I’m halfway through writing the 2nd post in the series CO2 – An Insignificant Trace Gas? – which is harder work than I expected and I came across a new video by John Coleman called Global Warming: The Other Side.
I only watched the first section which is 11 minutes long and promises in its writeup:
..we present the rebuttal to the bad science behind the global warming frenzy.. We show how that theory has failed to verify and has proven to be wrong.
http://www.kusi.com/weather/colemanscorner/81557272.html
The 1st video section claims to show the IPCC wrong but is actually a critique of one section of Al Gore’s movie, An Inconvenient Truth.
The presenter points out the well-known fact that in the ice-core record of the last million years CO2 increases lag temperature increases. And this appears to be the complete rebuttal of “CO2 causes temperature to increase”.
The IPCC has a whole chapter on the CO2 cycle in its TAR (Third Assessment Report) of 2001.
..Whatever the mechanisms involved, lags of up to 2,000 to 4,000 years in the drawdown of CO2 at the start of glacial periods suggests that the low CO2 concentrations during glacial periods amplify the climate change but do not initiate glaciations (Lorius and Oeschger, 1994; Fischer et al., 1999). Once established, the low CO2 concentration is likely to have enhanced global cooling (Hewitt and Mitchell, 1997)..
So the creator of this “documentary” hasn’t even bothered to check the IPCC report. They agree with him. And even more amazing, they put it in print!
If you are surprised by either of these points:
- CO2 lags temperature changes in the last million years of temperature history
- The IPCC doesn’t think this fact affects the theory of AGW (anthropogenic global warming)
Then read on a little further. I keep it simple.
The Oceans Store CO2
There is a lot of CO2 dissolved into the oceans.
“All other things being equal”, as the temperature of the oceans rises, CO2 is “out-gassed” – released into the atmosphere. As the temperature falls, more CO2 is dissolved in.
“All other things being equal” is the science way of conveying that the whole picture is very complex but if we concentrate on just two variables we can understand the relationship.
“All Other Things being Equal”
Just a note for those interested..
In the current environment, we (people) are increasing the amount of CO2 in the atmosphere. So, currently as ocean temperatures rise CO2 is not leaving the oceans, but in fact a proportion of the human-emitted CO2 (from power stations, cars, etc) is actually being dissolved into the ocean.
So in this instance temperature rises don’t cause the oceans to give up some of their CO2 because “all other things are not equal”.
Doesn’t the fact that CO2 lags temperature in the ice core record prove it doesn’t cause temperature changes?
It does prove that CO2 didn’t initiate those changes of direction in temperature. In fact the whole subject of why the climate has changed so much in the past is very complex and poorly understood, but let’s stay on topic.
Let’s suppose that there is an increase in solar radiation and so global temperatures increase. As a result the oceans will “out gas” CO2. We will see a record of CO2 changes following temperature changes.
But note that it tells us nothing about whether or not CO2 itself can increase temperatures.
[It might say something important about Al Gore’s movie.]
More than one factor affects temperature rise. There are lots of inter-related effects in the climate and the physics and chemistry of climate science are very complex.
Conclusion
Whether or not the IPCC is correct in its assessment that doubling CO2 in the atmosphere will lead to dire consequences from high temperature rises is not the subject of this post.
This post is about a subject that causes a lot of confusion.
I haven’t watched Al Gore’s movie but it appears he links past temperature rises with CO2 changes to demonstrate that CO2 increases are a clear and present danger. He relies on the ignorance of his audience. Or demonstrates his own.
“Skeptics” now arrive and claim to “debunk” the science of the IPCC by debunking Al Gore’s movie. They rely on the ignorance of their audience. Or demonstrate their own.
CO2 is certainly very important in our atmosphere despite being a “trace gas”. Physics and the properties of “trace gases” cannot be deduced from our life experiences. Have a read of CO2 – An Insignificant Trace Gas? Part One to understand more about this subject.
CO2 is both a cause and a consequence of temperature changes. That’s what makes climate science so fascinating.
Has the amount of CO2 released from the oceans in response to a 1 degree C temperature rise (“All other things being equal”) been calculated? How does that compare to what we have seen in the last 150 years?
I think you may be missing the point. While the IPCC addresses the lag in CO2 decrease at the start of a glaciation period, the more damning evidence is the lag in CO2 increase at the start of a warmer period — proving that temperature increases can happen quite naturally without being invoked by increases in CO2.
The paper below shows this nicely:
Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations, Hubertus Fischer, Martin Wahlen, Jesse Smith, Derek Mastroianni, Bruce Deck, Science 283, 1712 (1999), http://www.sciencemag.org/cgi/content/full/283/5408/1712
“High-resolution records from Antarctic ice cores show that carbon dioxide concentrations increased by 80 to 100 parts per million by volume 600 ± 400 years after the warming of the last three deglaciations.”
Nice material on your site, by the way! It’s definitely been added to my AGW favorites list.
Tim W:
Possibly, but I don’t know the answer. I’m sure someone has done some lab experiments as well but the subject in practice is very tricky. You could take a sample of the ocean and try it out but each experiment would depend on salinity, ocean temperature and the precise chemistry of that sample. As you go deeper the pressure changes and that also affects solubility of CO2.
I would also like to see the range of possible values for some representative ocean samples.
Note that the increase in CO2 in the atmosphere is not from the oceans. How do we know? Because of the isotope ratio.
There is one more factor involved in the ‘CO2-ocean-outgassing’ situation which you did not mention, but which is extremely influential….
Phytoplankton.
In particular, the growth of phytoplankton in response to increased availability of food (CO2) dissolved in the water (and,perhaps, further aided by the increase in solar radiation energy…). As the phytoplankton gobbles up the CO2, converting it into food for all the marine creatures higher up the food chain, it reduces the levels of CO2 dissolved in the ocean – and thus reduces the amount of CO2 available for ‘out-gassing’….
Photos of the planet over the last 5-7 years demonstrate a significant increase in phytoplankton, especially in temperate regions of the oceans. The pictures are green now, where they used to be blue….
This is not often addressed adequately in the scientific analysis – well, most of them – which use a straight mathematical relationship…this much dissolved therefore this much will be available for out-gassing.
Except that it isn’t.
It has entered the food chain instead.
Of course, I do not know the answers – I don’t think anyone has sufficient grasp of all the factors involved to have any definitive answers. Just that, hardly anyone ever mentions the increased growth of phytoplankton – and it IS a significant factor.
xanthippa:
You are right about phytoplankton. The rate at which the net removal of CO2 can proceed due to phytoplankton is limited by the availability of other nutrients in the top 200m of the ocean – as there is plenty of CO2 and solar energy for them.
The nutrients get depleted in the surface layer but are abundant lower down. So when there is upwelling of deeper ocean water the phytoplankton can increase their removal of CO2.
One finding was that the rate of exchange of CO2 between ocean and atmosphere in the mid-latitude Pacific varies from year to year by as much as a factor of 4.
You completely missed the point. Many scientists use this Vostok record to calculate CO2 sensitivities yet they really can’t say with any certainty what the proportion of amplification was: Severinghaus et al. suggested 30% but it’s a pure and utter guess. There is nothing in the physics that argues that the amplification can’t be negligible. Lowell Stotts empirical data indeed suggests it is negligible. Also nobody attempts to explain how this very weak trigger is supposed to overcome these powerful GHG feedbacks in order to restart the cooling period. For that you need a sudden carbon sink or a sudden cooling amplifier cutting in. Imagine it as a sudden removal of the blanket or the heater in the room being switched off. If it was all about temperature dependent heating amplifiers then the sharpness of the changes would be missing and the cooling would be more gradual. The Vostok record shows utter linearity of CO2 with temperature so it can’t be therefore a cooling amplifier – we need therefore a sudden carbon sink.
I’ve long asked people where is this large sink and i eventually discovered that the only argument that deals with the onset of cooling was Alley’s idea of rock weathering which also increases as the temperature gets warmer. Thus he gave CO2 the title of thermostat. I’ve a feeling this sits uneasily with most scientists, since they don’t talk about it much. Certainly I don’t see how that is any more than a handwave that fails to explain the extreme sharpness of the changes nor do i understand why CO2 should fill the role of Earths thermostat when H2O seems a far better candidate, and indeed is usually described as such in textbooks. ie If we say that H2O (polar ice albedo, clouds, tropical water vapour, ocean cycling) is both the heating and cooling amplifier then we don’t actually need to invoke CO2 at all. CO2 is only then a mere unimportant follower which may have been just put on a pedestal because of more political considerations, ie that it is produced by these big oil companies that are inherently despised by many earth scientists. I say that because in the 70’s there was an effort to blame cooling on fossil fuels too which seems like institutionalized bias to me.
