Arguments
Estimating climate sensitivity from 3 million years ago
Posted on 9 May 2010 by John Cook
A key question in climate science is climate sensitivity. If the amount of CO2 in the atmosphere is doubled, the change in global temperature without feedbacks would be around 1°C. However, a number of feedbacks do occur - water vapour, snow albedo, sea-ice albedo and clouds. These respond relatively quickly, over a time-frame of years to decades, and are called "fast feedbacks". Modelling all the individual feedbacks can be problematic. However, we can empirically sidestep all this by using paleoclimate data to calculate the net response from fast feedbacks. A number of studies looking at various periods of Earth's past converge on a climate sensitivity of around 3°C (Knutti & Hegerl 2008). This means any initial warming is further amplified by positive feedback.
A new paper Earth system sensitivity inferred from Pliocene modelling and data (Lunt 2010) looks further into climate sensitivity as determined from the past. It examines the mid-Pliocene warm period,about 3.3 to 3 million years ago. This period is useful because CO2 levels and temperature were higher than pre-industrial conditions, giving us an insight into how climate responds when it's already warm. At this time, the main external forcing driving climate was tectonic changes in mountain ranges which led to changes in atmospheric CO2 (driven by both tectonic-related emissions and weathering).
What they find is the temperature response to changes in CO2 is 30 to 50% greater than the response based on fast feedbacks. This is due to other feedbacks operating over greater timescales (there is still uncertainty over the timescales involved, from hundreds to thousands of years). These slow feedbacks include changes in dust and other aerosols, vegetation, ice sheets and ocean circulation. This is confirmed by the geological record which records changes to ice sheets and vegetation over this period.
This means climate may be more sensitive to carbon dioxide than previously thought. On top of the fast feedbacks that cause the climate sensitivity of 3°C, additional slow feedbacks will add another 1 to 1.5°C warming. This result is confirmed by another recent paper also studying the Pliocene (Pagani 2010). This higher sensitivity should be taken into account when targets are set for limiting greenhouse gas emissions.
John's post is on the money. A 2xCO2 climate get us about 1C warmer with no feedbacks. Fast feedbacks bring that up to 1.5 to 4.5C with 3C the most likely and less than 2C very unlikely. Slower feedbacks can bring these values up to 6C.
See: Impact of GHGs
Scott A. Mandia, Professor of Physical Sciences
Selden, NY
Global Warming: Man or Myth?
My Global Warming Blog
Twitter: AGW_Prof
"Global Warming Fact of the Day" Facebook Group
The figure below (Ruddiman, 2008) shows how carbon is cycled into and out of the atmosphere by plate tectonics over millions of years.
Through a process known as chemical weathering, rainwater combines with CO2 gas in the air and forms carbonic acid. Carbonic acid "attacks" the silicate bedrock and creates carbon-containing ions that are carried to the ocean by rivers. This carbon is ultimately stored in the shells of marine plankton. When marine plankton die, they fall to the sea floor where their carbon gets buried in the sediment. Therefore, chemical weathering removes atmospheric carbon and causes a cooler climate.
During the process of plate tectonics the sea floor spreads. As the sea floor spreads, sediment containing carbon is forced into the earth's interior (by a process known as subduction) and is melted. When magma rises and is ejected by volcanoes, the carbon is released back into the air. During increased periods of plate tectonics (more volcanism) there are higher levels of CO2 in the atmosphere and the climate warms.
Approximately 55 million years ago, India slammed into Asia and began to build the Himalayan Mountains. These mountains are still rising today. Due to the massive amount of material being uplifted by this collision, chemical weathering rates over the past 55 million years have been very high resulting in a gradual tectonic cooling since that time.
Scott A. Mandia, Professor of Physical Sciences
Selden, NY
Global Warming: Man or Myth?
My Global Warming Blog
Twitter: AGW_Prof
"Global Warming Fact of the Day" Facebook Group
Thanks for that. I don't doubt CO2 is released I'm just asking why is this released CO2 the primer for all the other processes that occured which lead to the warm climate.
Here's a short list of the things that were occuring in this period.
