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Runaway tipping points of no return

Filed under: — gavin @ 5 July 2006 - (Slovenčina)

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 phenomenon….

Regardless of the recent linguistic trends, the concept has been around for a long time. The idea is that in many non-linear systems (of which the climate is certainly one), a small push away from one state only has small effects at first but at some ‘tipping point’ the system can flip and go rapidly into another state. This is fundamentally tied to the existence of positive feedbacks and is sometimes related to the concept of multiple ‘attractors’ (i.e. at any time two different ‘states’ could be possible and near a transition the system can flip very quickly from one to another). Another ‘tipping point’ in non-linear systems occurs when as some parameter varies, the current attractor changes character or disappears. However it is currently being used interchangeably a number of potentially confusing ways and so I thought I’d try and make it a little clearer.

Positive feedback

A positive feedback occurs when a change in one component of the climate occurs, leading to other changes that eventually “feeds back” on the original change to amplify it. The classic ones in climate are the ice-albedo feedback (melting ice reduces the reflectivity of the surface, leading to more solar absorption, more warming and hence more melting) and the water vapour feedback (as air temperatures rise, water vapour amounts increase, and due to the greenhouse effect of the vapour, this leads to more warming), but there are lots of other examples. Of course, there are plenty of negative feedbacks as well (the increase in long wave radiation as temperatures rise or the reduction in atmospheric poleward heat flux as the equator-to-pole gradient decreases) and these (in the end) are dominant (having kept Earth’s climate somewhere between boiling and freezing for about 4.5 billion years and counting). But it is the postive feedbacks that make weather chaotic and climate interesting.

People often conclude that the existence of positive feedbacks must imply ‘runaway’ effects i.e. the system spiralling out of control. However, while positive feedbacks are obviously necessary for such an effect, they do not by any means force that to happen. Even in simple systems, small positive feedbacks can lead to stable situations as long as the ‘gain’ factor is less than one (i.e. for every initial change in the quantity, the feedback change is less than the original one). A simple example leads to a geometric series for instance; i.e. if an initial change to a parameter is D, and the feedback results in an additional rD then the final change will be the sum of D+rD+r2D…etc. ). This series converges if |r|<1, and diverges (‘runs away’) otherwise. You can think of the Earth’s climate (unlike Venus’) as having an ‘r‘ less than one, i.e. no ‘runaway’ effects, but plenty of positive feedbacks.

Tipping points

So are there ‘tipping points’ in climate? One way to assess that is by looking for elements of the physical system where we think that there is a threshold behaviour. Two frequently discussed examples are the overturning circulation in the North Atlantic and the summer sea ice in the Arctic. In both of these cases, the existence of these phenomena can be disrupted in models (and there is evidence of similar behaviour in the real world) by small changes in freshwater and increasing polar amplification, respectively. At some point, both could simply cease to be viable. But we are not very confident of where these points are or how sensitive the threshold is. These are examples of ‘known unknowns’.

There is also the existence of ‘unknown unknowns’ – tipping points that we are as yet unaware of. An example of this kind of surprise happened in relation to the Antarctic ozone hole, where unexpected chemistry on surfaces of ice particles lead to much more efficient destruction of ozone in the polar vortex than had been expected, making an existing concern into a serious problem. By their nature, we are not able to assess how important any such surprises might be, but it is impossible to rule them out entirely.

By far the most common examples of tipping points though are in relation to ecosystems. The extremely complex web of interdependencies that keep ecosystems dynamic and healthy give rise to plenty of potential thresholds and it is extremely difficult to predict consequences of external changes. The myriad influences on the health of ecosystems (habitat loss, logging, urbanization, species introduction etc. as well as climate change) means that it is most likely here that the tipping point concept will be most applicable. Examples such as a rise in minimum winter temperatures that allow a new insect species to gain a foothold in a new ecosystem (pine bark beetles in Alaska), or warming that leads to movement upward in altitude of ecosystem zones that end up reducing the area of existing alpine biomes. As the planet warms, it is easy to imagine an increasing number of ‘tipping points’ being passed, each related to some different sub-system of the climate or biosphere.

Points of no return

Are ‘tipping points’ the same as the ‘points of no return’ oft used in the media? For a species that becomes extinct as a result of crossing a threshold, the answer is obviously yes. But in the physical climate system, are there genii that can’t be put back in the bottle? This is really a question of time scale. Changes to aerosol concentrations can be reversed in a few weeks after an emission change. CO2 levels however are much slower to change and are already very unlikely to revert to pre-industrial values in any scenario over the next few hundred years. In this minimal sense the climate is already past the point of no return compared to pre-industrial climate.

The ‘known’ physical tipping points described above have natural timescales that determine whether ‘returns’ are possible. The Arctic sea ice, for instance, has timescales of around 5 years to a decade, and so a collapse of summer ice cover could conceivably be reversed in a ‘cooling world’ after only a decade or so (interactions with the Arctic ocean stratification may make that take a little longer though). Model simulations of the thermohaline circulation indicate that for small perturbations, recovery can occur in a few decades. For larger perturbations (i.e. complete collapses) intermediate-complexity models suggest that in some regimes these changes can be quasi-permanent, although this behaviour has not yet been fully explored in current state-of-the-art GCMs. The clues from the paleo-record indicate that there is likely a bi-modal spectrum of overturning states in glacial climates, but there is no evidence of such multiple steady states in the Holocene. Thus there is no strong reason to think either of these ‘tipping points’ are really irreversible – though that is not to imply that the process of loss and recovery wouldn’t have significant impacts.

