“…ERBE data appear to demonstrate a climate sensitivity of about 0.5°C which is easily distinguished from sensitivities given by models.”
On the determination of climate feedbacks from ERBE data
Richard S. Lindzen and Yong-Sang Choi
Revised on July 14, 2009 for publication to Geophysical Research Letters
Abstract
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. Therefore, the models display much higher climate sensitivity than is inferred from ERBE, though it is difficult to pin down such high sensitivities with any precision. Results also show, the feedback in ERBE is mostly from shortwave radiation while the feedback in the models is mostly from longwave radiation. Although such a test does not distinguish the mechanisms, this is important since the inconsistency of climate feedbacks constitutes a very fundamental problem in climate prediction.
Introduction
The purpose of the present note is to inquire whether observations of the earth’s radiation imbalance can be used to infer feedbacks and climate sensitivity. Such an approach has, as we will see, some difficulties, but it appears that they can be overcome. This is important since most current estimates of climate sensitivity are based on global climate model (GCM) results, and these obviously need observational testing.
To see what one particular difficulty is, consider the following conceptual situation:
We instantaneously double CO2. This will cause the characteristic emission level to rise to a colder level with an associated diminution of outgoing longwave radiation (OLR). The resulting radiative imbalance is what is generally referred to as radiative forcing. However, the resulting warming will eventually eliminate the radiative imbalance as the system approaches equilibrium. The actual amount of warming associated with
equilibration as well as the response time will depend on the climate feedbacks in the system. These feedbacks arise from the dependence of radiatively important substances like water vapor (which is a powerful greenhouse gas) and clouds (which are important for both infrared and visible radiation) on the temperature. If the feedbacks are positive, then both the equilibrium warming and the response time will increase; if they are negative, both will decrease. Simple calculations as well as GCM results suggest response times on the order of decades for positive feedbacks and years or less for negative feedbacks [Lindzen and Giannitsis, 1998, and references therein].
The main point of this example is to illustrate that the climate system tends to eliminate radiative imbalances with characteristic response times.
Now, in 2002–2004 several papers noted that there was interdecadal change in the top-of-atmosphere (TOA) radiative balance associated with a warming between the 1980’s and 1990’s [Chen et al., 2002; Wang et al., 2002; Wielicki et al., 2002a, b; Cess and Udelhofen, 2003; Hatzidimitriou et al., 2004; Lin et al., 2004]. Chou and Lindzen [2005] inferred from the interdecadal changes in OLR and temperature that there was a strong negative feedback. However, this result was internally inconsistent since the
persistence of the imbalance over a decade implied a positive feedback. A subsequent correction to the satellite data eliminated much of the decadal variation in the radiative balance [Wong et al., 2006].
However, it also made clear that one could not readily use decadal variability in surface temperature to infer feedbacks from ERBE data. Rather one needs to look at temperature variations that are long compared to the time scales associated with the feedback processes, but short compared to the response time over which the system equilibrates. This is also important so as to unambiguously observe changes in the radiative budget that are responses to fluctuations in SST as opposed to changes in SST resulting from changes in the radiative budget; the latter will occur on the response time of the system. The primary feedbacks involving water vapor and clouds occur on time scales of days [Lindzen et al., 2001; Rodwell and Palmer, 2007], while response times for relatively strong negative feedbacks remain on the order of a year [Lindzen and Giannitsis, 1998, and references therein]. That said, it is evident that, because the system attempts to restore equilibrium, there will be a tendency to underestimate negative feedbacks relative to positive feedbacks that are associated with longer response times.
Concluding Remarks
In Figure 3, we show 3 panels. We see that ERBE and model results differ
substantially. In panels a and b, we evaluate Equation (3) using ΔFlux for only OLR and only SWR. The curves are for the condition assuming no SW feedback and assuming no LW feedback in panels a and b, respectively. In panel a, model results fall on the curve given by Equation (3), because the model average of SW feedbacks is almost zero. In panel b, models with smaller LW feedbacks are closer to the curve for no LW feedback; the model results would lie on the curve assuming positive LW feedback. When in panel c we consider the total flux (i.e., LW + SW), model results do lie on the theoretically expected curve.
