This thread is sufficiently rancorous without silly and insulting interjections of partisan fluff.
Take this sort of thing to the Pit.
[ /Moderating ]
tomndebb, thanks for the mid-course corrections.
OK, so the terrestrial sequestration rate has been falling in the US since 1960, but the overall sequestration rate is not affected because non-terrestrial sequestration, and terrestrial sequestration elsewhere, has increased since 1960? Am I reading that correctly?
If so, surely it is not just CO2 concentration which limits sequestration rate either? For terrestrial mechanisms, is there not also a limit set by the nutrients in the soil, such that above a certain CO2 concentration, the plant simply cannot grow or metabolise any faster and sequester ever more CO2? And for non-terrestrial ocean systems, does increased CO2 dissolved in the water not make the shells of sea creatures like formanifera thinner, such that an increase in CO2 concentration does not yield a proportional increase in sequestration rate?
(By the way, I’m very impressed that you know the authors of these studies personally – I feel I am indeed getting the Straight Dope.)
Careful – I made the mistake of talking about amounts when I should have been talking about rates or annual amounts and I’d just like to check you’re not doing the same. The annual amount sequestered will equal the annual amount emitted when the atmospheric CO2 level is high enough that the sequestration rate equals the emission rate. The total amount sequestered will equal the total amount emitted *many years after the sequestration rate has overtaken the emission rate *. Am I right?
Thanks, those are very helpful numbers which I might well make use of with friend Blake (is there a sufficiently respectable citation that might convince him the numbers are correct?). However, all of it still depends on the sequestration rate increasing in proportion to the CO2 concentration, does it not? How much greater do you calculate the sequestration rate to be (ie. what slope does the orange line in your graph have) in order for this to occur?
Again, just help me out here – apologies for being a little slow. This still assumes that the sequestration rate will still be increasing even in 50 years time, (ie. the orange line will continue to curve upwards for 50 years) yes?
OK. intention seems to have some pretty solid evidence that the current sequestration rate is easily enough to decrease atmospheric CO2 concentrations by 60 ppmv within a century. This current sequestration rate is split into terrestrial and non-terrestrial portions which look eminently feasible in terms of measuring how much carbon, say, a square kilometre of trees or a cubic kilometre of plankton sequester and scaling up (the Nature report cited 2.2 Gt per year into oceans and 2.6 Gt per year into forests). What precisely is your problem with this evidence, exactly?
Well, yes, since it seemed like you considered them both as likely. Like I said – it’s Ockham’s Razor: start with the mechanisms you know about, and ask whether further entities are necessary. You seem to be suggesting they are, but I’m not sure why.
And I’ve since accepted that current sequestration rates could largely be maintained despite deforestation, so long as ocean-based sequestration keeps up. I don’t accept that natural sequestration rates will increase massively in future, as they would have to to prevent peak CO2 concentrations of 500-800 ppmv, given the 8 GtC we are demonstrably adding each year.
Yep.
Look at his reply above: “would” is perfectly accurate.
I never claimed that. I claimed that there are fewer trees than there used to be before humans came along. By the way, do you question whether humans are largely responsible for this 40% loss in 11,000 years as well?
But if we’re fitting an anthropogenic curve to that graph, one need not have its tail coincide precisely with the 1600 data points. I’m not arguing that natural factors cannot affect CO2 concentration, and would accept that the fall from 1500 and the rise from 1600 to 1700 is largely natural (though medieval European and Chinese deforestation might have some influence). But I cannot see how such a gentle exponent is evidence that the very steep exponent after 1800 must be natural. Like I said, you might be correct that a small natural increase would have occurred since 1600 without human activities. But the huge observed increase is easily explained by the 500 Gigatons of CO2 demonstrably added by human activities.
When you hear hoofbeats, think horses, not zebras – especially when a horse is standing directly in front of your very eyes, stamping its feet.
Well, the idea I have is all of it, since we can see the coal being loaded into the power stations and burned.
That when you fit a curve to the Law Dome data, the error bars on the later data points are smaller. This means that there is more latitude in the way you fit the curve to the earlier data points since they have larger error bars. I’m not sure why you’re extrapolating from this that I consider pre-1960 data unreliable.
No, I claim that you said it was so. Look through the thread: in numerous places you yourself state that temperature rises preceded CO2 rises in past events. I really don’t know why you’re asking me to provide suppt for a position that you yourself share.
Not rapidly enough to prevent a large peak, no, because the carbon we’re adding is over and above any natural souces.