The big ‘point of no return’ though is usually associated with the melting of the ice sheets – in particular, Greenland and the West Antarctic Ice Sheet (WAIS). Currently the ice sheets exist in part because they already exist i.e. the reason it snows on Greenland is in some large part because there is a large ice sheet there. Should the ice sheet start to melt in a serious way (i.e. much more significantly than current indications suggest), then lowering of the elevation of the ice sheet will induce more melting simply because of the effect of the lapse rate (air being warmer closer to sea level due to pressure effects). Thus if Greenland disappeared, it is unlikely that it would grow back even under current climate, let alone in a warmer world. So loss of either of these ice sheets would indeed be an effect with ‘no return’, at least on any reasonable human timescale.

10 years?

Jim Hansen was widely quoted earlier this year stating that there were likely only 10 years left in which serious actions could be taken to prevent ‘dangerous anthropogenic interference’ on climate occurring in the future. He described this as a ‘tipping point’, but it should be clear that he was not using the term in exactly the same way as I defined above. He very specifically was not indicating that some irreversibly large change in climate would happen in 10 years. Instead he was pointing to the trajectory of increasing CO2 emissions that continue to add to atmospheric concentrations. Actual and projected emission levels are already at the high end of Hansen’s ‘alternative scenario’ which was suggested as an achievable outcome (based on significant control efforts) that kept forcings (including Co2, CH4 and black carbon) below a level that Hansen considered would be ‘dangerous’ (specifically a level that would avoid the melting of any significant fraction of the WAIS or Greenland ice sheet). It is the inertia of societal infrastructure, the carbon cycle and the climate that implies that at any point there is a significant warming that is already ‘in the pipeline’ (and thus very difficult to avoid). We have estimated this at about 0.5 C. Hansen’s statement can therefore be read as a comment on a ‘point of no return’ of the human-climate system, rather than the climate system in a purely physical sense.

The ’10 year’ horizon is the point by which serious efforts will need to have started to move the trajectory of concentrations away from business-as-usual towards the alternative scenario if the ultimate warming is to stay below ‘dangerous levels’. Is it realistic timescale? That is very difficult to judge. Wrapped up in the ’10 year’ horizon are considerations of continued emission growth, climate sensitivity, assumptions about future volcanic eruptions and solar activity etc. What is clear is that uncontrolled emissions will very soon put us in range of temperatures that have been unseen since the Eemian/Stage 5e period (about 120,000 years ago) when temperatures may have been a degree or so warmer than now but where sea level was 4 to 6m higher (see this recent discussion the possible sensitivities of the ice sheets to warming and the large uncertainties involved). In 10 years time CO2 levels will likely be greater than 400 ppm and the additional forcing combined with the inertia of the system will be make it increasingly unlikely that we will avoid a further 1 deg C or more warming. While the ’10 years’ shouldn’t be read as an exact timetable, it is surely in the right ballpark. 30 more years of business-as-usual will make it impossible to keep temperatures from rising beyond Eemian levels (see here for some discussion of stabilisation scenarios), and decisions (on infrastructure, power stations, R&D, etc.) that are being made now will determine the emissions for decades to come.

One point or many?

Much of the discussion about tipping points, like the discussion about ‘dangerous interference’ with climate often implicitly assumes that there is just ‘a’ point at which things tip and become ‘dangerous’. This can lead to two seemingly opposite, and erroneous, conclusions – that nothing will happen until we reach the ‘point’ and conversely, that once we’ve reached it, there will be nothing that can be done about it. i.e. it promotes both a cavalier and fatalistic outlook. However, it seems more appropriate to view the system as having multiple tipping points and thresholds that range in importance and scale from the smallest ecosystem to the size of the planet. As the system is forced into new configurations more and more of those points are likely to be passed, but some of those points are more globally serious than others. An appreciation of that subtlety may be useful when reading some of the worst coverage on the topic.

207 Responses to “Runaway tipping points of no return”

  1. 51
    cwmagee says:

    Related to the runaway tipping point of no return is the magic number of 2 degrees. It has been suggested that this is the limit of warming that we should aim for, in order to rein in the tippy runaways. What is the precision on this number, and where does it come from?

  2. 52
    Hank Roberts says:


    By typing “two degree” into the Search box at the top of the home page, I found this quickly:

    In the main entry there you’ll find: “… Setting a limit to global warming at 2ºC above pre-industrial temperature is the official policy target of the European Union, and is probably a sensible limit in this sense. But, just like speed limits, it may be difficult to adhere to….”

    If you read a bit more you’ll find why; see the links in that thread.

  3. 53
    Mark Hadfield says:

    Re 50 and the magic number of 2 degrees…

    As I understand it, this number is due to James Hansen and appears in a New York Review of Books article at

    Note that this is two degress *Fahrenheit*.

    Hansen justifies the figure there. He srgues out that the warmest interglacials in the last million years or so were about 2 degF warmer than today and that a larger warming, of around 5 degF, would lead eventually lead to the disnitegration of the ice sheets. But read it for yourself.

    I sincerely hope that the full phrase “runaway tipping point of no return” will never be used again. Doh, I’ve just done it!

    [Response: Hansen is talking about the change from today. The 2 deg C number comes from the Eurpoean Union and refers to the change from the pre-industrial. -gavin]

  4. 54
    Mark Hadfield says:

    These thresholds are becoming confusing. Hansen’s use of 2 deg Fahrenheit is particularly unfortunate when a threshold of 2 deg Celsius has already been promulgated to the public.

