“I’m not sure I care whether it is or not, but it sure is important, especially given how much CO2 gets dumped into the atmosphere if the Amazon dies” – I think the loss of forest ecosystem would be a more important impact than the CO2.
You conclude “If some models underestimate the response, this is likely to have more to do with errors in the vertical mixing of heat than any missing fundamental physics.”
But there is missing fundamental physics – de Saussure’s Hotbox effect.
The sun warms the surface of the earth which loses it heat by radiation AND convection (conduction from the solid surface to the atmophere above it). The rate at which the surface loses heat to the air by convection depends on the difference in temperature between the two substances. Because the air is warmed by the greenhouse gases absorbing the infrared radiation from the surface, this temperature difference remains small. Hence the surface cannot lose its heat in that manner and its temperature rises. The rise in surface temperature causes an increase in infrared radiation which warms the air more. Thus the greenhouse gases act as a positive feedback on the direct warming by the sun.
This is the way the interior of an automobile heats up when exposed to the sun. The glass in its windows does not cause the warming. It is transparent to visible and to infrared radiation. The glass only acts to retain the hot air, and opening them by an inch will allow the interior of the car to cool. The interior temperature of the cabin does not depend on the area of glass, only on its insulating properties.
Thanks for this. It’s very important and quite germane to some of the side discussions that have been going on here. The fact that one can reproduce most of the solar variability without any exotic physics is a lot easier to swallow than trying to amplify the effects of a GCR flux of 5 particles per cm^2 per second into a significant global response. Do you know where this will be published? Is it possible to get a preprint somewhere?
Very interesting. The question of the true thermal intertia in the climate system and the extent to which perturbations penetrate into the deep oceans (or affect only the superficial “layers” of the of the “climate system” – atmosphere and ocean surface) is both fascinating and also rather important.
In this light, I wonder if anyone wishes to comment on a manuscript accepted for publication in J. Geophys Res. by Stephen Schwartz, which (although beyond my full comprehension) uses what seems to me to be a very crude and overly simplistic Earth heat capacity model to conclude that there is virtually no inertia in the climate system (intrinsic relaxation time of around 5 years) and thus, since the Earth is near equilibrium with respect to forcings, then there isn’t any significant warming “in the pipeline”, and since we’ve had pretty much the full whack of warming from the so-far released greenhouse gases, that the climate sensitivity must be rather small (around 1 oC per doubling I think he concludes).
my feeling is that he’s got this wrong because he doesn’t distinguish between short term forcing (like volcanic eruptions) that affect only the superficial “layers” (and thus the temperature recovers quickly – e.g. consistent with a relaxation time of a few years), whereas very long term forcings (effectively “permanent” enhancement of the greenhouse effect) take far longer for the climate to respond to. In one case there is a rapid recovery to the previous “equilibrum” following a short term perturbation….in the latter the entire Earth is relaxing towards a new equilibrium “set” by the new level of greenhouse forcing.
[Response: We discussed the Schwartz paper here, and there is a submitted comment on the paper available here – gavin]
I am glad that you can confirm the lack of a significant phase delay. If this can be confirmed then it has large implications for anyone trying to use simple single time constant models for thermal response.
I have stated my objection to such models whenever I see one.
The result does seem to cause a bit of an issue in that one has to be able to maintain the annual damping of ocean on temperature at the diurnal an annual timescale with its pi/4 or pi/3 phase delays and large attenuations to the response compared to the forcings with a different mode of operation to 11 year cycles.
Might I suggest that someone also has a close look at the response (amplitute and time lag) to the volcanic forcings as they would fit in the gap between the two timescales.
Comment by Alexander Harvey — 14 Dec 2007 @ 7:33 AM
There seems to be a window for misunderstanding concerning the “well mixed layer”. Well it confused me so perhaps it confuses others. It has a meaning (that the water is well mixed) but is often defined by the depth of a particular temperature horizon as a fraction of a degree (say 0.5C) below the surface temperature.
Given reasonably calm conditions then, during a heating phase the layer thins, during a cooling phase the layer thickens. This is not how it must behave in order to be modelled by a 50m slab. It behaves in a non-linear fashion with its thermal capacity varying inversely with temperature. Also there is not necessarily a great deal of heat transfer between different depths.
Given stormy conditions or excessive cooling of the surface true mixing occurs and heat is transferred between different depths.
One model that might apply is one with a diffusivity that is a function of temperature gradient. Ranging from small during the warming phase (strong normal gradient) and large during temperature inversion.
