As I write this, I’m watching the program Naked Science on the National Geographic channel. The episode is titled “Glacier Meltdown,” and that’s a subject of interest to me.
But already I’m extremely disappointed. They’ve tried to explain the progression of ice ages by mentioning changes in earth’s orbit; so far so good. But they claimed that when earth’s orbit gets more eccentric (more oval-shaped, less circular), earth goes further away from the sun and that plunges us into an ice age. This prompted me to turn to my wife and exclaim, “That’s @#$%&*!!!”
Earth’s orbit does change its eccentricity (on a cycle of about 100,000 years), but that changes the shape of the orbit, not the average distance from the sun. And when eccentricity increases, during one part of the year we’re further from the sun, six months later we’re closer. The net effect is to cause a slight increase in solar energy intercepted by the earth. Furthermore, the effect of eccentricity changes is minor compared to the effect of changes in precession (seasonal timing of closest approach and furthest recession) and obliquity (tilt of the earth’s axis), which don’t alter the total energy intercepted by earth, but dramatically change how that energy is distributed geographically.
In another example of the ridiculous, the “Watts Up With That” blog has a guest post by former California state climatologist Jim Goodridge. It’s all about how temperature change controls atmospheric CO2 concentration, not the other way around. I’m not sure which is more embarrassing: Goodridge writing this article, Anthony Watts posting it, or all the commenters (except one) who bought into this garbage. Even after a commenter named “Boris” points to the truth of the matter, readers there are sticking with the story.
Meanwhile, a small-town Nevada newspaper (the Ely Times) ran an editorial making a lot of silly denialist claims about global warming. One of the simpler errors in the editorial was the statement that the greenhouse effect keeps earth about 100 degrees F warmer than it would be with no atmosphere, because 33 deg.C translates to “about” 100 deg.F. Michael Mann (yes, the hockey-stick guy) sent a letter to the editor pointing out, among other things, that this was mistaken. The editorial’s author, in his rebuttal, stuck to his claim! He has since seen the error of his ways in regard to this point. But it’s unlikely he’ll soon see the error of his ways in general.
There are a lot of ridiculous claims bandied about in the global warming discussion. No wonder so many people are confused.
77 responses so far ↓
Molnar // November 12, 2007 at 2:20 am
I think the ridiculous claims and confused people relationship is much like that of global temperature and atmospheric CO2 concentration: each reinforces the other on the way up.
John Mashey // November 12, 2007 at 4:02 am
We actually have 3 different kinds of cases, here and they’re somewhat related to a discussion over in Deltoid about pro-active work with the press.
http://scienceblogs.com/deltoid/2007/10/john_mashey_what_to_do_about_p.php#more
2) Watts Up!: well that’s a blog.
3) The small-town paper: I suggested strategies for dealing with small local papers [mostly, try to get them not to opine about AGW unless they know what tthey're doing, and especially not to print letters about AGW offering opinions on scientific facts.]
This may or may not work in this case, but I think I’ve gotten some results with several local papers.
1) The NGC “Glacier Meltdown”: I think NGC tries to get it right, but it sounds like they goofed. I’m not sure about what can be done pro-actively, as this is different from continuing activities in newspapers.
But, here are a few ideas, following the general philosophy outlined in the Deltoid article:
a) Here’s the relevant website:
http://www.nationalgeographic.com/preserve-our-planet/tvshows/ns-glacier-meltdown-show.html
Certainly their heart seems in the right place, although I haven’t actually seen the episode.
b) Here’s a website where you can actually comment:
http://www.imdb.com/title/tt0990162/
It identifies relevant people, such as the writer, Nick Clarke Powell (?)
The question is: “is the show as a whole ridiculous, or was it generally OK, but they screwed up trying to explain that part?”
c) I’m right now watching “A Global Warning?”, a 2-hour show on the History Channel, which is:
http://www.history.com/shows.do?action=detail&episodeId=251203
and generally, it seems pretty good. Overpeck, Hansen, Alley, Lonnie Thompson (with 11000-year Kiliminjaro ice-cores), etc. They’re a little fuzzy about the Little Ice Age [don't really say whether or not they think it's global]. Nice comments on volcanoes, SO2.
A little fuzzy on AGW-hurricane relationship.
Permafrost melt/methane. This wil lbe on several more times.
d) Since video content often gets repeated, it might be nice to gather a quick list of recent climate-change programs/movies, with opinions, ranked, say from -10 to +10, i.e., TGGWS could have a -10, although maybe only a -8, in case the threatened Monckton video really surfaces. :-)
tamino // November 12, 2007 at 4:50 am
Most of the National Geographic Channel program was OK. They did mention a “direct relationship” between CO2 and temperature during ice ages, with no mention that they’re both cause and both effect. At least Al Gore mentioned that the relationship was compex! So I didn’t like that part. But overall, it was OK.
In part, my disappointment was due to the fact that I expected better from National Geo.
John Cross // November 12, 2007 at 6:08 am
Tamino: I have not looked at the numbers, but if I recall my gravitational mechanics correctly one of the properties of the elliptical orbit is that for the period further from the sun the earth will move slower and closer to the sun it will move faster. I don’t know if this is enough to counter the slight increase you point out, but could this be what they are referring to?
It is strange they wouldn’t mention the other orbital climate drivers.
Regards,
John
Adam // November 12, 2007 at 9:53 am
“Michael Mann (yes, the hockey-stick guy)”
Just to be pedantic, Michael Mann was “one of the hockey stick guys” as there were three authors to the paper(s).
JamesG // November 12, 2007 at 10:51 am
It’s just possible that the confusion was from the scientists involved. For example, Carl Wunsch is often having to remind other scientists that the ocean conveyer belt is almost entirely wind-driven so salinity changes would have minimal effect. Nat Geo (among many others) have also been misled on that. Richard Seager says that the idea that the gulf stream heats Europe is a deep-seated myth originating from one man’s idea, that has stuck despite the absence of proof. http://www.ldeo.columbia.edu/res/div/ocp/gs/. Fascinating! Sorting out the myths from the truths in science is not as easy as you might think.
JesusChristHimself // November 12, 2007 at 3:00 pm
At some point when they’re making a documentary, which is an art form, it has to be turned over to artists or nobody is going to watch it. Artist, thank goodness, aren’t really fact people.
NU // November 12, 2007 at 3:03 pm
It’s true that eccentricity forcing is considerably smaller than precessional or obliquity forcings. Nevertheless, a lot of paleoclimatologists do ascribe the 100 ky glacial-interglacial cycle to eccentricity variations at least in an indirect way.
There have been a variety of mechanisms proposed, including feedbacks, stochastic resonance, phase locking of internal climate cycles, etc. The effect of eccentricity to exaggerate or suppress precessional effects also plays a role. (Small eccentricity means precession can’t change seasonal timing very much, because it makes little difference whether summer or winter are closer or farther from the Sun.)
I know you’re criticizing their misleading explanation for the role eccentricity plays in ice age cycles, but one shouldn’t get the opposite impression that eccentricity can’t have anything to do with it either.
Also, I don’t know that wrong for them to say that the eccentricity variations change the average distance from the Sun. My orbital mechanics is rusty, but IIRC the eccentricity variations leave the semi-major axis invariant, which implies that the mean distance is unchanged when averaging over angle (the eccentric anomaly). But when taking a time average, over the mean anomaly, the mean distance does depend on eccentricity.
(I think this must somehow boil down to Kepler’s second law; the Earth moves faster at perihelion, and if you change the eccentricity, you’re changing the amount of time spent near the Sun.)