    Re the 2 degC number, I have just been reading the Steering Committee Report from the Conference on Avoiding Dangerous Climate Change, Exeter Feb 2005:

    Here I read:

    “…a regional increase above present levels of 2.7 degC may be a threshold that triggers melting of the Greenland ice-cap”

    with the footnote that

    “This [regional 2.7 degC increase] would be associated with a global temperature rise of about 1.5 degC above present or about 2 degC above pre-industrial temperature”

    and then

    “In general, surveys of the literature suggest increasing damage if the globe warms about 1 to 3 degC above current levels. Serious risk of large scale, irreversible system disruption, such as reversal of the land carbon sink and possible destabilisation of the Antarctic ice sheets is more likely above 3 degC. Such levels are well within the range of climate change projections for the century.”

    Later they talk about options for “limiting climate change to 2 C above pre-industrial”.

    OK so they seem to have settled on 2 degC above pre-industrial as a useful policy target and they’re saying that 3 degC above present would be really bad.

    Is this the source of the 2 degC threshold or has it appeared elsewhere?

    And Hansen is saying we shouldn’t risk 2 degF (1.1 degC) above present, which is 1.8 degC above pre-industrial (assuming present minus pre-industrial is equal to the 20th Centrury warming of 0.7 degC)

    Like I said, these threshold are becoming confusing.

    Not that anyone’s going to take any notice of me, but I think it unwise to use pre-industrial global temperature as a baseline when the global-average surface temperature seems to have varied by several tenths of a degC during the half-millenium or so preceding the industrial era. On the other hand, pre-industrial CO2 was relatively stable and is a sensible baseline.

  5. 55

    As I noted way up in #21, the IPCC TAR picked a number of 2-3 C from 1990 as the level at which tipping points start to become a significant risk. However, one can cause significant damage to the environment even without reaching a tipping point, so the threshold at which climate change becomes subjectively dangerous may well be below this.

  6. 56
    S Molnar says:

    As one who has taken Gavin to task on his English usage in the past (Gavin, people are trying to tell you that “phenomena” is plural. Pay attention.), I am obliged to confess admiration for his delightful pleonasm “runaway tipping points of no return” – I fully intend to plagiarize it. I am also charmed by his fanciful plural form “genii”, which is really the plural of “genius”, of course. Full marks.

    [Response: A little idiosyncracy in language should be allowed I think…. – gavin]

  7. 57

    Surely at a CO2 rise of 2 to 3 ppm/y, and rising, we will go crashing through every so called ‘tipping’ point like there is no day after tomorrow. At that rate, I would be very surprised to have any of our descendents see any vestige of continental or polar ice in 1000 years. Clearly 1000 years of fossil fuel combustion defines the concept of unsustainability, considering that almost everyone on the planet is already observing the local macroscopic effects of climate change. I’m not real confident of Paul Hearty’s 30 foot line, but I can clearly see the seven foot line, and the 19 foot line (the two meter and six meter fluxes), etched into my back yard. I’ve got 18 feet, most of it is at or just above sea level (mean high tide) that’s all I’ve got, and we’ve been into beach erosion now for almost 10 years, whereas things have been fairly static previously since the 30’s. On the Wisconsin side, well, the change in the snow line is nothing less than stunning. Everything is rapidly shifting north, even the relatively uneducated country folk in my area can easily discern it with just casual observations.

    Everything points to a shock associated with the spike. We’ve got one more hurricane seasons until another election, three more until another president. Local observations indicate this is supposed to be an off year for hurricanes, so we shall see. When the house of cards we have constructed for ourselves falls, well, it’s all over.

  8. 58
    Steve Latham says:

    From the original:
    “… if an initial change to a parameter is D, and the feedback results in an additional rD then the final change will be the sum of D+rD+r2D…etc. ). This series converges if |r|<1, and diverges (‘runs away’) otherwise. You can think of the Earth’s climate (unlike Venus’) as having an ‘r’ less than one.”

    But Venus’ climate has stabilized (“converged”, right?) — so really the Earth and Venus are similar (currently) in terms of this discussion because neither is currently running away. Correct?

    [Response: Point taken. I was implicitly thinking about the theoretical situation of two similar planets to Earth, one in Venus’s orbit, one here. – gavin]

    Re: 49 — I’m not worried about the meme “turning point of no return” — if it was so successful I think the Malaysians would already be saying it. A common Department of Redundancy Department phrase there is “another one more.”

  9. 59
    Alastair says:

    Re 58 Steve, you are right to say that Venus has stabilised, and so is similar to the Earth.

    The stabilistaion of Venus is caused by the surfur dioxide clouds which formed when the surface became hot enough to vaporise the sulfur. The Earth’s climate is also stabilised by its albedo, viz. clouds and ice sheets. When the size of the ice sheets change, the climate becomes unstable until the cloud system has altered to compensate. Continental ice sheets change slowly because of their uneven relief, and their slow retreat due to great thickeness. Sea ice sheets change suddenly because of their even relief, thinness, and the forcing of the ice albedo effect. They cause rapid climate change.

    When the Arctic sea ice suddenly disppears the climate will warm until it settles into a new state where there is increased cloud to compensate for the loss of albedo from the sea ice. One would assume that this would be a climate like that of the Eemian, when tropical animals cavorted in London’s river Thames. But what was the climate like in the mid-west of the USA?