Looking at Figure 3, we note several important features:
1) The models display much higher climate sensitivity than is inferred from ERBE.
2) The (negative) feedback in ERBE is mostly from SW while the (positive) feedback in
the models is mostly from OLR.
3) The theoretical relation between ΔF/ΔT and sensitivity is very flat for sensitivities
greater than 2°C. Thus, the data does not readily pin down such sensitivities. This was
the basis for the assertion by Roe and Baker [2007] that determination of climate
sensitivity was almost impossible [Allen and Frame, 2007]. However, this assertion
assumes a large positive feedback.
Indeed, Fig. 3c suggests that models should have a range of sensitivities extending from about 1.5°C to infinite sensitivity (rather than 5°C as commonly asserted), given the presence of spurious positive feedback. However, response time increases with increasing sensitivity [Lindzen and Giannitsis,1998], and models were probably not run sufficiently long to realize their full sensitivity. For sensitivities less than 2°C, the data readily distinguish different sensitivities, and ERBE data appear to demonstrate a climate sensitivity of about 0.5°C which is easily distinguished from sensitivities given by models.
Note that while TOA flux data from ERBE are sufficient to determine feedback factors, this data do not specifically identify mechanisms. Thus, the small OLR feedback from ERBE might represent the absence of any OLR feedback; it might also result from the cancellation of a possible positive water vapor feedback due to increased water vapor
in the upper troposphere [Soden et al., 2005] and a possible negative iris cloud feedback involving reduced upper level cirrus clouds [Lindzen et al., 2001]. With respect to SW feedbacks, it is currently claimed that model SW feedbacks are largely associated with the behavior of low level clouds [Bony et al., 2006, and references therein]. Whether this is the case in nature cannot be determined from ERBE TOA observations.
However,more recent data from CALIOP do offer height resolution, and we are currently studying such data to resolve the issue of what, in fact, is determining SW feedbacks. Finally, it should be noted that our analysis has only considered the tropics. Following Lindzen et al. [2001], allowing for sharing this tropical feedback with neutral higher latitudes could reduce the negative feedback factor by about a factor of two. This would lead to an
equilibrium sensitivity that is 2/3 rather than 1/2 of the non-feedback value. This, of course, is still a small sensitivity.
see the full paper here (PDF)
h/t to Leif Svalgaard
George Smith asked “Where on earth did you come up with the idea that when the ocean freezes, that the atmosphere above it will warm up.”
You can read here, for example, about latent heat:
HOW DOES FREEZING RELEASE HEAT ENERGY?
http://www.theweatherprediction.com/habyhints2/468/
peter_ga (16:52:04) : “So it would be good to have a theory that accounts for everything.”
A worthy goal, but I fear that there are too many moving parts . . . too many exogenous variables which are not repetitive in a reasonable time frame . . . too much “chaos” to develop a complete climatology theory that can be modeled. We can talk about influences, but to account for everything in the past — much less the future — seems doubtful to me.
Financial models have failed spectacularly, and the relevant issues for them are probably smaller in number than for the climate.
Paul (14:53:33) : Read the paper-he does use the corrected data.
@Nogw (09:50:07) :
“UN´s FAO forecasts only a variation of temperatures ranging from -0.1 to +0.1 degrees to the year 2099.
I’m just as skeptical of that projection as I am of a projection of +7 degrees. I am willing to go out on a limb here and predict another continental glaciation. I’m just not sure when it will happen.
All the scientific gobbledy-gook above hurts my brain. Does not the concept of the cooler atmosphere heating the (already) warmer planet violate the Second Law of Thermodynamics? The “debate” should end right there!
Nogw:
“This means one of two things: either the door of the greenhouse was open or there is no greenhouse at all!!”