So if the show was talking about time averages — which are more climatically relevant anyway — I think they’re correct. At least if my knowledge of orbital mechanics has not deserted me. Still, as you have noted, eccentricity variations have a very small effect on insolation.
[Response: You're right (and quite to the point) about everything but this: the show couldn't have been correct, because they suggest that when orbital eccentricity is high we get less total solar energy, but in fact we get more (time-averaged throughout the year, which is what counts).
I do know what you mean about how an explanation or idea gets misinterpreted and/or ingrained in the public consciousness. "Popular" explanations of relativity, for example, drive me absolutely mad! And I admit that this point is very minor in relation to the point of the show. I should probably just "cut 'em some slack."]
Chirstopher // November 12, 2007 at 6:04 pm
Re: What comes first? CO2 or temperature
Does anyone have a link to a clear exposition of this? Maybe something that an undergraduate with a basic background in environmental biophysics and statistics could understand? The treatments I’ve found are very obtuse, go both ways, and are not the best writing. I’d love to have something well written and sourced.
[Response: It depends.
Here's my understanding of the situation: during ice ages, warming starts because a redistribution of incoming solar energy (due to changes in the earth's orbit and tilt) triggers melting of ice sheets. This reduces earth's albedo (the reflectivity of the planet) causing more solar energy to be absorbed -- more energy absorbed heats the planet as a whole. The planetary warming reduces the solubility of CO2 in the oceans, increasing atmospheric CO2. Also, some CO2 is trapped in ice sheets and permafrost, and this too is released to the atmosphere. Increased atmospheric CO2 acts as a greenhouse gas, warming the planet further. Result: deglaciation. In this case, temperature comes first.
In modern times, industrial activity has put massive amounts of CO2 directly into the atmosphere due to the combustion of fossil fuels (carbon which had been sequestered for many tens of millions of years). The added CO2 acts as a greenhouse gas, warming the planet. Planetary warming will reduce the solubility of CO2 in the oceans, further increasing atmospheric concentration, and release CO2 trapped in ice sheets and permafrost, increasing atmospheric concentration yet further. This will lead to more warming. In this case, CO2 comes first.
One of the important, and oft-neglected, points to keep in mind is that CO2 does not increase for no reason. During ice ages, it's due to orbitally-triggered warming. In modern times, it's due to human consumption of fossil fuels. In either case, higher atmospheric CO2 concentration causes warming of the planet.]
B Buck // November 12, 2007 at 8:22 pm
What evidence is there in the ice core records that co2 effects temperature? Clearly, co2 is still falling when temperatures reverse trend and begin to rise, and conversely co2 is still rising when temperatures begin to fall at the other end of the cycle. I am not disputing the relationship between c02 and temperature as discussed in the modern times scenario, but where in the ice core record is there any evidence of co2’s role in effecting temperature?
[Response: Because the numbers add up when assuming CO2 affects temperature, they don't when assuming otherwise.
If you compute the net climate forcing due to albedo change from ice sheet wasting, it's not enough to explain the observed temperature change. Just as CO2 doesn't change for no reason, neither does temperature.
We note that over the 5000 years or more that temperature increases during a deglaciation, CO2 varies in strong correlation with temperature. So, we have warming during deglaciation which is not explained by non-CO2 factors, and an increase in CO2 of the right amount of climate forcing to explain the unaccounted-for warming. 2+2=4.]
Dave Rado // November 12, 2007 at 11:12 pm
Re. B Buck, in addition to what Tamino wrote, if you want to postulate that the rise in CO2 didn’t increased the temperature during that period, you would also have to find a physical explanation for why it failed to do so.
The radiation physics of CO2 as a greenhouse gas has been known since the mid19th century; since that time it has been known that if the CO2 level rises, temperature must increase, all other things being equal. This is very basic physics, as basic as Newton’s laws.
So if CO2 levels rose and the temperature did not increase, that can only possibly happen if some other factor (such as an increase is sulphate aerosol levels) is simultaneously having a cooling effect.
Alan D. McIntire // November 13, 2007 at 1:45 am
In response to John Cross and NU:
I hypothesized the same thing regarding distance from sun having an effect, but I worked it out, and it turns out I was wrong. The luminosity from the sun is inversely proportional to R^2, but the planet sweeps out equal areas in equal times, so the time spent at distance R from the sun is proportional to R^2, so the two figures cancel out. As long as the major axis is the same, a planet will average the same luminosity from the sun over the course of a complete year regardless of eccentricity.
I suppose the fact that most continents are in the Northern Hemisphere, and the
Northern Hemisphere’s albedo increases in winter could have some effect, depending on whether Northern Hemisphere winters are closer to perihelion or aphelion. I also watched part of the program, and I think it alluded to this factor.- A. McIntire
[Response: Actually there's a slight change in total annual solar insolation due to eccentricity changes.
The angular velocity is indeed inversely proportional to 1/r^2 (so time spent in a given angular range is proportional to r^2), but the *constant of proportionality* is inversely proportional to the square of the "specific angular momentum" of the orbit. This proportionality constant has eccentricity-dependence, so the total annual solar insolation for eccentricity e (and unchanged semi-major axis a) is proportional to 1/(1-e^2)^2. Note this means we get the most total insolation when eccentricity is highest, the least when eccentricity is lowest.
Perhaps I'll do one of those "very mathematical" posts about the details.]
Zeke // November 13, 2007 at 6:17 am
Chris,
On the lag vs. lead issue: I wrote a post over at the Yale Climate Media Forum on this subject a few weeks back in an attempt to present an approachable explanation to a lay reader. Tamino, feel free to pounce on any glaring errors on my part.
http://yaleclimatemediaforum.org/dept/1007_co2.htm
JamesG // November 13, 2007 at 3:55 pm
On lag vs lead
Again Tamino/Zeke/Severinghaus/Steig and everyone else like to explain the heating but they don’t bother to explain the onset of the ice age where the external cooling force has to overcome the heating effect of the still-rising greenhouse gases. Remember that the solar tilt by itself isn’t powerful enough to do anything without amplification. Remember too that GHG’s cannot amplify a cooling, they can only retard it (you can see this cooling retardation in the graphs). When I raised this conundrum in a previous thread we managed to cobble together a theory that albedo effect in cooling must have been powerful enough to overcome the combined GHG’s or we just wouldn’t get an ice age at all. We also agreed that H2O would have been a faster and more dominant feedback than CO2/CH4. So, since climate models assume that H2O feedback is 4 times more important than other GHG’s (and here H2O leads), and since the albedo effect (which must have the same energy in heating or cooling) must be stronger than the combined GHG heating effect then the individual effect of CO2 can only be from 10 to 15% at best - the higher figure allows for GHG’s approaching saturation when cooling takes place.
Of course I know this doesn’t materially affect the present day warming scenario but it seems to me that the effect of CO2 in the ice age cycles has been hugely overplayed. As I also mentioned before, this is what Lowell Stott’s data led him to believe too and as far as I know his data is the only data available. As for lag vs lead, the size of the lag is not actually important if you think about it this way.
[Response: Greenhouse gases can too amplify a cooling. When temperature drops, the solubility of CO2 in ocean water increases, CO2 is drawn out of the atmosphere, and the reduced CO2 levels lead to greater cooling.]
Hank Roberts // November 14, 2007 at 12:04 am
And see:
http://www.google.com/search?q=plankton+cooled+a+greenhouse
JamesG // November 14, 2007 at 10:26 am
Tamino
“Greenhouse gases can too amplify a cooling. When temperature drops, the solubility of CO2 in ocean water increases, CO2 is drawn out of the atmosphere, and the reduced CO2 levels lead to greater cooling.”
