Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Settings


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Twitter Facebook YouTube Pinterest MeWe

RSS Posts RSS Comments Email Subscribe


Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...



Username
Password
New? Register here
Forgot your password?

Latest Posts

Archives

Seawater Equilibria

Posted on 10 January 2011 by hfranzen

The audience for whom this piece is intended consists of people who know some chemistry and are uncertain about how to consider the often made claim by deniers that the oceans contain so much dissolved carbon that human production is inconsequential. What the article points out is that the elementary chemical concepts of chemical equilibrium and charge balance put restraints on the ability of the ocean to release carbon dioxide to the air. Because of these restraints the oceans locally can release only a small part of the total dissolved carbon dioxide and, more importantly, when averaged over a year the amount released equals the amount dissolved, i.e. there is not net addition of carbon dioxide to the atmosphere from the oceans so long as the temperature averaged over a year remains constant from year to year.

 This topic deals with  the acid-base chemistry of the species important in the solubility of. These are:  (g), (aq), , , , , and .  The amount of each of the dissolved  substances  is  described by its molality, which is the number of moles dissolved in a kilogram (kg) of water.  In order to consider the chemistry it is necessary to propose a model system.  A model  for  the average ocean  is: A 3.5% sodium chloride solution in water at T=288K in equilibrium with 387 ppm   in air  at a pH of 8.00 and in addition 0.416 millimoles of dissolved boric acid per kg of water.  The molalities of the seven solute species are fixed by seven independent  equations .  is known from the Keeling curve  so  is fixed by  the Henry’s law constant for   

                                                                                                                                                                          

 The molality of hydrogen ion is fixed by the measured  pH, and the observed quantity of dissolved  boric acid yields

                                                      

Thus there are three restraints placed on the solute molalities at 288K by the known properties of average seawater. There are  four more relations (restraints) relating the molalities namely the equilibrium constants for the four independent net reactions among the solute species. These were  obtained as functions of  T using tabulated thermodynamic data.  Algebra then yields the molalities of the remaining solute species at 288K, specifically the equilibrium molalities  of , , and, as well as the other species, are  determined for the average ocean.  The total carbon dioxide molallity

                                                 

is thus fixed in the equilibrium average ocean  (its value is 1.65 millimolal). Bicarbonate is 91.5% of this total  molality. An essential requirement for  the evolution of carbon dioxide from the equilibrium ocean into the atmosphere is a perturbing influence. The one property  of the solution that can be altered so as to affect the total molality is the temperature of the system.

E.g. consider the effect of changing the temperature at constant partial pressure of . The pH will change with T so the pH=8.00 restraint is lost.  On the other hand, by charge balance

                                                            

is constant ( are not included in the sum because they are present at such low concentration that they can be neglected).  Thus even when T differs from 288K there are as many restraints as there are molalities. Tabulated thermodynamic data were used to calculate the equilibrium constants (including the Henry’s Law constant) at each of eight  temperatures  between 276 and 304K and the molalities for all species were found algebraically at the eight temperatures.  In particular the three molalities in  were found at each T . The eight values for were fit to a straight line as a function of T with the result:      

                                                     .

This means that the locally in the ocean decreases by only 13.5 micromoles per kg for each degree that T increases.  The opposite is also true: the  increases by 13.5 micromoles locally for each degree of decrease.  Since 288K is the average T, when there is an increase in one place there is a decrease in another and thus the net exchange of  between the ocean and the atmosphere is zero if there is no other source of carbon dioxide such as human combustion of fossil fuels. Considering this human production leads to the conclusion that there is necessarily a net increase in dissolved carbon dioxide (see Henry's Law above) and the calculations yield in this case a decreasing average pH in the oceans. Perhaps someone more knowledgeable than I could add a comment about the effect of increasing acidity on coral reefs, plankton, fish, etc.

In conclusion :

 1: Thermodynamics and charge balance place serious restraints on the ability of dissolved carbon dioxide to pass into the gas phase as a result of local temperature changes. The significance of these restraints should be considered by the deniers when they assert that the amount of carbon dioxide dissolved in the oceans is so large that exchanges between the ocean and the atmosphere dwarf human production.

 2. The nature of the average temperature and the thermodynamics of the reactions means that there is, on the average, no net exchange of carbon dioxide between the oceans and the atmosphere i.e. the notion that somehow carbon dioxide is belched into the atmosphere by the oceans ignores the basic fact that whatever carbon dioxide is released in one part is compensated by an equal quantity dissolved in another. 

0 0

Printable Version  |  Link to this page

Comments

Prev  1  2  

Comments 51 to 85 out of 85:

  1. And there is the Chewbacca Defense also. Personally, I like the HamHightail. I think the GishGallop can be quite useful in bringing perspective. It seems like hfranzen is saying that the average temperature of the ocean is not rising. Am I missing something in conclusion #2?
    0 0
  2. @50 muonocounter What hfranzen is talking about is equilibrium over open sea. Ice covered sea is not open sea, hence, for all intents and purposes, no exchange. If the Arctic ever is ice free it will still be close to 273K reducing the average temperature of the ocean. This will tend to push CO2 down based on averages.
    0 0
  3. 48, Dan Bailey, No, it was much older than that. It was focused, I think, on a published paper. I can't remember any keywords that will help me find it. Dang.
    0 0
  4. Martin #16 Orbital forcing kicks in first, by changing the relative lengths of the seasons. (E.g., in a warming phase summer is the longest season, but in a cooling phase winter is the longest season). This results in ice-albedo feedback from the greater (or lesser) snow amount over the course of the year. Albedo is a huge forcing agent. Oceans warm, and CO2 feedback kicks in.
    0 0
  5. Tom Curtis #46 and as quoted by muoncounter #50 Two quick comments: 1) The CO2 sensitivity values I have seen are substantially smaller than that attributed to Bacastrow; more like 7 or 8 ppm increase in atmospheric CO2 per degree of ocean warming than 12 ppm. 2) More important, the correct sensitivity is not to SST (sea surface temperature, which encompasses only the upper few tens of meters of ocean depth), but rather to the change in average average temperature of the entire ocean (the average depth of the ocean is 3800 m). Whether the correct sensitivity is 7 ppm/degree or 12 ppm/degree, it is necessary to warm the entire ocean to gain this effect. Most of the deep ocean, e.g., below 1000 m, has not warmed significantly since the beginning of the industrial period. Consequently, since most of the volume of the ocean has not warmed historically, and the surface ocean has warmed on average less than 1 degree C, warming of the ocean cannot have contributed significantly to the recent rise in atmospheric CO2 (approx. 100 ppm). (Just a different way of agreeing with the original post of Dr. Franzen.)
    0 0
  6. Martin #16, Sphaerica #39 and keithpickering #54 Although Dr. Franzen is mainly referring to shorter time scales, the principles he describes apply to the end of the last ice age as well. The average ocean temperature (mainly deep ocean) warmed by about 3 degrees C with the end of the ice age. The exact warming is still debated, but it is not nearly large enough to account for the entire rise in CO2 (see above posts). At least three factors contributed to lower CO2 during the last ice age: 1) A colder ocean absorbed more CO2, 2) The biological pump was more efficient than today, transferring more carbon from the atmosphere to the deep ocean, and 3) The ocean's alkalinity (the negative charge that Dr. Franzen refers to) was greater than today. Furthermore, the efficiency of the biological pump depends on both the rate of biological processes that transfer carbon from the atmosphere to the deep ocean, and on the rate of physical processes that mix CO2 from the deep ocean back up to the surface where it can be vented to the atmosphere. These factors are interrelated in complex ways, and it is the complexity of these interactions that has made it so difficult for scientists to unravel the exact suite of processes responsible for glacial-interglacial changes in atmospheric CO2. The sequence of events at the end of the last ice age was summarized by G. H. Denton, et al., The Last Glacial Termination, Science 328, 1652 (2010): 1) Around 21,000 years ago changes in Earth's orbit (seasonality of solar insolation) started to melt the northern hemisphere ice sheets. 2) Around 18,000 years ago the amount of freshwater entering the North Atlantic Ocean due to melting ice became so large that it severely perturbed deepwater formation and global meridional temperature gradients. Note the timing here: The first signs of warming in Antarctic ice cores occurred at 18,000 years ago, long after ice started melting in the northern hemisphere, and coincident with the severe perturbation in the North Atlantic. There is general consensus among paleoclimatologists on these first two points. What happened next is the subject of substantial disagreement. One view is that a change in deep ocean mixing, around 18,000 years ago, caused by all of the meltwater flowing into the North Atlantic, vented CO2 from the deep ocean and also helped to warm Antarctica (D. M. Sigman, et al., The polar ocean and glacial cycles in atmospheric CO2 concentration, Nature 2010, 47 (2010)). The alternative view is that the change in global temperature gradients, around 18,000 years ago, triggered by all of the meltwater flowing into the North Atlantic, perturbed atmospheric wind patterns in a way that both warmed Antarctica and released CO2 from the deep ocean, a process that takes place mainly around Antarctica (R. F. Anderson et al., Wind-driven upwelling in the Southern Ocean and the deglacial rise in atmospheric CO2. Science 323, 1443, (2009)). Which ever view proves to be correct, the end of the ice age was triggered by a change in Earth's orbit that started melting northern hemisphere ice sheets. Some thousands of years later, the meltwater entering the North Atlantic Ocean perturbed ocean and atmosphere physics in a way that caused CO2 to be released from the deep sea - mainly by an increase in physical mixing that reduced the efficiency of the biological pump. Although the warming that lowered the solubility of CO2 in the ocean cannot be neglected, it had less impact on atmospheric CO2 than was caused by the change in ocean mixing.
    0 0