I wonder something else too that nobody seems to think about. Suppose the sharp changes in the Vostok record simply happened because of a regular shift in wind direction thanks to regular magnetic or orbital shifts. We know that can happen but it’s not even considered. This is the big problem with extending one data proxy in one location on earth and extrapolating over the entire globe. Where’s the other evidence – well we have stomata proxies that actively contradict the theory. Well we can’t have that inconvenience to our simplistic one-size-fits-all theory so let’s just cast doubt on those conflicting proxies shall we? Now do you see the point?
James Gardiner:
What point did you think I was trying to make?
You wrote –
“CO2 is both a cause and a consequence of temperature changes” and those who disagree with the causation part “rely on the ignorance of their audience. Or demonstrate their own”. Your words!
Yet neither Coleman, his scientific advisors, nor his audience are unaware of the realclimate.org inspired arm-waving argument that CO2, while clearly not a driver, might have been an important heating amplifier during the heating part of the ice-age cycles. It’s only a point of view though, and one that the data doesn’t actually suggest by itself, despite folk like Gore and Hansen trying to tell us otherwise.
The failure of the argument lies in realizing the blindingly obvious fact that it is only in actuality half an argument because you need a cooling mechanism for the other half of the cycle and that is very rarely defined (it took me long enough to discover the iffy rock-weathering argument). Instead Gore’s audience are given the impression that a follower heating amplifier magically switches into a follower cooling amplifier when it’s atmospheric concentration is at a maximum. Now while H20 CAN be a cooling amplifier via cloud formation, CO2 simply cannot unless a massive and sudden CO2 sink just happens out of the blue. This is the step 2 – “then a miracle happens” – part of the hypothesis which surely no scientist can be unaware of. Hence the promotion of this unscientific half-argument into an irrefutable causative effect by Gore and the scientists who advise him and defend him is utterly dishonest. Coleman understands that and his audience understand it. Perhaps only you don’t.
James Gardiner:
Perhaps you have read into my post more than I claimed. I think it’s important to move step at a time, rather than bite off “the complete theory of all climate change” in one post.
You said (comment Feb 1st):
I made no claim about CO2 sensitivities. From my post (what I actually wrote), CO2 could have a minor or insignificant role in amplification of temperature movements that began from other causes, or completely explain everything about climate. I made no claim, so it is a mistake to assume.
I did point out that the IPCC agreed with Coleman that CO2 lags past temperature rises. This was the major point of the post.
And a part that so many get confused by. CO2 lagging temperature in the past doesn’t mean that it can’t influence temperature now.
And on to your next comment (Feb 3rd):
You have re-arranged what I said, and inserted an editorial point I didn’t make. So in fact, I could just say, “Go and reread what I wrote because that isn’t it!”
But instead, in the cause of everyone getting along..
Your first quote “CO2 is both a cause and a consequence of temperature changes” is my final summing up.
The second “quote” is a misrepresentation of what I said.
What did I say (easy to go back and look):
See how it’s different from what you claimed I wrote. You said I claimed that “those who disagree with the causation part ‘rely on the ignorance of their audience..’ ”
For other readers who are confused just go back and re-read my conclusion and see what I really said.
It seems from this discussion of ice core data that the complexity of climate is such that even complicated scientific analysis is in comparison little more than informed speculation, the direction of which is established as much by the Author’s personal agenda/ group think as from the analysis.
Still, current temperature measures, albeit untrustworthy – tho’ satellites are maybe better, despite calibration difficulties – should soon enough reveal whether warming is continuing or not, and what the rate is.
But if natural as distinct from AGW, we risk killing millions by wasting resources on an irrelevant phenomenon.
I have just come across your site and appreciate your analysis. I am a reasoned skeptic, that started out accepting the AGW position until I got deep into the reports and blogs on both sides. I agree, and think most serious skeptics agree, there has been some climate variation which has led to recent warming, and that CO2 and methane have some effect on warming. However, without positive feedback, the increase is known to be only modest, and almost surely not dangerous. In fact, the increased CO2 as plant food and slightly warmer temperatures are all positive factors. What we are skeptical about is the extreme positions (Hansen, Gore, and the IPCC recent positions). I would ask you to state your position on positive feedback, and if you accept the extreme positions. While a point can be made that it is a precaution to worry about warming (rising sea level, storms, drought, dangerous heating), I am more worried about cooling (new LIA, crop failure, freezing, glaciers forming), and in fact the evidence is strong that we are approaching the back end of the present interglacial. In addition, many scientists now predict the next 20 years to be a cooling period.
For Leonard Weinstein:
You are right when you say that without positive feedback the increase is modest.
The approximate increase in the earth’s global mean surface temperature from a doubling of CO2 (from pre-industrial levels) would be about 1.2’C.
Scientists ability to confidently predict the future of our climate with so many factors in play does seem like stretch.
For example, the subject of aerosols which are quite a strong negative feedback – see Those Hazy Skeptics at the IPCC
However, new evidence has recently demonstrated that water vapor is acting as a positive feedback. This study by Dessler (2009) showed that relative humidity stayed constant when averaged across the globe and the 10 years of measurement. If relative humidity is constant then as temperatures rise, we will have more water vapor. And water vapor is a strong greenhouse gas. This would be quite a simple positive feedback – and not requiring complex climate models to predict.
Still this evidence is quite new. Others might find different results.
I’m not yet sure what to think about positive feedbacks, or about the ability of Global Climate Models (GCMs) to predict/project the future.
I’d also be very skeptical of the scientists predictions of the coming cooling period. How did they predict it?
To return to your main point (which wasn’t the subject of the post! but of course it is the hot topic) – there are a number of positive feedbacks in the climate system, and you can see this demonstrated in the past history of climate.
If there were only negative feedbacks in the climate system there wouldn’t be the big changes in temperature that we have seen in the past million years.
Ice albedo, CO2 out-gassed from the ocean and water vapor probably provide positive feedback. Putting a number on the outcome seems “over-confident”.
Other factors are like jokers in the deck. Watch out for the post on the thermohaline currents, hopefully with a more exciting name.
Reference
” . . . The approximate increase in the earth’s global mean surface temperature from a doubling of CO2 (from pre-industrial levels) would be about 1.2′C. . . . ”
Just curious as to “varibility” around this number and how well the physics back this up? e.g. is the number likely to be between 1.1C and 1.3C or 0C and 2C or 0C and 10C etc.
Also is this number a “widely” agreed value.
Not trying to make any particular point here under than further my understanding of the subject.
I very much like your blog and try to follow the analysis but am not able to follow through from first principles the effect of doubling of CO2 if we assume no feedback mechanisms.
If I could be so bold – if doubling gives 1.2 what would doubling again result in (assuming no feedback).
Many Thanks
This site has a healthy back-to-basics approach to CO2 and it’s effects. However, I thought the reply to James Gardiner comes across as defensive. While you have not said or supported it, the role of CO2 in the ice ages has been severely oversold to the public. Today, there is still an annoying rearguard action through the claimed amplification. While it may be there, I have not been able to locate anything conclusive. To the contrary, detailed calculations of the out gassing of the oceans after a significant temperature increase seem to match quite well with the observed CO2 trajectory.
I am not trying to deny the convective and radiative balance of the clear atmosphere. However, I do consider the possibility of negative cloud feedback from the slight change in temperature profile made by CO2 doubling. After all, we are trying to draw conclusions about climate from a very short interval with a poor signal to noise ratio.
Will
@Will:
Note that a strong negative cloud feedback would probably occur for other warming periods too, thus limiting the temperature rise. Large variations have been observed, and with strong negative feedbacks, the initial forcings should have been extremely large.
Note that you would somehow have to increase low level cloudiness, and that it is not at all clear that this happens of will happen from heating the atmosphere by CO2. There will be more moisture available for clouds to form, but you would need to increase the lapse rate for that moisture to actually condense.
Probably much too simply put, I would expect increases in solar irradiance to heat the surface, which would lead to increasing evaporation and a greater lapse rate near the surface and cloud formation (until the lapse rate very rapidly stabilizes again at a higher temperature and water content), but increases in GH forcing also heat the atmosphere, so it’s effect on the lapse rate is much more difficult to understand. Any feedback that reaches equilibrium shortly after the initial forcing perturbation can not amplify the forcing much.
@Arjan
Not sure I follow your argument. The lapse rate is a function of relative humidity. The relative humidity is not expected to change much in the troposphere.
I have been studying the following article in my quest to understand the subtleties of the atmosphere that we need to understand to draw conclusions. I thought you might find it of interest. Caution, not an easy read:
IDŐJÁRÁS
Quarterly Journal of the Hungarian Meteorological Service
Vol. 111, No. 1, January–March 2007, pp. 1–40, “Greenhouse effect in semi-transparent planetary atmospheres”, Ferenc M. Miskolczi, Holston Lane 3, Hampton VA 23664, U.S.A., E-mail: fmiskolczi@cox.net
Regards,
Will
Thanks for the site. It is very informative.
I have a few thoughts which I think are related to this particular post.
