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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 & Choi 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 & Choi 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 & Choi 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 & Choi (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 & Choi (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:

Comments

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Comments 201 to 225 out of 457:

  1. RW1 @ 200 239 W/m^2 is the albedo adjusted input at TOA, 494 W/m^2 is the input at the earth's surface. If you look at the more precise numbers cited at the top of the diagram, the input and output at TOA is: input: 341.3 albedo: 101.9 output: 238.5 difference: 341.3 - 101.9 - 238.5 = .9 W/m^2 of warming. I agree with KR that the diagram seems straightforward, I'm not sure why you find it so confusing.
  2. KR (RE: 191), KR: "- You have repeatedly asserted that cyclic variations (orbital distances, seasons) somehow affect the global energy balance differently than CO2 forcings." Funny that you say this when in fact I've argued the exact opposite. I've said that the CO2 forcings are treated differently than the same amount of incoming power from the Sun over "cyclic varations (orbital distances, seasons)". KR: "You are incorrect - they all affect the global energy in the same fashion. It's just that long term trends in averages will change global climate, whereas balanced cycles will not." I never claimed that balanced cycles change global climate long term. I'm well aware that they don't. How about you explain why the 1.6 gain factor works to explain the global average temperature difference of -3 C even with a +7 W/m^2 net solar input at perihelion, but not with a gain of 8 (or 4) needed for a 3 C rise from a doubling of CO2?
  3. E (RE: Post 201), I understand those numbers very clearly, as they are easy to see. I'm talking about all the additional numbers and relationships as far as power in = power out.
  4. RW1 @ 202, Can you explain the physical relevance of the gain factor you keep citing (not the numbers you divided to get 1.6, but what does this number physically represent)? Nobody here understands why you think this number is meaningful.
  5. RW1 @ 203, The numbers are right there in the diagram, you can add them up however you prefer. Precisely which numbers do you find confusing?
  6. e (RE: Post 204), e: "Can you explain the physical relevance of the gain factor you keep citing (not the numbers you divided to get 1.6, but what does this number physically represent)? Nobody here understands why you think this number is meaningful." I'll try again. The gain is simply a representation of the amount of post albedo power entering the system from the sun that is "gained" at the surface due to the presence of GHGs and clouds in the atmosphere, which delay the release of infrared heat energy by redirecting some of it back toward the surface, which makes the surface warmer than it would be otherwise. A gain of about 1.6 simply means it takes a 1.6 W/m^2 power flux at the surface for each 1 W/m^2 of power to leave the system, offsetting each 1 W/m^2 entering the system from the Sun. that 1 W/m^2 of post albedo power entering the system from the Sun, you get 1.6 W/m^2 of power at the surface,
  7. e (RE: Post 204), e: "Can you explain the physical relevance of the gain factor you keep citing (not the numbers you divided to get 1.6, but what does this number physically represent)? Nobody here understands why you think this number is meaningful." Using Trenberth's numbers, the gain is still about 1.6 (396/239 = 1.65). The gain is the simplest representation of how the system responds to each 1 W/m^2 of power entering, because it makes the fewest assumptions - like what all the energy flows may or may not be (cloudy vs. clear sky, how much absorbed power is re-directed toward the surface or space, how much passes through unabsorbed, etc.) The gain of 1.6 is the net measured result of all these things, independent of whatever specifically they may all be. Does that help clarify it?
  8. e, the 1.6 comes from the paper linked in #150 (RW1: I think it would have been better to post that paper at the beginning to show where you are coming from). After reading the paper, the data comes from ISCCP, the variables are described here http://isccp.giss.nasa.gov/products/variables.html I started with graph 1, albedo looks reasonable compared to some papers online. Next, input power is derived from Psun and albedo, also reasonable. That's the denominator in the "gain". The next section is where I have issues, both from lack of understanding of the data sources and from what looks like errors in a formula. As described in that document "The output power is calculated as Po = (1-ρ)*Ps + ρ*Pc + Pw, where ρ is the fraction of clouds, Ps and Pc are the power fluxes originating from the surface and clouds" First I do not know where Ps and Pc come from (in my link above). The Ps might be calculated from emissivity and temperature (but I have no idea really). The Pc may come from cloud top temperature but I think that lacks some parameter (clouds are not black body) Then my biggest issue comes from using the fraction of clouds (the corresponding variable is cloud amount). Then there may be a problem with "power consumed by weather" albeit small. The next step is subtracting the input from the output power, then comparing that to the change in temperature to conclude that "As expected, the net flux in and out of the Earth's thermal mass, Pe, closely follows the solar input variability." IMO that should have been followed with an analysis of thermal storage, namely something like #117 in this thread and the others muoncounter mentioned. After that fairly obvious and non-quantitative conclusion, the author gets to the "gain" formula which he conflates with sensitivity (I also have a problem with how sensitivity is defined, but I don't think the solution is this formula for gain). The numerator in gain is the power flux calculated from surface temperature using S-B. IMO the previous discussion came from an analysis that was supposed to yield a quantity but did not. The choice of surface power flux is quite limiting IMO due to issues I discussed in #144.