That’s not an amplifier of cooling, it’s just a gradual reduction in the heating effect. The greenhouses gases still continue to resist the cooling. That’s the basic physics of it. And the initial amplifier that causes the temperature drop in the first place could not be CO2 in any event as it is always lagging.
[Response: The cooling ends up more than it would be, if there were no carbon (hence no CO2) on the planet. I'd call that an amplification of cooling.]
JamesG // November 14, 2007 at 10:43 am
Hank
Thanks for that - to summarise:
“The study suggests that upheavals in the earth’s crust initiated a kind of reverse-greenhouse effect 500 million years ago that cooled the world’s oceans, spawned giant plankton blooms, and sent a burst of oxygen into the atmosphere.”
But this seems to indicate randomness rather than repeatability - unless that seismic event was also triggered by the sun’s tilt. In any event what causes the cooling or heating isn’t as important to the numbers as the probable dominance of the H2O feedback, which in the past would be driven by the warming, not the CO2 (because natural CO2 is also a feedback, not a forcing). Even if you assign only 20% of the heating to albedo changes then the percentage attributable to H2o feedback is likely 80% of that, which leaves only about 15% of the total effect to CO2.
Julian Flood // November 14, 2007 at 1:15 pm
Plankton? See http://idw-online.de/pages/de/news234669
It’s good to see the biologists stepping forward: the immense power of biological systems is not, as far as I can see, sufficiently considered.
From the paper:
“We expected the organisms to show distinct reactions to changing CO2 conditions. What really surprised us, however, was the dimension of this effect. Basically, we can now say that the biology in the oceans is significantly affecting the global climate system.”
Not exactly a surprise though, was it? Now I’d like to see them try starving their little plants and check to see if they switch to C4. What happens to the isotope signal in the detritus?
JF
Zeke // November 14, 2007 at 2:38 pm
JamesG,
Notice in the paleoclimate record that the onset of ice ages tends to be very gradual (often 75,000 years or more) while the end of ice ages happens quite quickly. So while it may be considerably harder to start an ice age than end it (at least in terms of the strength of the feedbacks involved), eventually a number of smaller feedbacks (ocean solubility, ice albedo, decreased vegetative decay, biological feedbacks such as ocean plankton, etc.) add up over time.
There is still considerably uncertainty regarding the magnitude of various feedbacks in glacial cycles. It does seem clear, however, that various greenhouse gases play a crucial role as feedbacks at the onset of interglacials and that their removal from the atmosphere contributes to the onset of glacial periods.
JamesG // November 14, 2007 at 4:44 pm
Zeke
I cannot see how GHG removal from the atmosphere can possibly contribute to the onset of cooling when the cooling happens despite, not because of, GHG’s. Greenhouse gases cause warming, not cooling, which is why our planet isn’t at -33C. A GHG that amplified cooling would take us there rapidly. But in fact we had slow cooling, exactly consistent with a logical retardation effect from GHG’s which heat less and less but still fight the cooling all the way. Those uncertainties you mention seem to be compounded by scientists not thinking logically about the actual processes involved.
[Response: Putting blankets on your bed while you sleep causes warming; blankets cannot cause cooling. But *removing* blankets contributes to cooling, does it not?
By your logic, a reduction in solar output could never contribute to cooling, because solar radiation causes warming not cooling, and whatever solar output remains will "fighting the cooling all the way."]
Mark Hadfield // November 14, 2007 at 6:56 pm
Tamino, your patience in explaining the obvious to someone who resists understanding is impressive.
sidd // November 15, 2007 at 6:37 am
in addition to the albedo effect of ice sheets, i would like to bring up the effects of weathering. CO2 can be fixed as carbonate through weathering of rocks. as ice covers rock surfaces this CO2 sink decreases. i believe, but am not certain, that orogeny such as the raising of the Andes, Himalayas caused fresh rock surface to be exposed, increasing the sink.
with regard to the title of the program: “Glacier Meltdown”: are there any good models for ice sheets which include effects of meltwater drainage, in both mechanical and thermal effects ?
in the same vein: a thought that occurred to me when i saw the slight increase in sea ice in the South: do any models predict an increase in icebergs and sea ice due to ice export from the GIS, (W/E)AIS ?
JamesG // November 15, 2007 at 11:44 am
Tamino
Yes a reduction of heating or insulation contributes to cooling but it certainly doesn’t contribute to the “onset of cooling” if that blanket is still getting thicker at the changeover, which was my main point. That greenhouse gases actually resist cooling is the whole basis of the greenhouse effect, which was my 2nd point. Using your analogy the sun, being the original source of the energy, is the heater in the bedroom . Turn down the heating and the room, the blanket and the bed all get cold eventually, but the blanket resists the cooling of the bed for a while.
Mark, is that not obvious to you? - it is just basic heat transfer. I am not trying to be difficult, just raising some points that people seemingly haven’t thought too much about.
[Response: Climate scientists have thought about it a lot. That's why the lag between temperature and CO2 during ice ages (with temperature change happening first, CO2 change happening later) was *predicted* by Claude Lorius, Jim Hansen and others 17 years ago, before the data showed it (Lorius et al. 1990, Nature, 347, 139).]
luminous beauty // November 15, 2007 at 4:18 pm
JamesG,
For a simple introduction to the very complex questions concerning the initiating of Ice Ages and the causal connectivity between multiple forcings and feedbacks, see Spencer Weart’s excellent exposition:
http://www.aip.org/history/climate/cycles.htm
A lot of scientists have put a lot of research and thinking into these issues over generations. A lot more than just a little armchair speculation.
JamesG // November 16, 2007 at 10:52 am
LB
Thank you for your comment, but that armchair speculation was actually backed up by a fair amount of reading on the subject, including your link. As I pointed out though, nobody who champions the weak forcing, dominant CO2 feedback theory has ever apparently bothered to consider the onset of cooling. When you do it is immediately clear that the theory falls flat on its face because that weak forcing has to be strong enough to counter the GHG heating. In fact, as I also pointed out, even on the heating cycle they have missed the simple fact that H2O feedback should dominate all other feedbacks by at least 4 to 1 leaving any CO2/CH4 feedback as very minor. So much for the appeal to scientific authority! Of course all theories are speculations until backed up by data. Lo and behold though, the only apparent data we have shows that the dominant CO2 feedback theory is a dead duck. So what simple physics and logic should have told these scientists from Petit onwards, was then backed by data. Of course this myth will probably never die, just like the Thermohaline circulation myths I referred to above.
John V // November 16, 2007 at 4:15 pm
JamesG:
H2O feedback is directly caused by temperature increases and decreases. It is not capable of causing temperature changes on its own because a surplus or deficit of H2O in the atmosphere is very quickly corrected by condensation or evaporation from the oceans.
Regarding the ability of CO2 to amplify heating and cooling, I put together a very basic simulation a few weeks ago. My original post was at CA. Here’s the link:
http://www.climateaudit.org/?p=2220#comment-152103
And here’s a link to a prior post that explains some of the details:
http://www.climateaudit.org/?p=2220#comment-151934
The simulation is of a solar forcing of +-0.25C with CO2 rising and falling based on its solubility in the oceans. There are a few things to notice:
1. CO2 amplifies the warming and cooling;
2. CO2 lags temperature for warming and cooling;
3. The system is stable;
JamesG // November 16, 2007 at 6:33 pm
JohnV
H2O feedback cannot cause temperature changes you say. Do you have a source text for that? It would certainly change some climate models if any surplus or deficit of H2O was immediately swept away. There’s the rub - either the GCM’s are wrong or H2O feedback is not important. You can’t have it both ways.