First, the rate of CO2 increase/decrease in the ice-core record would seem to be very different in its rate of change over the past 150 years. You might call it “d[CO2]/dt”. Those ice-core graphs tend to be very compressed time-wise. Plotting a portion of even one of the steeper increases in the ice-core record on the same time scale as modern CO2 and temperature increase would seem to me to be indicative of very dissimilar processes. Is there a simple conclusion we could draw from rates of carbon increase/decrease (and temperature increase/decrease?).
Second, (this one may be off-topic but I’ll throw it out anyway). Do the ice-core data tell us anything about CO2 residence times. I’ve heard conflicting claims about CO2 residence time in the atmosphere. Some say it would take hundreds of years for CO2 concentrations to fall back to (say) 350 ppm after cessation of emissions. Others (Freeman Dyson, I think) say that it is much shorter (and I think they draw their conclusions from analysis of the heights of the waves in the Keeling curve).
Again, thanks for the great blog!
I have seen on a couple of sites now people discussing “co2 follows temp” and generally most people can understand the idea that extra warmth from solar or orbital changes can in theory warm the oceans and permafrost etc to cause a release of co2. But when it comes to the opposite scenario of a cooling world absorbing co2 back into the oceans and resulting in a positive feed back in both directions some people just can’t see that it would be possible. To me it seems perfectly simple in either direction if it is just remembered that the changes in temp and co2 are happening at a glacial pace compared to today and so the climate would always be very close to equilibrium. Changes of co2 going into and coming out of glaciations were in the order of 1.5-2 ppm per century and so there would never be much potential warming waiting in the pipeline such as we have now and it would only require a small change in orbital or solar forceing to set the ball rolling in the other direction.
Congratulations on a fantastic blog.
There is little downside to the “threat” of additional CO2 in the atmosphere. Isn’t there a balance between the use of CO2 by plants, making plants more efficient in their use of nutrients and using less water, thus vegetating more marginal steppe regions. The conversly creating more O2?
The fact that temperture increases prior to CO2 rise only indicates that CO2 may be released naturally from “locked up” organic material. I don’t want to seem “cosmic” in my statement, but may be natural as the process to “recover” from “ice ages” might suggest “natures way” to provide aerial fertilizer to “jump start” Vegetation growth and enhance the recovery from the ice age.
Just a thought and thank you for sponsoring this web site.
Neil:
Just to clarify, I had said, in answer to another commenter:
The key point is – without feedbacks. As it is well-understood physics the uncertainty is low. But of course, there will be feedbacks and this is the difficult part about climate science. However, without first establishing the basics we cannot move forward.
Have a read of the CO2 – An Insignificant Trace Gas? series and you will see how the value is established.
SOD: You are outraged at the behavior of John Coleman: “So the creator of this “documentary” hasn’t even bothered to check the IPCC report. They agree with him. And even more amazing, they put it in print!” Do you have any comments on the behavior Al Gore and his scientific advisors who (with far greater resources) have spread misconceptions about climate science? They put it in a movie they are trying to distribute to every school in the world! If the IPCC really wanted the public to understand the role of CO2 in ice ages, they would put the information in the SPM, not bury it on p203 of a multi-thousand page report. The content of the SPM is controlled by political leaders, so this is unlikely to happen.
May I revert to the original topic of this post: “CO2 Lags Temperature in the Ice-Core Record. Doesn’t that prove the IPCC wrong?”.
IPCC may be wrong about a lot of things. However what the aforementioned lag tells us is that during glacial-interglacial (and v.v.) transitions changes (‘forcings’ in the jargon) in global atmospheric concentration of CO2 were not a driving force in local temperature changes at the Vostok site. CO2 may still have acted as a positive
feedback. However as far as I am aware the Vostok record taken in isolation provides no evidence regarding the size (or the existence) of such a feedback effect. But it does not rule out the possibility of a CO2 feedback operating during the glacial transitions, nor the possibility that recent anthropogenic increases in atmospheric CO2 content have caused earth’s surface temperatures to be higher than they would otherwise have been.
So to that limited extent the answer to the above question
seems to be ‘No’.
There’s something fundamental missing from both this page and the corresponding pages at Skeptical Science — a simple statement to point out an obvious fact that is overlooked by many of the anti-AGW arguments that refer to paleoclimate:
==> One big difference between the Earth’s circumstances now, and its circumstances at any time before the Industrial Revolution, is:
We now have billions of manmade machines emitting carbon dioxide. <==
Never before in the history of Earth has there existed this anthropogenic source of carbon dioxide increase that doesn't depend on ocean outgassing or any other natural source of carbon dioxide.
Volcanoes also emit CO2, but recently at less than 1% of the current anthropogenic rate. So, while volcanoes could have caused CO2-led temperature increases at some times, such as Snowball Earth episodes, the current CO2 increase cannot be explained by natural sources. Especially huge volcanic outbursts in the past might have emitted CO2 at rates comparable to, or dwarfing, current anthropogenic rates, but those have been rare and do not apply today.
There’s one more sentence to add after “We now have billions of manmade machines emitting carbon dioxide.”
==> This is what makes CO2 a forcing agent now, not merely a feedback. <==
Might you be overlooking the point that in light of the fact that for the last million years the Earth has been locked into a clockwork cycle of ice ages wherein the avg global temp is 8 degr C lower than at present, and that this cold part represents 90% of the cycle time? And that we are near the end of our present 10% comfy break from the cold? We had better hope our machines CO2 exhaust are producing a forcing!
Dear SoD
I would be I Interested in your opinion on the implications of the following two papers:
Roe, G. (2006), In defense of Milankovitch, Geophys. Res. Lett., 33, L24703, doi:10.1029/2006GL027817.
Toggweiler, J. R. (2008), Origin of the 100,000-year timescale in Antarctic temperatures and atmospheric CO2, Paleoceanography, 23, PA2211, doi:10.1029/2006PA001405.
In both papers it is found not only that CO2 lags temperature, but also that the role of CO2 is secondary.
Richard Lindzen mentioned the first paper in “Climate science: is it currently designed to answer questions?” (2008).
The same paper was discussed a few days ago at Lubos Motl’s blog. Motl points out that the Roe correction explains most of the NH 100,000 year temperature signal and leaves little for amplification by CO2 to account for.
I found the second paper by looking at papers citing Roe 2006. I noticed that Toggweiler has found much the same in the SH – only a secondary role for CO2 in explaining hemispheric temperature variations.
Although these are newer papers, newer theories, they seem to have been accepted by the community – or at least I can’t find papers refuting them. So don’t these results contradict the standard explanation that small Milankovitch forcings amplified by the large CO2 forcing explain the 100,000 year temperature variations?
Alex Harvey:
A while back, after reading 20+ papers on the theories of the ice ages including the paper you cited from Roe I found that I couldn’t:
a) make sense of the different theories
b) see clearly enough to write about the confusion between, or coherence of, the different theories
There appear to be many different theories going under the name of Milankovitch. There appear to be problems with finding a climate mechanism to explain how the small change in solar insolation at a particular latitude and time of year creates such a large change in climate.
The theory that might be produced to explain the plunge into an ice age usually has problems explaining the return to an inter-glacial.
As you mentioned Lubos Motl I had a look at his article. Motl notes the beautiful match between theory and data, but I’m not sure the results are so amazing. Or at any rate, more amazing than all of the other theories that have beautiful matches in certain areas.
The top graph is a record which is “tuned” by the Milankovitch cycles (because dating has some uncertainty). So the results which match the theory so well were partly generated by assuming the theory..
The bottom graph is a more reliable assessment. Here is a zoom in on the last 200,000 years:
Note that black is the rate of change of ice volume and green is the insolation at 65’N.
To get the theory to work we have to assume that the dating of some of the the most recent changes (last 100,000 years) in ice volume is wrong. (Because the change in ice volume precedes the solar forcing change). Or that other effects are just as significant.
All of which makes it tricky.
Still, all of this rethinking makes me want to take another longer look and finally write a useful article.
Dear SoD,
I note that studies that infer climate sensitivity from ice core data (e.g. Hansen et al. 1993, which looks at the last glacial maximum (LGM)) simply assume that equilibrium climate sensitivity (lamba) can be obtained from the equation, delta_T = lamba * delta_Q and that the change in total forcing (delta_Q) and change in temperature (delta_T) are quantities known from the ice core data. They write:
“Based on knowledge of conditions during the last major ice age…, we know the alterations on the Earth’s surface and in the atmosphere that maintained the lower temperature, regardless of what caused the climate change. These were: increased reflection of sunlight by the continents, due to ice sheet growth and vegetation changes, decreased greenhouse gases CO2, CH4, and N2O, and increased atmospheric aerosol particles, which scatter sunlight to space. These surface and atmospheric changes caused a total forcing of 7.1 +/- 1.5 W m-2 ….”
The argument seems to be circular in that there is an unstated assumption that only the globally and annually averaged radiative forcing can in principle cause climate change (Lindzen 1993).