  9. e (RE: Post 204), Put another way, regardless of who is right or wrong about the energy flows, the gain is still going to be roughly 1.6
  10. RW1 - Thank you for the explanation; that clarifies things quite a bit. Unfortunately, that leaves you with a non-constant 'gain', which I do not feel is a meaningful number. In the absence of greenhouse gases (first approximation, mind you, a Gedankenexperiment) the incoming solar energy at dynamic equilibrium will still be ~240, and the outgoing IR will be 240 to match (zero imbalance). Your 'gain' is then 1.0. As the greenhouse effect changes value (more CO2 in the atmosphere, for example), the incoming visible light still be ~240, and the outgoing IR close to that as well - with a higher surface temperature, and a 'gain' > 1.6. What matters is the surface temperature required (with the current emissivity of the Earth) to radiate ~240 W/m^2 out to space. As the emissivity 'e' decreases with GHG's, an imbalance occurs between sunlight in and IR out - resulting in a changing temperature 'T'. Not a 'gain' factor, but basic thermodynamics and math. Your factor of 1.6 is not a constant, but a result. You can't use that as an input - that's confusing cause and effect.
  11. Also note that the "global monthly gain" chart in the paper from #150 shows it to be almost exactly inverse to the solar input. That suggests that "gain" is actually representative of the excess power not being stored as OHC. IOW, despite the fact that solar power wanes in NH summer, the earth temperature rises more than in summer as a ratio of that power (ie the "gain" is higher) due to NH land mass (much less OHC storage). The author does point out the hemispherical differences earlier in the paper, but does not carry any of those conclusions to the gain section (again it may be because they are not quantitative). The whole paper seems like a genuinely interesting experiment in data analysis, but ultimately discards the interesting part (seasonal variation in "gain") which seems to preclude its use with long run CO2 forcing.
  12. RW1 - "Can you give me the power in = power out relationship between the numbers in your post #196": For the surface, I did. In post #196. Keep in mind that Trenberth's numbers split the Earth system into three layers - surface, atmosphere, and space. If you add up the numbers for any one of the three layers (interacting with the other two) the sums match up to zero. He explains the derivations and evaluations of these numbers in Trenberth 2009. As I said before, if you have issues with any of the Trenberth numbers, say so, and specify which, with some justification as to why. You have not done so to date.
  13. Eric and KR, Despite my efforts, I still don't think either of you understand what the gain is representing. The gain is the net result at the surface from the greenhouse effect in the atmosphere, which makes the surface warmer that it would be without it. KR, I know the gain isn't a constant, but an average. It fluctuates somewhat, but the range of fluctuation doesn't go anywhere near 8 (or 4) that is necessary to amplify 2xCO2 to 3 degrees C. Eric (RE: Post 211), That the gain is increasing as solar power is decreasing and vice versa has nothing to do with excess energy being stored. The ocean heat content is included in Pe, which is the power coming in and out of the Earth's thermal mass. If more power is arriving than leaving, Pe is a positive number; if more power is leaving than is arriving, Pe is a negative number. The averages are virtually zero, with power out being slightly more (0.1 W/m^2 higher on average). Also, the gain decreasing as radiative forcing is increasing - both hemispherically and globally, demonstrates negative feedback to increases in radiative forcing; meaning any small rise in surface power would be opposed rather than reinforced. This contradicts the AGW theory of large positive feedbacks greatly amplifying the small instrinic increase in radiative forcing from 2xCO2.
  14. RW1 - the 3 degrees C is the result of feedback amplification, which you have not acknowledged at all (as far as I can see - I would welcome being corrected). Doubling CO2 results in about 1.2°C direct warming - the 3°C results from climate sensitivity. And the same warming (depending on what you accept as climate sensitivity) results from volcanic aerosols, solar insolation, or any change in energy. Again, your 1.6 is a result, not an input. It's a nonsense number in terms of inputs. You would be much better served to look at the temperature required to radiate a power equal to insolation. Enjoy your (solstice related) holidays.
  15. RW1, you are right, Pe has nothing to do with "gain" in the paper in #150. It is mostly a tangent. Pe is 10 W/m^2 but the power flux from 3 x 10^22 J of seasonal OHC storage (#117) is only about 2 W/m^2 Robust-warming-of-the-global-upper-ocean.html. I suspect that Pe is overestimated in that paper due to problems with Pout (#208).