  10. 60
    Stephan Harrison says:

    I think a much better phrase is “catastrophic runaway tipping points of no return” which is easily reduced to CRTPNR. Rather elegant I think.

  11. 61
    pete best says:

    In the alarmist climate science book called “the last generation” linear climate change is labelled as Type I whilst the non linear type is labelled Type II. Apparantly the IPCC like type I more than Type II so as to not appear to alarmist in order to offend the climate skeptics.

  12. 62
    Simon Donner says:

    Mass coral bleaching is a non-linear response to stress; an individual event could be thought of as pushing a coral ecosystem past a “tipping point”. Corals may bleach – a breakdown of the symbiosis between the reef-building animal and the microalgae in its tissue – when the seawater warms past a threshold (e.g. temperatures are ~1-2 deg C warmer than the usual annual maximum for a whole month). Bleaching events, however, are individual episodes. As the oceans warm, the concern is that the frequency of events will surpass the rate at which coral reef ecosystems can either adapt (to warmer temperatures) or recover (from bleaching events).

  13. 63
    Bruce Marshall says:

    Re: #38, the Washington Post columnist in question is the conservative Robert Samuelson, not the great economist Paul Samuelson.

  14. 64
    Eric Swanson says:

    – In discussing “tipping points”, the THC may be one of the most important. It’s worth noting that this year (2006) the sea-ice cover in the Greenland Sea was reduced considerably compared to that seen in recent decades. The so-called “Odden Ice Tongue” did not appear in January, February or March, as may be seen from these graphics depicting monthly extent derived from satellite images:

    One may select individual months and years for viewing. The purple curve outlines the median extent. The Odden Ice Tongue is the “hook” seen in this curve just to the west of Greenland and north of Iceland. This feature has been associated with deep convective events or “chimneys”, which have been seen in the Greenland Sea in past years. Whether there is a direct link between the deep convection and the Odden Ice Tongue is a question of great interest and study. Previous measurements of the Greenland Sea indicated that there was a near shutdown of deep convection exhibited there during the late 1970’s and early 1980’s. Recent studies have shown variation in this feature and there have been other years in which it did not prominently appear.

    J. C. Comiso, P. Wadhams, L. T. Pedersen, R. A. Gersten, Seasonal and interannual variability of the Odden ice tongue and a study of environmental effects JGR. 106, Number C5, 9093-9116, May 15, 2001.

    This apparent change in sea-ice may be part of a multi-year oscillation, such as the NAO, or it may be an indication that larger changes are underway. If the disappearance of the Odden Ice Tongue is evidence of a weakening or shutdown of the deep convection, this may be a cause for immediate worry.

  15. 65
    sidd says:

    Re: 64 — the Odden ice tongue
    I cannot exactly tell from the picture in the link but it appears that the Odden ice hook forms north of the West Jan Mayen Ridge and Jan Mayen Island ? Can someone say if that is the case ? I ask because I notice that there is a hook in the 1000 fathom contour right about there.


  16. 66
    Lynn Vincentnathan says:

    It’s not tipping points for the climate I’m worried about. (Does weather die or feel pain? Or do ice sheets & other inorganic matter?) It’s people, other biota, and ecosystems & their death/harm & collapse I’m more worried about (which this article does suggest as the more common realm of discussing tipping points).

    So, what I’d be intersted in is how many people will die from all effects of GW if the average temp increases 1, 2, 3, 4, 5, or 6 degrees. And I’m more interested in “runaway” in human terms than geological terms — the point at which nature takes over the warming via positive feedbacks, even if people reduce GHGs 50% or 80% or 100%. That is, runaway from any human control — not that we shouldn’t keep reducing so as to reduce the harms even if we do lose our ability to halt and/or reverse the warming.

    Then there are social tipping points — when the material world gets really bad, society may devolve into a chaos of each man for himself (skip the women & children), or rachet up to some totalitarian regime, or both. Why would the contrarians want to risk the very things they fear???

    As the article rightly points out, contrarians may take “tipping point” as something not to worry about until we get right up to it, or not to worry about because it’s too late & already reached. And since no one really knows when we’ll reach the real tipping points (no matter how you define them), then contrarians would argue that it’s best to continue business as usual, without any concern.

    Where there’s life, there’s hope, and we should never give up efforts to reduce our GHGs, regardless of whatever tipping point or point of no return we reach, or how far away or close those tipping points are, until we reach our own personal tipping point of death. I suggest this be motivated not by a STATE OF FEAR, but by a STATE OF LOVE.

  17. 67
    Vicki Lesley says:

    Have been reading all the above comments with great interest. I am developing a documentary series based around the concept of tipping points in relation to climate change but am finding much of the information confusing/contradictory (no doubt some of this can be put down to lazy journalism but even amongst the climatologists I have been talking to there doesn’t seem to be much consensus).

    I have many questions and if any of you could spare the time to correspond with me via email I would be very grateful. In the meantime, could I just throw out one question which may seem a bit basic but which I am having trouble nailing.

    If we assume that there is some global tipping point that can be generally agreed on (perhaps 10-20 years in the future?), can we also assume that by bringing down carbon emissions to an agreed level, we can push this tipping point away into the future by a measurable amount (say to 50-60 years for example)? Or is it the case that we will either reach the tipping point, or avoid it?