  7. - Alexandre @ 23 "Gish gallop. I did not know this expression. Very descriptive." "A key technique that denialists use in debates, dubbed by Eugenie Scott the “Gish gallop”, named after a master of the style, anti-evolutionist Duane Gish. The Gish gallop raises a barrage of obscure and marginal facts and fabrications that appear at first glance to cast doubt on the entire edifice under attack, but which on closer examination do no such thing." - Real Climate As in Mr Pilmer does the "Gish Gallop"... http://scienceblogs.com/deltoid/2009/04/plimer_does_the_gish_gallop.php
    0 0
  8. 56, boba10960, Thank you. I've only skimmed it so far, but it looks like a fascinating paper, and an important set of details in understanding past events.
    0 0
  9. 56, boba10960, One thing nags at me. Ultimately, the ocean-atmosphere interface is a "rate of reaction" situation with a balance (which can then be altered by temperature, partial pressure, and other factors, such as acidity and the biological pump to which you refer). So if the ocean temperature change was insufficient to alter CO2 enough to account for the rise in CO2, but some other event injected CO2 into the atmosphere, would that not have put things out of balance and caused the ocean to begin to absorb CO2 to try to restore the balance? Shouldn't CO2 levels have fallen after such an event, or the ocean subsequently warmed enough to balance things (which you are saying clearly didn't happen)? Are we now in an environment where CO2 levels should be naturally falling (slowly reabsorbed by the ocean) even prior to the next orbital shifts towards a glacial period? Something in this doesn't make sense to me.
    0 0
  10. 59, Sphaerica You are correct. If there was a temporary change in physical processes at the end of the last ice age that caused the ocean to release CO2 to the atmosphere, and if that physical forcing came to an end, then one would expect the ocean to reabsorb some of the CO2 that had been released. In addition, the regrowth of the terrestrial biosphere in response to retreating ice sheets should have lowered the CO2 content of the atmosphere as well. The ice core records show that CO2 levels did fall slightly between roughly 10,000 and 8,000 years ago before they began slowly rising again. These back and forth trends illustrate the complexity of the multiple processes that affect atmospheric CO2. These processes are still subjects for ongoing research, but two things are clear: 1) The physical forcing that helps release CO2 from the deep ocean has not returned to the conditions that existed during the last ice age, and 2) The alkalinity of seawater (related to the negative ion balance referred to by Dr. Franzen) has changed since the end of the last ice age as well, in a way that keeps atmospheric CO2 high when other processes are tending to bring it down. We know that ocean alkalinity has changed because the dissolution of microscopic calcium carbonate shells that settle onto the deep ocean floor has been increasing steadily over the past several thousand years. That is, water in the deep ocean has become more acidic, and corrosive to calcium carbonate, reflecting the change in alkalinity. This change in seawater chemistry was recognized more than two decades ago, but the cause is still a matter of debate and ongoing research. I favor the hypothesis that the growth of coral reefs, and the burial of calcium carbonate on continental shelves, following the final rise of sea level has been a major factor lowering the alkalinity of the oceans (formation of calcium carbonate shells by organisms removes alkalinity from seawater), but not everyone agrees with this hypothesis. Whatever the cause, lowering the alkalinity of ocean water drives the chemical equilibria described by Dr. Franzen in the direction of converting carbonate ion and bicarbonate ion into dissolved aqueous CO2, which may then escape to the atmosphere. Undoubtedly, this partially offsets any tendency for the ocean to reabsorb CO2.
    0 0
  11. Starting to drift off-topic, but this has some bearing on the current focus of the discussion: Gas escape features off New Zealand: Evidence of massive release of methane from hydrates GEOPHYSICAL RESEARCH LETTERS, VOL. 37, L21309, 5 PP., 2010 doi:10.1029/2010GL045184 "Evidence that massive quantities of methane gas have been released from the sea floor during past ice ages has been reported. The discovery supports the hypothesis that huge releases of ocean methane contributed to the rapid warmings of the Earth that have ended past ice ages." As reported in Reporting Climate Science .Com. Free PDF here. Adds a bit of credence to the clathrate-gun hypothesis. Must've been a bumpy ride. The Yooper
    0 0
  12. 60, boba10960, You said:
    In addition, the regrowth of the terrestrial biosphere in response to retreating ice sheets should have lowered the CO2 content of the atmosphere as well.
    I would have expected this to perhaps be the opposite... that during the change into a glacial period, expanding ice sheets would cover a fair amount of vegetation before it has a chance to decay and return to the atmosphere as CO2, and so the subsequent retreat of the ice sheets when moving to an interglacial would expose this carbon and "release" it to the atmosphere (where it would again be used in the constant growth/decay life cycle).
    0 0
  13. TOP #51, #52, Yes, you are missing that the main point of the post is not that the oceans are not getting warmer, it is that they patently have not gotten warmer enough to support any claim that the additional CO2 in the atmosphere has the ocean as a source. Also, you are missing that the main reason that there is less Arctic ice is that the ocean is warming. A relatively warmer ocean will loose heat more rapidly than a cooler ocean, but the ocean is warming because it is receiving more energy. Receiving more energy will _not_ result in a cooling.
    0 0