Or that the greenhouse has a built-in climate control system.
The whole positive feedback scenario presupposes a very unstable equilibrium in climate. If water vapor acts as a feedback for temperature, then any perturbation in temperature – be it from CO2 forcing, solar variation, vulcanism, or some other cause – would be amplified into a major fluctuation. Any warming would cause the atmosphere to hold more water vapor and any cooling would cause the atmosphere to hold less water vapor. Minor warming would be amplified into major warming and minor cooling into major cooling. Any equilibrium the atmosphere reached would be very unstable. It would be like a pool ball balanced on the bottom of an upturned bowl. Any perturbation would cause the ball to roll off one way or the other.
What is remarkable about the history of the planet, though, is how stable the climate has been. Over hundreds of millions of years (at least) major changes in the composition of the atmosphere, variations in the arrangement of continents and oceans, solar and orbital variations, vulcanism, bolide impacts, and many other variations gradual or catastrophic have failed to push the Earth’s temperature outside the range where the oceans remain liquid and life can exist on the land and in the atmosphere. None of these large perturbations ever sent the Earth into a runaway warming or a runaway cooling. To me this suggests not an unstable equilibrium, but a very stable one. Like a pool ball in the bottom of an upright bowl: perturbations would push the ball a little way up the side of the bowl, but the ball would return to the bottom of the bowl when the perturbation ceased. To put it succinctly, I think the Earth’s atmosphere is self-stabilizing. It is a homeostatic system.
I have heard at least one hypothesis that might yield such homeostatic behavior. The tropical infrared iris hypothesis as mediated by precipitation efficiency (which increases as temperature increases) would tend to dampen any variations from an equilibrium. Of course, this would not yield a constant temperature, but one tightly linked to the factors that determine the equilibrium temperature. Thus you would see temperature variations tightly coupled to variations in incoming solar radiation, volcanic aerosols, anthropogenic sulfates, and internal dynamic phenomena like El Nino that release or store large amounts of heat in the ocean. If, however, the feedback system is based on the abundance of water vapor in the atmosphere, it seems unlikely that CO2 and other greenhouse gasses that are far less abundant and/or radiatively active than water vapor would be unlikely to change the behavior of the system, except in places where there is very little water vapor in the atmosphere. You would expect maybe a small warming of the polar winter, but little or no change in the tropics from an increase in atmospheric CO2.
The data we have is, like almost anything, is open to many interpretations. The way I see it, the correlation of atmospheric temperature to solar variations, volcanic areosols, and ENSO and PDO/AMO strongly suggest a stable equilibrium rather than an unstable one.
Simple calculations as well as GCM results suggest response times on the order of decades for positive feedbacks and years or less for negative feedbacks [Lindzen and Giannitsis, 1998, and references therein].
That is the exact same thing the Ice Ages tell me: It takes a lot longer to warm than it does to freeze up. The way it works.
Simple calculations as well as GCM results suggest response times on the order of decades for positive feedbacks and years or less for negative feedbacks [Lindzen and Giannitsis, 1998, and references therein].
That is the exact same thing the Ice Ages tell me: It takes a lot longer to warm than it does to freeze up. The way it works. Whatever warming we get out of CO2 or soot, all it takes is for the things that force it down to take a pot shot at our climate, and it’s all undone.
Dave Dodd (20:05:07) : See, this is why the name “global warming” is misleading. The atmosphere doesn’t “heat” the surface, but it effects the rate at which it cools. Global Warming should really be called “global less cooling”
More seriously:
http://www.drroyspencer.com/2009/04/in-defense-of-the-greenhouse-effect/
rbateman (20:19:37) :
That is the exact same thing the Ice Ages tell me: It takes a lot longer to warm than it does to freeze up. The way it works.