They won’t work fast enough to prevent a large peak. In my correspondence with intention, I’ve agreed several times that after[ this peak, natural sequestration mechanisms like trees, soils, plankton and so forth will bring down the CO2 concentration quicker than I thought. That still makes the next couple of centuries very uncomfortable for many in high CO2 concentrations have negative impacts.
Actually, yes it would. Do you have any evidence for them?
Wanting negative impacts on humanity does not evidence a dislike for humanity. Gotcha – thanks for straightening that out.
But we do know the mechanism by which 500 Gt are added: burning hydrocarbons and clearing forests.
But “a few centuries” is not rapid on a human timescale. That high CO2 concentrations won’t remain the case on a geological timescale is little comfort for those being born as we speak if those high concentrations, which are demonstrably anthropogenic in origin, end up having negative impacts on their lives.
Well, I do. You seem to be complaining that a stamping horse is obscuring your view of the magic zebras.
But if the 500 Gt is accurate, we can then ask what effect this would have on concentration, yes?
Well, I asked you a question, and it’s a perfectly reasonable one. You seem to think that human activity in the past few centuries could have prevented a natural CO2 rise being even bigger. I’m asking you how that’s even possible given the CO2 we are demonstrably adding.
So burning 1 Gt of lignite emits 2.8 Gt of CO2, agreed?
Well, I wouldn’t say my OP spelt doom exactly, just a few hundred million refugees here and there. Of course, I hope I’m wrong, but you’re not setting my mind at rest much.
Ah, net sink, no. intention said “Google ‘missing carbon sink’. I did, and found a claim that it was no longer missing. That it is not a net sink reinforces my point that natural sequestration mechanisms cannot cope with the sheer quantities of CO2 we are demonstrably emitting.
But, you see, here we are discussing the mechanism. I don’t see how you can discuss the mechanism while maintaining that we can’t.
How can 500 Gt of carbon be irrelevant? I could understand if you thought this was a gross overestimate, or if you thought that the volume of the atmosphere has been underestimated such that 500 Gt barely affects its composition. But this is like me taking you into a room, taking a CO2 measurement, burning a piece of coal, taking another CO2 measurement, and then you telling me that the act of burning the piece of coal was a red herring in figuring out why the second measurement was higher than the first.
OK, I’ll phrase it thus: How could adding 500 Gt of CO2 not increase CO2 concentration? What other realistic possibility is there?
Well, I’m not giving up on you, Blake – I value your contributions here. I hope this post, and intention’s posts directed at you, are enough to keep you engaged.
SentientMeat, I’ll say it one last time:
If you have anything to add in terms of facts or a coherent argument or facts then lay it out clearly in your next post. Trying to snip quote my posts is clearly leaving you confused and struggling to follow your own argument, much less mine.
To give a blatant example of this:
Compare with:
You quite clearly stated that there are not as many forests today as during rapid CO2 sequestration events. And we established very early on and in numerous later posts that such previous events included the last glacial maximum. I even challenged you to provide a reference that forest cover has declined since the last glacial maximum and you responded.
For you to now state baldly that you never claimed that global forest cover was higher at the time of the last glacial maximum is extraordinary. You quite clearly did state precisely that, and attempted to provide references to support same.
Your last post includes numerous similar provable examples that you have lost track of your own argument, including your continuing strawman claim that I stated that the current lag between CO2 rises and temperature are different to those in the past, a statement which I clearly never made. All the while you to fail to provide the requested evidence that the current lag is different, as you claimed.
Were you almost any other poster I would at this stage declare you to be deliberately dishonest and walk away. However I know you are not like that. So instead I will instead assume that your snip and quote posting style has resulted in you losing track of your own argument. That almost every factual assertion made in the OP has since been proven to be incorrect has presumably not helped the issue.
You have so badly lost track of the argument we have been engaging to date that there is no longer any coherence to your posts. You are arguing positions completely different to those you originally started with and have failed to inform me of this. (eg “I’ve since accepted that current sequestration rates could largely be maintained despite deforestation.” Well you never conceded that to me.)
So to avoid this I ask you to simply state your current argument in coherent form, along with any factual support for the same. If you still claim that the current lag between CO2 and temperature is different to past events then present the evidence. Don’t claim that I made such a claim unless you can quote where I said it was different. If you still claim that forest cover is less now than at the last glacial maximum then provide the evidence. And so on and so forth.
If you fail to present any previous claims in the post I will assume that you have conceded that point.