  16. KR (RE: Post 214), I know the 3 degrees C requires positive feedback amplification. The net effect of all the individual feedbacks in the system is already accounted for in the gain, because it's an aggregate empirically measured response of the total power entering vs. the power at the surface. This is not the same as the net feedback operating on the system as a whole, which is what the 3 C rise comes from. However, the amount of positive feedback needed for 3 C rise is NOT derived from first principle physics or empirical observation of the system's response to changes in radiative forcing - but from model estimates that involve numerous assumptions and fudge factors. That in and of itself doesn't mean the models are wrong, but being so diametrically opposed to what is empirically measured, suggests they likely are.
  17. RW1 at 15:36 PM on 24 December 2010
    "...but being so diametrically opposed to what is empirically measured...
    But we've already seen that contemporary (20th century) warming is entirely consistent with a climate sensitivity in the range 2-4.5 oC. Since we've already had virtually the warming expected from a climate sensitivity of 2 oC, even without factoring in the inertia in the climate system and the counteracting effects of man made aerosols as described here, and here, and here. The empirical data are simply incompatible with your model and it surprises me that this doesn't concern you.
    "However, the amount of positive feedback needed for 3 C rise is NOT derived from first principle physics or empirical observation of the system's response to changes in radiative forcing - but from model estimates that involve numerous assumptions and fudge factors."
    That's simply not true. It's worth familiarising yourself with the large body of data that informs us about likely ranges of climate sensitivity, ranging from empirical analyses to modelling. A good place to start is here. As for the analysis of seasonal temperature variations, which seems to play a large part in your argumentation, I think it might help if you were to consider more carefully why the Earth is overall warmer at aphelion (July) and cooler at perihelion (January).
  18. chris (RE: 217), "But we've already seen that contemporary (20th century) warming is entirely consistent with a climate sensitivity in the range 2-4.5 oC. Since we've already had virtually the warming expected from a climate sensitivity of 2 oC, even without factoring in the inertia in the climate system and the counteracting effects of man made aerosols as described here, and here, and here. The empirical data are simply incompatible with your model and it surprises me that this doesn't concern you." How do you figure we've had all the warming of a 2 C sensitivity? As stated earlier in the thread, we've already reached 75-80% of the intrinsic forcing from a doubling of CO2 and we've only seen about 0.6-0.8 C of warming. Even if all of the warming was attributed to CO2, that translates to only about a 1 C sensitivity. Also, I don't think you understand the model I've laid out. It's not a representation of all the things that can affect climate and temperatures - it's just a representation of how much can be expected to be added on top of natural variation from 2xCO2. The amount of warming we've seen so far is perfectly in line with about a 0.6 C upper limit from a doubling of CO2. "That's simply not true. It's worth familiarising yourself with the large body of data that informs us about likely ranges of climate sensitivity, ranging from empirical analyses to modelling." I'm aware of it. My point was the model estimates are not derived from first principle physics or empirical observation of how the system responds to changes in radiative forcing. Also, the model estimates are way outside the bounds of how the system responds to post albedo power from the Sun. "As for the analysis of seasonal temperature variations, which seems to play a large part in your argumentation, I think it might help if you were to consider more carefully why the Earth is overall warmer at aphelion (July) and cooler at perihelion (January)." I addressed this. That the earth is cooler at perihelion despite higher insolation and warmer at aphelion despite lower insolation totally fits with the numbers I've presented for sensitivity. The reason for this is the albedo is greater in January than it is in July (*do you want me to run the numbers again?) How about you explain why the sensitivity numbers I've put forth fit very well with the temperatures differences at perihelion and aphelion and why the sensitivity numbers for a 3 C rise do not fit and are much too high?
  19. #218. damorbel "As stated earlier in the thread, we've already reached 75-80% of the intrinsic forcing from a doubling of CO2 and we've only seen about 0.6-0.8 C of warming." Your maths or STILL wrong. CBDunkerson put you right on that way back in post #34.
  20. johnkg (RE Post 219), Your maths or STILL wrong. CBDunkerson put you right on that way back in post #34. And I then clarified in Post 96 I was referring to the intrinsic response of CO2 - not any additional increase as a result of feedbacks. My statement in #218 is accurate.
  21. #218: "...a representation of how much can be expected to be added on top of natural variation from 2xCO2." There's not currently a 'natural variation' that is doubling CO2. If your model is due to the effects of CO2 only, why do you start with planetary albedo and continue with emissivity? These points of basic physics are not CO2-specific. "The amount of warming we've seen so far is perfectly in line with about a 0.6 C upper limit from a doubling of CO2." Utterly incorrect and shown a number of times in this thread. Look at hfranzen's article; he arrives at 0.14 deg C/decade, which is far more than an 0.6 C sensitivity can produce. His results come from a strictly physics-chemistry calculation. You can't both be correct -- and his work agrees with measurements of temperature increase.
  22. RW1 at 05:24 AM on 25 December, 2010
    "How do you figure we've had all the warming of a 2 C sensitivity?"
