sum, this graph provides an excellent teaching opportunity. Specifically, it can be used to show how so called "skeptics" use incorrect values (3.25 instead of 3 for the IPCC central estimate of climate sensitivity; mislabel data (labeling a mathematical estimate as "Global Warming Models"); do not properly understand the data they are analyzing (ie, presenting it as a plot showing climate sensitivity, when the technique can show Transient Climate Response at best, and is likely to underestimate it); and do not take into account proper caveattes on the data (due to the unmentioned confounding factors). As such, it presents an excellent opportunity to show the difference between the pseudo-science of so-called skeptics and the genuine science as reported on by the IPCC. It also is an excellent opportunity to show that the vast majority of objections to climate science only masquerade as being science based, but are in fact political in nature, employing as they do pseudo-science rather than science to back up their claims.
  24. Sphaerica and Tom Curtis,
    Thank you for your replies. I have not heard of a response to this issue before. I will have to read it carefully and repeatedly to understand it all.

    If I have further questions I will ask.

    I appreciate your time.
  25. Continued from HERE

    Tom Curtis says:

    "RW1's bizarre claims assume that solar forcing results in no feedback response. That is, if the world's oceans are heated by 1 degree C by an increased GHG concentration, that will result in increased evaporation and an increase in absolute humidity (and hence a water vapour feedback), but that an increased temperature of the same proportion brought about by a brighter sun will not increase evaporation at all, nor melt any snow, or in any other way have feedbacks. RW1 can only attribute this view to climate scientists because, as always, he operates in complete disregard of what climate scientists actually say."

    What I'm saying is the ratio of surface radiative power to post albedo incident solar power, from which the so-called 'zero-feedback' response is ultimately derived, is already giving a measure of the lion's share of all the feedbacks operating in the system, including especially water vapor and clouds, as the two are by far the most dynamic components of the whole atmosphere.

    "Still more bizarre is RW1's claim that CO2 should result in less warming because of the energy needed to modify the internal energy structure of the atmosphere. What is bizarre here is that inside the troposphere, there is no significant difference in the change in temperature structure with time under GHG and solar warming. But solar warming heats the stratosphere, while increased GHG cools it - so as usual, RW1 gets the science completely backwards."

    GHG induced warming results in the warming of the atmosphere, does it not? Warming air expands and in doing so does work against its surroundings, which requires some of the internal energy to be expended, leaving less available to heat the atmosphere (and ultimately the surface).
  26. GHG induced warming results in the warming of the atmosphere, does it not? Warming air expands and in doing so does work against its surroundings, which requires some of the internal energy to be expended, leaving less available to heat the atmosphere (and ultimately the surface).


    RW1, an understanding of thermodynamics is not really something that you have under your belt, is it?

    I'm sure others will pick your statements to pieces, but do yourself a favour and in preparation learn about adiabatic processes.

    Seriously.
  27. RW1's original claim was that the forcing from Greenhouse Gases was three times that from solar.

    In defense of that claim he refers us to the ratio of incident solar radiation to upward long wave surface radiation to surface absorbed solar radiation, or 2.46 (396/161, see diagram below).



    With hesitance I say that RW1 should have used the ratio of LW surface radiation to total absorbed solar radiation, or 1.66 (396/239). I say "with hesitance" because his entire formulation is incorrect. For a start, 239 W/m^2 is not the solar "forcing". A "forcing" is the change in a value between two different, specified times. By convention, the reference time is 1750, notionally the pre-industrial era. Further, 396 W/m^2 is not the "greenhouse gas forcing" In fact, the difference between the upward LW surface radiation and the upward LW radiation at the top of the atmosphere (TOA) is the total greenhouse effect, but even that is not the total greenhouse forcing both because a forcing is a change between two times, and because it includes feedbacks as well as forcings.

