A translation into Slovak is available.
Great summary. My favorite use of “tipping points” thusfar was by Al Gore in a recent interview on PBS. He stated that he (I am paraphrasing here) “understands less about climate than many climatologists have forgotten, but he understands politics, and in politics there are tipping points, too.” He then continues to say that great things can happen almost suddenly when enough people get on board. This is the justification he gives for his new movie and his desire to train more people to give his slide show. Does anyone know where he is going to recruit the 1000 people from? I’d love to be trained to give his slideshow. The graphics are far better than those of my own slide show that I give fairly often.
I’m not sure about Al Gore’s “presentation training” plans, but it may be a large part of the nonprofit Alliance for Climate Protection that he is organizing.
Another source for presentation training is the nonprofit Green House Network (http://www.greenhousenet.org), which since 2000 has organized low-cost speaker training workshops in many parts of the country, including climate scientists, resource scientists, activitsts, and communicators among its trainers. These workshops have trained hundreds of presenters from many walks of life, who collectively have given thousands of presentations on campuses, to community and business groups, etc. The next workshop, billed as a “Global Warming Solutions Weekend Retreat,” is scheduled for Spring Green, Wisconsin on July 14-16. See the Green House Network’s Website for details.
fabulous posting! i have long wished for a blog entry or article that described this clearly. i had it on a list of things to do myself, but never got to it. i alluded to this idea frequently in discussions, the “tunneling” phenomena in some non-linear systems, but had nowhere to send people except things like Hirsch, Smale, Differential Equations, Dynamical Systems, and Linear Algebra, ISBN 0-12-349550-4, 1974.
thanks very much!
Excellent discussion, Gavin. Realclimate readers might also be interested in Gabrielle Walker’s discussion of this topic in the 15 June Nature:
Link for abstracts of the two papers Gavin refers to:
Re glacial cycle CO2 and temp correlation, it is useful to remember that the timescale of that record is 100’s of thousands of years, where as the CO2 rise today has occurred over ~100. The temporal resolution of the ice core records is also very coarse, millenia between samples, so one would have to wait maybe 10K yrs and look back to see if we have the same T and CO2 correlation (assuming there is ice left to core at that time). We may still see very good correlation on the one or two century scale but don’t forget that thermal inertia, mostly in the oceans, causes a long delay before T can catch up to CO2.
Gavin’s point about the physical mechanisms being totally different now still stands.
I think that this record also shows a significant tipping point scenario at ~12, ~22 and ~34 Myr bp with the formation and disintegration of the Antarctic ice sheet.
I suppose that one is still pretty far off, but I would not be surprise if a few hundred thousand years from now, or less, there was no ice left anywhere. If Greenland “tips”, the WAIS may follow then temperatures would go high enough to eventually melt the EAIS to the bedrock.
It is not for nothing that Al married Tipper.
“Eemian/Stage 5e period (about 120,000 years ago) when temperatures may have been a degree or so warmer than now ”
Just curious, since the CO2 levels are much higher now than they were back then, why was it hotter back then?
Also, CO2 and temperatures seem to line up very well in this graph:
They also seem to line up here:
So if CO2 levels are so much higher now (26% higher than any point since 420K years before the industrial era), why aren’t temperatures lining up?
[Response: The orbital configuration was different, with warmer NH summers than today (or even the early Holocene). That seasonal change may have been crucial for the ice sheets. See the recent Overpeck et al and Otto-Bliesner et al papers in Science for what climate differences one would expect. With respect to today’s CO2, that is not being changed by anything like the same mechanism, and so simply correlations with past data are not going to help. -gavin]
Regarding Hansen’s advice about 10 years, it seems like you are softening his statement. In his recent article in the New York Review of Books (see http://www.nybooks.com/articles/19131) he states “…we have at most ten years — not ten years to decide to decide upon action, but ten years to alter fundamentally the trajectory of greenhouse gas emissions.” So I take him to mean that we have to “start” seroiusly to reduce emissions somewhere between now and 10 years, not by 10 years from the present. Obviously Hansen’s is one very informed scientist’s opinion, so maybe 10 years is overly conservative. But given your description of tipping points and points of no return, a conservative approach seems to be in order.
