NEW 4/10/09: There is an update to this post, see below the “read the rest of this entry” – Anthony
Guest Post by Richard Lindzen, PhD.
Alfred P. Sloan Professor of Meteorology, Department of Earth, Atmospheric and Planetary Science, MIT
This essay is from an email list that I subscribe to. Dr. Lindzen has sent this along as an addendum to his address made at ICCC 2009 in New York City. I present it here for consideration. – Anthony
Simplified Greenhouse Theory
The wavelength of visible light corresponds to the temperature of the sun’s surface (ca 6000oK). The wavelength of the heat radiation corresponds to the temperature of the earth’s atmosphere at the level from which the radiation is emitted (ca 255oK). When the earth is in equilibrium with the sun, the absorbed visible light is balanced by the emitted heat radiation.
The basic idea is that the atmosphere is roughly transparent to visible light, but, due to the presence of greenhouse substances like water vapor, clouds, and (to a much lesser extent) CO2 (which all absorb heat radiation, and hence inhibit the cooling emission), the earth is warmer than it would be in the absence of such gases.
The Perturbed Greenhouse
If one adds greenhouse gases to the atmosphere, one is adding to the ‘blanket’ that is inhibiting the emission of heat radiation (also commonly referred to as infrared radiation or long wave radiation). This causes the temperature of the earth to increase until equilibrium with the sun is reestablished.
For example, if one simply doubles the amount of CO2 in the atmosphere, the temperature increase is about 1°C.
If, however, water vapor and clouds respond to the increase in temperature in such a manner as to further enhance the ‘blanketing,’ then we have what is called a positive feedback, and the temperature needed to reestablish equilibrium will be increased. In the climate GCMs (General Circulation Models) referred to by the IPCC (the UN’s Intergovernmental Panel on Climate Change), this new temperature ranges from roughly 1.5°C to 5°C.
The equilibrium response to a doubling of CO2 (including the effects of feedbacks) is commonly referred to as the climate sensitivity.
Two Important Points
1. Equilibration takes time.
2. The feedbacks are responses to temperature – not to CO2 increases per se.
The time it takes depends primarily on the climate sensitivity, and the rapidity with which heat is transported down into the ocean. Both higher sensitivity and more rapid mixing lead to longer times. For the models referred to by the IPCC, this time is on the order of decades.
This all leads to a crucial observational test of feedbacks!
The Test: Preliminaries
Note that, in addition to any long term trends that may be present, temperature fluctuates on shorter time scales ranging from years to decades.
Such fluctuations are associated with the internal dynamics of the ocean- atmosphere system. Examples include the El Nino – Southern Oscillation, the Pacific Decadal Oscillation, etc.
These fluctuations must excite the feedback mechanisms that we have just described.
The Test
1. Run the models with the observed sea surface temperatures as boundary conditions.
2. Use the models to calculate the heat radiation emitted to space.
3. Use satellites to measure the heat radiation actually emitted by the earth.
When temperature fluctuations lead to warmer temperatures, emitted heat radiation should increase, but positive feedbacks should inhibit these emissions by virtue of the enhanced ‘blanketing.’ Given the model climate sensitivities, this ‘blanketing’ should typically reduce the emissions by a factor of about 2 or 3 from what one would see in the absence of feedbacks. If the satellite data confirms the calculated emissions, then this would constitute solid evidence that the model feedbacks are correct.
The Results of an Inadvertent Test
Above graph:
Comparison of the observed broadband LW and SW flux anomalies for the tropics with climate model simulations using observed SST records. The models are not given volcanic aerosols, so the should not expected to show the Mt. Pinatubo eruption effects in mid-1991 through mid-1993. The dashed line shows the mean of all five models, and the gray band shows the total rnage of model anomalies (maximum to minimum).
It is the topmost panel for long wave (LW) emission that we want.
Let us examine the top figure a bit more closely.
From 1985 until 1989 the models and observations are more or less the same – they have, in fact, been tuned to be so. However, with the warming after 1989, the observations characteristically exceed 7 times the model values. Recall that if the observations were only 2-3 times what the models produce, it would correspond to no feedback. What we see is much more than this – implying strong negative feedback. Note that the ups and downs of both the observations and the model (forced by observed sea surface temperature) follow the ups and downs of temperature (not shown).