However I have no intention of continuing to point out where you have made claims that you now deny having made.
No, unfortunately you’re reading it backwards. The paper lists net carbon emissions, and then only from changes in land use/land cover. The US emissions from LU/LC went down below zero in ~ 1960, indicating that it became a net carbon sink. Curiously, this is because of the increasing efficiency of agriculture. As less and less land produced more and more food, marginal lands were left fallow. Many of these have returned to forest, increasing carbon sequestration.
However, there is a huge caveat on this number. It is an estimate from LULC changes only. It does not include other factors such as increased CO2 use by plants when the CO2 levels are higher.
Again, the answer to your questions in specific is … we don’t know. All that we have numbers on is the net atmospheric concentration and the net sequestration, not numbers for any given mechanism.
However, the fact that the e-folding time has not changed despite a large growth in atmospheric CO2 indicates that there has been no reduction to date in the ability of the earth to sequester carbon.
It is often naively assumed that an increased in dissolved carbon in the ocean will automatically make calcium using organisms (e.g. diatoms, coral reefs) grow more slowly. However, these are not ruled by simple chemistry, as they are living creatures.
I met Joey Hackler when he was a Peace Corps Volunteer in the Solomon Islands … one of the few researchers I know personally. However, I correspond with a number of the researchers online.
Yes.
It’s not a question of the sequestration rate increasing, that appears to be constant. It’s a question of the emission rate decreasing. And until the emission rate stops increasing, the atmospheric levels will continue to increase.
Hope this helps, ask more questions if you have them.
w.
Blake, that’s the only part of my previous post that you feel like engaging me on here? Sheesh, so be it.
This specification of the last Ice Age as the single event in the past that we’re comparing the current situation to is something of a shift in the goalposts, so apologies for not reading you posts carefully enough to spot this earlier. I thought we were comparing past events in general, when a greater forest cover than we currently see seemed a pretty unobjectionable claim. If that’s still an incorrect claim, I’m willing to stand corrected. If there are more trees now than the specific event you’re referring to, I also stand corrected in that specific instance, and would therefore seek to explain the rapid sequestration in that specific event by reference to ocean effects or tropical forests instead.
But my argument here, as it has been from the OP onwards, is not that natural sequestration wouldn’t eventually bring high CO2 concentrations down. I’ve admitted to intention (if not explicitly to you – sorry, it’s tricky to remember what one said to whom when one’s debating two people) that known, natural sequestration mechanisms would do this faster than I thought, and fast enough to bring down past CO2 maxima within a century or two. My argument is that natural sequestration is not fast enough to prevent a high CO2 concentration this time, resulting from humans demonstrably emitting enough CO2 to raise CO2 concentration.
If you remember, there were three ways in which my concerns could be allayed. I wished to be convinced that: [ul]the CO2 concentration is rising almost entirely naturally, or
[li]some natural carbon-sequestering mechanism will kick in cause a level off of 500 ppmv or less, or [*]500+ ppmv concentrations won’t have significant consequences any old how. [/ul][/li]
The second point is what I’ve been discussing with intention, and as you can see it seems we’re coming to a consensus that unless the emission rate stays constant while the sequestration rate increases pretty dramatically (both of which are pretty questionable assumptions, though that is not to say that either is impossible), that is highly unlikely. The third point has not been discussed much, and I’m happy to accept climate sensitivity to large increases in IR-absorbing gases as being so uncertain that negative impacts on humanity might not be forthcoming – it is, if you like, my best hope for the future despite it not allaying my concerns completely.
But my main argument with you is the first point:
I am seeking to engage you on this point, but all I’m encountering is a form of the Monty Python Argument Sketch. Let me try again.
We seek to explain the shape of the CO2 graph over the last few centuries. Yes, there have been dramatic natural rises in CO2 concentration in the more distant past. If a climate scientist proposed an explanation like “well, we think that increased solar warming caused the CO2 concentration to rise a bit, and the IR-absorbing properties of this extra CO2 amplified the temperature rise, and this feedback loop continued until the CO2 concentration peaked, after which natural sequestration mechanisms dragged CO2 concentrations back down again within a few centuries” I would have no problem broadly accepting it, while also accepting that there are important details which are understood very little.
But in seeking to explain the current rise, there is an elephant-sized fact sitting right in front of us. Thoughout all those past events, huge stores of carbon were sitting undisturbed, underground. Humans have dug up vast amounts of these stores and burned them, as well as clearing forests, making cement, and all the other things we do which demonstrably release Gigatons of CO2 every year.