A few hundred thousand years?
You are several orders of magnitude off with that comment. Current rates of carbon dioxide increase indicate total global deglaciation in the order of ~1000 years.
A name for the phenomenon?
defrost on the punkin’
Excellent post.Take that factor down by 10 to complete deglaciation and loss of all ice at poles within 100 years. Long before that thermohaline shutdown and superstorms and 20 foot sea rise. If co2 emmissions not reduced by 80 % NOW there is very little hope of bypassing the tipping point. Good post, good comments. Hope the Republicans(who hold all the power in all three branches) are listening.Some disappointment on lack of support for AB32 here in CA by certain “Democratic” state legislators.
Thankyou to all the posts and comments from your site. You guys are cool, and should be mandatory reading at Senate briefings.
“You guys are cool, and should be mandatory reading at Senate briefings.”
Senator Inhofe has already made Crichton’s “State of Fear” mandatory reading for Senators. I’m being dead serious btw.
“The orbital configuration was different”
Do you have any suggested reading on this? How exactly do they know what the orbital configuration was like 120K years ago?
Thankyou very much for the direct links.
This discussion of tipping points is very timely, as you point out, the press seems to be quite keen on it as people seem to be able to relate particularly well to this concept compared with some others such as “dangerous anthropogenic influence” or “catastrophic change”. Some other analogies:
“The horse has left the barn”
“Crossing the Rubicon” From Wikipedia — “The use of crossing the Rubicon derives from the crossing of the river Rubicon by Julius Caesar in 49 BC, who thereby violated Roman law and rendered armed conflict inevitable. As Caesar said at the time: “alea iacta est” (“the die is cast”).”
Or, related to having passed that tipping point, more figuratively, “he who mounts the wild elephant goes where the wild elephant goes” — I apologize for not knowing the proper credit for this.
I think that Figure 1 in [Falkowski, P. G. and others. 2000. The global carbon cycle: A test of our knowledge of the Earth as a system. Science 290: 291-294.] is useful in making this point. It shows the correlation between atmospheric partial pressure of CO2 for the last 420,000 years and the deuterium-based air temperature anomaly. I think it is appropriate that the figure is a little dated in that ‘modern’ atmospheric pCO2 (plotted on the figure) is now literally off the graph and if you mentally plot a reasonable assumption for an atmospheric pCO2 stabilization in the future it is hard to imagine how we will return to a climate experienced in the last 420,000 years, much less a ‘pre-industrial’ climate in the foreseeable future.
As intriguing a concept as it is, a ‘tipping point’ is less useful if poorly defined quantitatively or largely unknown, as apparently is the case with two key examples that you cite: thermohaline circulation and substantial melting of ice sheets leading to ‘dangerous’ sea level rise.
I agree that it is important to point out that there can be many tipping points depending on your frame of reference. For islanders that have already been forced to relocate 20th century sea-level rise has already passed a tipping point of no return.
Re #15: Here is one link on orbital parameters
One of the major reasons that the ice ages are potentially such a useful test of our understanding of climate sensitivity is that we know, from celestial mechanics, with remarkable precision, exactly how the Earth’s orbit has evolved in time, at least for the past few million years
With respect to the complete collapse of the Atlantic thermohaline circulation will you kindly clearify the following for me.
It is my understanding that a fluid initially at rest on a rotating mostly sphere-like surface which in turn is revolving around a sun cannot remain at rest. If this is not correct let me know. Otherwise will you summarize the patterns of the induced motions for fluid bounded by the same boundries that now bound the ATC. That is, for fluid between North-Central-South America on the Western edge and Europe-Africa on the Easten edge.