Thus, the Roe paper is cited in Hansen et al. 2007 (Climate change and trace gases, Phil. Trans. R. Soc. A 365, 1925–1954 doi:10.1098/rsta.2007.2052), and Hansen appears to accept Roe’s result, yet at the same time sees no problem for his earlier climate sensitivity estimate.
Richard Lindzen seems to be the only person who has ever disputed the idea that radiative forcing is the only that can cause climate change (e.g. Lindzen 1993: Paleoclimate sensitivity. Nature, 363, 25-26; Lindzen and Pan 1994: A note on orbital control of equator-pole heat fluxes. Clim. Dyn., 10, 49-57). I find it odd that there haven’t been more scientists disputing this apparently very simplistic approach to climate sensitivity.
Anyhow, I will look forward to your future post, should you get around to writing it.
Alex Harvey,
The rate of change in ice volume is reasonably well explained by Milankovitch forcing except during glacial/interglacial transitions. Then the ice volume change is much larger than the radiative flux change at 65N. Not coincidentally, the CO2 level only changes significantly during glacial/interglacial transitions. I doubt very many serious scientists in the field think that CO2 is the primary cause of glacial/interglacial transitions.
DeWitt Payne,
Maybe I should have used the word “minor” instead of “secondary”.
In any case, the standard explanation is (quoting the Skeptical Science website),
“As the Southern Ocean warms, the solubility of CO2 in water falls (Martin 2005). This causes the oceans to give up more CO2, emitting it into the atmosphere. The exact mechanism of how the deep ocean gives up its CO2 is not fully understood but believed to be related to vertical ocean mixing (Toggweiler 1999). The process takes around 800 to 1000 years, so CO2 levels are observed to rise around 1000 years after the initial warming (Monnin 2001, Mudelsee 2001).
The outgassing of CO2 from the ocean has several effects. The increased CO2 in the atmosphere amplifies the original warming. The relatively weak forcing from Milankovitch cycles is insufficient to cause the dramatic temperature change taking our climate out of an ice age (this period is called a deglaciation). However, the amplifying effect of CO2 is consistent with the observed warming.”
So CO2 may not be “the primary cause of glacial/interglacial transitions” but it does appear to be the primary cause of the “dramatic temperature change” in the glacial/interglacial transitions – in the standard explanation.
Alex Harvey,
That seems reasonable to me.
Indeed. The volume of CO2 released exceeds the change in solubility from the change in surface temperature. I did a crude analysis ( http://noconsensus.wordpress.com/2009/06/18/explaining-ice-core-co2-lag/ ) that suggests the time constant is more like 2,000 years than 1,000. That still produces what looks like an 800 year lag. If the time constant is too short, you get a too big a draw down during the Younger Dryas period than is reflected in the ice core record.
It looks somewhat like CO2 gradually accumulates somewhere in the deep ocean during a glacial cycle and it needs about 100,000 years after an interglacial period to reach a level where it can be discharged rapidly by an appropriately large Milankovitch excursion and help produce another interglacial period.
Dear SoD, Dewitt Payne, and other interested readers,
I decided to write to Dr. Roe for his opinion on the possible impact to understandings of climate sensitivity his 2006 paper might have. He gave me permission to reproduce his response at Lubos Motl’s blog.
In a few words, Dr. Roe appears convinced that his theory is right, and that it is accepted by others, but he does not seem to believe that it tells us anything about climate sensitivity.
http://motls.blogspot.com/2012/01/will-co2-save-us-from-next-ice-age.html
Interesting insight. The CO2 may not have initiated any increase in temperatures, but it may have contributed after the fact.
Richard: How much warming could CO2 have contributed once warming began?
The radiative forcing associated a rise in CO2 varies with the ratio of CO2 final to CO2 initial. This logarithmic relationship is usually expressed in doublings. From 180 to 280 ppm is approximately half of a doubling. So is “anthropogenic rise” 280 to 400 ppm. Or if you prefer, the rise measure by Keeling is 320 ppm to 400 ppm since 1960 is about 1/4 of a doubling. One needs a very high climate sensitivity for the outgassing of CO2 to contribute much warming. Judging by the warming in the 20th-century or since 1960, the outgassing of CO2 associate with the end of the ice age may have contributed 1 degC to warming.
Actually, I’m cheating here by not distinguishing between transient (current) warming and the equilibrium warming we will experience once heat stops flowing into the deep ocean in response to surface warming. That difference is sometimes called “committed warming”. Mathematically, the relationship between current warming (TCR, transient climate response) and equilibrium warming (ECS, equilibrium climate sensitivity) is given by:
TCR = 3.7 * dT/dF
ECS = 3.7 * dT/(dF-dQ)
TCR/ECS = 1 – dQ/dF
where dF is the change in forcing, dT is the change in temperature, and dQ is the amount of heat flowing into the ocean. When this post was written and AIT was filmed, dQ was believed to be about 0.9 W/m2, but the latest value from ARGO is around 0.5 W/m2. If anthropogenic forcing from all changes is around 2.3 W/m2 (there is a lot of uncertainty because of aerosols), the amount of committed warming has dropped. The idea that climate sensitivity is on the high end (say 4 degC per doubling) and that CO2 caused an important fraction of glacial/interglacial warming requires one to believe in a large amount of uncommitted warming.
In my post on The Air Vent linked above, about 30%. Remember, you’re going from ~180ppmv at the glacial maximum to ~280ppmv.
DeWitt: Very nice analysis. Have you ever noticed the CO2 outgassing from the 97/98 El Nino and absorption by the following La Nina. The usual 2 ppm/yr increase become 3 ppm and followed by 1 ppm.
Frank wrote:The radiative forcing associated a rise in CO2 varies with the ratio of CO2 final to CO2 initial. This logarithmic relationship is usually expressed in doublings. From 180 to 280 ppm is approximately half of a doubling. … One needs a very high climate sensitivity for the outgassing of CO2 to contribute much warming.”
Well, 64% of a doubling. It seems that observational estimates of ECS are about 1.8 K, so that would give warming of 1.15 K. ECS assumes the oceans come into equilibrium but that the ice caps don’t change much. The feedback from growing/shrinking ice caps adds to the sensitivity on very long time scales. If memory serves, ice cap contributions to glacial/integlacial forcing is thought to be a bit over 1 W/m^2 (globally averaged) compared to 2.4 W/m^2 for the CO2 change, so that would boost sensitivity by nearly 50%. So maybe 1.7 K for the glacial to interglacial T change. Actual global T change is more like 3-4 K (much larger on top of the Antarctic ice cap), so that would imply ECS in the range of 3-4 K per doubling. The ice ages are often cited is support of higher climate sensitivities.
But, since we really don’t understand the ice age cycles, or any other natural climate variations, any conclusion about sensitivity must be taken with a large grain of salt.
Mike M.,
It’s my recollection that albedo forcing from ice cap area change tends to be underestimated by those who believe in high ghg climate sensitivity. It’s much like aerosols and climate models. From what I’ve read, glacial to interglacial CO2 forcing is significantly less than half of the total forcing, not 2/3.
DeWiit wrote: “From what I’ve read, glacial to interglacial CO2 forcing is significantly less than half of the total forcing, not 2/3.”
I went looking for my source; it seems that DeWitt is correct and my memory in error. The estimates for ice cap forcing are around 3 W/m^2 (or even higher) for LGM. With 3 W/m^2 and an ECS of 1.8 K, I get 2.6 K for T change since LGM using just the CO2 and ice cap forcing. ECS of 3.2 K gives a T change of 4.5 K. Given that there are some additional forcings, it would seem that ECS is in the lower part of the IPCC range.
Mike M: wrote: “Well, 64% of a doubling. It seems that observational estimates of ECS are about 1.8 K, so that would give warming of 1.15 K. ECS assumes the oceans come into equilibrium but that the ice caps don’t change much. The feedback from growing/shrinking ice caps adds to the sensitivity on very long time scales. If memory serves, ice cap contributions to glacial/integlacial forcing is thought to be a bit over 1 W/m^2 (globally averaged) compared to 2.4 W/m^2 for the CO2 change, so that would boost sensitivity by nearly 50%. So maybe 1.7 K for the glacial to interglacial T change. Actual global T change is more like 3-4 K (much larger on top of the Antarctic ice cap), so that would imply ECS in the range of 3-4 K per doubling. The ice ages are often cited is support of higher climate sensitivities.”
Is it possible that you have double-counted feedbacks in this analysis?
For simplicity, let’s pick CO2 as the forcing (4 W/m2/doubling) and combine all fast feedbacks into one parameter FF (say 2 W/m2/K) and a Planck feedback of 4 W/m2/K (appropriate for a BB near 255 K). Before feedbacks, the CO2 alone produces 1 K of warming. One round of feedback produces 2.0 W/m2 of reduction of OLR and 0.5 K of warming, a second round of feedback 1.0 W/m2 and 0.25 K of warming …. Summing the infinite series gives us 1 K of warming from forcing and 1 K of warming from feedback; an ECS of 2 K. When you say that ECS for CO2 based on a century of observations is 1.8 K you’ve included all of the fast feedbacks and ECS refers to effective climate sensitivity, which I will call EfCS.