Ockham’s Razor is a useful guiding principle in science: when seeking an explanation, don’t introduce extra explanatory entities unless they are necessary. I wish to debate with you whether or not any explanation beyond these demonstrable human emissions is necessary. Ockham’s Razor can be restated thus: When you hear hoofbeats, think horses, not zebras – especially when a horse is standing directly in front of your very eyes, stamping its feet.
In order to debate this, we need to agree on roughly how much CO2 has been emitted by human activity: X Gigatons, let’s say. If we find that this figure is not enough to significantly affect CO2 concentrations, then we can propose further explanatory entities. But you keep saying that this number is irrelevant, a red herring. I could understand if you thought that the X Gt amount I propose is a gross overestimate, or if you thought that the volume of the atmosphere has been underestimated such that X Gt barely affects its composition. But to say that X is irrelevant is like me taking you into a room, taking a CO2 measurement, burning a piece of coal, taking another CO2 measurement, and then you telling me that the act of burning the piece of coal was a red herring in figuring out why the second measurement was higher than the first.
I contend that the amount of CO2 humans have demonstrably emitted, and demonstrably continue to emit is vast enough to explain the current CO2 concentration. I contend that a vast 500 Gigatons is not a gross overestimate for “X”, and that this amount is increasing by 8 Gt per year is a fact which can be demonstrated by adding up all the hydrocarbons we burn each year, forest we clear each year, cement we make each year and so on. If you disagree with these numbers, we can discuss them in more detail. intention also has access to respectable data in this regard, so if you don’t like something I set forth we might ask him to provide something you find more convincing (since he certainly is not an “AGW patsy”).
Thanks for your continued contribution here.
So the claim on page (iii) that “the terrestrial sequestration rate has been falling in the US since 1960” is not justified, in your opinion, because the increased CO2 concentration means that sequestration has increased enough to more than counteract the drop attributable to land use change?
Actually, I was thinking less of “will” and more of “has already” if the measurements in this second report are accurate.
OK, this is where I have genuine trouble understanding you. The bolded sentence suggests that you believe the sequestration rate to be constant, and I accept that, to date, “there has been no reduction to date in the ability of the earth to sequester carbon.”
But what I’m saying time and time again here is that even if the emission rate remains constant (and yes, yes, yes it might well increase, but let’s leave that aside for now), then if the sequestration rate remains constant, too, then the atmospheric CO2 concentration will continue to increase. I simply do not see how this can possibly fail to occur: if we add 1 litre to a vessel per second, and 500 ml per second leaks out, the vessel fills by 500 ml per second. The leakage rate must double, not just stay constant, to prevent the vessel filling up.
On your graph, the current emission rate is higher than the current sequestration rate: the blue line is steeper than the orange line. In order for atmospheric CO2 to stop increasing, the sequestration rate must increase, not merely remain constant, until it equals the emission rate. Apologies for badgering you, but if we could explicitly talk about the gradients of your graph lines, that will be the easiest way fo me to understand your apparent contention that the CO2 concentration will peak around 500 ppmv even if both rates remain constant. (If that isn’t your contention, an explicit disavowal of it would also be very helpful.)
Many thanks intention. And yes, you’ve correctly identified the key issue I’m discussing with Blake, and any further help on that score would be welcome - why do you believe that humans are responsible for the current CO2 concentration?
SentientMeat, as always, your collegial tone is greatly appreciated. Onwards to the questions.
In general, we don’t know the answer to that question. We have estimates of the carbon either sequestered or emitted through land use change, but they are just that — estimates. They depend (as does so much of climate science) on imperfect understanding of the processes involved. How much CO2 is released in the conversion of forest to brushland, for example? We can only make rough estimates. So we look at how much forest is cleared … but much of that doesn’t turn into carbon unless the entire forest is burnt. Some fraction of the wood is used for building, so the carbon stays locked up. How much of the wood cut in say 1922 to clear a forest was used to make railroad ties, and how much was burnt, and how much rotted? … Hard to tell, so we make educated guesses. However, there is a lot left out. Here’s what Houghton says about the study (emphasis mine):
This points to the larger problem, which is that we have much less information about the other sinks. Yes, I know that you found people claiming on the intarweb that they’ve found the missing carbon sink … and others who claim that they’ve found the Loch Ness Monster. I would encourage you to read the studies. Perhaps they have, and perhaps they haven’t.