Additionally, what are the expected consequences of a “complete collapse”? This article (http://www.americanscientist.org/template/AssetDetail/assetid/51963?fulltext=true&print=yes) seems to indicate that significant changes in weather/climate are not expected. Let me know if I have not correctly understood the article.
This is a bit surprising — I wonder if this is why the Russian astronomer predicts a drastic change in climate in the next few decades? The change illustrated is over a far longer time span, but it’s striking in the graphic. I have no idea if this is one individual’s work or a consensus among astronomers.
Gavin, Ray, worth at least a glance I suggest, I just stumbled on it:
In the IPCC TAR, the report of Working Group II suggested that it is unlikely that we would reach any global scale tipping points (they used the terms “singularities” and “discontinuities”) before temperatures rose at least 2-3 C about 1990 levels. In the middle of the road projections, this corresponds to sometime in the latter third of this century.
I realize Hansen is talking about the head long plunge of human and climate commitment, rather than the transition itself, but are there new results since the TAR to suggest that a tipping point might come earlier than previously expected? It seems rather severe to think a catastrophe is 60 or 100 years in the future, but we only have 10 years to ensure that it won’t happen. (Of course one does want to stay on the careful side in case the model results are too conservative.)
I guess I am also surprised by how much press is devoted to tipping points, if, as the IPCC suggest, most of us may not actually live long enough to see such events. Not that I want my grandchildren to have to worry about it either, but it would seem more natural to spend more time on the problems we will already have before we get to the IPCC’s reported tipping threshold.
Re: #15. I’d suggest Wikipedia is a good place to start: Milankovitch cycles.
Orbital mechanics is very precise, and we can reliable describe the changes in the Earth orbit going back more than 10 million years. The present interglacial occurs during a period of low orbital eccentricity, and consequently the scale of the orbital forcing is lower now than during the last several interglacials.
Re: #19 That is a very interesting article, and I certainly learned quite a bit from it. However, I don’t think you can read it to say that “significant changes in weather/climate are not expected”. What he points out is that the differences between London’s and New York’s climate are not caused by the heat transfer via the Atlantic current. As I read the article *both* New York and London would be somewhat (not hugely) colder if the current were turned off. Plus the equator would be warmer, and one could therefore assume that there would be more storms in the equatorial region and perhaps fewer in the mid-Atlantic.
Not that I’m an expert or anything, but that seems to me what he’s saying.
Aloha all. This is my first post here and actually my first visit here. I followed a link from ThinkProgress.org to a list of the recently ranked Top 5 science blogs and this was one of them. After a good read, I can see why.
I run a blog that is almost entirely political in nature but recently I decided to expand its horizons to include personal exeriences as someone who has spent so much time on and under the ocean.
It’s titled: “The Canary is Dead!. The title of a movie put together by the PCRF.
I am NOT a scientist by any stretch of the imagination. I’m a Navy vet who never graduated from college. But I have spent more time underwater by age 34 than most people will spend on or near the water in their lifetimes. So I would love to hear feed back from some of you smart folks. And possibly either encouragement to continue or suggestions to stop because it’s not my intention to put out any bad information.
Thanks in advance everyone!
Professional divers with the ability to operate underwater machinery are in demand by some, if not all paleoclimate labs. When I was a grad student, my officemate was an ex-diver who had come back to school to do a PhD. But because he was one of the few people at the school with the requisite hours to operate underwater drill corers, he went on every other reseacher’s field trips as a technician. I have no idea who, if anyone, is currently doing paleoclimate research in Hawaii. But if you are interested in getting involved and volunterring, they could probably use your know-how.
cwmagee… Thanks for the follow up comment. For the past several years I have been building websites and media/marketing consulting to help companies improve their image and increase their bottom line and its been killing my soul a little bit each day. About a month ago I started selling off many of my “things” and wrapping up my yuppie condo lifestyle and I was planning on sending my resume’ out far and wide to organizations doing ocean and paleo-climate research.
I don’t even mean to suggest that’s all I want to do. PCRF, research organizations of any kind. All I know is I want to use my talents to do something that won’t make me ashamed of what I’m doing with my life. Something I can actually do that would make me proud of myself again.