    (For what it is worth, the ratio of the total greenhouse effect to total insolation is 157/239, or approximately 66%. What is more, the insolation contributes approximately 80% of mean global temperature, with the greenhouse effect contributing the majority of the extra warming and redistribution of heat, which equalizes temperatures contributing the rest.)

    Ignoring the terminological issues, which render RW1's claim almost incoherent, the simple fact is that the total greenhouse effect acts as a multiplier of energy from the sun. If we were in the dark of space, no amount of greenhouse gases would raise our temperature appreciably above the 2.5 K temperature of the cosmic background radiation. Therefore if insolation increased, then the total greenhouse effect also increases in proportion. For small increases in insolation, the ratio of effective insolation (incoming sunlight minus albedo) to upward LW surface radiation would remain constant. And therefore the increase in temperature from an increase in insolation of 1 W/m^2 would be approximately the same as the increase from a 1 W/m^2 forcing from CO2.

    Turning to RW1's second point, warming a gas does result in expansion, which does perform work. But a GHG forcing warms the troposphere but cools the stratosphere. In contrast an increased solar forcing warms both troposphere and stratosphere. Because the solar forcing is warming more gas (by a small percentage), if RW1's argument had any merit, it would indicate that solar forcing was weaker than GHG forcing.

    In fact, however, it is without merit. It does indicate that solar forcing must use more energy for a given increase in temperature, all else being equal. But energy leaving the system is not a function of how much energy is stored in the system, but of surface and atmospheric temperatures. Because of this, the increase in temperature is the only factor in determining if equilibrium has been restored, and the equilibrium temperature for equal solar and GHG forcings is approximately the same.

    I write this solely for the benefit of interested readers who may be confused by RW1's ramblings. He himself has a long demonstrated inability to learn or apply even the most basic of the relevant concepts, so I doubt he will gain any benefit from it. For the same reason I am unlikely to respond to any response he makes to my post. Again, he has a long history of simply regurgitating his initial confusion in slightly different words and imagining that thereby he is "debating". At the moment I do not have the time to waste pandering to his misconception.
  28. Tom Curtis,

    Let me clarify what I'm trying to say:

    Designating the +1.1C as the 'zero-feedback' starting point from the so-called 'Planck response' (i.e. the effective emissivity) is not valid because it arbitrarily separates the physical processes and feedbacks in the system that will act on additional forcings, like from GHGs, from those that currently act to maintain and control the system from the forcing of the Sun, for which there is no physical or logical basis.

    Put another way, one can't derive the 'zero-feedback' starting point from the absolute surface response to solar forcing, which itself is the net result of and maintained by all the physical processes and feedbacks in the system, and then claim there is some nebulous feedback acting on top of this that will amplify 'forcings' or imbalances even further, let alone 3-6x times greater. The 'brakes' - if you will, have already been put on all the feedbacks in the system from the many years and years of forcing from the Sun, including especially water vapor and clouds, as the two are the most dynamic components of the whole atmosphere.

    If you think they have not been put on (the brakes), why did the net surface energy flux from the forcing of the Sun 'stop' at only 390 W/m^2? Why didn't the feedbacks in the system, including especially water vapor and clouds, ultimately manifest themselves to an 'effective' emissivity of 0.22 (3.7/16.6 = 0.22), where a net surface energy flux of 1077 W/m^2 (about 100C!) has 837 W/m^2 'blocked' by the atmosphere and re-circulated back to the surface (240/1077 = 0.22)?

    In short, the absolute solar amplification factor of about 1.6 (390/240 = 1.625) is already giving a measure of incremental sensitivity to additional forcings or imbalances, only it represents an upper bound on sensitivity because net negative feedback on imbalances (a net response less than 1.6) is required for basic stability and maintenance of the current energy balance from the forcing of the Sun.


    If the logic is still not clear, here it is broken down into a series of separate questions:

    Do you agree that at the Earth's current global average temperature of 288K, the Earth emits about 390 W/m^2 from its surface (assuming an emissivity of 1 or very close to 1)?