The “missing sink”, however, if found, would only roughly balance the books for the carbon cycle. It would not indicate, for example, how much more limestone is formed when CO2 goes from e.g 280 to 380 ppmv, or how much extra plant life will arise from the same change.
Here’s another example. The ocean is a huge source and sink, absorbing an estimated 92GtC and emitting an estimated 90 GtC per year. We estimate that the ocean is a net sink for ~ 2GtC annually. But the error bars on that are huge, because there is absolutely no way to measure the total CO2 either emitted or absorbed by the ocean. So it might be absorbing 6 GtC, or emitting 2 GtC … we don’t know.
So I fear that the only real hard evidence is our measurements of anthropogenic CO2 emissions, and the atmospheric levels. By comparing the two we can get a good idea of total sequestration … but that doesn’t tell us where or how it is being sequestered.
I see the problem, which is (as is often the case) the lack of clarity in my writing. Let me attempt to distinguish clearly between the e-folding time, and how much is sequestered.
When I have said that the sequestration rate is constant, I have meant that there is no observable change in the e-folding time. If the e-folding time is constant at say 38 years, each year about 2.5% of the atmospheric excess CO2 is sequestered.
Now, as you can imagine, the amount of CO2 sequestered is not constant even though the e-folding time is unchanged. The amount sequestered is 2.5% of the excess CO2 (the amount above the historical equilibrium level of ~ 280 ppmv). As the excess CO2 amount changes, so does the amount sequestered, despite the fact that the sequestration rate (2.5% of excess/annum) is unchanged.
Sorry for my lack of clarity on this question.
I think that humans are responsible for the recent (last couple hundred years) increase in CO2 because:
-
The curve of calculated human emissions and the curve of increasing atmospheric CO2 are highly correlated.
-
The ratio of atmospheric C12/C13 has changed in the direction that we would predict from the burning of fossil fuels.
-
Atmospheric CO2 is known to increase with increasing temperature. This is because CO2 is less soluble in warmer water. However, if the ice core data is correct, the recent temperature change (about 0.6°C in the 20th century) is an order of magnitude too small to explain the recent CO2 rise.
I hope this clarifies my position, but as always, if there are more questions I’m happy to answer them.
So the University of Illinois is full of it then?
http://www.ens-newswire.com/ens/jan2009/2009-01-20-02.asp
And I have seen you refer to those who accept the general scientific consensus as “warmers” so your offense at “deniers” rings very hollow.
Captain, thanks for raising interesting issues.
This was an poorly designed survey. I would rank the rate of agreement like this:
-
The earth has been warming since about 1650. There is wide agreement on this.
-
Humans are responsible for some part of the warming. Again, wide agreement.
However, that’s where the wide agreement ends. When we get to how much of the warming humans are responsible for, opinions start to diverge radically.
And when we get to what the mechanisms are, there is even less agreement. Some scientists say that half or more of the Arctic warming is due to black carbon. Others say no, it’s mostly CO2. Others say it is mostly natural swings, with only small human contribution. Is that a consensus?
So I fear that the citation you give does not clarify the question much. It is full of waffle words. The questions were:
90% agreed with the first question, as I said, wide agreement.
82% agreed with the second question … but what is “a significant factor”? Does that mean humans are responsible for 25% of the warming since 1800? 50% of the post 1800 warming? 75% of the post 1800 warming?
Most scientists that I read say the warming up until about 1975 was mostly from natural causes, with the post 1975 warming ascribed to partly or mostly human causes. So the total amount of “post 1800” warming caused by humans can’t be much, only the latest bit … but 82% of them called it “significant”.
So what does “significant” mean to them in this context?
I also note that only 2/3 of meteorologists believe that there is human involvement.
As to whether people doing active research in the climate field believe in AGW, that’s no surprise, they would have a very hard time getting funding if they didn’t. It’s the called the “Willie Sutton Effect”. Willie Sutton was a bank robber. When a reporter asked him why he robbed banks, he famously replied “Because that’s where the money is” …
So no, I don’t think the University is “full of it” … I think they have asked poorly designed questions, and misunderstood the answers.
Finally, science is not decided by consensus. Albert Einstein famously remarked, “No amount of experimentation can ever prove me right; a single experiment can prove me wrong.” Or as Abraham Lincoln said ““If the end brings me out all right, what is said against me won’t amount to anything. If the end brings me out wrong, then ten angels swearing I was right would make no difference.”
I would recommend Michael Crichton’s speech on the subject entitled “Aliens Cause Global Warming”.