I’ll look closer at your model but did you assume that CO2 by itself caused cooling, rather than a removal of CO2 causing some cooling? Remember that all that GHG heating is in the system already so a negative forcing is needed to initiate change. Since CO2 is a greenhouse gas it cannot by itself cause any cooling so it shouldn’t therefore amplify cooling. The equation needs the logarithmic CO2 effect to be always heating but amplifying on the way up and retarding on the way down, giving a sawtooth-type shape. On first glance you need to make a few changes to introduce some dependencies.
Jamesg // November 16, 2007 at 7:09 pm
JohnV
Excuse me I meant either the GCMs are right or water vapour feedback is not important. I’d better shut up now and respond via your blog if I have a comment on the model.
luminous beauty // November 16, 2007 at 7:53 pm
JamesG,
Atmospheric H2O as a gas is a GHG and a positive feedback. Atmospheric H2O as a liquid is an albedo enhancement and a negative feedback. Over time, they pretty much cancel. For a GCM to be an accurate model of the real world, clouds and water vapor do need to be taken into account, particularly concerning their temporal and spacial variability, but the increased H2O in the atmosphere from increased temperatures represents a negligible amount of total forcing. Atmospheric C2O is always a positive feedback.
H2O is mostly confined to the lower troposphere and is not homogeneously mixed. CO2 is well mixed and extends far into the stratosphere.
Your assumption that H2O is 4x as powerful a GHG has no real meaning for climate change. It is a buffer in the system. Pumping excess H2O into the atmosphere will not generate any excess greenhouse effect for very long as it will soon condense into clouds and precipitate back to equilibrium levels.
Removing CO2 from the atmosphere will amplify cooling. Why don’t you get this? It is simple physics.
george // November 16, 2007 at 8:04 pm
Tamino says above: “total annual solar insolation for eccentricity e (and unchanged semi-major axis a) is proportional to 1/(1-e^2)^2
Since, the eccentricity of earth’s orbit varies between about 0.05 and 0.005, that means solar insolation varies by about 0.5% between the extremes of eccentricity.
That is roughly in keeping with what is given in this presentation..
“Change in insolation due to e vary by ~0.2% about a mean value” [or about 0.4% total]
It should be noted that the 100k yr cycle does not cover both of the outer extremes of eccentricity, which is undoubtedly the source of the difference between ~0.4% and the 0.5% obtained using the outer extremes in tamino’s formula.
As you can see on the above eccentricity graph, the change in eccentricity between the (local) max and min over a single 100k yr cycle is not always the same), which means the change in insolation between max and min will also vary depending on which cycle you consider.
For example, between about 225k and 275k yrs ago, eccentricity changed from about 0.05 to about 0.02, so using Tamino’s formula, one would expect insolation to have changed by about 0.4%
But to bracket the temperature change for a single cycle, one can estimate the change in temperature between the extremes of eccentricity.
One can do this by considering a similar change in TSI. If TSI changed by 0.5%, that would be a change of about 6.8W/m^2, which would equate to a radiative forcing change of about 1.2 W/m^2 at the earth’s surface, which would cause about 0.9deg C change in temp at the earth’s surface. (assuming 1 W/m^2 change in forcing produces about 0.75C change in temp)
In other words, the change between the outer extremes of eccentricity will result in roughly a 1 deg C change in temperature at the earth’s surface.
So the 0.5% change in total insolation should result in the same amount of temperature change — about 1 deg C (WITH NO FEEDBACK)
Between the local max and min of the eccentricity for a single 100k yr cycle, the temperature change would be slightly less than this.
Hank Roberts // November 16, 2007 at 9:27 pm
This is wrong:
> nobody who champions the weak
> forcing, dominant CO2 feedback
> theory has ever apparently bothered
> to consider the onset of cooling.
I refute it thus:
http://www.google.com/search?q=plankton+cooled+a+greenhouse
Bill Bodell // November 17, 2007 at 9:24 pm
Re: What comes first? CO2 or temperature
Let me recap developing understanding of the issue and then pose a couple questions (this from a person who, until recently got most of his information from Stossel and Gore).
Gore presented a graph that seemed to imply that increases in CO2 caused a corresponding increase in temperature. If this were the case, one would naively expect the CO2 to rise first followed by increases in temperature. I am not sure if this is what Gore actually believed or if this was seen as a simplistic way of communicating to the public.
Contrarians responded that the CO2 rise actually lagged the temperature. This seemed to imply that it was actually the rise in temperature that caused the rise in CO2. This seemed eminently reasonable and from my naive perspective seemed to discredit the Gore scenario.
Now, it has been explained on this site that some initial event (solar activity, etc. in the past, CO2 increases in the present) initiates a warming process resulting in a rise in CO2 . Once the process is underway, a feedback loop begins where increases in CO2 cause temperature increases, which causes more CO2 and so on.
Now for some questions:
What causes the feedback loop to stop? It seems from what I’ve read that warming occurs quickly and cooling takes a long time. This seems to fit with the existence of a warming feedback loop. Whatever causes cooling seems like it would have to overcome the CO2 effect.
What is the nature of the feedback loop? Linear, Exponential or Logarithmic (I had to check with my 16 year old calculus student for the terms, I hope they’re correct)? If it’s exponential, it seems like there must be some natural condition that brings it to a stop or the warming would have gone out of control at some time in the past. Linear would also require an outside event to stop and logarithmic should end on its own.
Is it possible that warming is started by some other event and that that event might continue to cause warming in addition to that caused by the CO2 feedback loop? If so, do we know how much warming was caused by the CO2 feedback loop and how much by the other continuing event?
[Response: It's a misconception to think that something has to "halt" the feedback loop.
Suppose feedback causes warming of 1 deg.C to be amplified by "f" degrees C. The factor "f" is the feedback factor. Then the additional f deg.C causes, by the same feedback process, an additional f*f deg.C. The additional f*f deg.C causes a further f*f*f deg.C, etc. etc. The total warming due to the initial 1 deg.C is therefore
The infinte sum can be directly computed, and for feedback factor f <=1 is finite, given by
The factor G is the gain. Hence the feedback loops stops all by itself.
Also, ice ages (glaciation and deglaciation) are triggered by changes in earth's orbit and axial tilt. This changes the amount and geographical distribution of solar energy received by the earth, but the solar output doesn't change.]
John V // November 17, 2007 at 10:27 pm
JamesG:
Regarding CO2 amplifying warming and cooling:
We’ve been looking at the warming first, but the cooling may be better explained by looking at it first using a very simplified model of the earth.
Consider the earth a big ball covered by nothing but oceans. Its in a nice stable state, warmed 33C by the net greenhouse effect. Its orbit changes a little and the net solar radiation decreases, causing 3C cooling.
The cooled ocean can absorb CO2, so the global CO2 concentrations drop from 400ppm to 200ppm (for example). Now the greenhouse effect is reduced and the temperature drops another 3C.
In this example, CO2 absoroption by the oceans amplified the cooling.
The earth then reaches a new stable state, warmed 27C by the net greenhouse effect. Another orbital change warms the planet 3C, the ocean releases CO2, the enhanced greenhouse effect causes 3C more warming, and we’re right back where we started.
Now CO2 has amplified the original cooling and the subsequent warming.