Such a model has one interesting characteristic. It tends to reject heat more strongly during the cooling phase than it takes up heat during the warming phase. It also tends to maintain the temperature gradient with warmer water above cooler water.
Whether you believe any of that or not, I think it does show that this is a complex thermal mass that is unlikely to be simply modelled.
I suspect that only the best of the Ocean models will be able to answer questions on how the ocean is likely to behave to forcings on the duirnal, annual, and solar cycle timescales. I am afraid that simple models are likely to produce highly misleading results.
I presume that the GCMs do reproduce annual temperature variation with some accuracy but it would be good to see that they do reproduce the effects of forcings like solar variation with some accuracy.
Comment by Alexander Harvey — 14 Dec 2007 @ 8:51 AM
Ray, again, thank you for taking the time to treat us to your insights on the session you are attending.
[an interesting talk by Booth et al, of the Hadley center, showing the robustness of their simulation of Amazon dieback against variations in uncertain atmospheric parameters (it may die sooner, it may die later, but die it does).]
As I hear and read about the massive thin Arctic ice waiting for the sunrise and add your comment about the fate of the Amazon, what come to my mind is what is caught in the middle: i.e., the world grain basket in the plains of Western North America.
Good grief. It is enough to trigger a migraine.
Comment by John L. McCormick — 14 Dec 2007 @ 8:58 AM
Very interesting posters and I am somewhat reluctant to distract from them, but to the beginning of the post. From my reading Hansen has always been clear about his use of tipping points being commitments to irreversible events (e.g. the point at which Greenland goes slimy green and the ice cap disappears), and freely admitted that how long it takes is another problem, about which, as it turns out, he is a lot less optimistic than most. The economists are just catching on to this.
The tipping point concept is a simplification that has already caused much confusion. The idea of a climate “tipping point” is a form of dualism that impedes rational analysis.
The likelihood that models were missing a significant physical process seemed quite unlikely when we have long known that models of the air-sea interaction needed improvement. I hope that these results will help focus the community on the role of the oceans in climate change.
COPENHAGEN, Denmark – The head of the U.N. panel on climate change compared him to Hitler. Another leading scientist called him a parasite. A third described his latest book as a “stealth attack” on mankind.
The list of allegations against Bjoern Lomborg, one of the world’s leading climate change skeptics, almost reads like an indictment for war crimes.
As Al Gore shows off his Nobel Peace Prize and world policy-makers hammer out a new strategy for saving the planet, climate change contrarians say they have been elbowed out of the debate. They say mainstream scientists have stifled healthy intellectual discourse by demonizing dissenters as oil industry lobbyists or lunatics.
“I really think it reflects entirely on them,” said Lomborg, a mild-mannered Danish statistician who says global warming isn’t a big threat and that international treaties requiring sharp and immediate cuts in carbon emissions would cost a lot but do little good. …
“Whether or not it’s happening is not the point. It’s obviously happening,” said Pat Michaels, a senior fellow of environmental studies at the libertarian Cato Institute in Washington, D.C.
“How much will it be … and what should you do about it? That’s where the debate should be. But that debate is being driven by very shrill rhetoric.”
Another contrarian, meteorology professor Richard Lindzen at the Massachusetts Institute of Technology, said proponents of the predominant view on global warming started trying to stamp out dissent long ago.
“The harassment 15 years ago and earlier pretty much succeeded. Those entering the field thereafter knew the ground rules,” Lindzen wrote in an e-mail.
The solar radiance TSI is as measured in space, you need to adject for the geometry of the earth (divide by 4) and albedo (multiply by ~.7) and if required for absorption above the troposphere (multiply by ~.9+/-) the result is roughly a division by 6.
1 w/m2 => .16 (ish) w/m2
Comment by Alexander Harvey — 14 Dec 2007 @ 11:37 AM
Re Chris #3,
I have read the Brookhaven paper and as I recall it uses a simple model throughout (best recollection) it does however include the following caution:
“Here it must be stressed that C is an effective heat capacity that reflects only that portion of the global heat capacity that is coupled to the perturbation on the time scale of the perturbation.”
Aye there’s the rub.
It is all down to coupling. I think we will find that the coupling is highly dependent on the timescale and possibly the effective time constant will increase linearly with time scale on part of its domain (this is the diffusion model). The slab model (top 110m or well mixed layer totally coupled) does not have this property and leads to impossible results in some time frames.
I suspect that the truth is that the ocean deserves a complex and dynamic model if any real progress is to be made with relating forcings to responses.
