Another good TED talk about climate models

Just came across what seems to be an excellent TEDx talk, by Steve Easterbrook, about climate models. One take away message seems to be that climate models are less buggy than virtually all commercially available software, and they’re almost as good as that developed for the space programme. What was also interesting was the comparison – at about 8 minutes – between a year’s worth of weather from a climate model, and a year’s worth of satellite data. Fascinating; I’d never seen such a comparison before. Also included an amusing illustration of the difference between forecasting weather – which we can only do, accurately, for a about a week or so – and climate modelling – which is really about patterns and trends, rather than specifics.

Anyway, there was much more to the talk than just that, but you’ll have to watch it to find out more 🙂

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15 Responses to Another good TED talk about climate models

  1. John Mashey says:

    Yes, from experience Steve knows the topic quite well and can explain it.

  2. Mark Ryan says:

    What a terrific talk, and isn’t the tethered balloon such an effective demonstration of boundary conditions! Steve Easterbrook is one of the best communicators of this kind of thing. It’s easy to see how someone could set up a fan in such a way as to illustrate forcing (in fact, later this year I would like to try just that with some environmental politics students) -turn the fan speed ‘forcing’ up and the balloon’s average range rises (but with greater short term volatility); turn down the fan speed and the balloon’s average range drops. There are probably other ways to ‘perturb’ the balloon’s short term position within the range I guess…

    I have a question for the (many) folks here who understand the physics better than I do: Regarding GCMs overestimating recent surface warming, but underestimating ocean warming, is there a version of a model ensemble which standardises across all forms of heat uptake, so that ocean, surface, etc are represented as a single value? And is there a standard record of global weather that can be converted to a unit of energy in this way?

  3. Mark,
    This paper by Hansen et al. (2011) may be worth looking at. It shows how the response rate of the oceans can change the energy imbalance. Section 9 also includes a discussion of how discrepancies could be a mixture of the wrong response rate for the oceans and uncertainties in aerosol forcing.

    As far as the last part of your comment goes, I think the system heat uptake rate (planetary energy imbalance) is essentially giving what I think you’re asking.

  4. Mark Ryan says:

    Thanks -I’ll get on that

  5. Dan Hughes says:

    Yet another failed analogy that has been invoked to reduce climate process modeling to exceedingly simplistic, and incorrect, terms. The analogy uses the, Weather is an initial value problem, climate is a boundary value problem ( BVP ), approach. The boundary value problem argument is invoked so as to ensure us that climate process modeling is very straight-forward relative to numerical weather prediction ( NWP ). One important aspect of the argument is that the chaotic nature seen in NWP does not negatively impact climate calculations. These arguments are attempts to reduce climate process modeling to the steady-state/stationary case.

    Here is the concluding paragraph:

    ” We cannot predict what the weather will do on any given day far into the future. But if we understand the boundary conditions and how they are altered, we can predict fairly accurately how the range of possible weather patterns will be affected. Climate change is a change in the boundary conditions on our weather systems .” [ bold by edh ]

    The analogy in this case is especially flawed because a very limited fluid flow condition using a “system”, the balloon, that is more correctly described as a problem with a constraint, and not a BVP. The presented argument is meant to ensure us that the boundary conditions for the climate system process modeling solely and completely determine the solution of the IBVP-formulation of the climate process models.

    The boundary conditions at the top and bottom of the Earth’s climate systems include specification of the in-coming SW radiative energy from the Sun, plus energy transport considerations at the interfaces between the atmosphere and the material on the surface of the earth. Note that the out-going radiative energy at the top cannot be specified. Note, too, that the energy fluxes at the interfaces within Earth’s climate systems cannot be specified. These both are calculated by the process models in the GCMs. The out-going radiative energy is an out-come from the process-modeling formulations. In this sense, the boundary condition at the top does not, because it cannot, specify the steady-state/stationary conditions at the top. Relative to energy, Earth’s climate systems are an open system.

    It is very important to note that the out-going energy is determined by the process models that are used to calculate the states internal to the Earth’s climate system; especially including the energy interactions between the sub-systems of the complete system. The balloon, in contrast, is constrained by the string to which it is attached, and cannot affect through feedback the hydrodynamics of its environment. This constraint, very roughly, maybe is supposed to allow representations of the effects of processes internal to the Earth’s climate systems. In this sense the constraint does not model the important effects of the processes internal to the system that cause changes in the radiative energy balance at the top of the atmosphere.

    The BVP assumption requires that balance between in-coming and out-going radiative energy at the top not be affected by the energy exchanges and internal processes that occur within the climate system. I think that the assumption requires that energy exchanges at all the interfaces within the complete system also be in balance. At least to the extent that these processes are not significant relative to the balance at the top. It is difficult for me to envision that the required degree of balance at all the energy-important interfaces within Earth’s climate systems can attain a state of balance.

    Finally note that, in contrast to the characterization in the final paragraph quoted above, the effects of CO2 in the atmosphere are not boundary conditions at the top of the atmosphere and thus are not directly altering the boundary conditions. The CO2 instead causes effects internal to the systems that are included in the climate process modeling, and these effects alter the radiative-energy transport state at the top. The balloon cannot be an analog for the energy content of Earth’s climate systems.