  14. Sphaerica, #62, If you look under an ice sheet, you will find very little organic matter. In contast, regions with tundra and/or permafrost tend to have a lot of organic matter. The reason for this is that ice sheets flow from the center out. This flow scrapes the terrain underneath clean down to the rock. Also, in geologic time scales, the weathering of rock plays a large role in removing CO2 from the atmosphere. There is less weathering of rock under an ice sheet than there is when the rock is exposed to, umm, weather.
    0 0
  15. #52: "If the Arctic ever is ice free ... " ... it will be too late to worry about CO2. Open Arctic water will absorb summer sun; all that evaporation will make for some lovely early winter NH snow.
    0 0
  16. Sphaerica #59, I remember an analogy used in 1st-year chemistry course that might be useful. Imagine there are tennis players on both sides of a court. Each player has a propensity for knocking balls across the net and that a higher concentration of balls means that it is easier for each player to put balls across the net. Imagine that instead of there only being one ball in the game, there are lots, and a player is free to hit any ball across the net. For any given amount of balls there are, after some time, an equilibrium will be established based on each players propensity to hit balls across. Now add or remove balls from one side, the concentrations of balls on both sides will come to a new balance point. There is no inherent balance point of the system; whatever balance point exists depends entirely on how many balls there are on the court and what each player's propensity for putting balls across is. In this case, balls are CO2 molecules and the propensity of the players is determined by the temperature of the sea and air. Higher temperatures give the ocean-based player a higher propensity for hitting balls across. Sorry for the overly simplistic analogy, but you seemed to be stuck on thinking that there was some set balance point, and there isn't.
    0 0
  17. Re: Sphaerica (62) Bob, I've thought about it and my mind still keeps coming back to this one: http://www.realclimate.org/index.php/archives/2010/03/climate-change-commitments/. I know it's not as old as what you're looking for, but it matches my memory of things. Romm also discusses it here. Sorry if it's not the one (unless you mean Solomon et al 2008?). The Yooper
    0 0
    Moderator Response: There is a followup: Climate Change Commitment II.
  18. Sphaerica, #62 Chris G #64 has already noted that there is little organic matter stored under ice sheets. Nevertheless, the hypothesis you mention is still advocated by some people, as described by Ning Zeng . However, we can be certain that the source of the rising atmospheric CO2 as the last ice age ended was the ocean and not on land, either under the ice sheets or in permafrost. If the CO2 had come from a source on land, then it would have acidified the ocean, as is happening today in response to burning fossil fuels. Stated another way, following the chemical equilibria described by Dr. Franzen, adding CO2 to the atmosphere from a source on land would have shifted the chemical reactions in seawater in the direction that dissolves more calcium carbonate in the deep sea. By contrast, extracting CO2 from the ocean by increasing the physical mixing that exchanges gases between the deep sea and the atmosphere (described in my earlier comment) would shift chemical equilibria in the direction that dissolves less calcium carbonate in the deep sea. The geological record indicates that calcium carbonate in deep-sea sediments was less dissolved (better preserved) during the time period that atmospheric CO2 was rising as the last ice age ended. From this, we know that the CO2 (at least most of it) came from the ocean, and not from a source on land.
    0 0
  19. 67, Dan Bailey, That was it! Yes! Now I just have to remember why I was asking about it. I know it had to do with this statement from that post:
    CO2 concentrations would start to fall immediately since the ocean and terrestrial biosphere would continue to absorb more carbon than they release as long as the CO2 level in the atmosphere is higher than pre-industrial levels (approximately).
    I just don't know what my train of thought was that wanted to get at that statement.
    0 0
    Moderator Response: [Daniel Bailey] Try reading comments 38-47; maybe that'll jog your memory.
  20. 66, Chris G, 68, boba10960, Thanks to Chris for trying... although I am already comfortable with the concept of rate of reaction (and that variables can change the various rates "on either side of the net", resulting in different equilibrium points). My thought was more along the lines that boba10960 responded to... that on the land existing vegetation must be covered by snowfall as a glacial period progresses (perhaps I shouldn't have used the term "ice sheet") over much of the North American and Eurasian continents, and that would necessarily (I think) cover a whole lot of vegetation before it could decay. Subsequent warming would have to eventually reveal that carbon, which could proceed to decay, while the usual "new growth" isn't immediately present to do the opposite, and turn atmospheric CO2 into "wood" at the same rate as the stalled decay could do the reverse. But boba10960's logic about being able to measure this due to changes in ocean acidity makes perfect sense. [That's the part I love about science, that Sherlock Holmesian inference that one can make from seemingly inconsequential details.] At the same time, while walking the dog (through the woods!) earlier I realized that the time scales in my scenario could be very wrong. As much as such vegetation would be covered/uncovered, it would just mean (in geologic terms) a pretty rapid return to the status quo of old/dead vegetation decays and new vegetation grows, resulting in a relative CO2 balance there, maybe even a shift the other way as previously suggested (i.e. new growth extracts more carbon the old decay returns). So that image in my mind's eye was perhaps faulty, or at best uncertain. Thanks much, boba10960. I learned a lot today, and realized where I have big holes in my understanding and need to do more reading.