    Do you agree that the globally averaged solar constant is about 342 W/m^2 and the average albedo is about 0.3, resulting in a net incident solar power of about 240 W/m^2?

    Do you agree that the 240 W/m^2 of incident post albedo solar power is forcing the climate system?

    Do you agree that the 240 W/m^2 forcing the system from the Sun results in an amplification at the surface of about 390 W/m^2 entering the surface from the atmosphere to sustain 288K?

    Do you agree that this accounts for all the physical processes and feedbacks in the system? If not, why haven't all the physical processes and feedbacks fully manifested themselves after billions of years of forcing from the Sun? Or even after the last few hundreds or thousands of years of forcing from the Sun?

    Do you agree that in order to amplify +3.7 W/m^2 of 'forcing' from 2xCO2 into +3C at the surface it requires +16.6 W/m^2 entering the surface from the atmosphere (288K = 390 W/m^2; 291K or +3C = 406.6 W/m^2 and 406.6 - 390 = 16.6 W/m^2)?

    Do you agree that watts of GHG 'forcing' and watts of solar forcing must obey the same physics in the system? That is a watt is a watt, independent of where it last originates from.

    Do you agree that a watt of post albedo solar forcing and watt of GHG 'forcing' can only do the same amount of work?

    Do you agree that 390/240 = 1.625?

    Do you agree that 16.6/3.7 = 4.5?

    Do you agree that 4.5 is 2.8x times greater than 1.625?

    If watts are watts, how can watts of GHG 'forcing' have a 3x greater ability to warm the surface than watts forcing the system from the Sun?
  29. Tom Curtis,

    Regarding my other point. Unlike additional solar forcing, with additional GHG 'forcing' there is no increased energy coming into the system, leaving only the existing internal energy available.

    Since GHG warming requires the troposphere to warm and the pressure is higher in the troposphere than it is in the stratosphere, I stand by my claim that if anything a watt of additional GHG 'forcing' would be a little less than a watt of solar in its ability to warm the atmosphere (and ulimately the surface).
  30. I meant to say:

    "...I stand by my claim that if anything a watt of additional GHG 'forcing' would be a little less than a watt of additional solar forcing in its ability to warm the atmosphere (and ulimately the surface).
  31. RW1:

    "Put another way, one can't derive the 'zero-feedback' starting point from the absolute surface response to solar forcing, ..."


    You are correct, but nobody does derive the zero feedback response to forcing from the absolute surface response to insolation. There is no point in further discussing your straw man.

    "In short, the absolute solar amplification factor of about 1.6 (390/240 = 1.625) is already giving a measure of incremental sensitivity to additional forcings or imbalances, only it represents an upper bound on sensitivity because net negative feedback on imbalances (a net response less than 1.6) is required for basic stability and maintenance of the current energy balance from the forcing of the Sun."


    1) It does not represent an upper bound. To assume that it does you must assume that the albedo of a sunless Earth would be identical to the albedo of the Earth as it currently exists. That assumption is, however, simply absurd. A sunless Earth would have an albedo of 0.7 (0.3 for treeless land areas, and 0.9 for frozen oceans) or higher. Consequently an approximate measure of the "solar amplification factor", if it is intended to reflect all feedbacks, is 2.05. What is more, your argument assumes that the "solar amplification factor" is constant over the range of temperatures that might be experienced, which is known to be false. It also assumes it is constant with regard to continental configurations (also known to be false).

    2) Your whole presentation is nonsense. Let's define some terms:

    EI = Effective Insolation = Top of atmosphere insolation * (1-albedo);

    SR = Upward Long wave surface radiation

    OLR = Outgoing Longwave Radiation

    TGHE = total greenhouse effect = SR-OLR

    Given these definitions, we can define the solar amplification factor (SAF):

    SAF = (EI+TGHE)/EI

    Thus defined we see that your insistence that the Solar Amplification Factor remains constant under the greenhouse effect is just the insistence that (EI+TGHE)/EI = k, where k is a constant.