    Finally, really this time, because processes internal to the systems affect states at the boundary of the systems, it is impossible for modeling of Earth’s climate systems to be a BVP in the classic sense of the term for which the specified conditions at the boundary alone determine completely the states within the systems.

    BTW, has it been determined that the constrained balloon can in fact exhibit chaotic motions?

    Corrections for incorrectos will be appreciated.

  6. Dan,
    A long comment which I shall have to digest, but I’ll make a quick comment about this.

    The BVP assumption requires that balance between in-coming and out-going radiative energy at the top not be affected by the energy exchanges and internal processes that occur within the climate system.

    This is – I think – the crucial point. There is little (if any) evidence that internal processes can influence the boundary conditions of our climate. Clearly they can’t influence incoming solar flux, so they only two factors they could influence (in terms of energy balance) is our albedo (reflectivity) and the transmittance of our atmosphere. Maybe there is no definitive proof that internal processes can’t influence the boundary conditions (there are D-O events that may be unforced) but the evidence today suggests on the timescale of interest (decades) the boundary conditions are largely determined externally (i.e., how much energy do we receive, how much do we reflect, how much does our atmosphere trap).

    That, in a sense, is why we can have some confidence about the output from climate models. We have paleo data that is broadly consistent with the warming projections from climate models. We do can do basic physics calculations that also give us similar answers. Of course, there are resolution issues that may we have less confidence about regional effects than global, so climate models clearly are not giving us definitive answers about everything. There is however more evidence to support their global projections than to suggest that they are likely to be wildly wrong.

    has it been determined that the constrained balloon can in fact exhibit chaotic motions?

    Formally, I don’t know.

    You asked me on B-H about whether there was evidence for independent verification of climate models. If you watch the first few minutes of Steve Easterbrooks’ TED talk, it may answer your question (assuming I understand your question).

  7. Steve Bloom says:

    All analogies are imperfect, but some are useful.

    Maybe put a little more effort into understanding rather than misunderstanding, Dan? I seem to recall you’ve been at this sort of thing for years.

    This new paper seems relevant (note open access).

  8. Dan Hughes says:

    Thank you, Steve, for your clear and in depth explanation of explicitly where I have gone astray in the above discussions.

    In this vane, how, exactly is the balloon an analogy for the energy content of Earth’s atmosphere? Even imperfectly?

    Mathematically demonstrate how the constraint on the balloon is analogous to a boundary condition for a partial differential equation, on even an ordinary differential equation.

    Mathematically demonstrate that the constrained balloon does exhibit the spatial-temporal chaotic response observed in Earth’s climate systems.

    Thanks in advance

  9. Dan Hughes says:

    It is a fact that the model equations and numerical solution methods used in GCMs are formulated as an Initial Boundary Value Problem ( IBVP ). Yet we frequently read that the physical domain is actually a boundary Value Problem ( BVP ). This argument is usually presented as a defense against the known limitations encountered in Numerical Weather Prediction ( NWP ). The severe degradation in the fidelity of the NWP results relative to the physical domain is attributed to the chaotic response exhibited by NWP models and methods. The Climate Science argument is that the NWP problem is an Initial Value Problem ( IVP ), that the chaotic response is expected and the short time frame of weather forecasts are completely dominated by the chaotic response. In order to invalidate the argument that, If the weather can’t be accurately forecast for even a few days how can the climate be forecast for a period of 100 years. ( I don’t know where or when this argument was introduced. )

    It is at this point that the BVP concept of climate modeling is invoked. The fundamental hypothesis of the CO2-climate issue is that an equality between the out-going and in-coming radiative energy at the Top of the Atmosphere ( TOA ), when averaged over some, unspecified, time period will attain at some, unspecified, future time . My interpretation of the BVP argument is that this equality imposes a constraint on the climate problem. In essence, the argument says that the initial values and early-time chaotic response are immaterial to calculation of the response of the climate. It is also my understanding that nothing beyond the hypothesized radiative-energy equality at the TOP is given to support the argument.

    There are a few problems with the BVP argument in both the physical and mathematical domains. In the physical domain I think the argument means that the physical phenomena and processes occurring within Earth’s climate systems do not affect the out-going radiative energy. ( This statement ignores that the state of the atmosphere in fact affects the amount of energy that penetrates into the atmosphere. ) In other words, the climate-change problem is solely and purely a radiative-energy transport problem in a practically non-participating medium and is unaffected by conditions at interfaces within the climate systems. If this is the case, I think the problem would have been solved several decades ago.

    The non-isotropic, inhomogeneous time-variations of radiative-energy transport interactions within Earth’s atmosphere must somehow average out over the time-averaging period. Chaotic response does not decrease, so long as the conditions for chaotic response obtain, no matter the length of time of interest. The average of chaotic response is also chaotic. Long term averages of chaotic response are chaotic.