Also at short timescales, annual variations etc., the continental heartlands are not tightly coupled to the oceans and whereas it is true that the oceans should ultimately dominate at long timescales I think it would be circumspect not to neglect the weak coupling between oceanic and continental regimes when considering volcanism and maybe even solar forcing.
Comment by Alexander Harvey — 14 Dec 2007 @ 1:48 PM
Thanks for the post.
I was wondering: I just read the German “SPIEGEL ONLINE” today about the “tipping point” issue of J. Hansen. I was slightly confused about the threshold Hansen suggested that 380ppmv were the CO2 concentration at which certain “tipping points” were triggered and the results being irreversible. How is this in line with previous findings (avoiding “serious climate change” by keeping the levels below app. 450 ppmv) and the projections of the report of the IPCC recently released? Did Hansen really attain new results the IPCC has not? Is Mr Hansen just misquoted and the SPIEGEL provided some “Alarmism” as usual or what?
[Response: This is one of the many confusions possible in the “tipping point” business, because there are many possible things one can refer to as tipping points, and one encounters more of them as the temperature deviates more from the range of the past two million years. Jim emphasized the matter of multiple tipping points more clearly in this talk than on some previous occasions. I haven’t read the Spiegel article, but I imagine he was referring to the disappearance of perennial arctic sea ice with the “380″ figure. He’d argue that even at the CO2 level we have now, we are committed to losing the ice, given the warming in the pipeline. Based on the stuff Mark Serreze showed, that’s a fairly defensible position. –raypierre]
I would like to express my appreciation for this series of AGU posts. Good reporters combine expertise, concision, fairness, and a sense of what’s important with an engaging prose style. One couldn’t have asked for a better example than that provided by raypierre (supported by his trusty sidekick david and the town sheriff gavin). If only our newspapers could provide coverage one hundedth as good.
There seems to be something a little odd about the detrended NCEP data in their Figure 1.
Does the NCEP dataset differ markedly from the NCDC dataset?
Also what components other than the mean and the linear slope can be removed during linear detrending?
Comment by Alexander Harvey — 15 Dec 2007 @ 9:15 AM
I disagree with some points here.
First, the average response for the 11 models which include solar forcing is 0,10K. Even if one model gives 0,14 K, it means that models usually underestimate solar signature on short term climate variations by nearly a factor 2 (if Camp-Tung are correct). If we agree on that basic observation, we need to explain it. (Secondarily, it’s interesting to recall that half of IPPC models don’t need the Sun to simulate terrestrial climate, certainly the expression of their gripping realism).
Second, you take as a prior asumption that climate sensitivity should be the same for solar and CO2 forcing. But that is a result of models (running whit either solar or GHG forcings) and precisely, we’re not sure models fully implement solar effects. Looks like a begging the question: the proposition to be proved (no major problem with the Sun in models) is assumed implicitly or explicitly as one of the premises (identical sensitivity, so good simulation of solar effects).
Third, stratosphere-troposphere-ozone, clouds or cosmic rays are not “mysterious” or “exotic” physics, just scientific hypothesis currently under examination. At best, your rhetorical contempt exposes your prejudice, but there’s no reason to believe you here rather than specialists working specifically on that domains. Anyway, my opinion is that there’s no satisfying phycical explanations for the moment, but I think too there’s no reason to dismiss a priori your colleagues’ work in such a conservative way (especially if we recall that models are unable to constrain significatively climate sentivity for 30 years, not really the expression of major progress in uncertainties or level of understandings).
Fourth, because of the prior assumption (2), you look for adjustment in thermal inertia (which, with direct/indirect effects of aerosols, usually comes to rescue for model failures). So, it leads to suggest AOGCM have problem in representing the heat transfer in ocean layers. We can conclude that models have problem either with the Sun or with the oceans – a quite pessimistic conclusion for their robustness in attribution-detection or 2100 projection exercises.