Note that these results were sufficiently surprising that they were confirmed by at least 4 other groups:
Chen, J., B.E. Carlson, and A.D. Del Genio, 2002: Evidence for strengthening of the tropical general circulation in the 1990s. Science, 295, 838-841.
Cess, R.D. and P.M. Udelhofen, 2003: Climate change during 1985–1999: Cloud interactions determined from satellite measurements. Geophys. Res. Ltrs., 30, No. 1, 1019, doi:10.1029/2002GL016128.
Hatzidimitriou, D., I. Vardavas, K. G. Pavlakis, N. Hatzianastassiou, C. Matsoukas, and E. Drakakis (2004) On the decadal increase in the tropical mean outgoing longwave radiation for the period 1984–2000. Atmos. Chem. Phys., 4, 1419–1425.
Clement, A.C. and B. Soden (2005) The sensitivity of the tropical-mean radiation budget. J. Clim., 18, 3189-3203.
The preceding authors did not dwell on the profound implications of these results – they had not intended a test of model feedbacks! Rather, they mostly emphasized that the differences had to arise from cloud behavior (a well acknowledged weakness of current models). However, as noted by Chou and Lindzen (2005, Comments on “Examination of the Decadal Tropical Mean ERBS Nonscanner Radiation Data for the Iris Hypothesis”, J. Climate, 18, 2123-2127), the results imply a strong negative feedback regardless of what one attributes this to.
The Bottom Line
The earth’s climate (in contrast to the climate in current climate GCMs) is dominated by a strong net negative feedback. Climate sensitivity is on the order of 0.3°C, and such warming as may arise from increasing greenhouse gases will be indistinguishable from the fluctuations in climate that occur naturally from processes internal to the climate system itself.
An aside on Feedbacks
Here is an easily appreciated example of positive and negative feedback. In your car, the gas and brake pedals act as negative feedbacks to reduce speed when you are going too fast and increase it when you are going too slow. If someone were to reverse the position of the pedals without informing you, then they would act as positive feedbacks: increasing your speed when you are going too fast, and slowing you down when you are going too slow.
Alarming climate predictions depend critically on the fact that models have large positive feedbacks. The crucial question is whether nature actually behaves this way? The answer, as we have just seen, is unambiguously no.
UPDATE: There are some suggestions (in comments) that the graph has issues of orbital decay affecting the nonscanner instrument’s field of view. I’ve sent a request off to Dr. Lindzen for clarification. – Anthony
UPDATE2: While I have not yet heard from Dr. Lindzen (it has only been 3 hours as of this writing) commenter “wmanny” found this below, apparently written by Lindzen to address the issue:
“Recently, Wong et al (Wong, Wielicki et al, 2006, Reexamination of the Observed Decadal Variability of the Earth Radiation Budget Using Altitude-Corrected ERBE/ERBS Nonscanner WFOV Data, J. Clim., 19, 4028-4040) have reassessed their data to reduce the magnitude of the anomaly, but the remaining anomaly still represents a substantial negative feedback, and there is reason to question the new adjustments.”
I found the text above to match “wmanny’s” comment in a presentation given by Lindzen to Colgate University on 7/11/2008 which you can see here as a PDF:
http://portaldata.colgate.edu/imagegallerywww/3503/ImageGallery/LindzenLectureBeyondModels.pdf
– Anthony
UPDATE3: I received this email today (4/10) from Dr. Lindzen. My sincere thanks for his response.
Dear Anthony,
The paper was sent out for comments, and the comments (even those from “realclimate”) are appreciated. In fact, the reduction of the difference in OLR between the 80’s and 90’s due to orbital decay seems to me to be largely correct. However, the reduction in Wong, Wielicki et al (2006) of the difference in the spikes of OLR between observations and models cannot be attributed to orbital decay, and seem to me to be questionable. Nevertheless, the differences that remain still imply negative feedbacks. We are proceeding to redo the analysis of satellite data in order to better understand what went into these analyses. The matter of net differences between the 80’s and 90’s is an interesting question. Given enough time, the radiative balance is reestablished and the anomalies can be wiped out. The time it takes for this to happen depends on climate sensitivity with adjustments occurring more rapidly when sensitivity is less. However, for the spikes, the time scales are short enough to preclude adjustment except for very low sensitivity.
