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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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Working out climate sensitivity from satellite measurements

What the science says...

Lindzen's analysis has several flaws, such as only looking at data in the tropics. A number of independent studies using near-global satellite data find positive feedback and high climate sensitivity.

Climate Myth...

Lindzen and Choi find low climate sensitivity

Climate feedbacks are estimated from fluctuations in the outgoing radiation budget from the latest version of Earth Radiation Budget Experiment (ERBE) nonscanner data. It appears, for the entire tropics, the observed outgoing radiation fluxes increase with the increase in sea surface temperatures (SSTs). The observed behavior of radiation fluxes implies negative feedback processes associated with relatively low climate sensitivity. This is the opposite of the behavior of 11 atmospheric models forced by the same SSTs. (Lindzen 2009)

Climate sensitivity is a measure of how much our climate responds to an energy imbalance. The most common definition is the change in global temperature if the amount of atmospheric CO2 was doubled. If there were no feedbacks, climate sensitivity would be around 1°C. But we know there are a number of feedbacks, both positive and negative. So how do we determine the net feedback? An empirical solution is to observe how our climate responds to temperature change. We have satellite measurements of the radiation budget and surface measurements of temperature. Putting the two together should give us an indication of net feedback.

One paper that attempts to do this is On the determination of climate feedbacks from ERBE data (Lindzen et al 2009). It looks at sea surface temperature in the tropics (20° South to 20° North) from 1986 to 2000. Specifically, it looked at periods where the change in temperature was greater than 0.2°C, marked by red and blue colors (Figure 1).

Figure 1: Monthly sea surface temperature for 20° South to 20° North. Periods of temperature change greater than 0.2°C marked by red and blue (Lindzen et al 2009).

Lindzen et al also analysed satellite measurements of outgoing radiation over these periods. As short-term tropical sea surface temperatures are largely driven by the El Nino Southern Oscillation, the change in outward radiation offers an insight into how climate responds to changing temperature. Their analysis found that when it gets warmer, there was more outgoing radiation escaping to space. They concluded that net feedback is negative and our planet has a low climate sensitivity of about 0.5°C.

Debunked by Trenberth

However, a response to this paper, Relationships between tropical sea surface temperature and top-of-atmosphere radiation (Trenberth et al 2010) revealed a number of flaws in Lindzen's analysis. It turns out the low climate sensitivity result is heavily dependent on the choice of start and end points in the periods they analyse. Small changes in their choice of dates entirely change the result. Essentially, one could tweak the start and end points to obtain any feedback one wishes.

Figure 2: Warming (red) and cooling (blue) intervals of tropical SST (20°N – 20°S) used by Lindzen et al 2009 (solid circles) and an alternative selection proposed derived from an objective approach (open circles) (Trenberth et al 2010).

Debunked by Murphy

Another major flaw in Lindzen's analysis is that they attempt to calculate global climate sensitivity from tropical data. The tropics are not a closed system - a great deal of energy is exchanged between the tropics and subtropics. To properly calculate global climate sensitivity, global observations are required.

This is confirmed by another paper published in early May (Murphy 2010). This paper finds that small changes in the heat transport between the tropics and subtropics can swamp the tropical signal. They conclude that climate sensitivity must be calculated from global data.

Debunked by Chung

In addition, another paper reproduced the analysis from Lindzen et al 2009 and compared it to results using near-global data (Chung et al 2010). The near-global data find net positive feedback and the authors conclude that the tropical ocean is not an adequate region for determining global climate sensitivity.

Debunked by Dessler

 Dessler (2011) found a number of errors in Lindzen and Choi (2009) (slightly revised as Lindzen & Choi [2011]).  First, Lindzen and Choi's mathematical formula  to calculate the Earth's energy budget may violate the laws of thermodynamics - allowing for the impossible situation where ocean warming is able to cause ocean warming.  Secondly, Dessler finds that the heating of the climate system through ocean heat transport is approximately 20 times larger than the change in top of the atmosphere (TOA) energy flux due to cloud cover changes.  Lindzen and Choi assumed the ratio was close to 2 - an order of magnitude too small.

Thirdly, Lindzen and Choi plot a time regression of change in TOA energy flux due to cloud cover changes vs. sea surface temperature changes.  They find larger negative slopes in their regression when cloud changes happen before surface temperature changes, vs. positive slopes when temperature changes happen first, and thus conclude that clouds must be causing global warming.