    [Response: Interesting point. Essentially you are asking whether any such point might be related to the rate of warming rather than the absolute level of warming. For the ice sheets the answer is probably no (but experts on the subject might have a better idea), but for the overturning circulation or the ecosystem changes, the answer is probably yes – i.e. a slower rate of warming could lead to a different response (allowing time for ocean mixing to mitigate the effects, or adaptation of species to the new conditions). It would need to be a large slow down in the rate of warming though, I think, to make a significant difference (i.e. 20 years versus 10 years isn’t going to do it, but 100 years vs 10 years might). – gavin]

  18. 68

    Its rather further back to the past, comparing present day climate with….:

    “The Eemian/Stage 5e period (about 120,000 years ago) when temperatures may have been a degree or so warmer than now but where sea level was 4 to 6m ”

    …… May be good, but should we be well versed with the climate further back in time, when CO2 concentrations were about 400 ppm, several million years ago I take it. When there was sub-tropical forest, still in exixtence today on Axel Heiberg Island 500 nm from the North Pole. It is likely to this climate we are returning towards, a brief world wide climate description of that time would be rather important.

  19. 69
    Eric Swanson says:

    Re: #65

    Here’s some additional information on the Odden Ice Tongue, including some nice graphics.

  20. 70
    Gar Lipow says:

    I want to thank you a lot for this thread. This is going to come up repeatedly; it is really to good to have it all in one place.

  21. 71
    Ike Solem says:

    This was a great post on an important topic and I found it very helpful in thinking about these issues. Thanks! Especially for the discussion of ‘system return after perturbation’.

    Here’s another simple tipping point analogy –

    Put a pot of water on the burner, and wait for it to heat up -eventually, it reaches a ‘tipping point’ and starts to boil. It’s impossible to predict exactly where each bubble will form, however. This is somewhat analogous to the hurricane issue – there is a temperature threshold, and the hurricane tracks are chaotic. The ‘boils’ are also a dynamic effect which computer models of heated water pots might have missed – similar to ice sheet dynamics.

    Now drop in a fresh egg. It heats up, and at some point the egg proteins reach a ‘tipping point’ and denature(unfold), and you have yourself a hard-boiled egg. Now cool the whole system down. The bubbles disappear and the water returns to its initial state, but the egg proteins remain unfolded – now you have a cool hard-boiled egg. The two tipping points had different long-term effects. I’m unsure, but this seems analogous to the ice sheet issue – for example, under what climate regime would tropical high-altitude glaciers re-form? Are they best viewed as ice age remnants that wouldn’t form today (or yesterday)?

    RE#48 and #59: The long-term negative feedbacks are described by gavin in the first section; however the notion that increased water vapor leads to an increase in cloudiness and that this net effect is a negative feedback – this has been a topic of discussion for a very long time now, hasn’t it? However, a warmer atmosphere means less cloudiness even with more water vapor and then there are seasonal effects. I suppose this can only be addressed via high-resolution modelling – I’d hold off on notions of a tropical paradise in Britain. I searched RealClimate for cloud albedo and came up with these posts.

    I wish there was a RealEnergy site to go along with this one.

  22. 72
    Hank Roberts says:

    >wish there was a RealEnergy site … along with this one

    Me too. Closest I’ve found, not associated with RC, is this:

    That site was recommended in comments here:
    where Tom Athanasiou and Paul Baer wrote:

    “… we prefer to stay in the reality-based world of those (the E.U., the Climate Action Network) who draw the line at 2ºC maximum …. the all-important Who Pays? question has to be answered …. We believe that, if climate mitigation is to be adequate, …. the rich in the South have to pay for real development (which is also fundamental to real climate adaptation), even as the rich in the already developed world pay for accelerated decarbonization…. This is, to be sure, not a realistic position, not in the short term, but there is more to this than short-term politics….”

    That seems to me the basic energy question, written before ocean acidification was found to be heading us toward a food chain collapse by 2100.

    Lovins perhaps would answer that the market pays, because efficient energy is cheaper. Maybe.

    Energy questions, economics questions, intertwingled.

  23. 73
    Grant says:

    Re: #66

    Where there’s life, there’s hope, and we should never give up efforts to reduce our GHGs, regardless of whatever tipping point or point of no return we reach, or how far away or close those tipping points are, until we reach our own personal tipping point of death. I suggest this be motivated not by a STATE OF FEAR, but by a STATE OF LOVE.

    Not very “scientific,” but Lynn, I agree completely. Thanks

  24. 74
    Isaac Held says:

    You briefly mention the disappearance of summertime Arctic sea ice as a potential candidate for a “tipping point”. What is the best evidence from GCMs or other kinds of models that there is hysteresis or multiple equilibria at this point? I have heard speculation over the years about the possibility of changes in oceanic statification creating strong nonlinearity, but where does this discussion stand?

    In the 1970’s work with very simple diffusive energy balance climate models focused on the “small icecap instability” as well as the “large icecap (snowball earth) instability”. If there is an ice-free climate that consistently produces a temperature at the pole that is greater than freezing, then putting an ice cube at the pole, even if the ice reflects all solar radiation, will not be stable, since the warm air will simply diffuse in from the sides. So ice covers smaller than a critical size are unstable, which produces hysteresis and multiple equilibria. The critical size is dependent on the diffusivity. You can google ‘small icecap instability” for some references. But this instability tends to disappear when there is a substantial seasonal cycle in the ice, even in these simple models. Does sea ice in comprehensive climate models produce hystersis at or near the point of zero summertime ice? (I am not implying that I think that the disappearance of summertime ice is not of great concern, nor do I think that the models are necessarily right, I am just curious as to what models are currently telling us about nonlinearity near this point.)