That said, it has become standard in climate science that data in contradiction to alarmism is inevitably ‘corrected’ to bring it closer to alarming models. None of us would argue that this data is perfect, and the corrections are often plausible. What is implausible is that the ‘corrections’ should always bring the data closer to models.
Best wishes,
Dick
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Manfred-“water temperature in the arctic ocean is higher than the atmosphere’s temperature for most time of the year”
Sorry, that’s setting off my counter-intuitive sense-can you provide a ref? In any case, that would make it a negative feedback in the water but a positive feedback in the atmosphere.
timetochooseagain
Remember, liquid water can never be below the freezing point (of salt water). However, in the high arctic the air above typically is less than 29F. I’m not going to dig up references for the seasonal norms though.
timbrom (12:43:51) :
Graeme Rodaughan (03:00:10) :
Ha Ha…. Australia will Rule the next (Frozen) Millenium (Post 3000 AD). Just take my word for it……
***
And who are you going to play cricket against? No more fast, dry pitches, that’s for sure!
Oh my – I really haven’t thought this plan of Australian World Domination during a Glacial period through – (Runs in circles… screams and shouts…)
Consider the plan debunked… No cricket opponents (although there are the New Zealand team, and Sri Lanka and India are probably OK in a Glacial) – can’t have that.
Chris Colose
Can’t seem to get this comment on your site so I’ll stick it here:
Have you had a chance to look at the references Lindzen said backed up the original data? Presumably they don’t now back up the corrected version, or have they all been corrected too? That ocean heat content data which is now apparently comparable – within the uncertainties – is the same data that was also corrected for apparent cooling errors isn’t it? I’ve not heard yet of a data correction made due to an instrument showing too much warming, ie does it make sense that the corrections always seem to go only one way – towards the prevailing theory. I’d need to read that calibration study you mention but I’ve a funny feeling the corrected algorithm was defined with respect to a model output because that’s how the radiosonde corrections were made. After all, if you knew what the answer should be then you wouldn’t need the instrument measurements in the first place would you? It’s all sort of “cart before the horse”. In that light, can these corrections truly be objective? I’ll be interested in Lindzens response to these charges mind you.
For completeness, the original comment by Gavin on RC on this WUWT post was thus:
“[Response: A good sign of someone who is acting as an advocate is that they instantly take any unexplained anomaly and declare that it fits their prefered theory without doing any actual analysis or without any consideration of the alternatives. First off, the graph he shows was substantially corrected by the authors to remove some spurious aliasing in response to a comment. Secondly, there may still be issues with the data (since there is a clear jump in 1993) – something in any other circumstance, WUWT would have been all over. Third, the models may well be wrong (though it’s unclear these were the experiments to compare with since they didn’t have any forcings), but there is no analysis to indicate that fixing whatever the issue is would give a lower sensitivity – note that the NET fluxes are still all around zero, so the positive feedback in SW is matching the supposed negative feedback in LW. My take on it is very much a wait and see – wait to see if the CERES data seems to support those earlier results, wait to see whether more appropriate model-data comparisons change the picture etc. It may be surprising to some, but ambiguities abound in science and jumping to conclusions is very rarely sensible. – gavin]”
I wish some people could see that the criticism they dish out to others is just as appropriate to describe the behaviour of their own collaborators.
Sea ice changes the boundary conditions for the heat and radiation transfer between water and atmosphere.
The arctic ocean loses more energy than it receives from the sun. That appears to be clear, as the solar input is small and ocean currents transport warm water to the arctic.
Therefore, it may be not sufficient to look only at albedo and only one way (the incoming way) of transport, especially if the other way is the bigger.
“Chris V. (11:48:52) :
If clouds are a negative feedback (as Lindzen implies in the opening post) then the cloud feedback would “resist” the ice ages- not help them along.”
Not true.
You’re taking the wrong datum.
0K is the datum. temperature is all relative to that.