However, Dessler also plots climate model results and finds that they also simulate negative time regression slopes when cloud changes lead temperature changes.  Crucially, sea surface temperatures are specified by the models.  This means that in these models, clouds respond to sea surface temperature changes, but not vice-versa.  This suggests that the lagged result first found by Lindzen and Choi is actually a result of variations in atmospheric circulation driven by changes in sea surface temperature, and contrary to Lindzen's claims, is not evidence that clouds are causing climate change, because in the models which successfully replicate the cloud-temperature lag, temperatures cannot be driven by cloud changes.

2011 Repeat

Lindzen and Choi tried to address some of the criticisms of their 2009 paper in a new version which they submitted in 2011 (LC11), after Lindzen himself went as far as to admit that their 2009 paper contained "some stupid mistakes...It was just embarrassing."  However, LC11 did not address most of the main comments and contradictory results from their 2009 paper.

Lindzen and Choi first submitted LC11 to the Proceedings of the National Academy of Sciences (PNAS) after adding some data from the Clouds and the Earth’s Radiant Energy System (CERES).

PNAS editors sent LC11 out to four reviewers, who provided comments available here.  Two of the reviewers were selected by Lindzen, and two others by the PNAS Board.  All four reviewers were unanimous that while the subject matter of the paper was of sufficient general interest to warrant publication in PNAS, the paper was not of suitable quality, and its conclusions were not justified.  Only one of the four reviewers felt that the procedures in the paper were adequately described. 

As PNAS Reviewer 1 commented,

"The paper is based on...basic untested and fundamentally flawed assumptions about global climate sensitivity"

These remaining flaws in LC11 included:

  • Assuming that that correlations observed in the tropics reflect global climate feedbacks.
  • Focusing on short-term local tropical changes which might not be representative of equilibrium climate sensitivity, because for example the albedo feedback from melting ice at the poles is obviously not reflected in the tropics.
  • Inadequately explaining methodology in the paper in sufficient detail to reproduce their analysis and results.
  • Failing to explain the many contradictory results using the same or similar data (Trenberth, Chung, Murphy, and Dessler).
  • Treating clouds as an internal initiator of climate change, as opposed to treating cloud changes solely as a climate feedback (as most climate scientists do) without any real justification for doing so. 

As a result of these fundamental problems, PNAS rejected the paper, which Lindzen and Choi subsequently got published in a rather obscure Korean journal, the Asia-Pacific Journal of Atmospheric Science. 

Wholly Debunked

A full understanding of climate requires we take into account the full body of evidence. In the case of climate sensitivity and satellite data, it requires a global dataset, not just the tropics. Stepping back to take a broader view, a single paper must also be seen in the context of the full body of peer-reviewed research. A multitude of papers looking at different periods in Earth's history independently and empirically converge on a consistent answer - climate sensitivity is around 3°C implying net positive feedback.

Last updated on 6 July 2012 by dana1981. View Archives

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Further viewing

Andrew Dessler explains in relatively simple and short terms the results from his 2011 paper:


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Comments 51 to 100 out of 483:

  1. archiesteel (RE: Post 47), It's also inline with the sensitivity only being about 0.6 C - or any other amount for that matter, including zero. Again, you're assuming virtually all the increase we have seen is from CO2. While that is possible, it's also just a possible it's from natural causes.
  2. @RW1: "Vostok is in Antarctica - not the Arctic, which I know is more variable than global averages. Antarctica is considerably less variable than the Arctic. Even if you assume the global averages were only half of what Vostok depicts, that still means the amount of warming we've seen is only about average or maybe a little above." In other words, you do not have conclusive evidence that there have been other increases that were just as dramatic in the past (barring catastrophes). So, in the absence of evidence, we have to continue assuming that the current warming is unprecendented, *especially* since we can't identify other causes but for CO2. "It's also inline with the sensitivity only being about 0.6 C" Actually, it isn't, because not even all fast feedbacks have kicked in yet, let alone slow feedbacks. "or any other amount for that matter, including zero." Now you're not even making any sense. Typical of contrarians: in like a lion, out like a lamb. "Again, you're assuming virtually all the increase we have seen is from CO2." As is likely, as per the observed evidence. There is simply *no* other explanation for this warming, depsite your wishful thinking. "While that is possible, it's also just a possible it's from natural causes." There is no evidence supporting the latter. Personally, I like to go where the evidence is. Come back whenever you figure out what these mysterious natural causes are...
  3. Also, be sure to read Chris' excellent rebuttal of your untenable position. Hey, you gave it a shot...
  4. chris (RE: post 50), All those calculations are starting with the input assumption of a 3 C rise in temperature from a doubling of CO2. Start with an assumption of a 0.6 C rise and you're going to get a completely different and much lower result. Maybe the amount of CO2 was closer to 300 ppm in 1900 instead of 280 ppm. Still 300 ppm to 380 ppm equals about 70% of the forcing from a doubling of CO2, which still should have been over a 2 C rise in temperature. There was only about a 0.6 C rise from 1900-2000, which is still less than a third of the 2+ C predicted.
  5. RW1 at 09:45 AM on 20 December 2010
    "It's also inline with the sensitivity only being..."
    Not really RW1. And if you're going to use the non-argument that (paraphrasing) "anything is possible...we just don't know", why bother to attempt a (incorrect) quantitative argument in the first place!? I would have thought what you said earlier is appropriate:
    "The scientific method dictates modifying or discarding a hypothesis when it does not fit the evidence. It does not permit adding unsubstantiated things arbitrarily after the fact when the hypothesis is not in accordance with the evidence.
    Your odd hypothesis (that empirical observations are incompatible with the value of climate sensitivity that best fits the empirical evidence) is wrong (you mistakenly used faulty maths and logic). So you should "modify or discard" your hypothesis. You shouldn't "add unsubstantiated things arbitrarily after the fact". The empirical evidence simply doesn't support the unsubstantiated assertion that "'s also just as possible it's from natural causes".
  6. You've been shown how your math was wrong before, why do you keep repeating it? You don't get 70% of the effect from going from 300 to 380 (considering the baseline is at zero). As others have shown you, it represents just above 30%. 0.30 x 2C = 0.6C 'nuff said.
  7. #51: "it's also just a possible it's from natural causes." That's not even a decent denial. Its possible that ... fill in the blank. You'd have some credibility if you avoided these appeals to the great unknown. #54: "Start with an assumption of a 0.6 C rise" That assumption is plainly out in left field. Here's a graphic comparing the effect of varying sensitivities to the actual temperature anomaly record: The red dots and curve are the global LOTI temperature anomaly, shifted to 0 in 1880. The curves are dt = lambda dF, for 3 values of lambda, with dF calculated from log(each year's CO2 /CO2 at start). I used CO2 values from a composite of Law Dome cores and MLO records to drive each dt function. The small number below each curve is the equivalent sensitivity = deg C/double CO2. I'm no expert at this sort of thing, but your derived sensitivity of 0.6C would fall on the lowest of the three curves. That doesn't come anywhere near close to the data.
  8. Um, which natural cause are you postulating that can account for the change in ocean heat content? Thats a lot of energy to come from somewhere.
  9. I just realized why RW1 picked 1900 as his starting point: there was a spike in temperatures that year. He could have picked 1910-2010, but that would have provided a temp increase of nearly 0.9. RW1, may I suggest you stop cherry-picking dates in order to prove your point? A linear progression from 1880 to 1920 show the trend was remarkably flat, with an average that was about 0.8C colder than the present: As I said: nice try, but no cigar.