    That can only be true where TGHE = EI(k-1). So, your insistence that the ratio be constant is simply an assertion by fiat that the atmospheric greenhouse effect is completely independent of the concentrations of all greenhouse gases in the atmosphere. Put simply, your theory can only be correct if a pure nitrogen atmosphere has the same greenhouse effect as a pure CO2 atmosphere. And you want to assert this claim as a definition from which we are supposed to start reasoning.

    Well, you may be able to con some people, but I recognize the difference between science and utter nonsense, and it is the later that you are peddling.
  32. RW1 @279, increasing the GHG concentration will reduce the OLR radiation until equilibrium is reached. You assert that because it does not increase the incoming solar radiation, it cannot cause in increase in energy stored in the Earth's surface and atmosphere. This is logically equivalent to asserting that if you have a basin of water, being filled by a tap, and drained through a drain, that you cannot increase the water level by reducing the water flow out of the drain because doing so does nto increase the water flow from the tap. No more need be said.
  33. Tom Curtis,

    "You are correct, but nobody does derive the zero feedback response to forcing from the absolute surface response to insolation. There is no point in further discussing your straw man."

    390/240 = 1.625; 3.7 W/m^2 x 1.625 = 6.0 W/m^2 = 1.1C from S-B.

    "What is more, your argument assumes that the "solar amplification factor" is constant over the range of temperatures that might be experienced, which is known to be false."

    Actually, no. The amplification factor is not constant and is indeed non-linear; however, each incremental watt causes proportionally less and less warming in the system, which is the opposite of what would be consistent with the incremental response being greater than the current absolute response (i.e. greater than about 1.6)

    "So, your insistence that the ratio be constant is simply an assertion by fiat that the atmospheric greenhouse effect is completely independent of the concentrations of all greenhouse gases in the atmosphere."

    I never said or implied anything of the sort. The ratio is not constant. If, from GHG 'forcing', the surface temperature were to rise by 1.1C the absolute surface response to solar forcing would increase. The new ratio would be 1.65 (396/240 = 1.65).
  34. Tom Curtis,

    "You assert that because it does not increase the incoming solar radiation, it cannot cause in increase in energy stored in the Earth's surface and atmosphere."

    I don't assert this at all. What I'm saying is additional GHG 'forcing' does not increase the total energy input into the system as additional post albedo solar forcing would. This does not mean that GHG 'forcing' cannot increase the total energy stored in the Earth's surface and atmosphere, as of course it can.

    My original point was that, if anything, a watt of GHG 'forcing' would be a little less than solar because some of the existing internal energy would have to be expended for the expansion of warming air against its surroundings.
  35. Tom,

    RW1 refuses to look at this as anything other than a linear system equivalent to electronic circuits. As long as he is in that trap you cannot help him out of it. He has tied himself in knots with his personal model of the system, and there's no way out of it, because he won't abandon his (grossly flawed) model, nor will he expand it to properly reflect the system being modeled. He'll argue in a thousand circles before he recognizes that he is wildly wrong.
  36. RW1,
    Do you agree that 390/240 = 1.625?
    Yes.
    Do you agree that 16.6/3.7 = 4.5?
    Yes, but utterly irrelvant.
    Do you agree that 4.5 is 2.8x times greater than 1.625?
    Yes, but utterly irrelevant.
    If watts are watts, how can watts of GHG 'forcing' have a 3x greater ability to warm the surface than watts forcing the system from the Sun?
    Because the ratio is a meaningless number and the question as phrased is a nonsensical question.

    Put another way... if the sun increased its output by 3.7 W/m2, the earth would warm by roughly the same amount. An additional 3.7 W/m2 from any source would result in 16.6 W/m2 at the surface.

    The reason has to do with this thing called feedbacks, and the fact that the system does not consist solely of a big flaming ball (the sun) and a little floating ball (the earth).