To get equilibrium climate sensitivity (EqCS) or technically earth system sensitivity (ESS), we need to add the slow feedbacks from ice caps, which you assert are another 1 W/m2/K. One round of feedback (from the existing 2 K of warming) gives an addition 2 W/m2 of increased absorption of SWR and 0.5 K of warming. A second round of 0.5 K * 3 (not 2 or 1) W/m2 = 1.5 W/m2 of increased absorption of SWR followed by 0.375 K of warming. A third round of 0.375 K * 3 W/m2 = 1.125 W/m2 of increased absorption of SWR followed by 0.281 K of warming. Summing that infinite series, 0.5/(1-(1/4)) = 2 K of additional warming or 4 K total.
If I take the shortcut and sum everything (using the correct sign convention): -4 W/m2/K (Planck feedback) plus +2 W/m2/K (fast feedbacks) plus +1 W/m2/K affords -1 W/m2/K or an ESS/EqCS of -1 W/m2/K or 4 K/doubling.
I hate it when I’m wrong, but greatly appreciate the help.
Frank,
You wrote: “Is it possible that you have double-counted feedbacks in this analysis?”
I suppose it is possible, but I think not.
After a certain point, verbal arguments won’t do and equations are required. From energy balance, assuming no change in insolation:
Cp*dT/dt = F_R + lambda*delta_T + A_G – P*delta_T
where F_R is radiative forcing, delta_T is the resulting temperature perturbation, lambda is the feedback parameter, A_G is forcing due to glaciation, and P is the Planck feedback (4*sigma*T0^3 = 3.3 W/m^2/K). At steady state, dT/dt = 0, so we don’t need to worry about the heat capacity, Cp. Lambda here is for oceans at equilibrium and includes seasonal snow and ice feedback but does not include widespread glaciation; I think that is consistent with models. A_G is not a simple function of temperature since it exhibits enormous hysteresis and depends on things like ice sheath dynamics and astronomical factors.
At steady state:
delta_T = (F_R + A_G) / (P – lambda)
An ECS of 1.8 K means that delta_T = 1.8 K when F_R = 3.7 W/m^2, so P-lambda = 2.1 W/m^2/K and lambda = 1.2 W/m^2/K. With F_R = 2.4 W/m^2 (glacial to interglacial CO2 change) and A_G = 1.1 W/m^2 (from memory) we get delta_T = 1.7 K, as I estimated above.
With ECS = 3.2 K (IPCC best estimate, from memory), P-lambda = 1.2 W/m^2/K (lambda = 2.1 W/m^2/K) and delta_T = 3.0 K. With ECS = 4.5 K (upper limit), P-lambda = 0.8 W/m^2/K (lambda = 2.5 W/m^2/K) and delta_T = 4.3 K. Those numbers are roughly consistent with estimates of global T change from glacial to interglacial conditions.
There are also thought to be forcings from changes in methane, atmospheric dust, vegetation, and sea level. All pretty small, I think. My guess is that something fundamental is being left out, maybe changes in cloud cover induced by changes in ocean circulation.
Mike, M,
If the climate sensitivity to CO2 was high and albedo change forcing as low as you claim, then there is simply no way that orbital cycles could induce a glacial epoch.
Mike:
Frank asked above: “Is it possible that you [Mike] have double-counted feedbacks in this analysis?”
After I finished my calculations, I obtained an answer of 4 K of warming from the observed change in CO2 amplified by the fast feedbacks that produce an EfCS of about 2 K and a slow ice cap albedo of 1 W/m2. This was at the high end of Mike’s range of 3-4 K.
So MIke did NOT double count the feedbacks. I did say I was wrong, but I must have been unclear about what was wrong. An additional 1 W/m2 of slow feedback due to ice caps produces another 2 K of warming from CO2 when effective climate sensitivity is only 2 K.
Note: I simplified my calculations by using round number like 4 W/m2/ doubling for the forcing from 2XCO2 and 4 W/m2/K for Planck feedback. The latter value is higher than IPCC authors obtain from their climate models for no-feedback because they don’t apply a uniform warming everywhere to the planet. “Planck feedback” is 4oT^3 = 3.8 W/m2/K for a blackbody near 255 K, but only 3.2 W/m2/K, when more warming is applied at the poles and less at the equator.
I have some further thought on Mike’s reply and other deductions that might be made, but not enough time to write.
Mike:
I suspect neither of us have done this calculation correctly yet – I’m pretty sure I haven’t. I have been treating the rise in CO2 during the last termination as a forcing (W/m2) not as a feedback (W/m2/K). The same thing applies to the change in surface albedo as the ice caps retreated. Let x be the total warming. (I’ll return to using the best values like 3.7 (rather than 4) W/m2/doubling and -3.2 (rather than 4) W/m2/K for Planck feedback.)
180 to 280 ppm of CO2 is 64% of a doubling or 2.36 W/m2 as a forcing. However, it is 2.36/x W/m2/K expressed as a feedback
According to you, the albedo change from retreating ice caps was 1 W/m2. Expresses as a feedback, this is 1/x W/m2/K.
If effective climate sensitivity (EfCS) based on observations is 1.8 K/doubling or 0.49 K/(W/m2), then the climate feedback parameter is -2.06 W/m2/K from the sum of Planck feedback and the other fast feedbacks (WV, LR, cloud, and seasonal snow cover).
The total climate feedback parameter is (-2.06 + 3.36/x) W/m2/K. In theory, next we divide the forcing (F) that caused the end of the glacial period by this feedback. SOD’s series on ice ages talks about regional forcing caused by orbital mechanics, but global forcing is negligible.
If we assume that the total temperature change (x) was 5 K, we can calculate that a forcing of 7 W/m2 (amplified by total feedback of -1.39 W/m2/K) was needed to exit the ice age. At least if we reason by analogy with GHG-mediated warming.
So, when I asked above how much warming could the 180-280 ppm rise in CO2 have contributed, I was thinking in terms of forcing, rather than feedbacks. Forcing are linear; you can add them or subtract the warming due to CO2 from total warming. Feedbacks are not linear. So my question didn’t have a reasonable.
If you are correctly that the surface albedo change from retreating ice caps totaled only 1 W/m2, the regional albedo increase from orbital mechanics is far too small a forcing to be responsible for an ice age. To get a big temperature change from a small forcing, the climate feedback parameter needs to be near zero when the slow feedback for retreating ice caps (about +0.2 W/m2/K) and CO2 outgassing (+0.5 W/m2/K) are included. That would mean that the climate feedback parameter with only fast feedbacks needs to be -0.7 W/m2/K (EfCS = 5.3) before adding in these slow feedbacks. Reasoning in the other direction, an EfCS of 3.7 K/doubling, is a climate feedback parameter of -1.0 W/m2/K (based on only fast feedbacks) to which slow feedbacks of +0.2 and +0.5 W/m2/K are added. In that case, the climate feedbacks parameter with all feedbacks would be -0.3 W/m2/K, giving an ESS of 12 K/doubling. So AOGCMs with EqCS in the vicinity of 4 K would predict a runaway GHE if outgassing of CO2 and ice cap retreat add 0.7 W/m2/K of slow feedback. Even an EqCS of 3 K/doubling; climate feedback of -1.2 W/m2/K; plus slow feedbacks of +0.7 W/m2/K; gives -0.5 W/m2/K and an ESS of 7.4 K/doubling.
So, if one wants to avoid a runaway greenhouse effect (warming or cooling), the is an upper limit to EqCS!
Assumptions of perfect linearity for changes this large are unrealistic.
Frank,
You wrote: “I have been treating the rise in CO2 during the last termination as a forcing (W/m2) not as a feedback (W/m2/K). The same thing applies to the change in surface albedo as the ice caps retreated.”
I reply: There is no fundamental difference between forcings and feedbacks. Both represent radiative changes that, at equilibrium, must be compensated by other changes. The only difference is to what cause you attribute the change. That difference can be important for making predictions, but it does not matter for things that have happened in the past where the change that occurred is known. We know the change in CO2, so we can treat it as a forcing, no matter the cause. The same for ice cap albedo. We don’t know the change in water vapor, so the best we can do is to estimate it from the known temperature change; i.e., by treating it as a feedback. But that is merely a computational convenience, not a fundamental difference.
You wrote: “180 to 280 ppm of CO2 is 64% of a doubling or 2.36 W/m2 as a forcing. However, it is 2.36/x W/m2/K expressed as a feedback.”