Comment by Charles Muller — 15 Dec 2007 @ 10:59 AM
Other than the fact that the Bali Summit provided nothing other than to agree to agree to further climate talks (and that’s all that it was), it provided absolutely no change in stopping the constantly increasing global pollution and the life-threatening build up of carbon dioxide. Climate change added to the world’s emerging and dire problems (population explosion and its sustainability, famine and food shortage, energy resource depletion and increased energy demands, cyclic pandemics, global pollution and carbon dioxide saturation, dwindling water shortages for life etc, etc, etc), put together are immense. Indeed together, they are a recipe of nightmarish proportions that has never been seen before by humankind. But the greatest threat to human stability is the fact that people in high places do not realize that the time-span for solving these huge global problems has a finite period of time also. The writing is now on the wall I would say for all to see if they will only look and where humanity has to react without delay, but where, reaction to global problems takes decades to solve. Therefore the lead-time that we have now is the only thing that we have in our favour. Leave it for another 20-years and we shall not have the necessary lead-time to do anything about the really ‘big’ problems. This is what we really have to get over to our leaders, politicians and multinational industrialists, for it will affect them as much as it will affect you and me. Indeed, if they do not change quickly there self-preservation and vested interest thinking, we shall all end up with problems that are just unsolvable due to the time-served requirement to solve them and where time will literally run out on us all.
For only by people in high places realizing our dilemmas quickly now will be able to confront them and have enough time to solve them. It is no use therefore in pussy footing around until it is too late. For hesitancy and delay today is the greatest threat to the survival of humankind and where if we do not come to our senses quickly, in fifty-years time, the world will have become very similar to most probably how we can picture in our minds, a world very much like hell itself.
Dr David Hill
World Innovation Foundation
Again on Hansen:
So, what are the implications of having gone past certain tipping points after having reached 380ppmv? Can I still assume that the IPCC AR4 has the figures right or does it mean that they miscalculated and that 450ppmv is too high to avoid “dangerous climate change”? So far, I always had the impression that 450ppmv was the critical threshold and not 300-350 ppmv. I mean, on what a large scale do the suggestions of Mr Hansen on the loss of the perennial icesheets exceed the projections of the IPCC in what they call “dangerous climate change”? wouldn’t the passed thresholds that Mr Hansen suggests lead to a triggering of certain positive feedbacks which the IPCC hasn’t counted in? Would there then be still enough time to cut carbon emissions in order to avoid “dangerous climate change”?
Since I’m not connected with the climate community (thou I can say I coulda shoulda, but
grad schools/careers didn’t work out that way), take this with a small grain of salt:
It is easy to imagine several regional tipping points, i.e. changes of a local reqime between two quasi-stable equilibrium points. I can easily imagine a few arctic ones:
(1) A vegetation switch on land, taller shrubs if they get established decrease albedo and the warmer microclimate may be self-reinforcing.
(2) Sea ice.
(3) Extent of ice caps, especially GIC.
Now observationally we have seen (1), and the evidence from 2005:2007 is very suggestive (but not definitive) that (2) has probably happened.
Given (1) and (2) both likely lead to regional warming due to albedo feedback, it seems reasonable to assume that crossing them *MAY* be sufficient to trigger (3).
I don’t think the CC community has much of a handle on where the various bifurcations (I hate tipping point) are really located. The higher we drive delta T the greater the danger of passing any given point. IMHO 450ppm was choosen somewhat arbitrarily, not because of detailed knowledge of where these points are, but because it seemed to be possible with a very aggressive emissions reduction policy. I think the CC people made it clear (at least it was my understanding) that we probably won’t know when we have crossed a particular TP, and have observed the change. Due to system inertia (timescales), and natural variability we don’t even know if we have actualy crossed (2), but more and more scientists think that is now likely to have already occurred.
I agree that tipping points are ill-defined and prone to being misunderstood. But used correctly they are are useful device for communicating a complex physical process to the general public – once you push a physical system too far it tips into another state and cannot easily be righted.
However, even my intelligent friends tend to think there is ONE tipping point, rather than a series, and also overlook that much of the potential damage of AGW is incremental.
The loss of Arctic sea ice – if and when it occurs – will be a valuable illustration of the dangers of AGW and the nature of tipping points. Ultimately it may be helpful as it will probably be not be a humanitarian catastrophe (not the case for other species though), but serve as a warning to the public, business and governments, and ultimately disarm sceptics and denialists.
Hi Nico @16,
I’ve found Mark Lynas’ book Six Degrees useful on the implications of climate change. http://www.realclimate.org/index.php/archives/2007/11/six-degrees/
It’s actually difficult for climate scientists to say exactly how mach CO2 causes how much warming. Then there’s another step to estimate the impact of a given amount of warming. Lynas just takes the amount of warming (in one dregree increments) and uses published literature to describe the estimated effects.
If you read his book, once you get past 2 degrees to 3 degrees warming the effects start to look pretty serious. Among other things, there are expected to be large displacements of populations due to regional climate changes.
There is NO critical threshold and NO single tipping point. The 450 ppm/2 degC value is a consensus estimate to guide decision makers to the level at which scientists estimate the effects of AGW moves from being serious to very dangerous.