    It's more complicated than that, and you would be far, far better served studying the other issues than arguing, for the fifty millionth time, this same, old, tired point.

    Have you not yet figured out that no one on the entire planet agrees with you, or cares about your particular insight in this?

    Do you think you are Galileo? Or perhaps merely confused and lost?

    Take your pick, but either way, you're wasting everyone's time with the same, old, complete nonsense.

    It's time for you to get over yourself and go learn something.
  37. Hi! It is still very hard to grasp that incoming direct TSI can be modified by "earth climate" to such a high level that it in fact marginalizes the source's direct influence. A problem many sceptics seem to have, too.

    Coming from the discussion of the alternative TSI reconstruction from Shapiro e.a. http://www.skepticalscience.com/shapiro-solar-2011.html#comments , which is counter-argued in that linked article because his observations would imply a very low climate sensitivity when compared to the reconstructed temperature curves from Ljungqvist.

    I read here with special interest about Hansen 2008 and his long term comparisions from earth history.
    Hansen 2008 does not bring forth any TSI data, but from his footnotes you get the impression there is almost no significant shift in TSI levels throughout earth history. However, he also states "The possibility remains of solar variability on longer time scales.", which he debunks by pointing out the TSI development of the last decades (last page); which I find not entirly coherent.

    Is there any data on TSI levels throughout earth history?
    (For example, for the last 450k years from Figure 2 of this article? I never really understood what part of the 6 Degrees difference from the ice cores is attributable to GHG and what part to TSI. Sure is only that TSI was the driver of the shifts from warm to cold and vice versa. So, what level of TSI difference started and ended the shifts we observe from the ice cores?)
  38. Falkenherz wrote: "So, what level of TSI difference started and ended the shifts we observe from the ice cores?"

    Rather than explain to you again why the glacial / interglacial cycle is not caused by changes in TSI I'll just point you to the previous time I explained it.
  39. "it is still very hard to grasp that incoming direct TSI can be modified by "earth climate" to such a high level that it in fact marginalizes the source's direct influence"

    How about considering how different the climate of the earth would be (ice ball) without any GHG then? If you dont think that theory is believable then consider that you deduce surface temperature of any rotating planet anywhere given TSI, albedo, aerosol and ... atmospheric composition (ie GHG).
  40. Falkenherz, if you are referring tp the galcial/interglacial cycles, the evidence points to changes not in TSI but in its distribution over the surface. That itself is an argument for high sensitivity to radiative forcings in general.
  41. CBDunkerson, thanks for correcting me again. But my question is still open:

    So, are there really no significant changes in TSI throughout the last 450k years?

    Philippe, I take it I then have to talk about insolation instead of TSI? So, let me rephrase: What was the difference in insolation or whatever W/m2, in order to trigger the shifts during the last 450k years?
  42. Falkenherz, Tamino has a good explanation with the maths, Wobbles part1 and part2, on the WB machine:

    http://web.archive.org/web/20080501124634/tamino.wordpress.com/2007/11/19/wobbles-part-1/

    http://web.archive.org/web/20080419120634/http://tamino.wordpress.com/2007/12/02/wobbles-part-2/

    Wiki has the skinny on Milankovitch, I'm surprised you seem to be not yet familiar with that:
    http://en.wikipedia.org/wiki/Milankovitch_cycles

    Berger and Loutre have published quite a bit on the subject, check them out. The litterature is out there.
  43. Falkenherz, it depends on what you mean by 'significant'.

    Current TSI (sometimes still called 'the Solar constant' even though we now know it isn't actually constant) is about 1361 W/m^2. The Maunder Minimum ~1700 was less than 1 W/m^2 lower. Thus, the most profound swing in TSI of the past several thousand years was a change of less than 0.1%. The difference from peak to valley of the ~11 year cycles is also about 0.1%, but obviously maintained over a shorter period.