The Himalayan Mountains formed. In America, the Cascades, Rockies, Appalachians, and the Colorado plateaus were uplifted, and there was activity in the mountains of Alaska and in the Great Basin ranges of Nevada and Utah. The end of the Pliocene was marked in North America by the Cascadian revolution, during which the Sierra Nevada was elevated and tilted to the west. In Europe as well many mountain ranges built up, including the Alps, which were folded and thrusted. The Isthmus of Panama formed cutting off the Atlantic, completely altering ocean circulation and allowing conditions for greater ice accumulation at the poles.
Why can't the formation of these mountains in and of themselves alter weather patterns, change the hydrological cycle, cause savannahization and desertification, alter vegation patterns, change wind and circulation patterns, change precipitation to snow rather than rain, allow the beginning of glaciation and change aerosol and dust levels all independantly of how much CO2 is released by tectonics. Why are the other factors a result of extra CO2 in the atmosphere and not mountain building and isthamus formation.
(A large section of this was pasted from http://www.ucmp.berkeley.edu/tertiary/pli/plitect.html)
Dr. Roy Spencer
Anyone care to read his post and comment?
I think that is the same flawed approach that Tamino debunked in his post Spencer's Folly 3. (For the least technical explanation, search down that page for "You may also notice" and read down from there.) But I'm unsure, so I've asked Tamino.
I've also asked Chris Colose to please give a less technical explanation.
I can't even venture a guess about how accurate this method is, but it certainly takes the rocks into account.
tobyjoyce> Me too. I can't make sense of what Dr. Spencer writes either. I think it's best to wait for a fuller account before trying again.
HumanityRules> I think that your remark is that the world of mid-pliocene (-3.29 to -2.97 million years) was so different from the present world that we can't use present day models to describe the climate of that time. That is certainly an important objection, and I'm not sure how certain Lunt et al. are about the models they have to use to connect the dots, but they certainly do discuss ancient geography and flora.
To be more specific, I believe that the Panama Isthmus was alread formed at this time, and the mountain ranges you mentioned were not that drastically different from today. But I don't know for sure...:)
From the abstract:
Here we use a coupled atmosphere–ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures. Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature.
Since the authors are using a climate model, they should be able to directly analyze which forcings and feedbacks contribute to the warming.
Does that help?
so how could co2 be a "driver" and the others which are far more powerful be mere feedback.
When the water rumbles and moves with the tide, it is the water vapor that comes out of the heating of the ocean that causes the hiccup of released co2. It's not co2 overpowering the water molecules to rise out of the ocean and force them to release the co2 into the atmospere.
That is roughly similar to saying that the foot on the gas pedal is the driver and the person controlling the foot is merely along for the drive.
Thanks, that's given me some good reading From tamino's blog. Very helpful.
As a reult of the impact of growth and death on CO2 and methane levels, I would expect the effects to be significant.
The increase (and decrease) of living agents is (by definition, I would argue) exponential in nature. And this is without factoring-in any Darwinian selection processes such as, say, selection for flora that are better able to compete at higher concentrations of CO2.
Do paleo-climate reconstructions have the kinetic-resolution to adequately describe such changes? I whould hazard a guess that small photo-synthetic organisms do not leave leave much of a trace in the fossil record irrespective of their genome.
"how could co2 be a "driver" and the others which are far more powerful be mere feedback"
It has to do with 1. the life time, 2. the concentration and 3. the scattering frequencies of these gases in the atmosphere. The three most common gases in the atmosphere Oxygen, Nitrogen and Argon, if I recall right now, do not absorb outgoing long wave radiation, but do scatters radiation in the incoming spectra (hence creating a blue sky by means of incoming scattered short wave radiation). All other gases are traces gases but the most abundant of them is CO2.
CO2 – simply put, once there it stays there (I am deliberately ignoring the carbon cycle here). Methane, another trace gas, is broken down to CO2 and water vapor after a while and thus contribute to more CO2. Methane concentration is also significant lower than CO2 concentration, by a factor 200 about. Methane I believe is about 20 to 30 times more potent as greenhouse gas but far less abundant and not very long lived, therefore its effect fades compare to CO2.
Methane can have a strong short term effect if pumped out in massive amounts but due to it short life time its effect will go away within a decade or so and be replaced with a long term effect from CO2.