    0 0
  21. 67, Dan Bailey, 69, Me and Dan Bailey, I think my problem was this. The Mathews and Weaver letter says that if CO2 emissions stopped abruptly, CO2 levels would immediately begin to drop, because the ocean would continue to absorb the excess. I'm not sure, based on this post and discussion, that that is entirely true. As the partial pressure of CO2 in the atmosphere drops, the ocean could may well at a certain point "restock" the atmosphere and keep CO2 levels high. The point at which this happens depends partly on the temperature of the ocean when CO2 emissions cease. The warmer the ocean is, the higher the ppm at which it is likely to emit rather than absorb. That would be bad, because it would keep CO2 levels and temperatures elevated, which would in turn help to prevent the absorption of CO2 by the ocean. I'd be curious if Dr. Franzen or anyone else could compute the curve... the ocean temperature vs. CO2 ppm below/above which emission/absorption occurs. Some other process would be needed to get CO2 out of the atmosphere. Could this be an important "tipping point" in our own decision of when to reduce CO2 emissions? Or is the ocean likely to act as a very convenient sponge and clean up any mess that we make, no matter how tardy we are in recognizing our mistake?
    0 0
    Moderator Response: [Daniel Bailey] You may want to put down any hot liquids before reading this then.
  22. I said "restock" and "emit rather than absorb", but what I really meant was that the ocean/atmosphere would reach a balance in the exchange where CO2 levels in both the ocean and the atmosphere would stay relatively constant until temperatures found a reason to drop.
    0 0
  23. 66, Chris G, Before I forget... I explained rate of reaction to my daughter using a different analogy. Imagine a gymnasium full of thousands of mice, and kids with mouse-scoopers and terrariums. The kids have to collect the mice and put them in the terrariums, from which they do occasionally escape. At first, catching mice is easy, because there are so many. With time, there are fewer, and the buggers are fast, so the catching is slower. At the same time, the job is never done, because at some point it gets so hard to find and catch mice that for every mouse they catch, another escapes. One can change that balance point (the rates of reaction) by adding more mice or kids (more reactants of one type or the other), making the terrariums more/less secure (changing the rate of the reverse reaction with an inhibitor), introducing better mouse-scoopers (catalysts) or taking them away and making them catch mice by hand, or by doing the catching when the children and mice are tired (equivalent to reducing the temperature in many reactions).
    0 0
  24. 71, Dan Bailey, Not a problem. For safety I only drink Medieval Warm Beverages when reading about climate science.
    0 0
  25. "Adds a bit of credence to the clathrate-gun hypothesis". I've discussed this a no. of times with our researchers in this area and while clathrates might be important for PETM, what evidence we have is negative for much influence on glacial cycle. If there was a significant contribution from clathrates to atmosphere, then surely you expect a fossil signature in ice core methane? What measurements I am aware of (sorry dont have reference as away from office) show CH4 is swamp origin.
    0 0
  26. @#34: Just to be clear, I do not think the rise in atmospheric CO2 since the industrial revolution is due to the ocean outgassing. However, the well-seasoned skeptic will point out that all of the ocean deepwater has very high DIC concentration. Therefore, the observed meridional CO2 distribution with higher concentrations in the N. Hemisphere could be due to upwelling deepwater in the N. Pacific (for example). I doubt that time-dependent CO2 concentration measurements would show the rise in CO2 at Mauna Loa precedes the rise at Cape Gearheart by a few days (or whatever the mean transit time of tropospheric air masses across the Pacific), but that doesn't mean a skeptic wouldn't try to make the case. And it would be a bitch to beat down, in my opinion, because they would provide all sorts of wacked-out measurements showing you needed to bring a relatively small amount of deepwater to the surface and that area could easily be missing by the relatively coarse measurements over that huge area. No doubt this argument from the skeptic would contain several delusional assumptions, and violate some principles of ocean physics, but sorting out all the misconceptions would take days. Furthermore, at each turn the skeptic would layer on another level of scientific weirdness so you would be nearly literally tied in knots sorting out what was factual and what was fantasy. In order to avoid that waste of time (and this whole website is designed so that people will waste less time debating known science with skeptics), it is a good idea to nip it in the bud and understand the isotope argument *before* the whole upwelling line of attack gets started. I say this mainly because whatever you can do to create a latitudinal distribution of atmospheric CO2 from continental sources can also be done with some creative ocean physics and upwelling.
    0 0