DaveE.
Thank God for Richard. Is he is the only man on the planet who can see the obvious. Keep up the great work Richard. Let the world know what a sham the man made model of global warming is. I say “Down with the New Green Dark Ages”. Let’s bring back common sense, if ever such a thing was common !
[snip – if you have a criticism, justify it. Just calling it names doesn’t qualify.]
What!?
No mention of Atmospheric Window? (Not once)
Wien’s Law? (No mention, not once.)
Steffan-Boltzman? (Once, by 1 poster, different spelling, I searched)
Planck? (Okay, ONCE by one poster)
Citing of radiational (radiated) energy being proportional to T4 (Stefan-Boltzman law)? (Not once)
Not just T-squared mind you, not even T-cubed, but T_to_the_FOURTH power!
How do all these relate?
Simple, using Wien’s Law and earth surface temperatures a ‘peak’ can be calculated that according to Wien will land in the area of 8 to 14 um , the Atmosphereic WIndow for LW IR, with WV (water vapor) acting as ‘block’ below 8 um and CO2 above 14 um, although a little less so than what WV does above … and Stefan-Boltzman’s Law gives us continuous spectral curve with a peak where Wien’s Law specifies…
Is this a coincidence?
Here on Earth?
Hmmmmm ….
Another nail in the coffin of bad science. This article examines the restart of the conveyor belt that had been stilled during most of the past decade. It discusses the large melt in 07-08 that may have restarted the climate system back to cold.
http://www.underwatertimes.com/news.php?article_id=43100678251
Kevin (11:47:43) :
I’m having a problem with this:
“The wavelength of the heat radiation corresponds to the temperature of the earth’s atmosphere at the level from which the radiation is emitted (ca 255oK).”
Is he saying that the Earth emits radiation at 255K? Because that’s just not true. I’m sure I’m just misunderstanding something, and would appreciate someone ’splaining it to me.
Thanks!
Kevin (11:47:43) :
This is how I interpreted the “ca 255°K”. The long wave emissions to space from the troposphere are a summation of all the longwave radiative emissions from surface level to the top of the troposphere. Since there is a gradient from maybe 293°K at the earth’s surface to 220°K at the tropopause, 255°K is the average temperature for the purposes longwave emissions. Dr. Lindzen did say it was a simplistic exposition.
This article:
http://www.dailytech.com/Researcher+Basic+Greenhouse+Equations+Totally+Wrong/article10973.htm
States that part of the negative feedback is the assumption of an infinitely thick atmosphere. Don’t know exactly how it relates to this posting, but it looks to me like this posting is about observations that there is no runaway feedback whereas the article is citing a particular mechanism for it. Synergy?
A quote or two:
How did modern researchers make such a mistake? They relied upon equations derived over 80 years ago, equations which left off one term from the final solution.
Miskolczi’s story reads like a book. Looking at a series of differential equations for the greenhouse effect, he noticed the solution — originally done in 1922 by Arthur Milne, but still used by climate researchers today — ignored boundary conditions by assuming an “infinitely thick” atmosphere.
And also:
So Miskolczi re-derived the solution, this time using the proper boundary conditions for an atmosphere that is not infinite. His result included a new term, which acts as a negative feedback to counter the positive forcing. At low levels, the new term means a small difference … but as greenhouse gases rise, the negative feedback predominates, forcing values back down.
NASA refused to release the results. Miskolczi believes their motivation is simple. “Money”, he tells DailyTech. Research that contradicts the view of an impending crisis jeopardizes funding, not only for his own atmosphere-monitoring project, but all climate-change research. Currently, funding for climate research tops $5 billion per year.
Well worth reading http://www.ianschumacher.com/maximum_temperature.html
if ‘only’ to give a decent, science based reply to that annoying phrase ‘tipping point’….in short it does not exist in the real world, only in fearmongering imaginations.
So Simple, So Beautiful, So Clear.. Dr. Lindzen you are the man!!