“Deniers” is an attempt to connect scepticism about AGW with Holocaust denial. Perhaps you could explain the pejorative connotation of “warmers”?
In any case, although I’ve used the term in the past, I do not do so now. I say “AGW supporters”.
Why did I change terms?
Well, you called me on it back in August 2007, saying:
to which I courteously replied
So I’m not clear why you are bringing it up again. I thought we settled that two years ago.
Sorry, misquoted your user name as “Lance Armstrong”, my bad …
intention,
Good to see you here as always. I’ve taken a long break from this thread…and don’t want to get too involved, but thought that I should address a few points that you have brought up.
First, it is important to note that your modeling of the decay of excess CO2 released as a simple exponential process is not the accepted scientific understanding of what is physically going on. For a view into the scientific literature, see this RealClimate thread or, better yet, read David Archer’s book “The Long Thaw”. His basic picture is summarized as:
I believe there are several problems with such a simple analysis:
(1) The 10°C temperature change is accurate for the polar regions but the estimates of global temperature change are about half of this, say about 5-6°C.
(2) As you know, the dependence on CO2 concentrations is expected to be approximately logarithmic, so each additional 100 ppmv change will have somewhat less effect than the last. And, of course, the most natural way to discuss things is in terms of fractional changes in CO2 levels (since a logarithmic function like y = A log(x) + B has the property that a given fractional change in x leads to the same absolute change y, independent of the initial value of x).
(3) In fact, it is generally understood from estimates of relative forcings that only about 1/3 of the global temperature change between the last glacial maximum and now should be attributed to CO2. The rest is attributed to changes in the albedo (due to the ice sheets and vegetation changes), changes in aerosol loading, and changes in the concentration of other greenhouse gas like methane. [The changes in orbital forcings…i.e., the Milankovitch oscillations…are understood to be the initiator of the glacial - interglacial cycles although the direct change that they produce in the GLOBAL forcing is very small. Their role is instead to change the distribution of the solar forcing (both in location and time of year) so that they cause the growth or decay of the ice sheets, which then leads to the albedo forcing changes.]
jshore, good to see you as well. Using your numbers does not change my point, which is that the 20th century change of temperature is not enough to cause the change in CO2 levels seen during the 20th century. Thus, it is probable that the change is from fossil fuel burning.
Regarding exponential decay, what is usually used is the “Bern Model”. This model posits three different decay times which operate on different fractions of the airborne CO2. The three decay times are 171, 18, and 2.6 years. I do not agree with this model, and I use (as I cited above) the simpler model of Jacobson.
Since you are here, perhaps you could explain how the Bern model is supposed to work. The claim is that the three different decay times operate on separate parts of the airborne CO2 … but I know of no physical process which can operate that way. Your explanation of that would be greatly appreciated.
Well, I certainly agree with you on that. But, what I thought you were also implying in the sentence that I quoted (although it wasn’t completely clear) was that the sensitivity to CO2 determined from the glacial - interglacial cycles was much larger than what has been observed so far in the past century (i.e., when you said that a change of 100ppmv of CO2 was associated with a 10 C increase in temperature). So, I was explaining the various ways in which this estimate that each 10ppmv would lead to a 1 C temperature increase is erroneous. The real estimate, as worked out by Hansen and others, is that a doubling of CO2 (which, from pre-industrial values would be an increase of ~280 ppmv) should lead to about a 3 C temperature increase. [Although, Hansen has pointed out that this “Charney sensitivity” estimate considers any ice sheet albedo changes to be a forcing and not a feedback. And, from the glacial - interglacial cycles, he estimates that the feedback on the timescale that the ice sheets can disintegrate (which he believes might be quite a bit more rapid than current ice sheet modeling generally indicates) would be about 6 C per doubling. It seems that others like James Annan and William Connolley are skeptical that there is enough ice to melt in our current interglacial state to increase the climate sensitivity by that much above the 3 C “Charney sensitivity” estimate.]
I am not sure about the details of the Bern Model which may just be a fit to the results obtained from a more mechanistic modeling of the carbon cycle. However, as David Archer explains in Chapter 8 of his book, the carbon cycle is quite complicated because of the buffering reactions that occur in seawater. These buffering reactions allow the water to absorb a lot more CO2 initially than one would otherwise expect, but eventually the buffering saturates (due to the acidification of the ocean which reduces the availability of the carbonate ion that reacts with the CO2 and water in the buffering reaction to produce bicarbonate ions) and this leads to 20-40% of the released CO2 not being absorbed by the oceans. Hence, this CO2 has to wait until calcium carbonate dissolved from the land neutralizes the increased acidity in the oceans (or, to put it equivalently, increases the availability of the carbonate ion) thus allowing further absorption of CO2 or until the CO2 reacts with igneous rocks on land.
jshore, thanks for the reply. You say:
The numbers still come out too high, although not as much, when we use your numbers. If we divide the figures I used by six, per your estimate (1/3 of the rise due to CO2, temperature change of 5°C instead of 10°C), we get a sensitivity of 2.3°C/doubling.