#18, Nat’l Climate Data Center, includes a link to the same site I noted in #20 among many others, as a good recent calculation. Apparently the dating of geological epochs is now accurate to approximately 40,000 years (plus or minus, I think?), based on the best calculations of Earth’s orbit and the changes tied to that. Past 100k years chaos takes its toll.
“I wonder if any else has noticed that we appear to have crossed a threshold in the usage of the phrase ‘tipping point’ in discussions of climate? We went from a time when it was never used, to a point (of no return?) where it is used in almost 100% of articles on the subject. Someone should come up with a name for this phenomena….”
[Someone should hire an editor to check someone’s grammar.]
Do you think that the fact that Malcolm Gladwell wrote a recent best-seller named ” The Tipping Point” might account for the increased usage of the phrase? I do. You might as well simply acknowledge the obvious. Add that to “An Inconvenient Truth,” and, well…duh.
[Response: Possibly you might want to check your humour detection algorithms… -gavin]
I’m not sure I agree with CO2 levels .. are .. very unlikely to revert to pre-industrial values ..in ..the next few hundred years . Actually I mean flows not levels. Oil depletion could have a dramatic slowing effect on economic activity taking coal burning with it. This seems to introduce the case of a flow variable (industrial CO2) perhaps passing a ‘tipping point’ but then slowing.
The progenitor of nonlinear dynamics was the -equally celebrated and at the conclusion disappointing, but nevertheless enlightening- concept of Catastrophe Theory, back in the ’70s. The name itself is appropriate and revealing, identifying “tipping” points as “catastrophe” points, whose configuration depends on specific multi-dimensional geometric structures that best describe the phenomenon of interest according to the number of relevant parameters.
Nevertheless, the concept underlines the fact that these catastrophe points are not, actually, points of no return; they are rather points of not-feasible return, where the energy and time (or any other crucial governing factor) required to revert the system (like a planetary climate system) to a previous state is by far greater than the energy (or time, or…) that initially served as a feedback to drive it to the beyond-catastrophe state.
In other words, whatever scope we look at the climate problem, it is at least uneconomical to expect to remedy the system after the damage is done.
This is not doom-seering. A system of this magnitude, with this huge number of identified and unidentified governing factors, corresponds to a multi-dimensional geometric structure with proportionally numerous catastrophe points… When one of them is reached and crossed over, a new system state is reached, which rapidly leads to the next catastrophe point in line. And then to the next… and so on…
My point is: if the debate really stalls at the question whether it is viable to act now or not, simply think: we may not be able to prevent the first wave of catastrophe events that will upset the system initially. But, we have to start considering what we can do about the next set of catastrophe points, which will probably be much more drastic than expected. Change may be abrupt, but it also happens gradually, one could say quantumly.
Think about it. I am open to suggestions.
Thankyou for those that responded with the Milankovitch cycle links. I am aware of the fact that planets wobble, earths tilt effects seasons, mars caps are melting via topographic forcing, etc.
However, I simply don’t see a pattern regarding to orbital configuration vs. global temperature in this image:
I’m trying to find proof that those cycles were caused by a changing orbit and I’m having trouble doing so.
[Response: Hays, Imbrie and Shackleton, 1974. (or read The Ice Ages by Imbrie and Imbrie – highly recommended). -gavin]
The following review by Mark Maslin is worth a read:
I have been an appreciative reader of this site, not having anything useful to add. I have done quite much work on future research and virus marketing and this “Tipping point” -subject now seems a suitable place to try and perhaps contribute something.
It seems to me that the Tipping point -concept would be much more useful when studying how to win converts to join the work. Basically what the world needs is a “phase change” in the attitudes of politicians, voters and bureaucrats. The most efficient conversion method is not through media but through social networks and small world phenomena – you change your opinion when your friends or collagues change their opinions and express their opinions to you directly. This happens one by one and it succeeds, if on the average, each convertee succeeds more than once (within short enough time if we have only ten years). Al Gore’s concept of spreading good slides seems to be very efficient as lecturers always need good material and make many converts.