I reply: Yes, then when you multiply that by the temperature change x, you are right back where you started. But it is not a feedback since it is not a result of temperature change; the change in CO2 was most likely due to changes in the overturning circulation of the ocean. Which way you do it makes no difference for this calculation, but it might create mischief in other calculations.
You wrote: “According to you, the albedo change from retreating ice caps was 1 W/m2.”
I reply: Note that, as posted above, DeWitt called me on this and after checking I found that the number should be more like 3 W/m^2, or even higher. It is doubtful that this can be properly expressed as a feedback, or at least not as one that is linear in global temperature.
You wrote: “Forcing are linear; you can add them or subtract the warming due to CO2 from total warming. Feedbacks are not linear.”
I reply: Feedbacks are also linear in the sense of being additive. The only difference is that they are taken to be the result of temperature change, rather than the result of something external.
You wrote: “So, if one wants to avoid a runaway greenhouse effect (warming or cooling), the is an upper limit to EqCS!”
I reply: I did not follow the argument leading the this conclusion. But, a runaway greenhouse effect is infinite ECS.
SOD wrote: “I haven’t watched Al Gore’s movie but it appears he links past temperature rises with CO2 changes to demonstrate that CO2 increases are a clear and present danger. He relies on the ignorance of his audience. Or demonstrates his own.
“Skeptics” now arrive and claim to “debunk” the science of the IPCC by debunking Al Gore’s movie. They rely on the ignorance of their audience. Or demonstrate their own.”
You can see the relevant section of An Inconvenient Truth here: https://www.youtube.com/watch?v=9tkDK2mZlOo&list=PL1A6E2D304D264F58&index=5
The problem is that our fellow citizens, the press, our teachers and especially our children are being indoctrinated with Al Gore’s version of the truth – not the IPCC’s version, nor the skeptic’s version. Those who advocated getting lots of publicity by telling scary stories, making dramatic over-simplified statements, and hiding doubts shouldn’t complain when the same tactics are applied by their opponents. In a democracy and a courtroom, both sides have or should have equal opportunity to present their arguments – and the audience or jury doesn’t expect politicians or lawyers to present the whole truth without caveat. On the other hand, we do expect whole truth with all of the caveats from scientists and the issue is cleverly being presented as “pro-science vs anti-science”.
As Al Gore concludes, deeply unethical.
Mike wrote: “There is no fundamental difference between forcings and feedbacks. Both represent radiative changes that, at equilibrium, must be compensated by other changes. The only difference is to what cause you attribute the change. That difference can be important for making predictions, but it does not matter for things that have happened in the past where the change that occurred is known. We know the change in CO2, so we can treat it as a forcing, no matter the cause. The same for ice cap albedo.”
Frank replies: I pay a great deal of attention to the difference between forcing and feedback. A 3.7 W/m2 forcing from 2XCO2 is something that doesn’t change with time or surface temperature, it is always 3.7 W/m2 as long as CO2 remains doubled. The is no lag between a change in CO2 and the change in OLR is produces. The same is true for a -2 W/m2 forcing from aerosols or reduced solar activity and the effect of these radiative forcings add linearly.
Feedbacks are different and far more complicated. A feedback of 3.7 W/m2/K reduces OLR escaping to space (and SWR reflected to space) by 3.7 W/m2 only after the temperature has risen 1 K. If the temperature has fallen 2 K, it increases OLR+rSWR by 7.4 W/m2. Feedbacks have no effect without a surface temperature change. Fast feedbacks (Planck, WV, LR, cloud, and seasonal snow albedo) gradually change OLR+rSWR over a few days to a few months in response to a change in temperature. Feedback from outgassing/uptake of CO2 and retreat/advance of ice caps take one or more millennia of changed temperature to develop their full impact on OLR+rSWR. Most importantly, the effects of feedbacks are NOT additive.
As you said, given a specified temperature change, a feedback does produce a given change in TOA OLR+rSWR. We know post glacial warming is about 5 K, but we don’t understand what forcing (amplified by feedbacks) produced that warming. In the case of AGW, we know the forcing and want to calculate warming.
Equilibrium climate sensitivity is the amount of warming after a doubling of CO2 when heat uptake into the deep ocean has become negligible (which takes several centuries). When equilibrium warming is reached, the influence of fast feedbacks has long been felt, but slow feedbacks are far from developing their full influence. When they do, we are dealing with Earth Systems Sensitivity (ESS).
Surface temperature change can be caused by unforced variability in addition to forcing. For simplicity, I like to think about feedbacks following of a large unforced change in surface temperature due to a dramatic increase or decrease in heat transfer (upwelling and downwelling) between the mixed layer and deeper ocean. Planck feedback will instantly track the change in surface temperature and the other fast feedbacks will modulate Planck feedback within a few days to months. The sum of all of those fast feedbacks is called the climate feedback parameter (lambda), which tells us how OLR+rSWR change in response to surface temperature change within a few months. Lambda is a fundamental property of our climate system that is [fairly] independent of forcing and doesn’t require forcing.
If the climate feedback parameter is 1.85 W/m2/K and the forcing for CO2 is 3.7 W/m2/doubling, division of the latter by the former gives ECS, 2 K/doubling. So, if we know the climate feedback parameter, we know ECS (even though the climate feedback parameter doesn’t require any forcing).
“Planck feedback” for a blackbody near 255 K is -4oT^3 = -3.8 W/m2/K. According to AOGCMs 1 K of surface warming is something like 0.5 K in the tropics, 1 K in the mid-latitudes and 2 K in the poles and this reduces Planck feedback for the planet as a whole to about -3.2 W/m2/K.
The expected increase in OLR accompanying an increase in surface temperature is quickly modified by changes in clouds, WV, LR and seasonal snow cover. If positive feedbacks dominate and overwhelm Planck feedback then we have a climate feedback parameter that is near zero (or even positive), which means a runaway greenhouse effect exists. If changes in surface temperature have no impact on TOA OLR plus rSWR, nothings limits temperature change in either direction.
Since temperature change is calculated by dividing forcing by feedback, small changes in feedbacks when the climate feedback parameter is near zero have a large impact on temperature. Consider the possibility that ECS is 3.7 W/m2/doubling. The climate feedback parameter (from fast feedbacks) would be -1 W/m2/K. If we wait a few millennia, the climate feedback parameter will have changed due to CO2 outgassing (roughly +0.5 W/m2/K assuming 180-280 ppm and 5 K of post-glacial warming) and ice cap retreat (+0.6 W/m2/K from 3 W/m2 and 5 K or warming). Now the climate feedback parameter including slow feedbacks is +0.1 W/m2/K, producing a runaway GHE.
If we start with an ECS of 3.0 K/doubling (lambda = -1.23 W/m2/K) and add in the same slow feedbacks (lambda = -0.13 W/m2/K), and get an ESS of 28 K. Still effectively a runaway GHE.
If we start with an ECS of 2.0 K/doubling (lambda = -1.85 W/m2/K) and add in the same slow feedbacks (lambda = -0.75 W/m2/K), and get an ESS of 5 K. 2.5X more than “equilibrium” warming when flow heat into the deep ocean became negligible.
Mike wrote: “I did not follow the argument leading the this conclusion. But, a runaway greenhouse effect is infinite ECS.
Frank replies. Or infinite ESS when outgassing of CO2 and ice cap retreat included.
Frank,
Feedbacks and forcings are the same in some ways and different in others. I say that the ways in which they are different is not fundamental since, at least in some cases, whether you consider something a forcing or a feedback can depend on the calculation that you are doing.
I do not think that you can treat either ice caps or oceanic CO2 exchange as simple temperature dependent feedbacks. The temperature dependent part of CO2 exchange with the ocean is minor; the main effect is due to changes in overturning circulation. I am pretty sure that has no simple relationship with temperature. There is presumably some T dependence to ice sheaths, but the integral of temperature over time is surely more important than the temperature at any one time. Plus there are the ice sheath dynamics (probably highly non-linear) which in turn interact with ocean currents.
So I don’t think you can say much about ECS versus ESS using simple calculations; I would think some sort of a fairly complex model would be needed. But I think that you do raise a very interesting question as to whether finite ESS implies an upper limit on ECS.
Frank and Mike M.,
I don’t think infinite is a good word to use here. There’s always an upper limit to the surface temperature because there’s no significant internal energy source. You might be able to melt lead on the surface of Venus, but that’s still a finite temperature.
Potentially, you could evaporate the oceans on Earth and cook the CO2 from carbonate rocks, but the surface temperature would likely still be lower than Venus because the solar constant is lower at the orbit of the Earth. But you would have to get pretty hot to start with. IIRC, Ramanathan wrote that as long as there’s an atmospheric window in the IR spectrum, you can’t have a runaway greenhouse on Earth. But play with MODTRAN and see how hot it has to get to close that window.
DeWitt,
“Infinite” here just refers to the apparent behavior of a simple linear model. It really means “a large enough temperature change that a linear model is no longer a reasonable approximation”. Yes, it is a sloppy term, but a convenient one. What do you suggest instead?