This is Science as it was meant. It cuts to heart of the issue, the core of the hysteria around AGW. If CO2 induces negative feedback effects (as it appears to do from the satellite observations and supported in theory by Lindzen’s IRIS effect) then all else is just noise blowing in the wind…
I’m an electrical engineer. When I was in school, I had a whole semester devoted to stability of control systems with feedback. One thing I learned: When a control system with a significant positive feedback is allowed to run for very long, it will eventually hit some condition that drives into saturation (i.e., it surges to its limits).
A simple test of a control system’s stability is to hit it with an impulse. For example, if you turn a PA system’s microphone gain up just short of squeeling, it’s fine. But clap your hands together and it takes off.
What does that mean for climate? Think about the apocalypse that killed off the dinosaurs 65 million years ago and the various volcanic eruptions that caused major climate shifts. These were impulses that caused severe shifts in the system. Like the analogy of the PA system, climate showed no evidence of positive feedback to these impulses; otherwise, the climate would have never recovered to modern, hospitable levels.
If Earth’s climate system had positive feedbacks of any consequence, the planet would have turned into a ball of ice or another Venus millions of years ago in response to all the meteorites and volcanic activity that have upset the system.
It’s a no-brainer to anyone with a little common sense, but who said these scaremongers had any sense?
R Chris V. (06:41:10) :
If the climate sensitivity is only around 0.3 degrees, how do we get ice ages?
Nobody knows. Some people have hypotheses. Some hypotheses have “greenhouse” gases playing a starring role, some don’t.
Comparing temperatures during the last glacial maximum to today yields a climate sensitivity of about 3 degrees +/- a degree or so (basically the same as the models get).
You can derive this sensitivity if you assume greenhouse gases play a starring role. If you hypothesize other mechanisms, you don’t need this much climate sensitivity.
If the climate sensitivity is only 0.3 degrees, that implies that there is some HUGE completely unidentified forcing responsible for taking us into and out of ice ages. That could be, but it seems unlikely to me.
So you imply that the “greenhouse effect” is HUGE because you feel that there are no other HUGE forcings that seem likely. It is kind of like rounding up “the usual suspects”. It may be a valid hypothesis but it is yet only a hypothesis. Not having other suspects does not elevate it to theory. Climate science is in its infancy and climate dogma only impedes the acquisition of knowledge.
Robert Austin-the best explanation is still the heterogeneous Milankovitch forcing, which, as Lindzen has noted before, would alter equator to pole heat fluxes even though the net change in radiation is small. Coupled with strong negative feedback in the tropics, that would lead to mean temperature changes. The fact that Chris V hasn’t addressed this argument shows that he isn’t making his argument to illuminate anything, but to further an agenda.
See here:
http://eaps.mit.edu/faculty/lindzen/171nocephf.pdf
Ice ages are most likely based on our Earth’s wobble as it spins on its axis. Every 10,000 or so years the wobble produces a greater tilt away from the Sun, thus receiving glancing blows from the Sun’s heat during the Summer (and hardly making it to Earth during the Winter), leading to much cooler temperatures and less Arctic ice melt.
Pamela Gray-The change in net radiation is itself small. The real key is the change in the ~distribution~ of incoming solar radiation. See my comments above. 🙂
Mark T (15:01:31) :
Actually, your understanding of feedback is incorrect. If a feedback subtracts from the input, i.e., if the feedback is negative, then it will subtract from the input whether it is trending up or down. In other words, feedback is dependent upon its own sign, not the input signal.
No, your understanding of feedback is incorrect. As is used in climate science, a positive feedback amplifies the signal. If the original forcing is warming, then a positive feedback increases the warming. If the original forcing is cooling, then a positive feedback increases the cooling.
Think of ice albedo (which is a positive feedback). If the earth warms, you have less ice. Less ice means lower albedo, so less light is reflected, which increases the warming. If the earth cools, you get more ice. More ice means higher albedo, which reflects more light, and increases the cooling.