    [Response: Isaac, there are a couple of analyses making their way through the process that look at the IPCC AR4 model behaviour and see evidence for rapid transitions in the sea ice cover. I’m not aware of all the details though. – gavin]

  25. 75
    Paul Duignan says:

    The current dialogue around climate sometimes seems to go like this:

    Public: What’s with this climate change, should I be worried?
    Climate Scientist: Well there’s a reasonable chance that if we don’t make serious changes that temperatures will rise by between 2-5 degrees late this century.
    Public: OK, well I suppose we need to start thinking about it some time soon, and as the temperature starts to track up that will motivate people to do something about it, so thanks for letting us know, keep in touch, I’ll let you know when I get some free time to concentrate on it.

    An alternative version fo the dialogue could be:

    Public: What’s with this climate change, should I be worried?
    Climate Scientist: Well, for a start we know that if we don’t make serious changes soon the chances are that the temperature will rise at least 2-5 degrees. But that’s only the start, we know that there are tipping points which, if triggered would push the temperature way beyond that. We don’t know when these might be triggered, we haven’t factored them into our estimate of a 2-5 degree rise. Worse still, we now have clear evidence that the assumptions in our models are wrong (for example how fast Greenland will melt) and we are seeing things happen much faster than we expected.
    Public: So you can’t give me any guarantee that we are not right on track to trigger tipping points within a matter of years?
    Climate Scientist: No I can’t, one of the reasons is that we are already committed to a significant temperature rise which is in the pipeline. So even if I told you that I could see a tipping point coming up in the future, there may be no way to stop us crossing it as the temperature rise in the pipeline plays out. Frankly I am extremely worried about this it is a very very dangerous situation for the world.
    Public: Right, who should I vote for, what do I turn off, where can I park up my SUV?

  26. 76
    S Molnar says:

    Re RealEnergy, it would also be nice if there were a good introductory book on the subject to complement the recent slew of climate change books (Recommendations, anyone?). There’s a rumor that the estimable Gar Lipow, whose thoughts can be found here, on, and elsewhere, is working on one. I hope there is some truth to the rumor.

  27. 77
    Gar Lipow says:

    The rumor is correct. Actually it is finished, and is a solicited submission to a publisher – so I am in hope of seeing it published.

  28. 78
    Ike Solem says:

    As far as renewable energy science goes, the real problem is the lack of a scientific base of expertise in this country – ocean science departments, earth science institutes, meteorology departments – these are all very common. However, there are virtually no renewable energy research programs at any of the major research universities (people always seems surprised by this), and that’s because there is so little funding. There are people who do some research on the side, but it tends to be individual efforts, not ‘organized research units’. Then you have all the intellectual property issues to deal with as well – if you do come up with something useful, who ends up owning it? ExxonMobil has a 5-yr monopoly on any patents produced by Stanford’s Climate and Energy Project, for example.

    I do have a little personal insight into this issue. I received an MS in Ocean Sciences from the University of California, Santa Cruz a few years ago (in the area of marine nitrogen fluxes); at the time I was a recipient of an NSF Graduate Student Fellowship in microbiology – and I transferred into the Biochemistry department hoping to go into renewable energy research, which seemed to be very interesting, important and useful work – I was particularly interested in algal biochemistry (a great oil source) or fungal enzymes (for cellulose digestion) – but when I took these proposals to the Dean of Graduate Studies, he shook his head and said “You will never be able to find funding for this kind of work – can’t you do something else?” – no kidding (he was very nice about it). Compare the number of proprietary pharmaceutical research programs in this country to the number of renewable energy research programs, and you start wondering exactly what is going on. Look through course catalogs for renewable energy classes of any kind – generally, you find nothing. It’s a real travesty, and yet people seem largely unaware of this reality. Little funding means little research and development. If only this government would double NSF’s budget and create a renewable energy funding unit… but don’t hold your breath, they keep cutting the NREL budget while singing the praises of ‘switchgrass’ – unreal.

    There are a number of good renewable energy textbooks (mostly written by Germans or Australians, apparently) but very few publicly accessible books on renewable energy. One of the best is “From Space to Earth: The Story of Solar Electricity” by John Perlin, a fascinating historical treatment of the development of solar PV. You can also take a look at my personal favorite, (warning- 3.5 MB pdf file download) – the NREL Biodiesel from Algae program, killed off in 1997.

    (The Gelbspan link from #72 is interesting, (thanks) but it’s not a scientific discussion of renewable energy technologies, by any means).

  29. 79
    Mark Shapiro says:

    Gar –

    Hope to see your book soon. Please let us know when it comes out!

  30. 80
    Fernando Magyar says:

    RE 77:

    The NREL Biodiesel from Algae program, killed off in 1997

    Seems they really must have killed it because when I try to access the link this is what I get.

    Not Found
    The requested URL / was not found on this server.

  31. 81

    Okay, I’ve written a planetary temperature calculator in javascript and uploaded it to my web site. It gives fair approximations of the temperatures of Venus, Earth and Mars (691 K, 288 K and 221 K versus the observed 735 K, 288 K, 214 K), and is a little oversensitive to CO2 and H2O changes (3.4 K increase on Earth with doubled CO2 and 10.2 K increase with doubled CO2 and H2O feedback — way too high compared to GCM results). But it has the basic physics more or less correct, in a qualitative way. I would have to make the model much more complex to get better accuracy, but I think this one illustrates some basic principles.