As for what stops the feedback loop (CO2 –> temp –> CO2 –> etc), the logarithmic effect of CO2 concentrations plays a major role. As CO2 concentrations increase they become less effective as greenhouse gases. That’s why climate sensitivity is discussed in terms of “doublings”. Doubling from 300ppm to 600ppm will cause X degrees of warming. The next X degrees requires doubling from 600ppm to 1200ppm.
Alan D. McIntire // November 18, 2007 at 4:10 am
I concede I made a mistake in “averaging” the radius of a (1-e^2)/(1-cos p) and a(1-e^2)/(1+cos p). I originally tried computing the difference in luminosity at perihelion and aphelion and got [(1+e)/(1-e)]^2. I was going to average temperatures all the way around the sun, using a numerical approximation, then realized the times offset the luminosity balances. I just assumed that the “average was sort of a “harmonic” average of a /(1- cos p) and a/(1 + cos p), or a. Tamino is right about the “proportionality constant” not being a, but I think it should be 1/(1 - e^2)^0.5 rather than 2. That would more closely match the 0.02 figure given by george.
I got the above 1/(1 - e^2)^0.5 by comparing the luminosity around a small arc, dp, at perihelion, and computed the ratio of the area, {a(1-e)}^2 dp to the total are of an ellipse, pi* a^2*SQRT(1-e^2) , then took a similar fraction of earth’s orbit, compared the two average luminosities and got the above ratio.
I checked the region around a(1+e) and got the same 1/(1 - e^2)^0.5 factor. I’ll admit my math is pretty rusty after all these years, but given that my perihelion and aphelion calculations gave the same result, which matches georges 0.02 figure, I’ll bet I’m correct and Tamino’s ^2 was a typo for ^1/2.- Alan McIntire
[Response: Right you are.]
george // November 18, 2007 at 4:15 pm
The only problem with raising (1-e^2) to 0.5 rather than to 2 is that the numbers no longer match those that are given in the above source from the U of Hawaii
presentation from School of Earth Science and Technology at U of Hawaii that I linked to above.
granted, perhaps the U of Hawaii source is wrong, but they state that
“Change in insolation due to e vary by ~0.2% about a mean value”,
That means that the total change in insolation between extremes of eccentricity for a given cycle is about 0.4%.
As I indicated above, if one uses Tamino’s original formula with two sequential extrema in eccentricity (eg, between about 0.02 to about 0.05 between 275k and 225k yr ago), one gets a total insolation change of about 0.4%, which is consistent with the value given by U of Hawaii.
On the other hand if one uses the 1/2 exponent given by Alan above, namely 1/(1 - e^2)^0.5
one finds that the insolation should change by just 0.1% between the two subsequent extrema of eccentricity.
With the 0.5 exponent in the formula, even if one took the outer extreme values for the earth’s orbit — 0.05 and 0.005 — (which do not occur subsequently in the 100k yr cycle), one would still get a total change of only about 0.1%, or about 1/4th the number given by U of Hawaii.
I guess I’ll have to look into this a little more because now there is a discrepancy and I’m not sure who is right.
No offense Alan, but I’d have to see a full derivation to make that decision.
[Response: The exponent is indeed 1/2, not 2. I've done the full derivation myself, and you can find it in the literature in Laskar 1993, Astronomy and Astrophysics, 270, 522-533 (equation 13).]
dhogaza // November 18, 2007 at 5:45 pm
Why? There is not a single cause of warming. No one claims that increasing CO2 is the only way to cause the planet to warm.
I guess the word “naive” explains why (and I don’t mean this as an insult, you’ve used the word yourself and admit you don’t know much about the subject).
Contrarians are exploiting your lack of knowledge. You expect there to be a single cause of warming, which is not the case.
They show you the well-known (to ALL climate scientists) fact that when an increase in solar energy causes warming, atmospheric CO2 increases. They claim that this proves that increasing atmospheric CO2 can’t cause warming, based on the false premise that there can only be one possible cause of warming.
This is simply wrong. Contrarians are lying to you, because they count on your not taking the time to learn what science has to say, making it easy to trick you.
And of course they’re not telling you that though in the past, warming has preceeded increased atmospheric CO2, that additional CO2 has amplified the warming effect. Adding CO2 to the atmosphere always does so, whether it gets into the atmosphere due to the burning of fossil fuels or due to warming caused by another input into the system.
This makes two lies …
I suggest you visit Real Climate and start reading the introductory climate science material that can be found on that site.
Alan D. McIntire // November 18, 2007 at 6:18 pm
George, the reference you gave said “vary 0.2% about an average temperature.
Plug in e= 0.0607, and 0.005, and you get a difference of 0.18%, and allowing for rounding, that’s the 0.2% difference referred to by your site- Alan McIntire
george // November 18, 2007 at 9:36 pm
Alan, I misinterpreted the U of Hawaii statement “e vary by ~0.2% about a mean value” as +- 0.2%. Thanks for pointing out my error.
Tamino, thanks for the reference, but I don’t have access to that Laskar 1993 paper, so perhaps you might consider giving the whole derivation here as you suggested you might above?
But without that, I think I have convinced myself that the 1/(1 - e^2)^0.5 formula is at least plausible, however.
I integrated 1/r^2 (to which insolation is proportional) over the elliptical orbit using the polar orbital equation and came up with a value proportional to
1 + 0.5 e^2
which 1/(1 - e^2)^0.5 is approximately equal to for small e.
Of course, integrating 1/r^2 over the ellipse is not quite right, since the earth moves slightly faster closer to the sun so it spends less time at smaller r, but I’d guess that the approximation should be pretty close for small eccentricity.
JamesG // November 19, 2007 at 10:55 am
Hank
Yes I forgot about that article you had previously mentioned that discussed cooling. Thanks for the reminder. I did comment on it already though.
LB
“Removing CO2 from the atmosphere will amplify cooling. Why don’t you get this? It is simple physics.”
Trust me I get it! Physically, the maximum cooling would happen if we suddenly removed all those excess GHG’s which were created during the heating phase. That would however just revert us to “natural cooling”, which would still be slower than the forced heating phase. The distinction I make is the common difference in heat transfer calcs between forced and natural: The heating is forced, the cooling is natural but retarded by residual heating (from GHG’s) because the Greenhouse effect is always a heating effect.
JohnV
You have just said that that the solar (+albedo) effect could be 50%. I can agree with that though it could conceivably be 95%: We just don’t know. I also agree with your heating/cooling description but the heating is forced so the temperature climbs faster, whereas the cooling is unforced and retarded because the Greenhouse effect (from these GHG’s) causes only heating. This is the crux of the Greenhouse effect. For cooling amplification, see my comment to LB.
“As CO2 concentrations increase they become less effective as greenhouse gases.” Not true. Saturation means that they have reached the limit of their effectiveness, not that their effectiveness has reduced. Your model suffers from a basic misunderstanding of the greenhouse effect.
[Response: I'm afraid you're suffering from a basic misunderstanding of the effect of CO2. The "saturation" argument is one of the most common, but completely false. CO2 is saturated in the middle of many of its absorption bands, but not at the edges of the bands, and there are some very weak lines which only become significantly active at very high concentration. So adding more CO2 still increases absorption of infrared radiation.
Furthermore, *even if it didn't*, more CO2 would *still* warm the planet. It's due to the *lapse rate* in the atmosphere; see this post.]
JamesG // November 19, 2007 at 11:20 am
LB
From the IPCC tar:
“Water vapour feedback continues to be the most consistently important feedback accounting for the large warming predicted by general circulation models in response to a doubling of CO2. Water vapour feedback acting alone approximately doubles the warming from what it would be for fixed water vapour (Cess et al., 1990; Hall and Manabe, 1999; Schneider et al., 1999; Held and Soden, 2000). Furthermore, water vapour feedback acts to amplify other feedbacks in models, such as cloud feedback and ice albedo feedback. If cloud feedback is strongly positive, the water vapour feedback can lead to 3.5 times as much warming as would be the case if water vapour concentration were held fixed (Hall and Manabe, 1999).”