In 1990, the CO2 levels were about 290 ppmv. They are now about 385 ppmv. During that time the earth has warmed about 0.6°C. Somewhere around a quarter to a half of that rise is generally ascribed to factors other than CO2. Let’s call the “CO2 caused” rise 0.3°C. That gives a sensitivity of 0.8°C/doubling. Even if we use the full 0.6°C observed, making the illogical assumption that 100% of it was from CO2, that’s still only a sensitivity of 1.6°C/doubling, about half of your 3°C and also below the numbers from the Vostok ice data.
You’re still in a cleft stick with this one, however. If we take your numbers for the ice age, it implies that a temperature change of 0.6°C would lead to an increase of some 60 ppmv since 1900… which only leaves 30 ppmv which can be ascribed to human emissions …
My problem with the Bern model is that it assumes something that I don’t understand. This is the idea that a quarter of the CO2 is subject to 171 year e-folding time, 28% is subject to an 18 year e-folding time, and so on. I don’t understand how this works in a physical sense, since all CO2 molecules are identical.
As you say, this may just be a convenient fit to a more complex model. However, given the fact that this fit does not represent any known physical principles, we are left depending once again on a complex, untested model which has not been subjected to V&V and SQA … and yes, before you say it, I know that most scientific models are not subjected to that kind of testing. But most scientific models are not used as the basis for multi-billion dollar decisions, either.
Once again, I refer you to Jacobson.
Finally, do you have a citation for the “20-40% of the released CO2 not being absorbed by the oceans”? I ask because the numbers I’ve seen have been much smaller. This is called the “Revelle factor”. Revelle’s original paper on the subject is here, and is well worth reading. It doesn’t say the things that it is usually cited to uphold.
Thanks, intention, for your reply.
There are two main problems here:
(1) Your estimate that only 0.3°C of temperature rise could be attributed to CO2 is almost certainly too small. And, in fact, there is nothing illogical about assuming that 100% of the rise is due to CO2…In fact, it could be more than 100% of the rise (the best estimate of which is now ~0.7°C, by the way) since there were also negative forcings during that period, most notably anthropogenic aerosol contributions. The truth of the matter is that because of the uncertainty in the aerosol forcing and also to some degree because of internal variability, the 20th century temperature rise does not provide good constraints on the climate sensitivity…i.e., within uncertainties it is compatible with a wide range of sensitivities. Better constraints are provided by looking at the change from the last glacial maximum (plus other things such at the cooling from the Mt Pinatubo eruption).
(2) To correctly obtain the equilibrium climate sensitivity from the temperature rise, one would have to know how much temperature rise is “still in the pipeline”…i.e., how much additional rise would be expected if we froze greenhouse gas concentrations at their current values. The best estimate that I have seen for this is something like 0.5°C of additional warming, although admittedly with fairly large error bars.
I lost you. For one thing, the argument that only about 1/3 of the warming is due to CO2 is not reversible if you are going to try to determine how much of the CO2 rise is due to warming. Hence, a more reasonable estimate is that 0.6°C of global temperature rise should result in ~15 to 20 ppmv rise in CO2. However, even this is only true over the long term. I.e., the often-noted fact that initial changes in CO2 levels often lag the initial change in temperatures by several hundred years implies that the process by which increasing temperature causes increasing CO2 levels (and vice versa) takes several hundred years to play out. And, it has been suggested that this corresponds with the time it takes to overturn the oceans.
It comes from Chapter 8 of Archer’s book “The Long Thaw”. He references David Archer, “Fate of fossil fuel CO2 in geologic time,” Journal of Geophysical Research Oceans (2005); David Archer and Victor Brovkin, “Millenial atmospheric lifetime of anthropogenic CO2,” Climatic Change (2007); Timothy Lenton, “Enhanced carbonate and silicate weathering accelerates recovery from fossil fuel CO2,” Global Biogeochemical Cycles (2006); Philip Goodwin et al., “Ocean-atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales,” Global Biogeochemical Cycles (2007); and Andrew Ridgwell and J. Hargreaves, “Regulation of atmospheric CO2 by deep-sea sediments in an Earth system model,” Global Biogeochemical Cycles (2007).