    The initial state of Earth’s climate systems do in fact affect the response to changes internal to the systems. The initial surface albedo, for example. The initial temperature level is important relative to changes in the phases of water; liquid-to-vapor, liquid-to-solid, and versa vise. The different calculated responses whenever the boundary conditions are changed in the modeling approach; fixed Sea Surface Temperature vs. coupled atmosphere-ocean modeling, etc. Cloud covered vs. cloud free, water vapor present or not, and etc.

    In the mathematical domain, the energy leaving a solution domain cannot be specified. A useful rule of thumb is that if you can’t built a physical realization of the boundary condition in the laboratory, it’s not a valid boundary condition. If you don’t want to go with a rule of thumb, you can work out the compatibility conditions and associated eigenvalues and eigenvectors for the model equation system. Generally, any physical quantity that can be affected by the processes occurring within the solution domain cannot be specified at the exit from the domain; temperature, density, internal energy, enthalpy, among others. You will find that the eigenvectors for these quantities always point out of the solution domain at the exit surfaces and into the domain at the entrance surfaces.

    Mathematically the purely radiative-energy transport problem for a grey ( isotropic, homogeneous ) interacting media can be set up as a boundary-value problem by setting the out-going energy equal to the in-coming energy at the TOP. An analytical solution to the Schwarzchild equation, under sufficient simplifications including a 1D solution domain, does exactly this. The approach introduces discontinuities into the solution at both boundaries.

    Given the measured data at the TOP it is highly unlikely that the equality is set in GCMs. Doing so when data indicate that out-going exceeds in-coming would ‘trap’ excess energy internal to Earth’s climate systems, and when the data indicate in-coming exceeds out-going allow ‘to much’ energy to be rejected.

  10. Dan,
    It is just an analogy. None of them are perfect.

    I’m rather failing to see your issue with the whole Boundary Value Problem aspect of this situation. On long timescales the evidence suggests that our climate respond to forcings. These forcings produce feedbacks, and together set the global properties of our climate. In that sense it is a boundary problem. On the other hand, there is clearly internal variability that can move energy around the climate system. It’s also possible that this variability may influence the feedback response, but there is little evidence to suggest that internal variability – alone – can produce long-term variations in our climate.

    So, I don’t quite understand the issue you have, unless you’re saying “maybe it varies a little more than we think” which I would argue is represented by the range of results from the produced by an ensemble.

    Here’s a question for you. Do you think that there is a good chance that doubling atmospheric CO2 could produce a transient warming response outside the range 1 – 2.5 degrees and a equilibrium response outside the range 1 – 4.5 degrees?

  11. Dan Hughes says:

    Some analogies are useful. Useful analogies are those that correctly capture the essence of the situation interest.

    In the physical domain, this analogy purports to present some information related to the effects of the addition of CO2 to Earth’s atmosphere on changes in the state of that atmosphere. Specifically, to increases in the energy content of the atmosphere and the effects of those changes on the spatial-temporal chaotic nature of Earth’s climate systems.

    In the mathematical domain the analogy also introduced mathematical-modeling aspects by use of the phrase Boundary Value Problem.

    Kindly map the components of the analogy to (1) the physical domain comprised of the atmosphere, its energy content, and its spatial-temporal chaotic nature, and (2) the mathematical properties and characteristics of boundary value problems for partial differential equations.

    Some analogies are imperfect. Imperfect analogies are those that falsely present conditions that are not related to the situation of interest.

    In the absence of any additional clarification by Steve Bloom, it is an absolutely certainty that it is he who has failed to understand that the purported analogy cannot be mapped to the physical domain of interest.

  12. Dan,
    I’m really not getting your issue. As I see it, the analogy is really just trying to suggest that the broad (energetic) properties of our climate are largely constrained by the incoming solar flux, our albedo, and the composition of our atmosphere (greenhouse effect). However, other factors can influence the actual properties (internal variability) so these external condition (boundary values, if you like) don’t precisely determine the properties, but they do constrain the conditions to remain close to the equilibrium condition set by these external factors. So the balloon can move around, but it can’t move too far away from the equilibrium conditions set by these external factors.

    To be honest, I’m not terribly interested in having an argument about whether or not an analogy is perfect or not, or even good enough or not. If you don’t like it, don’t use it.

  13. To me this is not a case of analogy but directly a statement about the nature of the problem rather than of the method used to solve it.

    The problem has the nature of a boundary value problem, when the result is determined by the boundary values rather than initial values. That’s true even, when the method used to solve it solves first a set of initial value problems.

    Climate is characterized by the statistical properties of a set of variables rather than by any single instant or trajectory, Thus the climate projections can be determined by calculating a sufficient number of trajectories and calculating the statistical properties of variables specified by the trajectories.

    It’s not uncommon in other physical problems that a stationary state is determined by boundary conditions, while it’s most easily determined in practice using a dynamic model that represents an initial value problem. The result may represent a single asymptotic state or statistical properties of a fluctuating state as the do in the case of climate projections.

    Whether a climate model converges to a well defined description of climate is not self-evident, as some types of chaos would not allow for that, but evidence for an answer can be found out with a large enough number of calculations that start from different initial states. Whether the real climate would have such well defined properties in case of stationary boundary conditions is not self-evident either, but it makes sense to assume so, if the models behave that way.

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