Mike: When two quantities have different units (like acceleration and velocity), they are always different. However, they can be closely related: Acceleration*time is velocity; feedback*temperature change appears to be equivalent to forcing. The biggest difference for me is that the warming from forcing adds linearly, while feedbacks do not.
I agree that slow feedbacks associated with ice caps and outgassing of CO2 are complicated for a variety of reasons, especially time-dependence (and for ice caps hysteresis). However, even fast feedbacks have time-dependence: The average water molecule remains in the atmosphere for about 9 days, for example. From the climate perspective, we don’t need to worry how long it takes fast feedbacks to have an impact, but it does take time.
Mike wrote; “So I don’t think you can say much about ECS versus ESS using simple calculations; I would think some sort of a fairly complex model would be needed. But I think that you do raise a very interesting question as to whether finite ESS implies an upper limit on ECS.
The beauty of focusing on the climate feedback parameter (which does have time dependence when it includes slow feedbacks) is that we don’t need to worry about the path taken to get to a particular climate state (how deep and fast heat penetrates the deep ocean before ECS is reached; how quickly CO2 outgases as the ocean overturns; whether ice caps melt, flow or collapse by some other mechanism), at equilibrium warming can still be found by dividing forcing by feedback. If this is correct, then ESS and slow feedbacks place constrains on possible values for ECS.
I agree with you and DeWitt that infinite wasn’t the best term to use. When the climate feedback parameter approaches zero (in the denominator), the assumption that feedback is linearly proportional to dT probably breaks down.
Frank wrote:” The biggest difference for me is that the warming from forcing adds linearly, while feedbacks do not.”
I reply: Feedbacks DO add linearly, the individual feedbacks add up to give the total feedback. They also have a linear dependence on temperature. For some purposes that is an important difference. For others, such as when the temperature is fixed or known, it makes no difference.
Frank wrote: “The beauty of focusing on the climate feedback parameter (which does have time dependence when it includes slow feedbacks) is that we don’t need to worry about the path taken to get to a particular climate state (how deep and fast heat penetrates the deep ocean before ECS is reached; how quickly CO2 outgases as the ocean overturns; whether ice caps melt, flow or collapse by some other mechanism), at equilibrium warming can still be found by dividing forcing by feedback.”
I reply: That is not true for either ice caps or CO2 changes driven by ocean circulation. The former does not appear to ever be at equilibrium (at least not in the last 2.5 million years) and the later does not appear to be driven by temperature.
Mike M.
Feedbacks are linear with temperature until they’re not and the system becomes unstable. Thermal runaway happens in semiconductors and batteries, particularly lithium/ion. I do see references to infinite gain in a positive feedback loop, so maybe it’s the correct word after all.
Mike M.
The point of the article is not using linear approximations in non-linear regions, it’s the non-linearity in the first place. AFAIK, there is no mechanism in the real world, other than what’s buried in model code, that would cause a small change in flux to space from a large change in surface temperature. That non-linearity is what causes the large difference between ECS and TCR in models. So far, there is no evidence that this effect exists in the real world.
We’ve been conditioned to think that a large difference between ECS and TCR is a well known phenomenon. But it’s not at all clear that it’s anything other than a model artifact.
Mike, DeWitt: My obsessively focus on feedbacks still leaves an elephant in the room: A climate feedback parameter including slow forcings can make ESS very high, but what forcing is being amplifying.
Mike suggested that ice cap albedo was too complicated a phenomena to describe with a constant linear feedback. Feedback certainly could depend upon Milankovic’s irradiation at 65 degN or individual orbital parameters. This feedback could be a function of dust (ice cap surface albedo), which increases dramatically before every termination
Frank,
Did you ever read Paul_K’s articles on The Blackboard about the linearity of net flux at the TOA with forcing (links below)? GCM’s tend to produce results that aren’t linear at long times, i.e. small changes in net flux for large changes in temperature, and it’s not at all clear why. There’s hand waving about clouds and stuff that never made much sense to me.
http://rankexploits.com/musings/2012/the-arbitrariness-of-the-ipcc-feedback-calculations/
http://rankexploits.com/musings/2012/ocean-heat-uptake-efficiency-chicken-laying-eggs-and-infinite-silliness/
I’d like to see an equation that produces high ESS with slow forcings.
DeWitt,
The Paul K articles seemed pretty meaningless to me. But I did not spend much time on them, because they seemed pretty meaningless.
In the first article, Paul K wrote: “The elephant is the application of a linearised response function to the nonlinear response observed in the GCMs when a large forcing is applied”.
Seems to me more like a gnat than an elephant, since physicists do that all the time. It is perfectly valid to use a linear model for small changes, even when the system is non-linear for large changes. You just have to be careful about what qualifies as small vs. large. Paul K never defines “large”, which makes his argument indecipherable (to me, at least). He claims that models are non-linear for “large” changes. Why should we care? According to AR5, in almost all models 4*CO2 gives twice the forcing (as per the logarithmic response) and roughly twice the warming of 2*CO2. Roughly linear, for the conditions of interest.
In the second article, he seems to have “discovered” that ECS is different than TCR and that both are idealizations that are never achieved in practice. Ho-hum. But again, I did not spend much time on this, so I might have missed his point. If so, feel free to correct me.
Clicked on the wrong reply link. https://scienceofdoom.com/2010/01/15/co2-lags-temperature-in-the-ice-core-record-doesnt-that-prove-the-ipcc-wrong/#comment-114385
Also, look at what they’re doing for linear approximations. They’re not taking the slope of the curve at a particular temperature, they’re drawing an arbitrary line from the initial to the final temperature, completely ignoring the actual curve. The actual slope would imply that climate sensitivity late in the process is very, very high. I find it very hard to believe that’s possible.
This thread is getting rather confused. This comment may be out of place, or maybe the comment of DeWitt’s that I am replying to is out of place.
DeWitt wrote: “The point of the article is not using linear approximations in non-linear regions, it’s the non-linearity in the first place. AFAIK, there is no mechanism in the real world, other than what’s buried in model code, that would cause a small change in flux to space from a large change in surface temperature.”
I reply: The models are essentially linear in that forcings and feedbacks are additive and in that temperature change is proportional to forcing. They are non-linear in that temperature change is inversely proportional to the sum of the feedback parameters (see equation below). That is not “buried in the model code”; it is present in the simplest box models that can be solved algebraically with paper and pencil. There are simple physical mechanisms for that behavior, such as the increase in water vapor with increased temperature.
I am using feedback as in AR5, so that feedback parameters have units of W/m^2/K.
DeWitt wrote: “That non-linearity is what causes the large difference between ECS and TCR in models. So far, there is no evidence that this effect exists in the real world.”
I reply: No, the difference between ECS and TCR is due to heat uptake by the deep ocean. That has been directly observed using the ARGO network, and its predecessors.
DeWitt wrote: “We’ve been conditioned to think that a large difference between ECS and TCR is a well known phenomenon. But it’s not at all clear that it’s anything other than a model artifact.”
The difference is well known. How large it is depends on how large the sensitivity is.
ECS = forcing / (Planck – lambda)
where lambda is the sum of all non-Planck equilibrium feedbacks.
TCR = forcing / (Planck + kappa – lambda)
where kappa is the (time dependent) heat transfer coefficient into the deep ocean. The closer (Planck – lambda) is to zero (i.e., the larger lambda is), the greater the effect of kappa. Large lambda may well be a model artifact.
Mike M.,
My understanding of the difference is TCR specifies a finite period of time in response to a forcing. That is, the change in surface temperature in response over a specified period of time (like a few decades). ECS on the other hand, is the final response (or change in surface temperature) to the initial forcing, no matter how long it takes to reach equilibrium. Both TCR and ECS responses/changes are non-linear.
DeWitt wrote: “Also, look at what they’re doing for linear approximations. They’re not taking the slope of the curve at a particular temperature … I find it very hard to believe …”
Who might “they” be and where are you suggesting I look? If it is the Paul K article, then you are probably right not to believe it.
RW,
Yes, ECS is the final response, after the deep ocean has come into equilibrium (so that kappa has become zero).
Strictly speaking, since ocean heat uptake is time dependent, to get an unambiguous TCR one must specify a particular history for forcing. IPCC uses an exponential increase in CO2 (linear increase in forcing) with a specified doubling time (70 years, if memory serves). But as long as the change in forcing occurs on a time scale short compared to the time scale for ocean equilibrium (500 years or more), the specific forcing history does not have a large effect.
I think it is not very useful to say that “Both TCR and ECS responses/changes are non-linear”. They are linear in some things and non-linear in others. Consider the equation
y = a + b*x
where x and y are variables and a and b are parameters. Obviously linear. But if you solve for x, it depends non-linearly on b.
Nope. Pure hand waving. Any heat transfer must come from somewhere. That means that heat transfer into any part of the ocean at any time must be exactly matched by an imbalance at the TOA. There is no non-linearity if that happens.