Yes there are “tipping points” at which things suddenly get worse, but mostly the damage from emissions can be thought of as cumulative.
I thought the bali meeting was a virtual waste of time, with the usa as usual showing absolutely no leadership and practically vetoing the whole process. It clearly shows the white house still doesn’t understand it’s responsibily in the issue. For the vast part of last century the usa was the single biggest emitter of greenhouse gasses therefore it should stand to reason that it is also the usa that should take greatest responsibilty in initialting emission cuts. Yes Bush it could slightly strain the economy..but it was that same reckless polluting economy that has plunged the world to the edge of the abyss. So if any country should take the lead in this it’s america. If america only had more guts and leadership, china and india would have had the confidence to go with achievable emission targets.
Comment by Lawrence Coleman — 16 Dec 2007 @ 7:48 AM
I, for one agree, that the “tipping point” notion is not necessary, at least for my personal policy implications.
Well before I became aware of positive feedbacks such as melting permafrost & hydrates (and the possibility of the problem spiralling way beyond human control), I had already by the mid-90s reduced my GHGs substantially, just based on my misunderstanding at the time that global warming was a linear function of our human GHG emissions, and not nearly so serious as I understand it today.
However, I was aware that even small increments in a slow warming process might have drastic or tipping point effects in other systems — such as triggering droughts. For instance, a slight ocean warming could pull the rain clouds over the Indian ocean, so South Asia would experience drought. Things like that.
Also it was untenable to me that my emissions (along with everyone else’s) could lead to harming or killing even a few people.
So, all other knowledge I’ve gained since then that makes GW much much more serious a problem, is all just gravy or unnecessary info from my policy perspective. I reached my tipping point into action with my misunderstanding that AGW wasn’t nearly so serious a problem that it is turning out to be.
Comment by Lynn Vincentnathan — 16 Dec 2007 @ 10:31 AM
Raypierre, you take for granted that climate sensitivity should be the same for solar and CO2 forcing. But that is a result of models (running whit either solar or GHG forcings) and precisely, the question is to evaluate if models fully implement solar effects. It looks like a begging the question: the proposition to be proved (no major problem with the Sun in models) is assumed implicitly or explicitly as one of the premises (identical sensitivity, so good simulation of solar effects, at least as good as CO2 effects).
Because of this prior assumption, you look for adjustment in thermal inertia of the oceans (for the 0,10 / 0,18 K gap of solar signature). So, it leads to suggest AOGCM have problem in representing the heat transfer in ocean layers. We can conclude that models have problem either with the Sun or with the oceans – a quite pessimistic conclusion for their robustness in attribution-detection or 2100 projection.
I’m curious as to whether others weren’t intrigued by Hansen’s presentation too. It seems to me that it logically undercuts most of the huge political framework (UNFCC, Kyoto, Bali) that we’ve set up to deal with climate. I mean, if there’s a red line somewhere around 350, don’t we need to be working with an entirely different intensity to get back there?
Was there much pushback? Is there a strong scientific argument that the real danger line is 450? Or is that just what we’ve gotten used to in the last couple of years.
Given Hansen’s track record, I’m interested in people’s takes on this.
Charles #20, you seem awfully eager to give up conservation of energy. Why should we not assume that forcings of similar magnitude have compararable effect? There is zero evidence to the contrary, and most feedbacks are more likely to have a thermal dependence, rather than be, say photo-activated. How would you even construct such a system in the absence of any physical model to guide it? This idea is really reaching.
Gavin, how much do you understand about the significance of vast fresh water lakes beneath antartica and greenland shown by laser satellite? Have they been there for ever or are they larger now due to the increase in numbers of moulins. Water obiously decreases the friction of the rock/ice layer. Could it mean that the greenland and antartic pack ice is melting and thinning from the bottom as well as the top?
Comment by Lawrence Coleman — 17 Dec 2007 @ 9:52 AM
Just a thought experiment : you force terrestrial climate with 1 W/m2 in UV band and 1 W/m2 in IR band. Do you expect the same feedbacks ? No, because feedbacks are not just bound to the amount of energy, but also to energy-matter interactions. (Another thought experiment : you force climate with 1 W/m2 of the same spectral band, but in one case concentrated on the Tropics, in the other case concentrated on the poles : same conclusion, climate will not react in the same way, because water vapor feedback and ice melting feedback are not strictly equivalent).