Water vapor, perhaps the most potent greenhouse gas, has its own life and its concentration varies by god know what and how many factors and it tends to crystallize and fall out now and then. Water and its vapor is an important substance when it comes to transport heat around, in seas as in air, and its vapor has an great effect on the greenhouse effect – when it pleases to be present that is - but its behavior is erratic and the understanding of water vapors life cycle and it effect on global warming is poor at best. For the rest of the trace gases they do simply not contribute significantly to the energy balance.
Does this motivation make sense for you?
Rather than 'just sayin' skepticstudent needs to do some actual studying. If he were to do so he would learn all the reasons why he doesn't have a clue what he's 'just sayin' about.
Such as the very reason that CH4, N2O, O3, CFCs and the other purely man-made less common greenhouse gases are more potent than CO2 is precisely due to 1) their being so much less common: doubling them requires adding so much less of them to the atmosphere, times 2) their life in the atmosphere.
Such as although those gases are more potent than CO2, meaning they have a much higher potential for influencing earth's radiative balance, the 38% and growing increase in CO2 dwarfs their combined increase by sheer volume.
Such as the fact that water vapour, the one greenhouse gas in greater supply than CO2, by a factor of 10, can only act as a feedback to some initial change in temperature of the atmosphere, what ever the cause or sign of that change, while CO2 can act as either a feedback to an initial change in temperature, OR as an initial forcing when added to the atmosphere independent of an initial change in temperature.
Such as the fact that the 'water' is currently a net absorber of CO2, which is why ocean surface pH is falling as CO2 increases in the atmosphere.
In that paper, the main result seems to be that they partition the Earth of that period into 27 vegetation zones like "desert" or "open conifer woodland" etc. I don't believe that they speculate on how evolution might have adapted plants to higher CO2 levels.
2nd is the fact that individual water vapor molecules have a significantly shorter residence period in the atmosphere than CO2 (days to weeks compared to years to decades). 3rd is that water vapor contributes to both greenhouse effect & albedo wheras-to the best of my knowledge-CO2 contributes nothing to albedo-only to greenhouse effect. Thus its easy to see why CO2 is a driver, but water vapor is only a feedback.
That seems like a fairly static understanding of the processes. Surely anything in a process in transition can act as a driver for other aspects of the system. It's about cause and effect. At the moment we see CO2 being pumped into the system by us and ask what secondary affects is this having. If other things are changing under their own control these can then be generating their own feedbacks.
For example the evolution of life and later green plants and their spread across the planet had a huge affect on atmospheric chemistry and all the subsequent effects that had on climate. In this case bacteria, plants and animals are the driver of change, generating their own feedbacks and CO2 becomes a feedback at this moment.
So specifically in the Pliocene why shouldn't the geological changes be driving changes in climate directly. Certainly the joining of N and S America seems to have had massive repercussions on ocean circulation it's impossible to imagine this didn't have an affect on climate which would resolve itself over many timescales
11.Marcel Bökstedt
I don't doubt all these processes resolved themselves over a much longer periods but it does seem that the Pliocene is often described as a mountain building epoch. We seem to accept that mountain building and tectonics could have a significant affect on CO2 why not other aspects of climate. This is a dominant process of the epoch. I've still not read anything here that rules out this as a driver of aspects of climate, I'm happy to find the big hole in my understanding. Again as an example the continued rise of the Himalayas must have had huge affects on the hydrological system of the regional and all the subsequent affects on vegetation, rivers, erosion and the like.
Another description of Pliocene here http://www.enotes.com/earth-science/pliocene-epoch
Where do you get these numbers? I think it's more like tens of thousands to hundreds of thousands. Do you have any references for these numbers?.
I have read that it amounts to 0.0075W/m2 per year. Is that correct if not what is the accepted rate?
By the way, here's full text link to Lunt et al. (2010):
http://www.leif.org/EOS/ngeo706.pdf
you can calculate the forcing F (in W/m2) for an increase in CO2 concentration from C1 to C2 by the aproximate forumula:
F=5.35 ln(C2/C1)
It is also worth a look to: Comment on "Aerosol radiative forcing and climate sensitivity deduced from the Last Glacial Maximum to Holocene transition", by P. Chylek and U. Lohmann, Geophys. Res. Res. Lett., 2008.