  27. Sphaerica, Yeah, was afraid I was explaining a point already well understood. Mice work as well; the same principles apply, but I like the net as an analogy for a boundary layer. In any event, I think you have hit on the problem being related to timescales. Organic matter decays a lot faster than permanent snow cover advances; I would think. I suspect the Nat. Geoscience article linked by D Bailey was the primary source for the Science Daily article linked earlier. I'd also like to add some more complexity to the model by observing that there is an overturning of benthic ocean with the surface layers. I'm not sure what the rate of that is compared to the rate at which the surface layers find equilibrium with the atmosphere in terms of CO2. But in any event, I'm thinking that the upwelling water went down in a lower CO2 world; so, it might have a higher capacity to absorb CO2 than the water going down now will have when it returns. So, I'm forming a hypothesis that there will be echoes of past CO2 levels as the oceans overturn. Can't claim to sufficient knowledge to know if this hypothesis has any merit. My guess is that any echoes that do exist would be pretty blurry, considering there will be other factors at work and the rates of overturn for the worlds oceans are highly unlikely to be the same. It could also be that it stays down long enough that it is buffered back to a consistent level by chemistry that takes place with the rock and falling organic matter down there. I'll risk exposing a potentially foolish thought.
    0 0
  28. I have missed out on a lot of the discussion above and as I now read it I see that much of it has to do with the deep ocean which is not a discussion to which I can contribute. However I did see one important question about which I can make a comment in terms of my model of the surface ocean. That question has to do with what happens when we (if we ever do) start to decrease the ppm of CO2 in the atmosphere. No matter what the temperature does the primary vapor-solution interaction will be governed by Henry's Law. This law states that at equilibrium the molality of the dissolved CO2 (that is molecular CO2 itself dissolved in the ocean) is proportional to the partial pressure in the atmosphere The proportionality constant, called the Henry's Law constant, does depend upon temperature but if the average temperature of the ocean warmed by 4 degrees the total solubility of CO2 (as CO2, bicarbonate, and carbonate) would drop by only 1.4% at constant ppm (but given the size of the ocean that will be a lot of CO2. On the other hand, if the ppm of CO2 in the atmosphere (the one variable over which we might still have control) were decreased at constant temperature the ocean. in accordance with Henry's Law, would start releasing CO2 into the atmosphere. If the quantity of dissolved carbon dioxide in the ocean that equilibrates with the atmosphre were very large relative to the quantity in the atmosphere the ppm would simply rise back to the value it had before our attempt to decrease it until the amount in the ocean dropped to a value closer to that in the atmosphere.. The actual situation will depend upon quantities like diffusion rates and bulk mixing rates in the ocean i.e. an important factor is the fraction of the ocean that will equilibrate with the atmosphere in the relevant time scale. It therefore is not possible (at least for me) to predict what the ultimate result of a serious attempt to cut our emmissions will be, but I can say with certainty that we are likely to be disppointed because attempts to decrease the ppm by curbing our use of fossil fuels will bring about exactly what the deniers are claiming now, namely the ocean will become a major source of atmospheric CO2. This simple law (Henry's) tells the tale - right now the partial pressure of CO2 (the ppm) is increasing so the surface oceans are a net sink for CO2. When we try to cut back it will become a net source and our efforts will be frustrated by the large amount of CO2 in the oceans. As stated above, this frustration will be augmented by increases in the temperature of the surface ocean that will occur as a result of GW.
    0 0
  29. Re: hfranzen (78) So you're basically saying CCS is an idea doomed to failure & we're all screwed by the CO2 we're emitting. Nice. Unsettling even to one who's studied this for a long time. Sigh. Thanks for the honesty and the insights, Dr. Franzen. Time for a beer... The Yooper
    0 0
  30. Respons to #72: I hope I'm not that pessimistic. However so far as the surface ocean is concerned I believe we should alert people to the fact that, unlke many of the unwise things we humans do, the production of CO2 has an effect that is like a runaway semi - very hard to stop and reverse. I cannot say how hard (I could if I knew what fraction of the ocean surface will equilibrate with the atmosphere on the relevant time scale) but I can say that we should all be aware that the exsolution of carbon dioxide from the oceans will occur and if we wait to act until many are suffering ill effects we will have many years (decades? years?) of suffering before relief comes (if at all). Those who deny the observed and calculated reality without knowledge or wisdom will bear a heavy burden of guilt if they are wrong, and there is every reason to believe that they are.
    0 0
  31. I have recalculated the equilibrium results for surface seawater acid=base reactions using the data from F.J.Millero, Geochim. & Cosmochim. Acta, V 59, #4, pp 661-677, 1995. I now have linear equations for the total molality of dissolved CO2 vs. T at 387 ppm and vs P(CO2) at 288K and for the molality of hydrogen ion vs. P(CO2) at 288K. The results (and I will be happy to provide as much detail as anyone wants) show that if at 288K we could reduce the ppm to 350 instantaneously the decrease in equilibrium molality (the value toward which the total molality would drop if 350 ppm could be maintained) would be such that the total amount of CO2 removed from the atmosphere to get down to 350 ppm would be equal to the decrease in the total dissolved carbon dioxide in only 4.11 times 10 to the 19th kg of ocean. I say only because this is only 3% of the total ocean. In other words at an average depth of 3000 meters it would take only 90 meters of the surface oceans to provide, through the decrease in solubility, the same number of moles of CO2as were removed to get down to 350 ppm. Of course the ppm will not drop instantaneously to 350 ppm but this calculation shows the dimension of the problem faced by humankind. When we decrease our CO2 production slightly the oceans will respond by taking the gas phase content back in the direction of the starting point. In the instantaneous hypothetical about half way back. In the case of a slight decrease most of the way back. As the deniers have always said there is a very large amount of CO2 dissolved in the oceans- I just don't think they reasoned their way to the time bomb that represents for all mankind.