For a more realistic example, I still don’t clearly understand why solar forcing and CO2 forcing should have the same effect on oceans, as LW radiations are limited to the skin whereas SW radiations interact deeper in the first layers (0-100 m). I would say (naïvely, I’m not physicist) that IR radiation on the skin is fastly re-radiated toward space for cooling (or used for evaporation at surface-air contact), whereas SW radiation modifies more slowly heat content of the oceanic layers.
Comment by Charles Muller — 17 Dec 2007 @ 10:17 AM
Re #23 (Lawrence Coleman) “I thought the Bali meeting was a virtual waste of time, with the USA as usual showing absolutely no leadership and practically vetoing the whole process. It clearly shows the white house still doesn’t understand it’s responsibility in the issue.”
That it was a waste of time is very much Monbiot’s take on it (http://www.guardian.co.uk/commentisfree/story/0,,2228615,00.html),
but he argues the problem with the USA is much deeper than the current occupant of the White House, pointing out that it was Clinton, Gore and the Senate (both parties) who sabotaged Kyoto, which he puts down to the amount of political funding from fossil fuel, auto and related interests. If he’s right, it won’t matter who wins the US Presidency in 2008. I’m a little more optimistic – all governments represented at Bali are at least on record as agreeing that deep cuts in emissions are necessary. But, all those of you with a vote in the USA, please tell your senators/representatives/candidates you will not be voting for anyone who takes money from these interests!
Ray keeps talking about “warming in the pipeline”. Could we please have a definition of this pipeline. Where is located, what are its characteristics and so on?
The word conjures up a vision of warming in the future, so it may be a good one to scare people with, but isn’t it a bit too vague to be used so much in a scientific context.
[Response: Current estimates are that the planet is out of radiative balance – more energy is coming in than is leaving. This will cause more warming in the future as the oceans heat up slowly. If you don’t like ‘in the pipeline’, think ‘thermal inertia’. – gavin]
36. Thanks. So if I understand correctly, it is a question of estimated heat transfers in the future, and there really is no place (or object, like a pipeline) where some latent heat is waiting to be released. Therefore I propose that everybody stops using the pipeline analogy and starts talking about thermal inertia, if that is really what is meant.
Dodo, think of it this way. Energy comes into the climate via insolation and can only leave via longwave IR. If Earth were in equilibrium the outgoing LWIR would approximate a blackbody spectrum appropriate for Earth’s equilibrium temperature–with integrated energy equal to incoming solar energy. Now put in ghgs–they take a big bite out of the “blackbody” spectrum. Energy can still escape in this wave band, but only when it gets to the point where the ghg concentration is low enough that its chances of getting absorbed are small. But that will only be high in the atmosphere where temperatures are much colder, and so less energy will escape. That energy will warm Earth until total outgoing radiation again equals total incoming radiation.
Does this help? Check out the Saturated Gassy Argument series–it was quite helpful.
Climate Science has a question for Real Climate (the answer of which will also be posted on that website). The 2007 IPCC Statement for Policymakers [Figure SPM.2] has the following caption
“Global average radiative forcing (RF) estimates and ranges in 2005 for anthropogenic carbon dioxide (CO2 ), methane (CH4 ), nitrous oxide (N2O) and other important agents and mechanisms, together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU).”
but also the footnote on page 2 that
“Radiative forcing is a measure of the influence that a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism. Positive forcing tends to warm the surface while negative forcing tends to cool it. In this report, radiative forcing values are for 2005 relative to pre-industrial conditions defined at 1750 and are expressed in watts per square metre (W m–2)…..”
Which of the two are correct?
Assuming that you agree that the footnote is correct, and the figure caption is in error, what is the Real Climate estimate in Watts per meter squared in 2005 (or in 2007) of the radiative forcing components and range for a figure analogous to Figure SPM.2 in the Statement for Policymakers?
[Response: I fail to see how you are parsing this to find an inconsistency. The footnote is clear that the term ‘radiative forcing’ in the IPCC report refers to the change in forcing from a 1750 baseline. More precisely, it is defined as the change in radiation at the tropopause after stratospheric temperature adjustment but with all other factors kept fixed when going from 1750 conditions to a new value. The caption to the figure discusses the radiative forcing (which remember is defined relative to 1750) in 2005. i.e. the forcing calculated in going from 1750 conditions to 2005. What is the problem? – gavin]
Gavin – You have avoided answering the question (the issue that you are spinning an error in the figure caption should be obvious to most). The more important issue, which you have not addressed is
“What is the Real Climate estimate in Watts per meter squared in 2005 (or in 2007) of the radiative forcing components and range for a figure analogous to Figure SPM.2 in the Statement for Policymakers?”