  32. 82
    Stormy says:


    Thanks for the link. I was specifically interested in the Maunder Max/Min, which is one of the latest contra-arguments. The references in the paper were very helpful.

    As the general public latches on to each factor, that factor presumably overrides anthropogenic forcings. Not true, of course. Then I have to dig out the facts. Your site is a gold mine.

    Suggestion for the editors of RealClimate:

    Because economists are central to our dealing with GW and the environment in general, I would suggest dropping in on some of the major economic blogs when GW is an issue. And it is just starting to be an issue, a healthy sign.

    The Economic Roundtable gives a brief daily summary of all the major economic blogs. By looking there, you can see if your expertise would be useful. Quickly perusing this site once a week would be sufficient.

    I find your expertise informative and helpful. I would like key economists to have it as well.

  33. 83
  34. 84
    Hank Roberts says:

    >77, 80
    The NREL study PDF file is
    The link in 77 that looks the same has actually been mangled.

    (Practice SAFE TEXT: “copy link” — paste to a text* editor first, to see what you’re actually getting, instead of clicking. What you see is NOT what you get in HTML; typos and malware can be hidden in any editor that ‘interprets’ HTML. Eschew Microsoft Word for this purpose, use Notepad.)

  35. 85
    Eric Swanson says:

    Re: #77

    Your comments on biomass production, particularly algal production as described in the NREL reference point to some big problems. Working in the lab to pick the best species out of thousands or manipulating selected species to improve production may not result in a workable system in the real world. As mentioned in work discribed on page 147, maintaining the proper culture in open ponds is difficult. Any monoculture is unstable and, given the many native species, keeping an algal system “pure” will be nearly impossible.

    Then, there’s the basic engineering problem. Building any pond system as described will require considerable material and effort to construct. If the energy produced is not large, the net return on the capital invested may be small or the production cost of the resulting fuel may be large relative to other energy sources. Economies of scale become difficult to imagine, as the construction of ever larger, gently sloped structures does not seem practical. One should think in terms of building 1,000 square meter parking lots as an example of the difficulty of controlling the flow with these large, shallow ponds. The ground below the ponds is not likely to be completely stable, especially after disturbance due to grading and pond construction. Then, there are the other problems of temperature and salinity maintenance and harvesting to add to the mix. What happens when it rains heavily over a short time period and lots of fresh water is added to the ponds? One implementation (page 162) involved an enclosed system, using a greenhouse type enclosure, which would be very expensive compared to open ponds. One reason what other types of solar systems have had difficulty competing against fossil energy sources is the cost of the material, be it glass, aluminum or plastic, which initially intercepts the solar energy. This becomes especially critical if the overall system has low overall energy conversion in real world operating situations. In sum, I think the engineering difficulties and costs involved would likely kill any large scale operation (see pages 245-247). Smaller scale operations for waste water purification may be a reasonable approach, as there is a secondary benefit to include in the calculations.

  36. 86
    Hank Roberts says:

    Re 82 on the Economic Roundtable page —

    Alternative suggestion — could RC offer an ‘Economists’ link akin to the one you offer journalists? For journalists it’s “embargoed” stories.

    For economists — you could host a conversation for them, invited, with climate scientists. RC has the reputation to attract their interest. Doing it by invitation would cut the chaff.

    I did just peruse the Roundtable link — it does seem to do a good job of summarizing and linking out. Worth a look.

    For example, a link there to discussion of the July 5 Brooks NYT column, here: — discusses how fairness, equity and attachment are important but usually ignored by politicians, for instance. Climate change is one of those equity problems.

  37. 87
    Blair Dowden says:

    Re #81: Barton, your calculator does not work properly in Firefox. When you press the buttons to pre-set the values, the numbers flash on, then disappear.

  38. 88
    Fernando Magyar says:

    Re #85:

    I have just begun to read the study so possibly my opnion will change by the time I finish it. However this excerpt from page 18 seems to contradict your arguments even though your point about the laboratory strains not proving to be optimal in the open pond systems seems to be upheld. It seems that proof of concept was verified nontheless.

    “At the conclusion of the smaller scale tests conducted in California and Hawaii, the program engaged in a competitive bidding process to select a system design for scale up of algae mass culture. The HRP design evaluated at UC Berkeley was selected for scale-up. The â��Outdoor Test Facilityâ�� (OTF) was designed and built at the site of an abandoned water treatment plant in Roswell, New Mexico. From 1988 to 1990,1,000 square meter ponds were successfully operated at Roswell. This project demonstrated how to achieve very efficient (>90%) utilization of CO2 in large ponds.

    The best results were obtained using native species of algae that naturally took over in the ponds (as opposed to using laboratory cultures). The OTF also demonstrated production of high levels of oil in algae using both nitrogen and silica depletion strategies. While daily productivities did reach program target levels of 50 grams per square per day, overall productivity was much lower (around 10 grams per square meter per day) due to the number of cold temperature days encountered at this site.
    Nevertheless, the project established the proof-of-concept for large scale open pond operations. The facility was shut down in 1990, and has not been operated since.”

  39. 89
    Grant says:

    Off topic I know, but I’m very curious…

    Why have nighttime temperatures warmed faster than daytime temperatures? It seems to me that the effect of greenhouse gases is strongest when *temperatures* are highest — during daytime — so the greenhouse warming would be strongest during the day. But I’ve looked at plenty of data, so I know that in fact nighttime temperatures have gone up faster than daytime temperatures.

    And a related question: why have wintertime temperatures warmed faster than summertime?