Since water vapour feedback is temperature dependent, not CO2 dependent, it should also apply to the ice age cycling too. Alternatively the GCM’s might be overly pessimistic - using your own argument that “increased H2O in the atmosphere from increased temperatures represents a negligible amount of total forcing”. You decide!
Hank Roberts // November 19, 2007 at 8:29 pm
> water vapour feedback is temperature
> dependent, not CO2 dependent
You can’t say water vapor depends on temperature not CO2. They covary.
Water vapor has a far shorter residence time.
Cloud behavior is still an area with a lot of work being done, no argument there.
luminous beauty // November 19, 2007 at 11:20 pm
JamesG,
Water vapor is an important feedback, but it does represent a negligible forcing. Increase the temperature and water vapor feedback will quickly stabilize around temperature increase + feedback. Something other than just pumping water vapor into the atmosphere is needed to increase its net effect.
In the same manner, under most natural conditions, CO2 is a feedback, not a forcing. However, due to its long residence time and its domination of upper atmosphere greenhouse effect, CO2 is a more persistent feedback than H2O, and if some external cause is pumping CO2 into the atmosphere it can become a powerful forcing.
All temperature sensitive feedbacks are co-dependent on temperature, and consequentially co-dependent on each other.
JamesG // November 20, 2007 at 2:48 pm
Now quoting realclimate.org:
“When surface temperatures change (whether from CO2 or solar forcing or volcanos etc.), you can therefore expect water vapour to adjust quickly to reflect that. To first approximation, the water vapour adjusts to maintain constant relative humidity. It’s important to point out that this is a result of the models, not a built-in assumption. Since approximately constant relative humidity implies an increase in specific humidity for an increase in air temperatures, the total amount of water vapour will increase adding to the greenhouse trapping of long-wave radiation. This is the famed ‘water vapour feedback’. A closer look reveals that for a warming (in the GISS model at least) relative humidity increases slightly in the tropics, and decreases at mid latitudes.”
If this is correct, then the GCM H2O feedback scenarios should apply to the past climate. If it isn’t correct then the GCM’s are too pessimistic. It’s one or the other I’m afraid.
Hank Roberts // November 20, 2007 at 6:41 pm
James, what are you trying to say? It seems you’re trying to argue with something, but I can’t figure out what you’re arguing against or for.
The scenarios for current conditions all include burning fossil fuels. Do you know of a past climate simulation that also includes burning large amounts of fossil fuels?
Think rate of change.
JamesG // November 21, 2007 at 11:45 am
Hank
As you ask, it’s not an argument, it’s a discussion. I just put out ideas to see how well they were challenged or supported. In the process I’ve learned some things. It’s interesting to try to understand what drives climate but if you don’t reject invalid assumptions then you derive the wrong conclusion. Scientists in all disciplines are often guilty of that, so we can’t just give anyone a free ride. All theories should withstand robust challenges and it seems to me the theory of the dominant role of CO2 in past climate change can be shown to have been way overplayed even regardless of any lag.
H2O feedback, as described by realclimate.org, clearly applies regardless of the original heating source. But you, LB and JohnV argued quite well that H2O feedback theory is not so robust when considered out of it’s AGW context. That was interesting too: You were using the scientific method to challenge it, rather than just accepting the IPCC line. In doing so, did you already know that the feedback effect in the GCM’s was about 3.5 times the effect of CO2 alone? What then are the implications on GCM’s if you three are correct? Think rate of change in the absence of that substancial, pessimistic H2O feedback! Not so dramatic is it?
Hank Roberts // November 21, 2007 at 4:50 pm
Sorry, I still can’t figure out what you’re trying to say. Things like this without a cite to a source are claims you’re asking readers to agree with, and conclusions based on them without a cite.
> the feedback effect in the GCM’s was
> about 3.5 times the effect of CO2 …
> rate of change in the absence of that
> substancial, pessimistic H2O
> feedback! Not so dramatic …
Ask yourself “sez who” when you post such statements, and give us the source you’re relying on for them.
There are online and downloadable climate models, are you using one of those? Which one?
John V // November 21, 2007 at 6:05 pm
JamesG:
I must not have been clear when trying to explain the greenhouse effect of H2O. You apparently misunderstood.
I could try to explain again, but I don’t seem to have the right words. Luckily, Gavin Schmidt over at RealClimate has covered this in great detail already:
http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/
Quoting from the intro paragraph:
“Any mainstream scientist present will trot out the standard response that water vapour is indeed an important greenhouse gas, it is included in all climate models, but it is a feedback and not a forcing.”
And further down:
“While water vapour is indeed the most important greenhouse gas, the issue that makes it a feedback (rather than a forcing) is the relatively short residence time for water in the atmosphere (around 10 days). ”
“Compared to the residence time for perturbations to CO2 (decades to centuries) or CH4 (a decade), this is a really short time. “
Hank Roberts // November 21, 2007 at 6:46 pm
Apt observation elsewhere on the sources of the ridiculous, from
http://www.boingboing.net/2007/11/17/fox-news-porn-the-pr.html#comment-83596
“… look at the difference between a thread on global warming and one on some other complex scientific subject. These guys get their talking points dished out to them by the source feed right-wing weblogs. This means that if global warming comes up, they swarm the comment thread because they know something they can say. But if an entry’s about some scientific development that isn’t covered in their spoon-fed talking points, they’re at a loss, and so that thread will instead be full of science buffs discussing the actual entry.”
JamesG // November 22, 2007 at 10:37 am
JohnV:
I previously also quoted that same realclimate.org article. I clearly understood it better than you. Read a bit further on, or read the repeated quote below. In fact, regardless of feedback, forcing or residence time the actual effect of H2O feedback can be 3.5 times that of CO2 alone according to the IPCC (see my earlier post or see the repeated quote below) and it happens regardless of the origin of the warming.
Repeated quotes for JohnV, Hank:
From the IPCC tar (that’s who sez):
“Water vapour feedback continues to be the most consistently important feedback accounting for the large warming predicted by general circulation models in response to a doubling of CO2…the water vapour feedback can lead to 3.5 times as much warming..”
and from that realclimate.org post that seems to have confused people:
“When surface temperatures change (whether from CO2 or solar forcing or volcanos etc.), you can therefore expect water vapour to adjust quickly to reflect that…the total amount of water vapour will increase adding to the greenhouse trapping of long-wave radiation. This is the famed ‘water vapour feedback’.
I gave the full cited quotes further up this thread. But I repeat, I find it amazing that you guys really didn’t know about the crucial importance of water vapour feedback as an amplifier in the GCM’s. I thought everyone knew about it - it’s the main contention.
JamesG // November 22, 2007 at 10:54 am
Epilogue
It’s actually quite funny that the assertion that H2O feedback isn’t all that important is an argument used often by Lindzen. You showed us just how easy it is to fabricate a scenario based entirely around a desired end point - something both sides are guilty of. I was wondering who’d fall in the trap.
dhogaza // November 22, 2007 at 2:24 pm
dhogaza // November 22, 2007 at 2:27 pm
Sorry, had two blockquotes rather than one open and one close blockquote.
Anyway, having read many of Hank’s and JohnV’s posts, they’re both aware of the amplification effect of H2O vapor.