Except that the temperature rose rapidly after glaciations, while therm was a long. slow slide down to the next glaciation. E.g. Figure 4 of http://www3.hi.is/~oi/Nemendaritgerdir/Ice%20core%20evidence%20for%20past%20climates%20and%20glaciation.pdf
George E. Smith:
You are correct that only radiation loss and conduction cooling from the air can contribute to cooling and thus freezing of the water. However if the air is warmer than the water, the radiation alone can still freeze the water as long as the radiation out exceeds the heating input from warmer air, and the surface water temperature has dropped to the freezing point (about -2 degrees C for seawater). In extended dark conditions, the radiation out is typically several times as large as the heat transfer in from the air, so it is quite possible to freeze even with a significant higher air temperature (think of frost on a car in above freezing air temperature on a clear night). If the air is colder than the water or ice, just conductive heat transfer to the air will bring the air temperature at the surface closer to the water/ice temperature. The phase change requires additional cooling to overcome, but this is not ever going to raise the air temperature warmer than the forming ice temperature.
Stephen Skinner:
The freezing does not release heat energy at an increased temperature, it just requires additional radiating or air cooling to remove that much more energy at constant temperature (think of ice cubes melting in water. Once the water reaches the freezing temperature, the remaining ice and water coexist at the same temperature, and the remaining ice only melts due to added heat loss from the container wall). Pure ice requires 80 calories per gram to be removed to freeze at constant temperature. Seawater is slightly different, but same ballpark.
Leif Svalgaard (20:30:19) :
“Except that the temperature rose rapidly after glaciations, while therm was a long. slow slide down to the next glaciation.”
Which would be why I feel like the sensitivity number is a variable, and not a constant 0.75°C, or a constant 0.5°C. I know you don’t like the ‘I feel like’ part, but I don’t see anyone else nailing it down either. 🙂
Mac (08:53:59) :
There is also this paper which is causing a stir.
http://www.agu.org/pubs/crossref/2009/2008JD011637.shtml
A deserved stir Mac. The conclusion of this paper is yet further confirmation of the near certainty natural variation is the predominant climate influence.
“That mean global tropospheric temperature has for the last 50 years fallen and risen in close accord with the SOI of 5–7 months earlier shows the potential of natural forcing mechanisms to account for most of the temperature variation.”
Leif Svalgaard (20:30:19) : Not that it matters as unfortunately rbateman misunderstood what he was quoting.
“Simple calculations as well as GCM results suggest response times on the order of decades for positive feedbacks and years or less for negative feedbacks [Lindzen and Giannitsis, 1998, and references therein].”
Has nothing whatsoever to do with the rate of change from interglacial to glacial or vice versus. It simply has to due with the climate system taking longer to respond the more sensitive it is. So the rate of change coming in and out of Ice Ages is only relevant in terms of what the change is in response to. My understanding is that Milankovitch variations are slow compared to the apparent sudden warming out of Ice Ages and maybe not so much going into them, but the Ice Age situation is really complicated and it’s hard to say how everything fits in. But Short response times are found in analysis of volcanic eruptions and the annual cycles of insolation, and now ERBE data corroborates the implications of such.
lweinstein (20:48:06) :
Thank you for the very clear explanation. That helps. My initial post had an extract (NSIDC – November 10, 2008 An expected paradox: Autumn warmth and ice growth) which I understand to fit with your explanation to George E Smith. The extract before that from the BBC and Dr Stroeve looks like they took the same data as NSIDC and observed the same phenomena, but interpreted as evidence of a positive feedback.
Anyway having asked similar questions to the BBC, The MET office, The Hadley Centre and more, over a number of years, yours is the FIRST reply.
Pamela Gray (17:27:10) :
Thank you for your comments, but I think you are confusing me with someone else.
rbateman:
Pinatubo had a rapid and pronounced cooling effect… this should be a lesson for us all. Cooling is FAR more of a threat than warming can be.
Planetary atmospheres are far better at shedding heat than retaining it. Even Venus’.
Summer of 2008, we were being told that oil would NEVER be below $70 again, there just was no possible way the market would allow it, what with China and everything.