You say that there is “nothing illogical” about saying that all of the 20th century changes are from CO2. The obvious conclusion is that the IPCC list of other forcings as black carbon, fluorocarbons, LULC, methane, and a host of other things is illogical …
Gosh, funny how that hasn’t come out of the pipeline in the last decade … during that decade we should have had both CO2 forcing, and “pipeline warming”. But we’ve seen no sign of either. “It’s all natural variability” is what the AGW supporters say now … but they must be wrong, because you tell me it’s reasonable that natural variability had absolutely nothing to with the 20th century changes, since it’s logical to ascribe it entirely to CO2.
Thanks for the references, much appreciated, although I get nervous when Archer cites Archer citing Archer …
Well, real life has caught up with me again so I’ll be saying au revoir to the SDMB once more.
There were 3 ways my concerns for the future might have been allayed here. To summarise:
[ul]The CO2 concentration is rising almost entirely naturally[/ul]
This is clearly not the case, as attested to by Blake’s resounding silence since I set forth the argument in the way he requested a few days ago. Human emissions are right there in front of us in volumes easily vast enough to explain the current level and the current annual increase, such that to even seek another explanation is a grave violation of Ockham’s Razor.
[ul]Some natural process will prevent CO2 levels rising past about 500 ppmv[/ul]This is what I have been discussing with intention. Yes, the annual emission rate due to humans might rise further, confounding any hope of a natural limiting mechanism. However, even if this rate stays constant at around 8 Gt CO2 per year, I consider the possibility of a roughly 500 ppmv level-off to be remote. intention has now identified what I see as the problem here:
Calling this the “sequestration rate” is unhelpful and confusing, IMO. If the emission rate is measured in Gigatons per year, so should the sequestration rate. And since the excess is increasing so dramatically, then proposing a ‘constant’ sequestration rate of 2.5% *of the excess * per year actually implies a dramatic increase in the sequestration rate. I simply cannot see how this will continue to happen indefinitely, given the obvious limiting mechanisms which prevent ever more CO2 being sequestered as atmospheric CO2 rises: soil fertility, ocean acidification and so on, all in addition to the tropical deforestation and desertification which continue apace. In intention’s graph, the orange line will have to become as steep as the blue line - ie. 2.5% of excess will have to be sequestered every year even when that excess has increased dramatically as the steeper blue line continues to pull away from the orange.
I might be optimistic enough to accept a small increase in the sequestration rate ove the next few decades, but I cannot see how it can continue to eat up 2.5% of a dramatically increasing excess. Of course, I hope intention is right in this regard, but I hope he would also consider my concerns to be reasonable.
Finally:
[ul]CO2 concentrations of 500-800 ppmv won’t have particularly negative impacts anyway[/ul]If there is hope, it lies here. Maybe intention’s increased cloud cover will kick in and reflect the heat which the extra CO2 would otherwise have captured. If so, well, those extra clouds better start measurably forming pretty soon. Maybe the climate is sufficiently insensitive to extra IR-absorbing gases that large temperature rises are not forthcoming. If so, it would have to be the bare minimum sensitivity allowed for the Greenhouse Effect to exist at all, and even a modest sea level rise would surely have highly negative impacts on countries like Bangladesh.
But both of these are possible, even though in my admittedly amateur eyes they don’t seem all that likely. So I guess these are what I’ll have to Believe in, since the consequences of large temperature rises do not bear thinking about. Is this mere positive thinking on my part, or positively wishful thinking? Again, I’m not sure I wish to examine that question too closely lest my optimistic bubble bursts.
Many thanks to all who contributed here, and all who spent time reading those contributions.
My point is not that there weren’t any other forcings but rather that the NET forcings of all the other components other than CO2 could be close to zero, or even negative. I’m not saying that is definitely the case but, within the error bars on the aerosol forcing, it is certainly a reasonable possibility.
Noone is saying that natural variability had noting to do with the 20th century changes, but rather that it is unlikely to account for very much of the change (and is as likely to have been negative rather than positive). In fact, I noted that internal variability is one of the contributing uncertainties when one uses the 20th century temperature record to try to constrain the climate sensitivity.
Well, experts in an area do have a tendency to cite their own work in the area. But, 3 of the 5 cites are to papers that he is not an author on.