Authors: Hargreaves JC and JD Annan; said: "The sensitivity of the climate system to external forcing has long been a subject of much research, the bulk of which has concluded that the climate sensitivity to a doubling of CO 2 is likely to lie in the range 2–4.5 deg. C (IPCC 2007: Summary C (IPCC 2007: for Policymakers, Solomon et al. 2007; Knutti and Hegerl 2008.). Chylek and Lohmann (2008) (hereafter CL08) claim to have found evidence that the true value is much lower, AROUND 1.8 deg. C ...[...] (commentary by the authors: is a mistake Chylek and Lohmann)";
... and for discussion:
http://www.clim-past.net/5/143/2009/cp-5-143-2009.html
In addition, skeptics still notify the three basic concerns:
1. Signs of ancient CO2 concentrations may be subject to substantial error, excessive smoothing - low resolution, etc.
2. This temperature rise is always first, then the concentration of CO2. So once the CO2 could only possibly enhance the warming. There are, however, periods of significant decrease in temperature. Despite the lack of decrease in the concentration of CO2. Why? - Is a topic for another discussion.
3. "It turns out that UNCERTAINTIES IN THE ENERGETIC RESPONSES of Earth climate systems are more than 10 times LARGER than the entire energetic effect of increased CO2." - (The claim that anthropogenic CO2 is responsible for the current warming of Earth climate is scientifically insupportable because climate models are unreliable; Frank p., 2009 - using, among others: Prof. Carl Wunsch, Prof. Paul Switzer, Prof. Ross McKitrick, Prof. Christopher Essex, Prof. Sebastian Doniach ...).
it would be nice and usefull to all of us if you could focus your expertise and knowledge of the litterature on the topic at hand. Your generic rants bring nothing to the discussion and they might dangerously be confused with propaganda.
It has always seemed clear to me that there were further 'long term' warming impacts to be expected... for instance the expected decline of Greenland and Antarctic ice for centuries to come would perforce indicate changing albedo and more warming. This new Lunt paper seems the most robust quantification of those eventual impacts I've seen thus far... but is it really a concern?
I mean, if we get through the ~2 C temperature rise expected just this century then why should a subsequent ~1.5 C rise over the course of 1000+ years be cause for concern? Whatever changes we make to avoid the looming crisis should also help to mitigate the long term impacts... and we've got centuries more to work on that.
The thing that worried me about the article on Spencer's blog was the bit that said "I’ve been slicing and dicing the data different ways", which sounds to me a recipe for (unintentional) cherry picking.
Also, the bit that said:
"these feedbacks can not be estimated through simple linear regression on satellite data, which will almost always result in an underestimate of the net feedback, and thus an overestimate of climate sensitivity."
isn't it the net feedback that the model is aiming to estimate, if so how can you know it is an underestimate? It will be interesting to read the full paper when it is available (and reading the discussion by those who understand the science rather better than I do! ;o)
Nevertheless, climate feedbacks have been directly measured from satellite data, and the sensitivity calculated to be 0.7K.
Some papers use models, some papers use analysis of historical data, and some use direct observations. For example, Chung, Yeomans, & Soden (2010) directly measures climate feedbacks via measurements of outgoing radiation, and finds close agreement with models. When hundreds of papers using independent methods all converge to the same answer, it makes a very compelling case that the answer is correct. A couple papers outside the mainstream do not overturn an entire field of science.
Furthermore, as others have pointed out, the Lindzen paper has been refuted. Even Roy Spencer has serious issues with it, and he's one of the leading proponents of low climate sensitivity.
If the value of 0.0075W/m2 is correct, and that is the additional energy not lost due to an additional 2ppm CO2, then surely the additional 0.027W/m2, being the average heating rate released from energy consumption is of even greater significance.
That figure is based on the 2002 figure of 13.76TW averaged across the world.
Would someone like to confirm, or otherwise, any of these values?
I am not sure of your numbers (although they are available) but one problem with the 0.0075 W/m2 from CO2 is that it is additive. Any heat released from energy consumtion is dissapated and radiates into space. After 10 years the CO2 contribution is .075 W/m2 and after 20 years it is .15 W/m2. Meanwhile energy consumption still releases 0.027 W/m2 (obviously adjusted for different energy consumtion). After 50 or 100 years it starts to add up.