This site is also supplying very good material for all of us who wish to convince others. Especially important is the cautious avoidance of overextending the facts for a shock effect. This very easily leads to a backslash as happened in Finland with H5N1. (People generally think that the threath is passed as everything did not happen at once and then newspapers stopped reporting on the developments almost totally. And reality is that due to the events in Indonesia and few other places the probability has continuously risen. It may still take years for H5N1 to realize as a pandemic if ever and the popular support for efficient measures against the threath should last equally long as the threath.)
Critical mass is required for efficient action against global warming and some of it has to be gained by other means than direct facts. Professionals can be converted by facts. Amateurs like me are unable to follow all the facts and know that one can be mislead. What convinces us is partially things that we believe to be facts and this kind of open high quality discussion, which one in principle could join. But most laypeople do not follow this kind of discussions. They may instead see one soothing article, which says that there is nothing to worry. And then they cling to this belief as it makes their life so much easier. It may also be that they just do not care what happens after they die. It requires a networked approach – each person needs to be converted by someone they can trust. Social pressure is also important. You do the right thing because your friends expect you to do it. Here the Tipping point -metaphor, Meme theory, Virus marketing and other related approaches may be very useful. Naturally getting converts will become easier when people have seen some major changes but then precious time has been lost.
The BBC have gathered a panel to consider climate change. The unanimity of agreement in some of their conclusions have surprised me (OK stunned me). See here: http://news.bbc.co.uk/1/hi/sci/tech/5152590.stm Perhaps we could be approaching a tipping point in public acceptance of this as an issue? I’ll put my inate cynicism on hold and cross my fingers. :)
I suspect RC may have some comment on this to come, but thought posters/readers here might find it as interesting as I have. I do NOT want to spark off comments on this issue under this thread.
CobblyWorlds, aka Chris Reed.
It seems rather severe to think a catastrophe is 60 or 100 years in the future, but we only have 10 years to ensure that it won’t happen.
A parachutist insures the soundness of his silk well before getting into the plane.
To the Editors of RealClimate
Other than studies detailing anthropogenic forcings for present global warming, are there well-document, peer-reviewed, well-accepted studies showing that are other factors at work as well?
[Response: Papers that look at the 20th Century tend to include all forcings – though not just anthropogenic ones (i.e. volcanoes and solar are included) – see Hansen et al for an individual assessment of almost all the forcings we can think of. Prior to that, the natural mechanisms are obviously more prominent. Going back to the mid Holocene and further, orbital forcings figure strongly. Did you have anything specifically in mind? – gavin]
Thanks for the article! It’s a bit better to read than some of the latest posts, since the technobabble has been reduced. Not that I’m not intested in the details, but it takes me some time when it’s becoming too flux-compensator-warp-core-like. I nevertheless dig through all of the more complex posts, since I can learn a lot from you guys. I usually find helpful references here to papers I can use in building up climate-related articles in the German-language Wikipedia. I don’t know if there are any German-speaking people here, but if you are, it would be great to see more of you working on articles like Globale Erwärmung (global warming) or my newest ambitions on Folgen der globalen Erwärmung (effects of global warming), and whatever climate-related article you can find. Don’t hesitate to get involved, it’s fun (or isn’t it, William!)
A DANGER IN TALKING ABOUT TIPPING POINTS is shown in Paul Samuelson’s poorly thought-out opinion column (Washington Post 7/5, free registration)
He argues that our knowledge and our political and economic systems make it impossible to “relieve global warming.” So we can do nothing… except pray for a magical deus ex machina (invention of free energy, geoengineering, whatever). Samuelson’s error is that he thinks climate change is an all-or-nothing matter. Talk of a tipping point, a point-of-no-return, etc. is only too likely to encourage this fallacy. It just doesn’t occur to him that there could be a range of policies, with a policy that keeps the temperature in 2100 only five degrees higher better than a policy that lets it get six degrees higher, etc. Hansen & others have shown that there are economically and politically feasible policies with current technology that will reduce the problem. And even if it is already too late to avoid some damage, the sooner we start the better.