  40. 90
    Gar Lipow says:

    In response to question – “why greater warming effects at night and in winter?”

    According to the Scientific American Blog:

    >”Greenhouse gases also have distinctive effects on the range of temperatures experienced by the surface. At night, the ground cools down by emitting infrared radiation, whereas during the day, the infrared cooling is secondary to solar heating. Because greenhouse gases impede the cooling but not the heating, they exert their greatest influence at night. If they are the cause of global warming, average nighttime temperatures should increase more than daytime ones — reducing the total daily temperature swing. (To be sure, the trend can be offset by changes in cloud cover and soil moisture.)”

    >”For the same reason, greenhouse gases affect wintertime temperatures more than summertime ones, reducing the total annual temperature swing, and high-latitude surface temperatures more than low-latitude ones. These effects are magnified by snow and ice: by reducing snow and ice cover, warming reduces the reflectivity of the ground and allows more solar energy to be absorbed, further increasing the warming; conversely for cooling.”

    I’ve also heard arguments that as global dimming is lowered this effect will be reduced.

  41. 91
    Grant says:

    Re: #90

    I had seen the SciAm blog, but frankly, I wasn’t satisfied with that explanation. So I made a very crude computer model of diurnal heating and cooling, and when I increase the greenhouse effect the diurnal temperature range goes up.

    Any suggestions?

  42. 92
    Gar Lipow says:

    Umm – I’d have to see your computer model. You have the words “very crude” bolded, but no link. Anyway your computer model depends on assumptions. I suspect there are some physics or engineering going on that the popularization I linked to does not go into. For that you will have to wait for actual scientists.

    I can take a guess – but it probably will not be right.

    I’m guessing that heat gets stored during the day. Because you have heat coming in less of it radiates out than at night when the air is cooler. (Smaller temperature differences result in smaller heat losses; the warmer daytime air acts as insulation – reducing additional flow of heat from thermal mass into the air; real engineers and scientists – is there where I start to go wrong?). At night you no longer have heat added. The air is cooler. So the heat stored in various types thermal mass gets radiated out faster. And of course since it is stored heat it is almost all radiated out in wavelengths that reflect back from greenhouse gases.

    Wothehell – if I’m wrong the real scientists can use this post as their straight-line when they get around to it.

  43. 93
    Steve Bloom says:

    Re #60: Let’s go whole hog: “*abrupt* catastrophic runaway tipping points of no return” = ACRTPNR :)

  44. 94
    Hank Roberts says:

    I’m thinking of a short form — “lemming points” — the precipices defined by a propensity for rushing blindly toward them, eh?

  45. 95
    Lynn Vincentnathan says:

    RE #89, the (unscientific) way I figure it is the GHG blanket effect. Of course days are usually warming than night because of the sun, but if you keep a blanket on during the night & during winters, it keeps you fairly toasty….

  46. 96
    Grant says:

    Re: #89 etc.

    Actually, it’s a mathematical model — I just used the computer to solve the differential eq.

    Input is solar energy, given by
    E(in) = S sin h,
    where S is solar constant * (1-albedo), h is solar altitude. This is given by
    sin h = cos d cos L cos(wt) + sin d sin L
    where d is the sun’s declination, L the observer’s latitude, w the (radian) frequency (= 2*pi /day), and t the time (in days). If the solar altitude is negative, then E(in) is set to zero. Output is blackbody radiation, given by
    E(out) = a T^4
    where a is a constant (emissivity * Stephan-Boltzman) and T is the temperature. Then I used
    dT/dt = const * (E(in) – E(out))
    I simulated greenhouse warming simply by lowering the constant “a”.

    There are a *lot* of oversimplifications here. Even so, when I lower the constant “a” the daytime peak temperature rises more than the nighttime low.

  47. 97
    Gar Lipow says:

    >There are a *lot* of oversimplifications here. Even so, when I lower the constant “a” the daytime peak temperature rises more than the nighttime low.

    How about more than the nighttime *high* not *low*?

  48. 98
    Wacki says:

    If Al Gore’s movie, which was quite favourably reviewed here…….

    Comment by David Goforth � 6 Jul 2006 @ 2:04 pm

    Gavin, you’ve known about this article for a while. You really need to do a piece on this or open up a forum so we can attempt to collectively tear it apart.

  49. 99

    Re #96: A meaningful greenhouse effect model really needs to have both the Earth and the atmosphere. The atmosphere is an enormous reservoir of energy that is maintained in large part by the ability of greenhouse gases to capture thermal radiation. It is so large in fact that averaging over 24 hours at a typical midlatitude site there is significantly more energy transfered from the atmosphere to the ground than there is transferred from the sun to the ground. See:

    I suspect that the problem you are having is that without the natural recycling effects of the interactions between the atmosphere and the Earth you are dissipating energy too rapidly during the night and hence cooling too rapidly. Keep in mind that since most of the radiation that makes it into space is emitted from the atmosphere, it is not merely a matter of adjusting the emissivity, but there is also an effective temperature, T_atmosphere, from where those emissions are eminating that can be substantially cooler than the surface.

  50. 100
    Hank Roberts says:

    Night time:

    I searched here:

    and found this clue, which may lead you to an answer:

    “… “fingerprints” were found that pointed directly to greenhouse warming. One measure was the difference of temperature between night and day. Tyndall had pointed out more than a century back that basic physics declared that the greenhouse effect would act most effectively at night, as the gases impeded radiation from escaping into space. Statistics did show that it was especially at night that the world was warmer….”