Is that not how climate sensitivity responds?
Additionally CO2 does not have a total franchise on absorbing IR radiation, heat energy, as it's absorption bands overlap that of water vapour, and water vapour like CO2 is also additive.
In fact whilst CO2 can be sequestered and removed from the atmosphere, water vapour, as it changes form, remains still with a surface exposed directly to the atmosphere, (that surface area relative to the prevailing conditions) and the heat energy circulating within thus exercising control over that heat energy, ready to provide immediate, short and long term feedback, positive or negative.
Palaeoclimate: Global warmth with little extra CO2. Birgit Schneider & Ralph Schneider (2010).
http://www.nature.com/ngeo/journal/v3/n1/full/ngeo736.html
(3 - 4C once thought to be associated with CO2 at 500 - 600 ppmv therein put at 385 ppmv)
"Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years. Tripati et al (December 2009)
http://www.sciencemag.org/cgi/content/abstract/1178296
Earth system sensitivity inferred from Pliocene modelling and data. Lunt et al (December 2009)
http://www.nature.com/ngeo/journal/v3/n1/abs/ngeo706.html
Here’s a chart:
http://www.paleo.bris.ac.uk/~ggdjl/conferences/egu2009_ess.pdf
High Earth-system climate sensitivity determined from Pliocene carbon dioxide concentrations. Pagani et al (December 2009)
http://www.nature.com/ngeo/journal/v3/n1/abs/ngeo724.html
Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100. Breecker et al (October 2009)
http://www.pnas.org/content/107/2/576
The point that I made is that the forcing from CO2 is additive while the forcing from heat released by using energy is not. Thus the forcing from CO2 grows each year while the energy forcing stays the same. Over time the CO2 forcing greatly exceeds the energy forcing. Heat released this year does not add to heat released next year. CO2, once released into the atmosphere, is essentially permanent. CO2 released next year adds to this years CO2. After a certain period of time the energy forcing becomes negligable compared to the CO2 forcing, even though this year the forcing from energy exceeds this years CO2 forcing.
I would not agree with your characterization of the CO2 forcing as "very tiny". One year of CO2 is a small forcing, but we have been emitting CO2 for 150 years. The current CO2 forcing is equal to the difference between current CO2 and pre-industrial CO2. Wikepedia says current CO2 is 389 ppm versus 284 in 1832. Using your numbers that is about 0.4 W/m2 and growing. This is a very large forcing, much greater than the forcing caused by direct heat release (your 0.027 W/m2 for direct energy release).
Given global temperatures have risen about 5 deg C since the last ice age a simple calculation suggests that water vapour has increased from about 15,000ppm to about 20,000ppm whilst CO2 has increased from 280ppm to 380ppm. The numbers may not be exact but they are meant to illustrate that water vapour is additive and not tied directly to CO2, but responds directly to heat input.
johnd, michael sweet is right. I also don't know if those numbers for "industrial heat"are correct. However the "forcing" from any industrial heat generation applies only to the extent that the heat generation takes place (if all industrial activity were to cease, the heat would be rapidly dissipated to space). So this tiny forcing is essentially a constant.
The forcing from increments of atmospheric CO2 is cumulative. Doubling of atmospheric [CO2] gives a net radiative forcing of 3.7 W.m-2.
Notice that the feedbacks are manifest only in the presence of the forcing. If the forcing is (i) reduced or is (ii) a steady state, the feedback will (i) fall back, or (ii) steady out to a new level. In fact since the industrial heat has been fairly constant for several decades, we've likely had most of the tiny, tiny feedback from this tiny tiny forcing.
Water vapour is only "additive" as a feedback response to a radiative forcing, or some other phenomenon (volcanic eruptions, changes in solar output) that changes the atmopheric temperature. It is the latter that governs the water vapour concentration. In fact the enhanced water vapour concentration in response to greenhouse gas forcing is readily measured in the real world [***], consistent with the expectations from well-established theory of radiative effects in the atmosphere and their feedbacks.
Incidentally, the observation that atmospheric humidity is rising as predicted from theoretical understanding of the greenhouse effect, is one of the additional bits of evidence that a low climate sensitivity (less that 2 oC of warming per doubling of [CO2]) is unlikely.