    Over longer time scales TSI is increasing by about 0.1% per ~140,000 years as the Sun grows older and hotter.

    Yet, these 'tiny' changes in TSI have noticeable effects on the Earth's climate due to feedback sensitivity. The fact that current greenhouse gas forcings are already larger than any solar variation of the past few hundred thousand years should thus be of some concern.
  44. Philippe, I ignored Milankovitch cycles (MC) because they are uncontested and I assumed they would have a certain known impact on global temperature, thereby initiating ice ages. Reading through the links you provided, this assumtion is wrong. If I understood correctly, nobody really seems to know the physics of the trigger for global temperature changes, only that MC must be a trigger, and it is assumed that glacial changes on the landmass-rich northern hemisphere play a key role. In other words, there is no initial rise of global temperature as the initial trigger, but rather some severe local imbalances. This just in short, because there is that other article specifically on MC. My research here is about climate sensitiviy, and specifically why consenus seems to be that it is high. So right now I am puzzled why people assume a high climate sensitivity if we don't know the physical trigger process. After all, if I understood correctly, it seems like local insolation can peak at 600 W/m2, which would probably be a very strong trigger with only a low sensitivity required.

    I am unsure where to continue discussion. Maybe I best move on to the MC article. (I start feeling like a hyperlink nomad and comment-parasite. Do you guys maybe have a forum?)

    CBDunkerson, thanks for confirming no real strong TSI changes connected to the ice age cycles.
  45. @ Falkenherz
    "I ignored Milankovitch cycles (MC) because they are uncontested"
    Perhaps not by you (at this moment) nor by most scientists (some do) but there are those who deny this, daily.
    "nobody really seems to know the physics of the trigger for global temperature changes"
    You project here. Try reading this post (including the comments threads, which should be mandatory).
    "My research here is about climate sensitiviy, and specifically why consenus seems to be that it is high."
    Um, "consensus" is that climate sensitivity is bewteen 1.9 (or so) and 4.2 (or so) with a central estimate of 3.0 being strongest. That you characterize that as "high" speaks volumes.
    " if we don't know the physical trigger process"
    More projection, again.

    Suggestion: more research & reading (by you), less trying to shoehorn reality into the worldview you have chalked out for it.
  46. "we don't know the physical trigger process"

    How on earth do you deduce that? The physical trigger is change in insolation distribution in the northern hemisphere, which in a low CO2 atmosphere sets up a web feedbacks on albedo and GHG. Untangling this web quantitatively has been a slow process. Have a look at fig 6 of Hansen and Sato 2011 and tell me again that this isnt understood.
  47. Daniel, I do question about reality, and if reality is reality, I am confident that my questions will be answered.

    scaddenp, Hansen and Sato 2011 are a very difficult to read for me. If I understand their chapter 5 on the Holocene correctly, they use climate forcings calculated from GHG and sea level changes (=ice sheet approximisations) and apply climate sensitivity "consensus" values and thusly produce temperature curves which match the ice core data.

    Seeing that there is yet another article which again specializes within more details with regards to my questions on the ice core data, I will move on to the discussion of Shakun e.a., link provided by Daniel#295.
  48. Guys, can someone tell me if the Knutti & Hegerl graph is free to be reproduced in Wikipedia? Is it already in the Commons? The Nature Geoscience page says "all rights reserved"...
  49. Dear Moderator, I am stuck. Apparently, the comment function on the article "Shakun e.a." seems to be bugged. It took several days before my questions actually appeared. Now, sometimes I can see my questions I posted there, sometimes not. I suspect that some answers to my questions might not have gotten through or are stuck. Could you pls check?

    (http://www.skepticalscience.com/news.php?p=4&t=151&&n=1391)
  50. I'm sure Ari will be loading this one into the next weekly installment, but Trenberth and Fasullo have apparently constrained sensitivity even further -- or at least made a major advancement.

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