Re 31 – IMHO, the reason that the Eemian was warmer was because the Arctic sea ice had melted, and so the amount of solar radiation absorbed in the northern hemisphere was greatly increased. The fact that the Greenland ice cores can only reach back as far as the Eemian shows that the Greenland ice may also have melted then too.
As Gavin mentioned in his post, the Greenland ice is self sustaining, but so is the Arctic sea ice! When it disappears, we will have to lower global temperatures well below those of today to get it to reform.
Gavin, you do not seem to have resolved the problem of what a tipping point is. Is it when the Arctic sea ice goes and we can’t get it back, or was it when the ice started to melt and made it inevitable that it would go?
Samuelson’s editorial seems to me to be either a counsel of despair or a stalking horse for the nuclear industry. By dismissing the moral aspects of continuing behavior that may lead to a disaster of global proportions, he minimizes one of our most potent sources of motivation: conscience. And he is simply wrong in saying that people won’t make sacrificies. People have accepted draconian change in the past once their leaders have shown an understanding of the dangers and made a committment to eqalitarian sacrifice. By dismissing the possibility of shared sacrifice, he’s attempting to rhetorically finesse away any objection to a nuclear solution.
Re: 33: ‘Converting’ people:
I entirely agree with this post. Someone suggested that we need an “environmental Winston Churchill”; someone with credibility who speaks well. Gore has little credibility with many because of US government and industry efforts to attack him (rather than the science) and the general willingness of ‘free’ Americans to reduce everything to a partisan issue. I also entirely believe that the time has come to stop arguing with ‘climate change skeptics’ and start doing things. I think we need a ‘Gandhi for the planet,’ or better, many of them. Climate change skeptics are irresponsible but powerful fools, and need to be treated as such.
Think of it this way: as severe climate events happen and thus the evidence becomes unignorable, the majority of people will realise they’ve been duped. If we also happen to have passed some tipping points and PONR’s along the way, then how will those people react? The BBC article suggests that people may give up and live in the now, or despair and commit suicide. How about anger? Do you think anyone will be just a little upset, and perhaps may want to take out their anger on the world’s largest contributor both to climate change and to suppressing the truth about it?
I find it fascinating that many fields are converging: the hard sciences, ethics, religion, social sciences, and so on. Climate change cannot be considered just a ‘science’ problem.
PS – the BBC article stated that ‘experts convened by the BBC concludes [sic] that climate change is “real and severe”, but maybe not “catastrophic”,’ where Lovelock leaned toward the latter.
What is “severe” climate change?
If Al Gore’s movie, which was quite favourably reviewed here, is a possible ‘tipping point of no return’ on public awareness of climate change, perhaps someone with knowledge and credentials can comment on the inevitable negative feedback loop in public debate, e.g.,
“Someone should come up with a name for this phenomena (sic)….”
Its called ‘climbing on the bandwaggon’. The biggest threat to the case for AGW is ‘crying wolf’.
Re: T. Elifritz
Due to the thermal inertia of the Greenaland and Antarctic ice sheets won’t it be several millenia before they could completly melt away even under conditions much hotter than now?
[Response: Dynamics are as important as thermodynamics here. Recent evidence (e.g. as reviewed by us a few months back) suggests that the demise of large parts of the major ice sheets could potentially take place far faster–on timescales of perhaps several centuries–due to the influence of ice sheet dynamics. For example, crevices at the surface of the ice sheet are now known to sometimes penetrate all the way down to the bottom of the ice sheet forming channels (“moulins”) that allow surface meltwater to reach the bottom of the ice sheet, where it lubricates the ice, allowing it to stream into the ocean at velocities potentially far greater than once envisioned. These processes are still far from perfectly understood, because they require a representation of the fairly complicated rheology involved in ice sheet dynamics. But it appears far more likely that a better understanding of these processes will act to revised our estimates of ice sheet collapse timescales downward, rather than upward. – mike]
re: #38 I take heart in the Samuelson piece’s two concluding statements:
“The trouble with the global warming debate is that it has become a moral crusade when it’s really an engineering problem. The inconvenient truth is that if we don’t solve the engineering problem, we’re helpless.”