------------------------------------------------
[***]
Dessler, A. E., Z. Zhang, and P. Yang (2008), Water-vapor climate feedback inferred from climate fluctuations, 2003–2008, Geophys. Res. Lett., 35, L20704
Gettelman A and Fu, Q. (2008) Observed and simulated upper-tropospheric water vapor feedback J. Climate 21, 3282-3289
Buehler SA (2008) An upper tropospheric humidity data set from operational satellite microwave data. J. Geophys. Res. 113, art #D14110
Brogniez H and Pierrehumbert RT (2007) Intercomparison of tropical tropospheric humidity in GCMs with AMSU-B water vapor data> Geophys. Res. Lett. 34, art #L17912
Santer BD et al. (2007) Identification of human-induced changes in atmospheric moisture content. Proc. Natl. Acad. Sci. USA 104, 15248-15253
Soden BJ, et al (2005) The radiative signature of upper tropospheric moistening Science 310, 841-844.
If people are keen to look for lot of climate sensitivity papers, here's a list of some of them.
there's no formal definition of slow or fast feedbacks, they must be considered relative to the time scale analyzed.
Is there any justification for putting one year memory rather than leaving it out?
Your list doesn't seem to include any of the so-called sceptics papers?
It would be worrying if the IPCC were to do the same. Having divided off a group of scientists, labelled them denier, questioned their motives it then seems possible to behave as if they don't exist.
Lindzen and Choi has been objectively shown to be incorrect. They cherrypicked their timepoints, and made incorrect assumptions that are fatal to their interpretations.
Schwarz's paper on climate sensitivity using a simple model of ocean heat capacitance and "guessed" response times was shown to be objectively incorrect. He recognized this and published a correction which now shows that in his model the apparent climate sensitivity isn't below the IPCC range anymore.
Chylek's paper on the estimation of low climate sensitivity from examination of temperatures and atmospheric reflectance during ice age transitions was shown to be objectively incorrect. Like Lindzen and Choi, Chylek et al made non-objective selection of time points.
Similar flaws effectively sink papers on climate sensitivity by Spencer and Braswell, and by Shaviv.
etc. etc. Why would one include papers that are objectively wrong in a list of papers that inform us about earth climate sensitivity? If we want to understand phenomena in the real world we reject analyses that have been demonstrated to be incorrect.
which papers did you consider should be on your list?
on your:
That's silly HR. The IPCC consider all scientifically valid research. The authors consider the topic of their particular remit in its entirety, assessing all the published literature and other relevant data sources. So they will know aboput your so-called "skeptic papers" and these are considered on their merits in line with the available science. So if a paper is shown to be incorrect, this may not be mentioned, or more likely will be discussed in terms of the data that denonstrate its flaws (since bad science does have its uses).
Your notion of "skeptic papers" is a curious one. As far as I can see there are only papers. Anything that is published in a scientific journal is a scientific paper, and having got there it lives or dies according to the interest it generates, the criticisms it generates and so on. The notion that there is some sort of alternative "science" of "skeptic papers" is a dodgy one to me. Of course there are a tiny amount of knowingly scientifically invalid papers that are winkled into the scientific literature (of the thousands of papers on climate science published a year, there might be 3 or 4 of these; they're often the ones we hear about!). But if that's what you mean by "skeptic papers" why would the IPCC or any scientific body or group consider these when assessing the state of a scientific field???
Your second sentence in the quote from your post is breathtakingly hypocritical! Clearly some rather scurrilous groups are attempting to do what you suggest (witness the pathetic and rather disgraceful attacks on Professors Mann and Jones). You can see by reading some of Poptech's post the way in which some people use these attacks as a means of attempting to disregard (in the manner you suggest) anything from the sources (e.g. Poptech on the CRU temperature data). But in fact the situation from the scientific side is straightforward. Spencer and Braswell, and Chylek, and Schwartz, and Lindzen and Choi were published (flaws notwithstanding). The reason that we reject these papers as valid contributions to our knowledge is that they hve been objectively shown to be flawed. mostly by extensive critique in the form of publications by others. It's certainly not because we reject them out of hand. Obviously we are likely to be a little suspicious of papers from certain sources but that's the price paid by those that attempt to sneak bad science into the scientific literature!