JamesG (16:46:22) :
Chris Colose
For completeness, the original comment by Gavin on RC on this WUWT post was thus:
“[Response: A good sign of someone who is acting as an advocate is that they instantly take any unexplained anomaly and declare that it fits their prefered theory without doing any actual analysis or without any consideration of the alternatives. First off, the graph he shows was substantially corrected by the authors to remove some spurious aliasing in response to a comment. Secondly, there may still be issues with the data (since there is a clear jump in 1993) – something in any other circumstance, WUWT would have been all over. Third, the models may well be wrong (though it’s unclear these were the experiments to compare with since they didn’t have any forcings), but there is no analysis to indicate that fixing whatever the issue is would give a lower sensitivity – note that the NET fluxes are still all around zero, so the positive feedback in SW is matching the supposed negative feedback in LW. My take on it is very much a wait and see – wait to see if the CERES data seems to support those earlier results, wait to see whether more appropriate model-data comparisons change the picture etc.
ok lets change the picture.
sw flux anomaly erbe/isccp
http://i255.photobucket.com/albums/hh133/mataraka/cloudeicomp.jpg
sw anomaly erbe and ceres
http://i255.photobucket.com/albums/hh133/mataraka/ceres.jpg
The International Cloud cover climatology project Icccp is well detailed Kondrateyev (1983). The parametrized schemes to climate sensitivity are part of a number of international projects eg Scaraab, and ERB Marchuk1988 and UKMO Saundes and Mitchell 1988.
With UKMO the scheme is 11 layers.ie 3 with lower,middle etc. plus convective.
Each series has 3 schemes
1)Relative Humidity (rh)
2)Cloud water (CW)
3) Cloud water radiative properties (CWRP)
Enumeration in the UKMO model had the following RH with strong positive cloud feedback, CW was neutral, and CWRP was negative this underlies the importance of correct parametrization with cloud climatologies.
As we see all phases are possible then why do all the models only include positive feedbacks eg Isaac Held.?
The importance of SW forcing (ie in the absence of cloud or Ozone attenuation is a significant issue eg Pavlakis et al 2008
Figure 6b shows the time-series of the DSR-A (black line) in the central Pacific region (7 S–5 N 160 E–160 W) and on the same diagram we have overlaid the time-series of the Ni˜no-3.4 SST index (red line). The DSR-A is out-ofphase
with the Ni˜no-3.4 index. There is an excellent anticorrelation between the Ni˜no-3.4 index (a sea parameter) and DSR-A over two neighbouring regions: the Ni˜no-3.4 region and the central Pacific region. The latter reflects mostly the
variations in cloud amount caused by atmospheric circulation anomalies. We have calculated the 3-month smoothed anomaly of the mean monthly total cloud amount with respect to the average monthly total cloud amount for the study period 1984–2004 for the central Pacific region. A linear regression between the DSR-A time series and the total cloud amount anomaly time series yielded a correlation
coefficient of r=−0.91 (anti-correlation) showing that cloud amount variations are the primary determinants of the DSR variability.
http://i255.photobucket.com/albums/hh133/mataraka/dsrregions.jpg
The Effects of Sea-Ice and Land-Snow Concentrations on
Planetary Albedo from the Earth Radiation Budget Experiment
Gorodetskaya et al 2006
ABSTRACT The high-latitude ice/snow-albedo feedback is a principal element in many paleoclimate theories and global warming scenarios. The strength of this feedback is determined by the ice/snow effects on the top-of-atmosphere
(TOA) albedo, which is also strongly affected by clouds. Using currently available satellite observations, we estimate the radiative effectiveness (RE) of ice and snow with regards to the TOA albedo, which we define as the change in the TOA albedo corresponding to changes of 0% to 100% in the ice or snow cover. The REs of the
northern hemisphere (NH) sea ice, land snow, and southern hemisphere (SH) sea ice are found to be 0.22, 0.23 and 0.16, respectively. This means that, for an incident solar flux of about 400 W m–2 reaching the TOA in the polar latitudes in summer, local reduction in ice/snow concentrations from 100% to 0% will result in a decrease in reflected short wave radiation of approximately 80 W m–2. These changes in the TOA albedo are significant, yet smaller than the associated changes in the surface albedo. Comparison of the TOA albedo values with available surface
albedo observations helps to identify the role of clouds in the RE of ice/snow. The analysis is based on the whole time-space domain where the sea ice and land snow appear, and reveals a remarkable similarity in the ice and snow RE in the areas with high sea-ice and land-snow cover variability, despite the varying nature of the surface cover, seasonality, and locations. These estimates provide a useful constraint to test current climate models.
timetochooseagain (14:36:21) :
Chris V., how about addressing my response to your claims instead of the easy pickings?