    Come on RW1, this was explained here, and here, and here. Remember we're using your own argument, (but doing it correctly). It's very straightforward (use the equation here) to determine the full warming expected at equilibrium from the rise in [CO2] between 1900 and 2000 (the dates you chose yourself). [CO2] in 1900 was 298 ppm. [CO2] in 2000 was 371 ppm. The warming at equilibrium for 3 oC climate sensitivity is 0.95 oC. The warming at equilibrium for 2 oC climate sensitivity is 0.63 oC. The actual temperature rise during this period was 0.75-0.8 oC. In other words we've had all the warming already that we expect from a climate sensitivity of 2 oC (Earth surface temperature rise per doubling of [CO2]), even though the Earth surface hasn't come to equilibrium with the enhanced greenhouse forcing during this period, and even though some of the warming has undoubtedly been countered by the large increase in made made aerosols. We know the solar contribution to warming has been small during this period (very likely less than 0.1 oC) as the very competent solar scientists inform us [see e.g. Lean and Rind (2008) and Hansen et al (2005)]... (and if were being very careful we should factor in the small contribution from man-made rises in methane and nitrous oxides atmospheric concentrations). So your assertion that 20th century warming is "in line with about a 0.6 C upper limit from a doubling of CO2" is clearly incompatible with empirical observations. That should contribute a warming of 0.19 oC at equilibrium from the 20th century rise in [CO2]. If your assertions are so wildly at odds with empirical observations RW1, then there's something very wrong with your argument.
    "How about you explain why the sensitivity numbers I've put forth fit very well with the temperatures differences at perihelion and aphelion..."
    I expect the numbers (you got them from someone's website I think) match rather by chance, unfortunately. It’s clear that you haven’t made any headway with your numerology with the set of rather bright individuals who have tried to help you out on this thread! In any case, the dominant effect on the relative hemispheric warming/cooling at aphelion and perihelion is the relative amount of land (low heat capacity) and ocean (high heat capacity) in the two hemispheres. Since the sinusoidal seasonal solar forcing is paced much faster than the Earth (and especially the oceans due to its high heat capacity) can come towards temperature equilibrium with the rapidly varying forcing, there is a strong mismatch between the rates that the hemispheres gain and lose heat. The N hemisphere (lots of land) warms more quickly than does the S hemisphere (90% ocean). Clearly, if one were able to determine climate sensitivity from analysis of the seasonal response to insolation variation there would be a nice body of scientific literature on the subject! There isn't. Unfortunately these analyses are bedevilled by difficulties in determination of the characteristic time constant of the climate system response to forcing. More importantly, the response to the very rapid (monthly) changes in insolation during the Earth's speedy passage around the sun, means that only the elements of the climate system that respond more rapidly are (partially) sampled (atmosphere and land surface). So as described in Foster et al (2008), for example, analysis of transient responses to rapid changes in forcing generally produce climate sensitivities that are biased low relative to the climate sensitivity of interest, namely the full Earth response to a strong, persistent (and progressively increasing) enhanced greenhouse gas forcing.
  23. RW1 - Sorry, your gain makes no sense whatsoever to me. The energy trapped at the surface is a function of the insolation and the ability of the Earth/atmosphere system to radiate that heat away in a temperature dependent fashion. I think we are all much better served by using the actual relationships there rather than a non-physics based 'gain factor' that isn't actually a constant. There's no difference between insolation changes, aerosol changes, albedo changes, and CO2 changes in terms of forcing beyond their "efficacy", and the only factor with an efficacy close to 1.6 in anyone's estimation (and I consider that an outlier) is cloud albedo (Figure 2.19).
  24. KR (RE: Post 223), The gain is not a subjective number or "my gain". It's a very simple objective number. You have power coming in from the Sun. Some of that power is reflected back out via the Earth's albedo. The rest of the power "forces" the climate system. The amount of power at the surface is greater than the post albedo power entering the system from the Sun and greater than the power leaving the at the TOA. The surface power divided by the post albedo power is the gain in the system. It's simply a representation of what about each 1 W/m^2 of power coming in is amplified to at the surface due to the greenhouse effect. Power from the Sun is measured in W/m^2. Increased power from CO2 is measured in W/m^2. A watt/meter squared of power is watt per meter squared of power, independent of where it comes from; thus power from the Sun is proportionally the same as power from CO2.
  25. muoncounter (RE: Post 223), I'm sorry, I was under the impression that you and everyone else here knows that the climate doesn't do anything but change. You do understand that even if mankind never emitted a single CO2 molecule, that the climate would still be doing what it has always done - change (go through periods of warming and cooling, etc.)?? A roughly 0.6 C sensitivity is at least as consistent with a 0.8 C rise so far, and probably more so, because 0.8 C is much closer than 3 C.
    Response: Comment on that topic in the relevant thread: "Climate’s changed before."

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