I definitely agree… projections are only ever to be used as a possibility. Nobody can ever really project anything with certainty.
Although, I tend to believe that projections of an overall neutral anomaly in 100 years are the most likely. Then again, treasure these days, if GISS has their way in 100 years today’s high will be remembered as -20C
timetochooseagain (21:41:49) :
I did not misunderstand. I was relating microcosm to macrocosm.
First I have seen of rapid warming out of Ice Ages.
The references in the paper are very recent and some governmental.
Alternate view boring down into individual regions.
Depending on where the data was taken and how closely one zooms in, the overall picture is different even in that paper. No surprises there.
Keep going down and you might find Grand Minimum and Maximums to toss about.
As far as I know the topic here is how the overall planet Earth responds, though there is the Baranyi study that demonstrated certain areas of the Nothern Hemisphere that are more affected than others to certain kinds of events.
This is important since most current estimates of climate sensitivity are based on global climate model (GCM) results, and these obviously need observational testing.
Quote of the week?
George E. Smith (14:21:48)
“You want to specify where abouts in the equatorial oceans, at high noon the water temperature gets to 181 F or 83 C. You realize that 1360 W/m^2 is just 6 below the extra atmospheric TSI level. And just how did the emissivity of the oceans get down to as low as 0.67; it should be more like 0.97, certainly for the LW radiant emissions.”
It doesn’t, that’s the point. See for example, Willis Eschenbach’s article on this site a few weeks back which gives an explanation of how the tropics are cooled by convection and cloud formation. He notes in passing at the end that without these cooling mechanisms the tropics would be ferociously hot.
The emissivity is at the wavelengths of the incoming solar radiation that heats the surface.
I should have made my point more clearly. The surface temperature of the earth is naturally quite high. For comparison, the moon, which receives the identical solar flux, has a daytime surface temperature of 107C. The cooling forces due to convection and the various phase changes of water vapor, evaporation, condensation, and clouds are very large and bring temperatures down to the livable range. The difference is about 60 C, a lot more than the puny 1-2 C predicted by models from doubling CO2. The real question is not warming, it’s why the earth’s surface stays so cool.
George Smith asked “Where on earth did you come up with the idea that when the ocean freezes, that the atmosphere above it will warm up.”
Michael Jackson
George DeBusk says:
Well, alas, those who study paleoclimate tend to disagree with you ( http://www.sciencemag.org/cgi/content/summary/sci;306/5697/821 ):
George DeBusk says:
Well, you may indeed be correct that, on these very large geologic timescales, there are negative feedbacks. In fact, it is believed that one of the most important such feedbacks involves CO2 and how changes in weathering of rocks influence its concentration in the atmosphere (a short discussion of which is given here: http://en.wikipedia.org/wiki/Faint_young_sun_paradox ). Unfortunately, negative feedbacks that operate on long geologic timescales won’t save us and (as the Schrag and Alley paper points out) the evidence is that on shorter timescales (but still quite long in comparison to the decades-to-century-scale timescales of interest to us) the climate system is quite sensitive to perturbations.
Hi Joel. Again, how can you compare the climate sensitivity of a glacial maximum with what we are experiencing now? Why would the climate mechanisms be the same?
Joel Shore (10:29:02) : Jeez, why won’t this stupid “paleo argument” for high sensitivity die already? At the very least, even not taking into account any unknown effects or the non-homogeneous nature of Milankovitch forcings, the idea that “climate sensitivity may be even higher than suggested by models” is totally absurd! At best the paleoclimate might indicate sensitivity around 2 degrees C per CO2 doubling:
Chylek, P., and U. Lohmann, 2008. Aerosol radiative forcing and climate sensitivity deduced from the Last Glacial Maximum to Holocene transition. Geophysical Research Letters, 35, L04804, doi:10.1029/2007GL032759.
BTW responding to a post about actual observational data by pointing to proxy evidence is…pitiful. Is this what alarm has come to?