    0 0
  32. Dr. Franzen, I was late coming back to check, but I just saw your replies and calculations in 74 and 80, in reference to my fear expressed in 72. Thank you very much!!!
    0 0
  33. I have redone my calculation and found that a better (perhaps more careful) calculation yields a result that is not quite so discouraging. The result depends upon how deep the surface is taken to be, i.e. to what depth the ocean is in equilibrium with the surface, and the time allowed for eqilibration. Since the numbers are generally considered on an earth-year basis I think that is the relevant time scale. For the ratio of actual ppm decrease that would occur to the decrease that would result from a decrease in our production in the absence of the ocean I get the relation 1/(1+5.2d) where d is the depth (in meters in the ocean of average depth 3790 meters (from Wikipedia)). This yields a 22% return for a depth 200 meters. Of course there will be other response mechanisms as well, but this is one that is easily calculated. This result also means that 22% of our current increase in production is going into the surface ocean if it can be taken to be equilibrated to a depth of 200 meters. Since 22% is in the right ball-park I would guess that 200 meters is not too far off the mark.
    0 0
  34. Re. #83 Oops. I wrote 1/(1+5.2d) where I should have written 1/(1+5,2f) where f=d/3790.
    0 0
  35. #31 you asked what effect organic carbon has. Fair enough question. Here is my rough answer at the question Dr Franzen has avoided for reasons of space I assume. The answer is complicated. Multiple cycles are at work in the ocean. For the AGW deniers who want to excuse increases in CO2, looking at the organic carbon in ocean life does not help them. The slow addition of calcium bicarbonate (from calcium silicate minerals) and other minerals by weathering (historically the major process) involved in the drawdown of CO2 into ocean sediments have been vastly exceeded by the fossil fuel CO2. Looking at the Paleo record the CO2 peaks go up quickly and down very slowly. The drawdown of CO2 by life in the oceans had a large historical example. The Azolla Event 49 million years ago, is thought to mark the end of the Hot House Earth and lead to the start of the glacial cycles. It took 800,000 years. Even in optimum conditions like the Azolla Event life is not quick at drawing down CO2. Azolla Event We will need to manage ocean pH sooner or latter due to poor CO2 level control in the atmosphere. Any idea that just adding alkali will fix the oceans needs to be quickly dropped. Aquarium keepers are already doing this on a tiny scale and the below is to help shine a light on what it takes to keep salt water at a healthy pH 8.2 to 8.3 for tropical species. A short answer to your question is the effect of healthy life in the ocean seems to be to add to the alkaline buffer strength. This seems to be because life increases the species that can bind to a H3O+ ion. My reference for this is: marine aquariums The aquarium keepers have a challenge with keeping stable pH in salt water aquariums as the complex cycles that are in the oceans are not present. The buildup of fish waist quickly turns acid. Attempts to gain good pH control by just adding calcium carbonate or bicarbonate powder just work for a few days as the pK of the buffer shifts to 7.6 and away from the sweet spot of 8.2-8.3 for tropical creatures. The salt aquariums challenge to get stable pH is achieved by adding the complex mixture of buffers that are similar in their levels to the ionic species found in the oceans. commercial aquarium product marine aquariums pH control The shortest answer to the problem of ocean acidity it seems to me is that the oceans ability to absorb CO2 is coming to an end as evidenced by the rise in average pH of the oceans, so quickly limiting the use of coal, oil and gas, till atmospheric CO2 is below 350 ppm is the most direct solution.
    0 0
  36. DB, in response to your response here http://skepticalscience.com/news.php?n=870#57760 we are talking about two different scenarios. Mine was the hypothetical ceasing of all emissions (I should have added the caveat including cement making and deforestation) in response to the comment that even ceasing emissions will result in CO2 rising. In this case it some sort of decrease in CO2 that is being proposed. I would note that my scenario is completely academic , we are not going to cease fossil fuel burning, deforestation and cement making. But it is quite true that if did cease adding CO2 to the atmosphere, the CO2 amounts would drop immediately despite the ocean outgassing that is described above. My model (linked in this post /argument.php?p=2&t=113&&a=80#54888 incorporates all current ocean outgassing (it has to since I am modeling the rise in atmospheric CO2). The model shows an exponential decay that fits the data and results in a drop to 350 ppm in about 40 years. Obviously such a rapid drop won't be sustained after that and it will never drop below about 300 (best case) due to our total added CO2 from previously sequestered sources. Now I do understand the point hfranzen is making in 81, he is proposing a hypothetical drop to 350, essentially instantly (this could be done by both stopping fossil fuel use and launching a massive sequestering operation). At that point the surface ocean would outgas to undo about 1/2 of that drop. However, the ocean would not be able to sustain that outgassing beyond that. Furthermore that scenario is just as academic as my scenario. Finally, the ceasing of CO2 production in his scenario would still result in the same exponential decay as I described above which would, in a matter of a decade or two take us back down through 350ppm.
    0 0
    Response:

    [DB] Not wanting to be the mouthpiece for Artful Dodger (as he is an extremely learned individual in his own right), Dodger was referring to the inertia of the Arctic as it struggles to reach temperature equilibria with the forcings acting upon it.  This means the ongoing melting of the Arctic Sea Ice cap, the land-based permafrost and the observed melting of sub-seafloor clathrates, which will continue to happen for many decades/centuries even after (should it ever occur) after antropogenic GHG emissions cease).

    While Dodger was venturing his opinion (which many who have taken the time to adequately research the matter share to some degree or fashion but choose not to publicly air those concerns), do not think that there is no scientific basis to his rationale.

    In the absence of inertias, perhaps the case regarding CO2 concentrations would follow the route you outline.  But as you indicate, that is primarily an academic exercise, rendered moot in the face of record GHG releases (30+ Gt in 2010) with no plan in place to even taper off said emissions (remember the old saw: "Those who fail to plan, plan to fail").

    But thank you for taking the time to read furnished links and to place ensuaint comments on relevant threads.  That is an utter delight, from a moderation perspective.

  37. Please allow me a complementary (and hopefully much simpler) explanation of the idea in post 86. Humans added 337,000 Gt of carbon to the atmosphere from 1750 to 2008 of which 224,000 Gt remained in the atmosphere as of 2008. The rest was "sequestered" in the ocean. I use quotes around sequestered because as hfranzen points out in post 81, it is still ready to escape back into the atmosphere. However, as with the "sequestered" atmospheric warming, the ocean effectively sequesters CO2 and warmth on decade to century time scales through overturning. Furthermore it is ultimately diluted through most of the ocean depths thus lowering the P(CO2) overall (including the surface), so it will end up at an equilibrium with the (almost) full ocean and atmosphere. I certainly welcome and appreciate any response and corrections. Also there are caveats, my model assumes no ocean warming (each 1C will add about 10ppm, other things being equal).
    0 0
  38. One more note (and I promise the last for tonight), which is that 337 GtC (I was using MtC in post 87 but mistakenly labeled it GtC) that we added is mostly fossil fuel origin, taken out of long term storage. It was added to the 597 GtC in the atmosphere and 1000 Gt in the surface ocean, and slowly mixed into the 40,000 Gt in the combined ocean and atmosphere reservoirs. But it is more complex since the ocean overturning is slow, less mixing is possible with the deep ocean reservoir. So our added 337 represents as much as a 18% (atmosphere + surface ocean) or as little as 1% (atmos plus entire ocean) addition to the total existing reservoirs (depending on mixing). That is how our new equilibrium is calculated if we stopped emitting today (and it would require a long exponential decay to get there). We've bumped surface carbon up a notch (the notch height depending on ocean mixing) and continue to do so.
    0 0
  39. Eric (skeptic) @88, based on recent research, if we add 1 to 2 thousand Gigatonnes of Carbon to the atmosphere, atmospheric CO2 will still be 22% of the amount added above the pre-industrial average. If we add 4 to 5 Gigatonnes, the amospheric CO2 levels would increase by 34% of the amount added once full ocean equilibrium is reached. Even though the 5 thousand Gigatonnes represents just 11.6% of the total quickly equilibrating reservoirs of Carbon (Ocean 40,000 GT, Soil 1600 Gt, Atmosphere 750 Gigatonnes, Biosphere 610 Gt), the additional CO2 changes the Ph balance of the Ocean, reducing the amount of carbon it can hold. Thus with total emissions of 5,000 Gt, we are looking at atmospheric levels of CO2 that are 3.25 times preindustrial levels for many thousands of years into the future. Indeed, we are looking at 4.8 times preindustrial CO2 out to a thousand years from now, and 2.9 times preindustrial levels out to ten thousand years from now.
    0 0
  40. Eric, care to comment on comparison of your model with that of Matthews & Weaver zero emission scenario?
    0 0
  41. Tom, thanks very much for the reference. I think you had pointed it out before, because it was in my saved papers folder. Reading through it again I see how some people may read it too quickly and conclude that one scenario represents "if we stopped producing CO2 today...." (my academic scenario I described above) But Archer is describing two potential, realistic scenarios, one where a moderate amount of 1000 GtC is released (compared to 2008's 337) and another with 5-6,000 GtC. Both have long tails and the 5-6,000 scenarios is especially long due to positive feedbacks. The first is essentially "we start to take action", the second, BAU. The simple model I use assumes that the CO2 reservoirs are passive. Substantial ocean warming (more than 1-2C) will negate that assumption as would permafrost melting or any other positive feedback. But as it stands, my model incorporates the current state (as of 2008) of all potentially active reservoirs or other positive feedbacks (as measured, not predicted) and the result is not substantially different from what one would expect looking at the diagram in Tom's link: http://earthguide.ucsd.edu/virtualmuseum/images/ReservoirsOfCarbon.html Given a slug of anthro-carbon into the atmospheric reservoir, the atmospheric concentration decays exponentially by migrating into the other reservoirs. Again, that depends on the rest of the system being passive (no substantial positive feedbacks). But exponential decay in that case is incontrovertible. Scaddenp, while I wrote the above I struggled with nature.com trying to purchase the article you linked. I'll comment here once I succeed and have a chance to read it.
    0 0
  42. scaddenp, finally got that article. It is short and sweet. It confirms everything I have said above, namely "In response to an abrupt elimination of carbon dioxide emissions, global temperatures either remain approximately constant, or cool slightly as natural carbon sinks gradually draw anthropogenic carbon out of the atmosphere at a rate similar to the mixing of heat into the deep ocean" They then conclude that the elimination of CO2 will result in stable temperature. Then they issue a "hopeful" warning that " if we can successfully coordinate international emissions reductions in the coming decades, we can successfully restrict global temperature increases to a level that will prevent dangerous impacts on both human and environmental systems." For future reference, we can call this the "saved by the ocean" scenario.
    0 0
  43. Eric (skeptic) @91, you may find Eby et al, 2009 more useful than Archer and Brovkin, 2006. They examine the impacts of both smaller, and a wider range of CO2 slugs than to Archer and Brovkin. In particular they examine the impact of a slug of 160 Pg on top of 2000 levels of CO2 in the atmosphere (estimated at around 300 Pg). The slug of CO2 adds an additional 69 ppmv of CO2 to 2000 levels. This slug then decays exponentially so that its contribution to the atmosphere is just 41% of the original after 50 years (34.5 ppmv), just 37% after 100 years (25.5 ppmv), just 35% after 150 years (24.2 ppmv), and 27% after 200 years (18.6 ppmv). After a thousand years it declines to 23% (15.9 ppmv), and after 10 thousand, to about 18% (12.42). These decay rates are an overestimate of expected decay rates for stopping all emissions now. That is because if the CO2 is introduced slowly rather than as a single slug in one year, it has time for some of it to reach enter the deep ocean before emissions cease. Consequently the initial peak of atmospheric CO2 concentration is not as high, but the decay rate from that peak is slower. For example, in the 160-A2+ model run conducted by Ebi et al, peak atmospheric CO2 was just 37.7% of that in the 160 model run. In the 160-A2+ run, CO2 was introduced over several centuries, and the decay pattern follows a similar path to the 160 run from the point where that run decays to 40% of the peak. As it happens, Eby et al ran a control experiment with no emissions after 2000. The result was that after ten thousand years, the CO2 concentration dropped by 55 ppmv from a peak of 376 ppmv. That represents a fall to 33% of the peak increase after ten thousand years. It also suggests that after 150 years of exponentially increasing emissions, 16% of CO2 that would otherwise be stored in the atmosphere has been stored in the deep ocean.
    0 0
  44. Further reflection on Eby et al suggests that if we were to stop all emissions instantaneously, CO2 levels would fall to about 315 ppmv after 10 thousand years, but take 50 to 100 years to fall to 350 ppmv. That is, of course, irrelevant. The only target we have a realistic hope of achieving at the moment, and only if we act decisively in the next few years is around 450 ppmv, locking in a 2 degree temperature increase that is likely to last for a century or so, and take over three thousand years to fall back below 1.6 degrees C.
    0 0

Prev  1  2  

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.



The Consensus Project Website

THE ESCALATOR

(free to republish)


© Copyright 2021 John Cook
Home | Links | Translations | About Us | Privacy | Contact Us