  10. RW1 at 10:10 AM on 20 December, 2010
    "...There was only about a 0.6 C rise from 1900-2000, which is still less than a third of the 2+ C predicted"
    Nope. It's easy to do the maths RW1. Let's be very explicit. [CO2]1900 was 298 ppm. [CO2]2000 was 371 ppm.[*] The equilibrium temperature rise expected from that increase in [CO2] is 0.95 oC at equilibrium. The observed temperature rise was (1900-2000) 0.75-0.85 oC. So we're not that far off the warming expected for a 3 oC climate sensitivity already even discounting the known contributions from the inertia in the climate system and the fact that a significant amount of the warming has been offset by anthropogenic aerosols. [*]Data are from: D. M. Etheridge et al (1996) "Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn J. Geophys Res. 101, 4115 -4128 and direct measurement from the Mauna Loa station from 1959
  11. No one is answering my initial question, so I'll try to break it down into a series of separate questions: Do you agree that the albedo adjust power from the Sun is "forcing" the surface? Do you agree that increased power from additional CO2 is also "forcing" the surface? Do you agree that 1 W/m^2 of albedo adjusted infrared power from the Sun is equal to 1 W/m^2 of infrared power from CO2? Do you agree that about every 1 W/m^2 of net incident solar power is amplified to 1.6 W/m^2 at the surface for gain of about 1.6 (390 W/m^2 divided by 238 W/m^2 = about 1.6)? Do you agree that the increase in radiative forcing from a doubling of CO2 is about 2 W/m^2 (or at least 4 W/m^2)? Do you agree that in order to get a 3 C rise in temperature (288K to 291K), the 2 W/m^2 needs to be amplified to 16 W/m^2? Do you agree that 16 W/m^2 divided by 2 W/m^2 equals a gain of 8? If not, do you agree that 16 W/m^2 divided by 4 W/m^2 equals a gain of 4? Do you agree that a gain of 8 is greater than a gain of 1.6 (or at least a gain of 4 is greater than 1.6)? Do you agree that the AGW theory is saying that the system is going to amplify each 1 W/m^2 of increased power from CO2 by a much greater amount than it amplifies each 1 W/m^2 of power from the Sun?
  12. archiesteel (RE: Post 56), I'm considering 280 ppm to be the baseline - not zero.
  13. RW1 said "The response of incrementally more CO2 is not linear - but logarithmic, which means each additional amount added only has about half of the effect of the previous amount." From the 2nd link in #50 (2008_Lean_Rind.pdf) the amount of added forcing for 280 to 380 is 1.5 W/m^2 So for 380 to 480 is another 0.75 (according to your formula) and for 480 to 560 is another 0.3 (80% of 0.375) for a total of 2.55 W/m^2 (not 4) for the doubling of CO2. That hinges on your statement of "half the effect of the previous amount".
  14. #32 Are you conscious that you are comparing temperatures variating in a specific place on the Earth with the average variation for the WHOLE PLANET? Do you see how wrong can be that?
  15. Also you (RW1) kept mentioning a 1W/m2 gain in TSI (which is mentioned in the same Lean/Rind paper). But that increase in TSI has to be divided by 4 since it is hitting a sphere not a perpendicular surface. So 0.25 W/m^2 is the increase in forcing from TSI AFAIK.
  16. Eric (RE: Post 65), The reference to 1 W/m^2 of power from the Sun is already divided by 4. 1360 W/m^2 TSI divided by 4 is 340 W/m^2. Subtract out the albedo of about 0.3 and you get 238 W/m^2 of average net incident solar power at the surface.
  17. @RW1: plenty of people have adressed your arguments. The current increase in temperature is in line with a climate sensitivity of 3C. It is not in line with your suggested 0.6C value. As I said earlier, the burden of proof is on you, and so far you have failed to make a convincing case challenging the established science.
  18. RW1, sorry to be a pain, are you talking about a hypothetical 1W/m^2 increase in solar forcing or actual? The actual increase over the last century was about 0.25 according to (link was in latest thread at WUWT)
  19. Eric (RE: Post 63), Something must be wrong with those calculations if the total isn't about 4 W/m^2 for a doubling (3.7 W/m^2 precisely). The initial 1.5 W/m^2 from 280 ppm to 380 ppm is probably wrong. It should be about 2.7 W/m^2 from 280 to 380 ppm.
  20. RW1 at 08:07 AM on 20 December, 2010
    "The response of incrementally more CO2 is not linear - but logarithmic, which means each additional amount added only has about half of the effect of the previous amount."
    That's obviously incorrect too. We can easily calculate the equilibrium temperature response expected from incremental enhancement of atmospheric [CO2]. If we use a climate sensitivity of 3 oC and normalize the Earth's temperature to near 15 oC at a [CO2] = 280 ppm, then the equilibrium temperature rise expected after each 20 ppm increment (all else being equal!) is:
    [CO2]   equil. temp     increment
    280	14.9567
    300	15.2554		0.2977
    320	15.5347		0.2793
    340	15.7971		0.2624
    360	16.0445		0.2474
    etc Clearly the assertion that "...each additional amount added only has about half of the effect of the previous amount." is quite wrong. In this case "each additional amount" adds around 94% "of the effect of the previous amount". Obviously the specific amount depends on the particular increment. So for 100 ppm increments:
    280	14.9567
    380	16.2786		1.3219
    480	17.2898		1.0112
  21. chris, when I asked about effect in #63, I should have said "forcing effect" not temperature effect. What is the forcing effect of incrementally more CO2?
  22. #69 RW1, the link in #68 shows it to be 1.5 W/m^2. Also the Lean/Rind paper.
  23. Eric (RE: Post 68), Either. We know the actual total is about 238 W/m^2, and each 1 W/m^2 of that 238 W/m^2 is amplified to about 1.6 W/m^2 at the surface for a total of about 390 W/m^2. We also know that the net incident solar power is not constant - it varies by about 20 W/m^2 from perihelion to aphelion (a net of about 14 W/m^2 albedo adjusted). What I'm saying is that there is no difference between 1 W/m^2 of power from the Sun, existing or hypothetically added, and 1 W/m^2 of additional power from CO2. The AGW theory is saying that the system is all of the sudden going to respond to an additional 2 W/m^2 of power at the surface from a doubling of CO radically differently than it does the original 238 W/m^2, including the + 14 W/m^2 at perihelion, from the Sun. Understand?
  24. @chris #70 Why you bother? Evidently an assertion that states "logarithmic, which means each additional amount added [undetermined amount] only has about half of the effect [mensurable effect] of the previous amount." makes no sense. Don't offer your figures to people who doesn't offer them. Ask them to provide those figures. If they're commenting in good faith they'll do.
  25. Alec (RE: Post 74), Are you saying the response of CO2 is not logarithmic - but linear?
  26. Eric (skeptic) at 11:50 AM on 20 December, 2010 "What is the forcing effect of incrementally more CO2?" Eric, I believe the temperature increment is proportional to the forcing increment i.e. deltaT = sigma.deltaF [where sigma is the climate sensitivity in units of oC/(W.m^2)] so I guess the forcing scales as the ln of the [CO2] increment much the same as the temperature in my post #70 above. Does that seem right?
  27. Chris (RE: Posts 60 & 70), Those numbers are useless because they're all based on the assumption of a 3 C sensitivity to a doubling of CO2. You cannot start with a conclusion, assume it is correct, and then derive the specific numbers in support of it by simply back fitting calculations to your original assumption. How about you address the series of individual questions I laid out in post 61?
  28. RW1 (#73), yes, thanks, you were not referring to the last century and I thought you were. As for the difference at perihelion, my understanding is that the extra energy (14 W/m^2) falls on land masses in the NH winter which reflects away much of the extra energy (versus SH ocean which is a better absorber of solar energy). Hence the NH winter has a bit colder global average temperature than NH summer even though the energy from the sun is greater. If I am mistaken, someone will correct me.
  29. Alec Cowan at 12:04 PM on 20 December, 2010 yes, I see your point Alec!
  30. #76, chris, I think that assumes that "climate sensitivity" is a constant that can be subdivided like you are doing. My understanding is that sensitivity as it is defined here is the temperature response to a CO2 change of 280 to 560. It cannot be used for any other purpose in a linear fashion.
  31. In #80, I meant to say CS is a constant that can not be subdivided.
  32. Eric (RE: Post 78), Global average temperatures are about 3 C colder at perihelion because - yes, I think a lot of the increased power is reflected from off the ice and snow accumulations that occur in the NH winter in January. But most of the additional 14 W/m^2 at perihelion then still affects SH summer in January because at that time the SH is tilted toward the Sun.
  33. @RW1: "Those numbers are useless because they're all based on the assumption of a 3 C sensitivity to a doubling of CO2. You cannot start with a conclusion, assume it is correct, and then derive the specific numbers in support of it by simply back fitting calculations to your original assumption." That's not what has happened, here. Rather, multiple scenarios were proposed, and the one closest to reality (following observations) is the one that puts it in the 2-4.5C range. It is false to claim people decided that climate sensitivity was 3C, then tried to fiddle their calculations to make it fit. In fact, I'd say you're venturing dangerously close to accusations of conspiracy theories, there... Further reading: James Annan explains why sensitivity is at 3C. "Are you saying the response of CO2 is not logarithmic - but linear?" No, that's not what he's saying. Rather, he's (correctly) noting that your description of the logarithmic curve was too vague to be useful. Or perhaps you think all logarithmic scales are the same?