Or perhaps you’re just playing word games - “. I was wondering who’d fall in the trap” - in which case, the fact that you’ve confused people only proves that setting out to intentionally confuse people often results in people being confused.
guthrie // November 22, 2007 at 2:32 pm
“All theories should withstand robust challenges and it seems to me the theory of the dominant role of CO2 in past climate change can be shown to have been way overplayed even regardless of any lag.”
On what evidence do you claim this? Who on earth is saying that CO2 is dominant in past climate change?
luminous beauty // November 22, 2007 at 2:56 pm
JamesG plays gotcha.
But no one is saying that water vapor isn’t an important feedback. Just that it cannot, at least at the current temperature range of the earth’s surface, act as a forcing.
Surely with your superior understanding you do realize the difference.
John V // November 22, 2007 at 5:31 pm
JamesG:
You’re obviously trying to make some important point, and you seem to think you’ve made it well, but I have no idea what it is.
Were you trying to say that H2O feedback amplifies warming and cooling? You’re right. Were you trying to say that H2O feedback is the same regardless of the cause of the initial perturbation? You’re right again.
But so what? H2O amplifies AGW. H2O amplifies albedo effects. H2O amplifies orbital eccentricity effects. In the end, the total warming for a given increase in CO2e is what matters in the context of AGW.
A lot of the misunderstanding in this “conversation” seems to come from the difference between feedback and forcing. Are you sure you’re clear on the difference?
Hank Roberts // November 22, 2007 at 7:18 pm
At the top of the atmosphere; CO2 is the greenhouse gas increasing, as the chlorofluorocarbons did til the Montreal Protocol limited production. Water doesn’t.
guthrie // November 22, 2007 at 10:48 pm
Hang on, off the top of my head, the point was that doubling Co2 alone gives about 1.6 degrees of warming, but its about 3 degrees once the feedbacks are included. No one is disagreeing with that are they?
Heretic // November 22, 2007 at 10:57 pm
James G, can’t help but to repeat John V’s question: do you really understand the difference between feedback and forcing? In other words, do you realize that there is no feedback without a forcing in the first place?
H2O feedback is a major reason why adding CO2 to the atmosphere is likely a problem.
JamesG // November 23, 2007 at 12:29 pm
Well I’m sorry about the confusion but if I consistently wrote about temperature dependent feedback, and other people seemed to read forcing, am I really to blame? What has actually happened is that you perceive skepticism and you all jump on the first gainsaying argument you can think of, regardless of accuracy or relevance. Start with Petit, continue with Ruddiman, perhaps look at Kevin Trenberths recent statements or perhaps visit the realclimate site archives. Hey look again at “An Inconvenient Truth” why don’t you. All say or imply that CO2 drove the climate by translating a weak forcing into a strong feedback. By physics, and by logic I was arguing that the idea is nonsense because clearly albedo and H2O feedback must have been far more dominant, regardless of any lag. I also noted such was proven by experimental data. But I repeat that downplaying the role of CO2 in the past doesn’t affect the AGW theory. Peace. I promise I’ll shut up now and stop kicking your dogma.
Petro // November 23, 2007 at 2:43 pm
JamesG,
there is no feedback, if there is no forcing.
You see, forcing preseeds feedback.
Also, humans affect forcing, not feedback.
These are the reasons, why focus is in forcing, not in feedback.
JamesG // November 23, 2007 at 3:25 pm
From JohnV above:
“H2O feedback is directly caused by temperature increases and decreases. It is not capable of causing temperature changes on its own because a surplus or deficit of H2O in the atmosphere is very quickly corrected by condensation or evaporation from the oceans.”
JohnV later:
“A lot of the misunderstanding in this “conversation” seems to come from the difference between feedback and forcing. Are you sure you’re clear on the difference?”
Cute. Seems like some folk confused themselves without any help from me. Ok now I’ll shut up.
luminous beauty // November 23, 2007 at 3:30 pm
JamesG,
All I ‘jumped on’ was your claim that water vapor, by itself, was 4x as powerful a feedback as CO2. That was your basis for saying CO2 has an insignificant role in past climate.
You support that with a quote from IPCC 2001 which actually says:
“Water vapour feedback acting alone approximately doubles the warming from what it would be for fixed water vapour.”
A statement in the context of a doubling of CO2. This suggests that CO2 and H2O are approximately equal as feedbacks.
Do you understand, now, why I am not particularly impressed with your reading skills, nor your comprehension of logic or physics.
Saying that CO2 is an important GHG and climate feedback, whether in the distant past or the immediate present, is not the same as saying it is the only GHG or feedback, or even the largest, regardless of what you might infer.
John V // November 23, 2007 at 4:31 pm
JamesG, my quotes are consistent. H2O is a feedback, not a forcing.
Let’s review the steps in the ice-age cycle in a very simple model, to figure out where we disagree:
1. Orbital cycle –> increased solar forcing
2. Increased solar forcing –> small temperature change
3. Small temperature change is amplified by H2O feedback
4. Increased temperature causes slow release of CO2 (from oceans)
5. Increased CO2 causes more warming, which is also amplified by H2O
6. Time passes
7. Orbital cycle –> decreased solar forcing
8. Decreased solar forcing –> decreased temperature
9. Small cooling is amplified by H2O feedback
10. Decreased temperature causes decrease in CO2 (to oceans)
11. Decreased CO2 causes more cooling, which is amplified by H2O feedback
With which step do you disagree?
[Response: Just a refinement -- I have recently learned that CO2 release from the oceans may not be the only, or even main, cause of CO2 increase due to temperature increase. Apparently the response of the biosphere is also important.]
Chris O'Neill // November 23, 2007 at 4:38 pm
“the dominant CO2 feedback theory”
What theory is this? The CO2 change from the peak of the last ice age to preindustrial was probably responsible (along with short term feedbacks) for less than 2 deg C of warming out of the total 5-6 deg C of warming. This short-term sensitivity can be calculated from observations as shown by Annan without making any use of GCMs.
Hank Roberts // November 23, 2007 at 5:58 pm
JamesG, search on your own name +climate +CO2 +feedback +forcing -”air force” (all but the last hit seem to be someone arguing the very same thing, in other threads here and on other climate sites). Have you found one where people agree with you on this? I haven’t, but I’m looking. It’s confusing enough that this could be a misunderstanding about terms or based on some source I haven’t found.
Hank Roberts // November 23, 2007 at 8:46 pm
> the response of the biosphere
Thanks for picking up on this, Tamino, and I hope to see more as you dig into it. Species changes (plankton) are only beginning to be considered in models, as far as I know. Scholar searches for “le quere” find a lot of that recent work in papers or cites.
Steve Bloom // November 23, 2007 at 8:57 pm
Poorly chosen terms can indeed lead to confusion. Consider e.g. “dominant” as between CO2 and H2O. Is H2O dominant if it results in more warming than CO2? No, because H2O is not persistent in the atmosphere.
Jamesg // November 24, 2007 at 11:11 pm
JohnV
It seems we agree. For the record I didn’t argue that water vapour is a forcing. I only quoted LB using the word forcing, but as it seems to be a common word switch (ie Hansen does it too) I didn’t think it important enough to argue about.
LB
Naughty. Your superior reading skills are not up to reading all the way to the end of a paragraph are they? The relevant quote was “the water vapour feedback can lead to 3.5 times as much warming.” I had remembered it as 4 to 1 - slight memory fault but not so drastic.
SteveB
“H2O is not persistent in the atmosphere”. Maybe you want to rephrase that too.