I’m not sure I understand your original response, but here are some numbers for you to mull over:
According to Lindzen, the climate sensitivity to CO2 doubling is 0.3 degrees. The radiative forcing from CO2 doubling is about 3.7 W/m2.
The climate responds pretty much the same to any radiative forcing of the same magnitude, so any change in radiative forcing of 3.7 W/m2 (from a change in solar irradiance, say) should also change temperature by 0.3 degrees.
During the last ice age, the earths temperature was (off the top of my head) something like 5 degrees colder.
So if 3.7 W/m2 yields a temp change 0.3 degrees, the total radiative forcing needed to change temperatures by 5 degrees would be about 60 W/m2.
For comparison, the total solar irradiance striking the top of the atmosphere is about 350 W/m2; the amount of solar radiation absorbed by the earth is about 170 W/m2.
Where the heck does that 60 W/m2 of forcing come from???? 60 W/m2 is HUGE- that’s 1/3 of the solar irradiance that is absorbed by the earth!
FYI, the total ice albedo forcing during the last glacial maximum has been calculated to be only 5 or 6 W/m2.
Robert Austin (19:21:58) :
See my previous response to timetochooseagain.
Michael Hammer came to a similar conclusion, using a different approach here:http://jennifermarohasy.com/blog/2009/04/role-of-water-vapour-in-climate-change/
Chris V-Failing to understand my response is not an excuse for simply restating your argument an totally ignoring the point that I made.
“The climate responds pretty much the same to any radiative forcing of the same magnitude, so any change in radiative forcing of 3.7 W/m2 (from a change in solar irradiance, say) should also change temperature by 0.3 degrees.”
This is true of spatial heterogeneous forcings-but Milankovitch forcing is not heterogeneous!
Chris V. (22:04:33
Where the heck does that 60 W/m2 of forcing come from???? 60 W/m2 is HUGE- that’s 1/3 of the solar irradiance that is absorbed by the earth!
You do know how zonal climatology works eg Z. T. Guo et sl 2009
The cause of the enhanced asymmetry of hemispheric climates
during MIS-13 remains to be addressed. Greenhouse
warming may cause similar asymmetry of sea ice (Manabe
et al., 1992; Cavalieri et al., 1997), but cannot account for
MIS-13 because of its lower CO2 and CH4 levels.
Insolation is a possible cause. Although the CO2 concentration
was 40 ppmv lower (Luthi et al., 2008) in MIS-13
than the pre-industrial level (equivalent to a radiative forcing
of −0.82Wm−2), high northern latitudes received more
energy during their summer when this season occurred at
perihelion, i.e. three times in MIS-13 at 529, 506, and 485 ka
BP. For example, summer insolation at 65 N was 50Wm−2
higher at 506 ka ago (Fig. 2f) when eccentricity was much
larger (Berger, 1978). The consequent net increase of energy
received by the northern high-latitudes would favour
ice melting. On the contrary, summer insolation at 65 S
was 50Wm−2 lower (Berger, 1978) at 506 ka ago. This, associated
with the lower concentrations of greenhouse gases….
….(Loulergue et al., 2008; Luthi et al., 2008), would favour
ice building in the Southern Hemisphere. This also happened
at 485 ka BP, but at 529 ka BP the amplitude of the
seasonal anomaly was reduced due to a lower eccentricity.
On the other hand, insolation anomalies at MIS-5e were
even larger than at 506 ka BP due to a larger eccentricity
(Berger, 1978), consistent with the stronger summer monsoon
(Fig. 3a), weaker winter monsoon and lower dust intensity
in Asia (Fig. 2e and 3a). In addition, MIS-13 and MIS-
11 coincide with a mid-Pleistocene interval of lower amplitude
changes of summer insolation at northern high-latitudes
(Berger, 1978) from 570 to 340 ka BP (Fig. 2f). The higher
values of the insolation minima would oppose ice building in
the Northern Hemisphere.
Chirality a paradox for paleoclimates and Global “averages”