  34. #83, RW1, I agree, but the bigger point is that the hemispherical asymmetry makes it impossible to use the 14 W/m^2 change and the global average temperature change as a case for much of anything and especially your last two paragraphs in #14.
  35. #77: "You cannot start with a conclusion, assume it is correct, and then derive the specific numbers ..." Indeed. We have to test the calculations that derive from a set of assumption to see if they match observation. On that fundamental point, I have no doubt we all agree. No such assumptions went into the preparation of the graphic for #57. The plotted curves are straight from the literature of radiative forcing which is not under discussion here. However, in #63, "incrementally more CO2 is not linear - but logarithmic, which means each additional amount added only has about half of the effect of the previous amount," a major flaw in your thinking is revealed. The function deltaT = 5.35 lambda log (C/C0) flattens as C (ie, CO2) increases; this gives the impression that adding more CO2 will gradually not be as bad. What you've ignored is the fact that C is a function of time that is strongly concave up. As a result, both the first and second time derivatives of the deltaT function are positive: deltaT is an increasing function of C and C is an increasing function of time. So while each additional ppm of CO2 causes a smaller temperature increase, we are adding CO2 at a rate that forces deltaT as function of time to increase at an increasing rate. Referring back to the figure in #57, your 0.6 deg C sensitivity produces neither the correct temperature anomaly nor the correct rate of change. One must therefore conclude that the assumptions made to calculate 0.6C sensitivity are incorrect, taking those calculations with them.
  36. Eric (skeptic) at 12:29 PM on 20 December, 2010 I don't think that's right Eric. The climate sensitivity is defined by convention as the amount of warming at equilibrium resulting from a radiative forcing equivalent to a doubling of atmospheric [CO2]. But it can be (and is) used to determine the equilibrium temperature response expected from any change in forcing including that resulting from small increments of [CO2]. Clearly if the wealth of empirical data supports a climate sensitivity near 3 oC (say), then the warming contribution expected from a rise of [CO2] from 280 to 380 ppm (say), should be predictable within that climate sensitivity (according to the ln of the ratio of [CO2]s). It would be perverse to consider otherwise. Of course the climate sensitivity is obviously a shorthand estimate of a response in a complex world! So the climate sensitivity in a world with a certain amount of sea ice (say) will differ from that of a world with no sea ice (say), since the albedo feedbacks will differ. In the real world the "climate sensitivity" will likely "dance around" somewhat temporally and according to precise conditions. ----- O.K. I've just seen your correction so maybe my post doesn't quite address your point. But (re your correction), the climate sensitivity isn't being subdivided. We're considering the Earth's equilibrium temperature response to a forcing as parameterized within a single value of the climate sensitivity. What's being subdivided is the forcing and its response, not the CS! I suspect that we might be talking at cross purposes, btw! If you think I haven't addressed your point properly have another go and I'll try again in the morning.
  37. Eric (RE: Post 84), Why not? OK, so it's not about 14 W/m^2 net - but something less because the total albedo in January is greater than 0.3 you're saying?
  38. RW1, the 0.3 value may be an average over all seasons, but the effective albedo must be greater in January since the solar forcing is greater but the global average temperature is lower. My parenthetical statement about the SH oceans in #78 is probably incorrect. But my main point again is that your statement in #14 "That the global climate doesn't even appear to be phased by a 14 W/m^2 increase in radiative forcing, suggests the net feedback operating on the system as a whole is strongly negative - not positive,..." is not a logical conclusion. The reason why the global climate is not affected by the 14 W/m^2 is due to the differences between the hemispheres, not net global feedback.
  39. Eric (RE: Post 88), I agree that the difference between the hemispheres is one of the main reasons, but the whole climate is affected (i.e. about 3 C colder globally at perihelion - not just in the NH). Without the +14 W/m^2 at perihelion, the global average temperatures would probably be even colder in January than they are now. It should also be pointed out that global temperatures are actually 3 C warmer at aphelion in July when net incident solar power is about 14 W/m^2 less. My main point is the aggregate confluence of factors that actually determine global average temperatures don't appear to be even phased much by 14 W/m^2 increase in radiative forcing - an amount much larger than what would come from a doubling of CO2. The perihelion point aside, what then is so special about each 1 W/m^2 of increased power from CO2, that the system is all the sudden going to respond to it radically differently than it does each 1 W/m^2 of power from the original 238 W/m^2?