Hank
If you mean I’ve not yet seen a compelling argument from anyone then you are right. People tend to parrot other peoples dodgy arguments rather than actually think for themselves. However, happily the data supports me and says everyone else was indeed wrong, so that’s nice. I didn’t believe the vast majority of expert economists either when they said that there would be no housing slump and the debt burden and deficits don’t matter. Perhaps your trawl through the archives revealed I’m a Gore supporter, environmentalist, active in renewable energies and expert in FEA computer programming. I also think most GCM’s are utter rubbish and only a carbon/water cycle model is sensible as it would reduce the number of independent variables and halt the incessant fudge factoring which can produce any result at all - even massive cooling - within their huge error bands.
Hank Roberts // November 25, 2007 at 1:30 am
Nope, I found nothing but what I pointed to with that one search.
I’ll rely on RC til you publish.
Maybe you can, do give it a try.
http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/
John V // November 25, 2007 at 1:50 am
Tamino:
Thanks for the clarification re the biosphere and CO2. I should have explicitly defined my “very simple model” as a lifeless, ocean-covered, Earth. (That’s what I was using for my previous CA posts and got lazy in defining it here).
JamesG:
I’m glad we agree. I guess we can stop arguing past each other. I’m still not sure what you’re right about (and presumably I and the others are wrong about), but let’s just let it slide and move on.
If I may speak for Steve Bloom, I think he meant “a surplus or deficit of H2O is not persistent in the atmosphere”. That should have been clear from the context of this conversation.
luminous beauty // November 25, 2007 at 2:53 am
JamesG,
The relevant quote was ‘the water vapour feedback can lead to 3.5 times as much warming.’”
Bullcrap! With context:
“Furthermore, water vapour feedback acts to amplify other feedbacks in models, such as cloud feedback and ice albedo feedback. If cloud feedback is strongly positive, the water vapour feedback can lead to 3.5 times as much warming as would be the case if water vapour concentration were held fixed (Hall and Manabe, 1999).”
Big if. And what is not stated but inferred (it is in the context of doubling CO2, after all) is that CO2 also acts to amplify other feedbacks, including water vapor. That gives CO2 + H2O, together with other feedbacks producing 3.5x what would be produced by either CO2 or H2O acting alone.
Read further down the page and you’ll find this:
“It has been estimated that, without changes in the relative area of convective and dry regions, a shift of water vapour to lower levels in the dry regions could, at the extreme, lead to a halving of the currently estimated water vapour feedback, but could not actually cause it to become a negative, stabilising feedback.”
By using such selective quote-mining you not only are being intellectually dishonest but deluding yourself.
H2O is not persistent in the atmosphere. It precipitates out within weeks, often within a single day. This is in contrast with CO2, which is well mixed high into the stratosphere, where very few molecules of H20 ever go, and has a residence time of days to centuries, perhaps millenia.
If one simplifies a complex system by removing most of the dependent (not independent) variables, one has a model that does not accurately represent the real world and totally useless. The only independent variables are those that determine temporal and spacial relations. Without those one has no real world to describe.
JamesG // November 26, 2007 at 2:25 pm
LB
I actually quoted that full text further up this thread so I wasn’t quote-mining at all. When you use the lower estimate for water vapour feedback you get the lower estimate for future temperatures ie 1.1 degrees C, so it is relevant to discuss the higher values.
The real world radiative model has really only one independent variable - the sun (ignoring seismic events and asteroid strikes). Everything else is dependent on it. All input parameters in GCM’s are independent variables by definition - because they are inputs. Only if they were calculated in the software would they be dependent.
JohnV
I stated about 4 or 5 times the point I was making in absolutely the plainest terms, and it was just a discussion so nobody was right or wrong. As for the persistence of a surplus or deficit of H2O. So what! It’s inevitable, someone mentions water vapour and the irrelevant riposte is “residence time”. But if the model properly calculated the radiative effect of all greenhouse gases then it would be the quantity present at each timestep that was more important, not how fast or slow it got there. So residence time seems to be a red herring just like the “forcing versus feedback argument” when nobody has ever actually called H2O a forcing (forcing itself being a GCM artificiality having little to do with the real world). Also, if a surplus or deficit of H2O is never present then there is no such thing as H2O feedback so you lead yourself up a blind alley without even realising it.
John V // November 26, 2007 at 6:12 pm
JamesG:
A surplus or deficit of atmospheric H2O (water vapour) is temperature dependent. The equilibrium level of water vapour increases with temperature. Therefore, warmer temperatures lead to more water vapour which leads to even warmer temperatures. That’s feedback.
Conversely, surplus water vapour can not start the warming because it condenses and precipitates too quickly. If the amount of water vapour magically increased, it would not force temperatures noticably higher. That’s why it’s not a forcing.
However, if the amount of atmospheric CO2 magically (or otherwise) increases it will force temperatures noticably higher because it remains in the atmosphere long enough to do so.
I still think you’re unclear on the difference between feedback and forcing. Especially when you call forcing vs feedback a red herring. Your statement that no surplus or deficit of H2O implies no H2O feedback is further evidence of your confusion. The lack of a surplus or deficit is the argument against forcing, not the argument against feedback.
dhogaza // November 26, 2007 at 6:26 pm
Uh, how do you think they calculate the quantity present at each timestep? By ignoring residence times? Not likely …
Hank Roberts // November 26, 2007 at 7:14 pm
> not how fast or slow it got there
Still wrong.
Residence time is how long it _stays_ in the atmosphere, not how fast or slow it gets there.
Marion Delgado // December 1, 2007 at 3:01 am
tamino:
Where the editor saw the error he did explain it decently. FWIW. And I admit it - when it comes to this stuff, I am no longer a nice person. It actually pleases me if the denialists want to make obvious math errors and propagate them to the sympathetic press (a perusal of the LTEs to that paper gives me the impression it’s in a deeply conservative and not very science friendly county). We’ve beaten the hell out of them on the science, repeatedly, but what they’ve maintained is the respectability to be “one side” of a “balancing” discussion. So every time we can get them to overcommit to something “ridiculous” that’s one fewer sources of distortion to worry about. It does also mean eventually you will select out the worst idiots, but that’s fine, because then you argue with the best/most moderate, and they don’t have the weird political advantage of the absolutely ridiculous existing “to the right” of their position. Maybe the Dover thing would have gone differently if it were creationism that was quasi-legal in the schools and they were only pushing the “ID” line.
[Response: Those who have studied the science objectively are already convinced, and actual denialists will not be persuaded by anything. It's the "unwashed masses" I'm mostly concerned with. They are easy prey for denialist propaganda, usually not very savvy about the science of things, and if you adhere to a strict standard of accuracy they sometimes feel overwhelmed by complications; climate science is not really a simple matter. That's why I think it's generally better to be more civil and cool-headed (although I myself have my bouts of hot-headedness). The uncertain observers see angry argument as unflattering to both sides. It's really not important to put denialists "in their place" -- it's important to show the common person the truth of things.
They're listening.]
Marion Delgado // December 3, 2007 at 9:41 am
Fair enough. I still say the editor did do a good job explaining his error, just too far down in comments.
Actually, that was a chance to do some VERY interesting science story stuff - raise the same issue - a difference of x degrees C, here’s the formula for C to F - so what’s the answer. And most of the readers say blahblahblah. But no! And then it’s like the Monty Hall “paradox” - the writer says, covert the two temperatures to F and what’s the difference? And then explains that that’s a good example of how tricky it can be to discuss even something as simple as what is the temperature (Remember about a year or two of debate on blogs about that, actually?) or in this case a temperature change.
I did a lot of science stories and this would be interesting to lay readers.
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