[Response: I’m still not following you. RC doesn’t have an ‘estimate’ – if asked, most of us would probably point to the IPCC values in the figure you highlight. I often use the GISS numbers (which are a little more complete, have some accounting of indirect effects and efficacy factors and are available as a time series), but there isn’t much in it. Your point about spinning the caption is completely obtuse – there is no contradiction as far as I can see. If you want to convince people that there is, you need to be more specific about what you mean. – gavin]
I agree that the figure in the IPCC Figure is the forcing differences for each climate forcing for pre-industrial to 2005. However, the caption states that this is the “Global average radiative forcing (RF) estimates and ranges in 2005″. The implication in this statement is that the climate forcings in figure SPM.2 are the current radiative forcing.
The reason that this is important is that the climate system has warmed since preindustrial times such that the radiative forcing is smaller since there has been some adjustment towards equilibrium. The time history of these forcings is different so their contributions each have had different time periods to result in some adjustment.
For example, if the difference of a climate forcing since preindustrial were 1 Watt per meter squared, some of this radiative imbalance would be adjusted for by warming since preindustrial time. The current radiative forcing for this example, therefore, would be less than 1 Watt per meter squared. If there were no adjustment (i.e. no increase in outgoing long wave irradiance from the Earth), of course, the current radiative imbalance from this example would be 1 Watt per meter squared. Figure SPM.2, therefore, does not present the current radiative forcing, but this is what is needed to describe the current state of the global average radiative forcing.
A simple example further illustrates. When you heat a pot of cold water, the heating is in imbalance until the water warms enough such that its heat loss is equal to the heat input from the stove. The heat imbalance at any time after the burners are started is less than the difference in heat between the time before the burners were turned on and any subsequent time. Eventually, the heat imbalance (i.e. analogous to the radiative forcing) becomes zero. It is the current imbalance in the radiative forcings that should be plotted (estimated in a figure of the form given in Figure SPM.2).
If this is still not clear (and we remain in disagreement that this is a significant issue) I will write a more detailed weblog on Climate Science on this subject. The request that I have is to provide us with an estimate of the movement towards radiative balance of each of the forcings in Figure SPM.2.
[Response: I think I see the problem. You are using the term ‘radiative forcing’ to mean the current radiative imbalance. However, this usage appears to be unique to you. Radiative forcing in the IPCC sense and in most of the literature is a diagnostic of the external inputs to the climate system, not a measure of the result. It was designed to provide predictability of a model response at equilibrium after the system responds to an external perturbation. Therefore any use of the term ‘radiative forcing’ in the IPCC report refers to that, not the current imbalance. These are of course related: given an instantaneous forcing, the system will have an initial imbalance of the same magnitude, but as the system adjusts the imbalance will decrease. The key concept is that radiative forcing is by definition referenced to a previous state. In IPCC, that state is defined as 1750 conditions, but it would be fine to define the forcing with respect to any other period you want. The current imbalance is simply an instantaneous number.
Getting back to IPCC, there is still no problem with figure SPM-2 – it is a diagnosis of all the forcing elements and their uncertainty since the pre-industrial and is in a section entitled ‘Drivers of climate change’. The current imbalance however, cannot be apportioned based on forcing factor, it’s just one number. We’ve discussed estimates of that based on ocean heat content changes or what the models say previously. But if that is what you want to discuss, why didn’t you just say so initially? Redefining terms unilaterally just leads to confusion. – gavin]
Why should we try to define “tipping points” as orthogonal to the commonly understood concept of “bifurcations”? Ultimately, aren’t the the equations of state for the climate system a bunch of partial differential equations? It seems entirely appropriate that we should expect bifurcations (e.g., period-doubling cascades) and look for them in the GCMs. Wouldn’t this definition of “tipping points” avoid the hand-waving problem?
National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties, where on page 13 it is defined as
“A climate forcing is an energy imbalance imposed on the climate system either externally or by human activities. Examples include changes in solar energy output, volcanic emissions, deliberate land modification, or anthropogenic emissions of greenhouse gases, aerosols, and their precursors.” [from http://www.nap.edu/openbook.php?record_id=11175&page=13.
I am defining that “the term ‘radiative forcing’ (i.e. the climate forcing) means the current radiative imbalance, but this consistent with the National Research Council report of which at least one Real Climate author participated in.