In his (lame) attempt to redefine the term “inconvenient truth” and dispossess Al Gore of it, he endorses the Gore stance that the issue is not partisan, but moral. And he steps up to the need to fix the threats to our climate or be lost–for Mr. Samualson at least, the “debate” is over. And finally, no publicity is bad publicity.
So this is now where the climate debate is headed, towards the non linear dynamics of the earth system and whether they can magnify climate change to make it suddenly flip to a new state. these sub systems being
The Amazon and other rainforests drying out
The Siberian bogs (the size of germany, france and the UK combined) start to release methane in accelerating annual volumes
Ice Albedo decreasing
Ocean conveyor (thermohaline systems to some)weakening due to freshening of the seas
And there are probably more sub systems that can feedback and potentially acelerate warming which accelerates the disturbance of the subsystem which accelerates overall warming.
I would imagne that climate has been treated as a linear system since the early days of climate modelling until recently when observed changes are not being picked up by the simulations as much as was hoped and hence the real climate might be taking on a suprisingly rapid (non linear) warming that is yet to be accounted for in the models.
Non linear dynamics and far from equilibrium thermodynamics of which the climate is one such system is a relatively young science and hence maybe as the parameters are pushed from the equilibium to the far from we may see what dynamicists call more interesting system behaviour Doom as people like Lovelock are predicting.
What are the chances of natural, negative feedbacks kicking in at some point? An example of a positive feedback is Arctic sea ice melting, which exposes the ocean, which absorbs far more energy than the snow and ice did, causing the ocean to heat (or the air to cool?). Do similar negative feedbacks occur that tend to keep the climate in its current state?
The phrase “tipping point of no return” has now been used twice in this discussion, once in the title and again in comment 16. I sincerely hope this phrase never escapes into the wild and propagates, You wouldn’t want that on your conscience, now would you Gavin?
>similar negative feedbacks
That was the question that started Lovelock on his research decades ago. There’s a whole lot out there; one simple model is here: http://www.carleton.edu/departments/geol/DaveSTELLA/Daisyworld/gaia.htm
But if acidity goes too high in the oceans, the organisms that produce the sulfates that produce the clouds that cool the ocean could die off, and we’d lose a major feedback loop when most needed, one that’s been observed from space when it blooms:
http://news.bbc.co.uk/2/hi/science/nature/4226917.stm1 February, 2005, 16:31 GMT
Dr Carol Turley, from Plymouth Marine Laboratories told this week’s Met Office and UK government-organised climate conference in Exeter she was very worried.
Countless species, she said, depend on a relatively stable pH to extract calcium to build their shells or skeleton. These include shellfish, snails, starfish, sea urchins and some sea worms that play an important part in cycling minerals in the ocean mud.
Tiny coccolithophorids form vast populations
She is particularly concerned about the effects of acidification on plankton at the bottom of the fisheries food chain called coccolithophorids.
These precipitate calcium to make tiny shells called liths. Each lith is only about 2.5 micrometres (millionths of a metre) across but when the algae bloom en masse the effects can be seen from space.
Unpublished research from Norway suggests that increasing acidity harms the coccolithophorids. This might have consequences for fisheries. Scientists think coccolithophorids will probably be replaced if they drop out of the food chain but they cannot be sure.
Coccolithophorids also play a role in climate change. The algae give off CO2 when they bloom and thus contribute to climate change. But they also produce dimethyl sulphide when they bloom which helps the formation of clouds which reflect back heat from the Sun. The science here is still in its early stages….
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