The physics has to work both ways. A large change in surface temperature can’t produce a very different change in flux to space at different times unless something other than heat content changes. About the only thing that fits would be a slow decrease in albedo. But that would have to be substantial and things like the Antarctic and Greenland ice cap don’t melt in a few centuries. If it’s cloud cover, then I don’t believe it because GCM’s are useless for clouds.
Mike M.
Kappa is a classic kludge or fudge factor. It seems to explain the phenomenon until you start looking under the hood. Climate feedbacks are actually forcings that vary with temperature. Ocean heat uptake efficiency is not a forcing at all whether it varies with temperature or not. It’s also completely model derived.
Is posting working again? Last time I tried, the site went into an apparent infinite loop of “please wait five minutes while a maintenance cycle is completed”.
DeWItt asked: “Did you ever read Paul_K’s articles on The Blackboard about the linearity of net flux at the TOA with forcing (links below)? GCM’s tend to produce results that aren’t linear at long times, i.e. small changes in net flux for large changes in temperature, and it’s not at all clear why.”
I’ve read, but only partially retained, some of this material. AFAIK, if you calculate TCR and ECS from AOGCM years 0-70 and 70-140 when CO2 is increasing at 1% per year (4X over 140 years), you will find that climate sensitivity is significantly higher during the second period. I ignored this problem in recent comments, because I simply wanted to explore the implications of the standard linear feedbacks: an ECS of 3+ K/doubling plus slow feedbacks from outgassing/uptake of CO2 and advancing/retreating ice caps brings the climate feedback parameter near zero (and a runaway greenhouse effect). In that case, temperature change is large and the assumption of linearity becomes more dubious.
Aside: This has caused me to contemplate/speculate that ESS could be very high (“heresy” for me) when GMST is between typical glacial and interglacial temperature , but lower above and below these temperatures. This would explain why the planet seems to have two stable states, glacial and interglacial, and the ability to switch between these states without a large forcing being applied. This doesn’t mean that climate sensitivity for future warming must be very high. The forcing from 100 ppm of CO2 outgassing at the end of an interglacial should have caused far more warming than another 100 ppm from 560 ppm to 660 ppm.
Back to non-linearity: According to AR5, there is now a substantial (50%?) disagreement between the climate feedback parameter (ECS) extrapolated from abrupt 4X scenarios and the sum of the feedbacks extracted from climate model output.
I believe I have seen at least one paper showing that ocean heat uptake efficient increases with time in AOGCM runs.
The thing that confuses me the most is ocean heat uptake in abrupt 4X scenarios. My calculations show that a 50 m mixed layer over 70% of the planet warms at an INITIAL rate of 0.2 K/year in response to a +1 W/m2 radiative imbalance. In an abrupt 4X scenario, the mixed layer will be 3 K warmer in just 2 years – ignoring heat transfer below the mixed layer and the climate feedback parameter (which has begun to reduce the radiative imbalance). So, as best I can tell, this scenario should quickly produce an unrealistic scenario where the ocean is much more stably stratified within a decade or so – which should reduce vertical overturning by convection. I’ve asked Nic Lewis about this prediction and he says there is no evidence for a slowdown in heat uptake by the ocean as the top warms faster than the bulk.
Lastly, chaotic fluctuation in ocean heat uptake efficiency is probably the major cause of unforced variability in temperature, at least during period of radiative imbalance.
Frank wrote: “So, as best I can tell, this scenario should quickly produce an unrealistic scenario where the ocean is much more stably stratified within a decade or so – which should reduce vertical overturning by convection. I’ve asked Nic Lewis about this prediction and he says there is no evidence for a slowdown in heat uptake by the ocean as the top warms faster than the bulk.”
I reply: I think that heat transfer into the deep ocean is by means of turbulent diffusion across the thermocline. The thermocline is already stably stratified, so there is no large scale convection. So far as I know, the turbulence is driven by velocity shear. I think that as long as such turbulence is weak (which I think it is), it is little affected by the density gradient.
The overturning circulation transfers heat (technically, internal energy) back to the surface (against the gradient) and keeps the deep ocean cold. It is driven partly by wind and partly by the pole-to-equator T gradient. It surely does vary on various time scales. And there has been much speculation about possible large excursions, for example caused by ice melt shutting down North Atlantic deepwater formation. It is not clear to me if changes in overturning circulation have a large effect on heat transfer on short (decadal) time scales.
There are also areas of deep convection, I am not clear as to what effect they might have on heat transfer. It should be upward from the deep ocean (since that is the direction of the T gradient that causes the convective instability), but it might be small since the T gradient is small.
Frank wrote: “Lastly, chaotic fluctuation in ocean heat uptake efficiency is probably the major cause of unforced variability in temperature, at least during period of radiative imbalance.”
I reply: i don’t think that is the case. If it were, then the deep ocean should have been warming during the mid-20th century cooling, cooling during the strong warming of the late 20th century, and warming again during the “pause”. The ocean heat content data don’t seem to support that.
Dewitt wrote about kappa (ocean heat uptake efficiency): “Nope. Pure hand waving. Any heat transfer must come from somewhere. That means that heat transfer into any part of the ocean at any time must be exactly matched by an imbalance at the TOA. There is no non-linearity if that happens.”
As I remember, kappa is the heat transfer into the ocean in a simple model with one box for the atmosphere and one for the ocean. Heat transfer into the ocean doesn’t seem to be handwaving to me. The problem – as I see it – is fluctuation in the rate of heat exchange between the mixed layer and the much colder deeper ocean. This can produce large changes in surface temperature (El Nino, for example) without a radiative imbalance. I don’t think we know how long such fluctuations in heat exchange can persist: a few years (ENSO), a few decades? (AMO, PDO), a few centuries? (LIA, MWP). To describe this behavior, one needs a separate box for the mixed layer (which is in “near steady state” with the atmosphere and therefore radiative cooling to space, the climate feedback parameter) and for the deeper ocean.
DeWitt: Kappa is a classic kludge or fudge factor.
Possibly. As with aerosols, one apparently can adjust a models with a with a variety of climate sensitivities to agree with the instrumental record by changing the rate at which heat is transported in the ocean. If your climate sensitivity is “too high”, you can delay surface warming by sending more heat into the deep ocean.
I am starting a new thread since I am tired of searching for the reply button.
DeWitt wrote “Pure hand waving. Any heat transfer must come from somewhere. That means that heat transfer into any part of the ocean at any time must be exactly matched by an imbalance at the TOA. There is no non-linearity if that happens.”
I reply: It is not hand waving, although describing it as (kappa*T) is a simple parameterization of a complex process, as are feedbacks and radiative forcings. The heat comes from the warming surface ocean and is transferred across the thermocline by turbulent diffusion. It has been measure to be about 0.5 to 0.6 W/m^2, averaged over the entire surface of the planet. It must be exactly matched by an imbalance at the top of atmosphere, but that has not been measured. For short time scales (decades) it can be treated linearly, but I think that breaks down on long time scales (centuries). Linearity has nothing to do with radiation balance at TOA.
DeWitt wrote: The physics has to work both ways. A large change in surface temperature can’t produce a very different change in flux to space at different times unless something other than heat content changes. About the only thing that fits would be a slow decrease in albedo. But that would have to be substantial and things like the Antarctic and Greenland ice cap don’t melt in a few centuries. If it’s cloud cover, then I don’t believe it because GCM’s are useless for clouds.
I reply: I have no idea what this means. I think DeWitt is assuming something no-obvious, but I don;t know what that might be.
DeWitt: “Kappa is a classic kludge or fudge factor. It seems to explain the phenomenon until you start looking under the hood. Climate feedbacks are actually forcings that vary with temperature. Ocean heat uptake efficiency is not a forcing at all whether it varies with temperature or not. It’s also completely model derived.”
I reply: No, it is a simple parameterization of an observable process. In models with a slab ocean, it can only be included as a parameterization. Some of those models may have used it as an adjustable fudge factor. Now that we have numbers to constrain it, I would hope that is no longer acceptable. AOGCM’s model the process. If the modelers are doing proper science, they use the observations to constrain the models. Ocean heat uptake is treated mathematically as a feedback for certain useful purposes. I see no point in quibbling about whether it is really a feedback.
At Curry’s, Nic Lewis touched on this subject recently. Figure 4 and others in this paper Nic cited are interesting:
http://iopscience.iop.org/article/10.1088/1748-9326/8/3/034039
Frank,
I don’t know what Nic Lewis article your refer to, but the Caldeira and Myhrvold paper seems to confirm what I have been saying. In case this is not obvious, a linear ordinary differential equation gives an exponential time dependence.
The sign of the net feedback acting on the system is independent of the time rate of response (due to ocean heat uptake or anything else), which is all that really matters. Of course, higher sensitivities (if real) take longer to reach equilibrium, but that itself is not evidence of high sensitivity.
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