[Response: I disagree. The NRC definition is fine (but the version on p15 is more complete) but your paraphrase is not (the problem is that ‘imposed imbalance’ is not the ‘current imbalance’). But now that we have sorted out the semantic confusion, what is it that you really want to discuss? – gavin]
Gavin – What I am requesting is an estimate of the fraction of the current radiative imbalance associated with each climate forcing.
[Response: I don’t think it can be done robustly. A straight-forward apportioning based on the fractional contribution to the original forcing neglects the differing transient behaviour. For instance if one forcing agent rose quickly and stabilised, while another increased later, then the impact of each on the current imbalance should be weighted towards the latter. So that’s no good. Maybe you could do it by examining the single forcing transient runs we did for our recent paper (table 1) and looking at the year 2000-2003 (say) imbalances in Ann/Net TOA radiation. You’d need to check that the individual components do in fact add up to something close to the combined effect (not obviously true). However, different models might give quite different results, and you can only do this for forcings we’ve run. Other groups didn’t do as many single forcing experiments and so you might not be able to find another set of numbers to compare with. Attribution requires models however, and so I don’t see how you could do it any other way. – gavin]
> The request that I have is to provide us
> with an estimate of the movement towards
> radiative balance of each of the forcings
> What I am requesting is an estimate of the
> fraction of the current radiative imbalance
> associated with each climate forcing.
How do you get a “current imbalance” number — something like Triana would offer, an observation that covered the entire visible half of the planet and averaged its heat signature, compared to the insolation? That would change as the planet turned, clouds moved, ocean or land or ice presented itself to the satellite, wouldn’t it?
I gather without Triana or equivalent there’s no simple answer to this basic question, but that it’s possible to determine it for other planets because they’re far enough away that an instrument can capture their entire radiation signature in a snapshot.
Don’t let me lead the conversation astray, just groping to understand how and when it’s possible to get a ‘curent imbalance’ as a global snapshot of the moment.
Levitus, S., J.I. Antonov, J. Wang, T.L. Delworth, K.W. Dixon, and A.J. Broccoli, 2001: Anthropogenic warming of Earth’s climate system. Science, 292, 267-269.
Barnett, T.P., D.W. Pierce, and R. Schnur, 2001: Detection of anthropogenic climate change in the world’s oceans. Science, 292, 270-274.
to see how the radiative imbalance can and has been diagnosed for relatively short time periods using the accumulation of Joules in the climate system over a this period.
On Gavin’s latest reply,
“A straight-forward apportioning based on the fractional contribution to the original forcing neglects the differing transient behaviour. For instance if one forcing agent rose quickly and stabilised, while another increased later, then the impact of each on the current imbalance should be weighted towards the latter. So that’s no good.”
Why is this “no good”. This analysis would be quite informative. I agree that this does require models, as Gavin stated, but difference among models would be quite useful to know. Gavin has outlined a way this issue can be explored.
I plan to weblog on this subject further in a new weblog on Climate Science. Thank you Gavin, Hank and others for your feedback.
These ideas could be tested by more complete diagnostics of heat burial in the NCAR model, and solar-cycle response runs with a two-layer mixed layer model in which the upper layer is shallow. I think I’ll give it a go, if I can find the time.
Did you ever happen to do this? Or do you know anyone who has done anything along these lines?
Curbing a notorious form of industrial pollution may ironically harm Amazonia, one of the world’s natural treasures and a key buffer against global warming, a study released Wednesday has found.
Its authors see a strong link between a decrease in sulphur dioxide emissions from coal-fired power plants and a rise in sea temperature in the northern Atlantic that was blamed for wreaking a devastating drought in western Amazonia in 2005.
University of Exeter professor Peter Cox and colleagues created a computer model to simulate the impact of aerosols — airborne particles that, like sulphur dioxide, are also spewed out by fossil-fuel power plants — on Amazonia’s climate.
The aerosols, while a bad pollutant, indirectly ease the problem of global warming as they reflect sunlight, making it bounce back into space rather than warm the Earth’s surface.
In the 1970s and 1980s, according to Cox’s model, high concentrations of aerosols over the highly industrialised northern hemisphere had the effect of buffering the impact of global warming on north Atlantic surface waters, which led to more rain over Amazonia.
But tighter curbs on sulphur dioxide emissions from power plants led to a reduction in aerosol levels, causing these Atlantic waters to warm. This changed patterns of precipitation, leading to the 2005 drought.
Projecting into the 21st century, the study estimates that by 2025 a drought on the same scale as in 2005 could happen every other year.
By 2060, forests would be starved for rainfall nine out of every 10 years, says the study, published in the British journal Nature.