  40. Eric (RE: Post 88), That last paragraph in my post 89 should have read: The perihelion point aside, what is so special about each 1 W/m^2 of increased power from CO2, that the system is all the sudden going to respond to it radically differently than it does each 1 W/m^2 of power from the original 238 W/m^2 sourced from the Sun?
  41. The "radical" difference comes from the difference in the way the two hemispheres respond to the seasonal solar changes. There's no way to get away from that fact and it means that the global average temperature response to CO2 which is evenly distributed worldwide, has more effects in polar regions, etc, is going to be radically different. It's sort of like saying that a giant fire in one hemisphere is going to have the same effect as a lot of smaller fires adding up to the same amount of heat and smoke, but distributed worldwide. Clearly the effects on weather and thus temperature will be quite different in those two cases.
  42. Eric (RE: Post 91), Why would CO2 have more effect in the polar regions? The numbers I've used throughout are global average numbers.
  43. Because there is less water vapor in the polar regions so CO2 has a proportionally greater effect and so a change is CO2 would also have a greater effect than outside of polar regions. As for using average numbers, I'm not a big fan of those for many reasons, one of which is demonstrated in your #14 which didn't mention the large differences in seasonal responses between the hemispheres.
  44. Eric (RE: Post 93), Well yes, but the polar regions are also largely snow and ice covered, which means a lot of the incoming power is getting reflected back out (back through the CO2), so incrementally more CO2 in those areas won't do much at all. Also, if there is a global increase in temperature from CO2, there will likely be a global increase in water vapor. That should offset any increase in CO2 for areas in the polar regions not snow and ice covered - as far as water vapor/CO2 absorption overlap is concerned.
  45. @RW1: "My main point is the aggregate confluence of factors that actually determine global average temperatures don't appear to be even phased much by 14 W/m^2 increase in radiative forcing - an amount much larger than what would come from a doubling of CO2." Temperatures are very much affected by the seasonal effect - that's why we have seasons! The warming due to CO2 is in addition to the normal variations. That's why it matters. Also, RW1, by not responding to muoncounter at #85 you are ignoring a strong rebuttal to your argument. Are you conceding defeat?
  46. muoncounter (RE: Post 86), I now see the problem. When referring to the logarithmic response of CO2, I mean only the intrinsic radiative forcing response - not any theoretical increase in temperature in addition to the intrinsic response via potential feedbacks and so forth (i.e. a 3 C rise). The intrinsic increase in radiative forcing from a doubling of CO2 is 3.7 W/m^2. When I say we've already reached 70-80% of a doubling going from 300 to 380 ppm (or 280 to 380ppm), I mean 70-80% of 3.7 W/m^2 or about 2.6 to 2.9 W/m^2 of intrinsic forcing.
  47. muoncounter (RE: Post 85), I meant post 96 above to be in response to your post 85 (not 86).
  48. RW1 - No, CO2 at the poles will act like CO2 at the tropics - retaining a percentage of the thermal radiation at those locations. That's a bogus argument. As to water vapor - that's a feedback to any forcing, whether it's CO2 or solar or aerosol. It doesn't counteract CO2 forcing in itself. If you wish to argue for a cloud feedback, take it to the cloud sensitivity thread.
  49. archiesteel (RE: Post 95), I'm well aware that any CO2 warming will be in addition to, or on top of, the normal variations. I don't dispute this, and nothing I've written disputes it. Also, I know temperatures are affected by the seasons - I've written so multiple times in this thread. The +14 W/m^2 at perihelion is a global average addition - not isolated to just one hemisphere or the other.
  50. RW1 - Please keep in mind that the perihelion/aphelion cycle is just that - a cycle. Which means it goes down as well as up. The added greenhouse effect, on the other hand, is a long term increase in both perihelion and aphelion irradiance, a long term uncompensated change in total irradiance. And hence an energy imbalance. The climate response to shifts in overall irradiance appears to be (including ocean responses) at least 40 years for mid-length feedbacks, centuries for long-term (weathering) feedbacks. The perihelion and aphelion cycles average out over those time scales. CO2 does not.

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