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Chaos theory and global warming: can climate be predicted?

What the science says...

Select a level... Basic Intermediate
Weather is chaotic but climate is driven by Earth's energy imbalance, which is more predictable.

Climate Myth...

Climate is chaotic and cannot be predicted
'Lorenz (1963), in the landmark paper that founded chaos theory, said that because the climate is a mathematically-chaotic object (a point which the UN's climate panel admits), accurate long-term prediction of the future evolution of the climate is not possible "by any method". At present, climate forecasts even as little as six weeks ahead can be diametrically the opposite of what actually occurs, even if the forecasts are limited to a small region of the planet.' (Christopher Monckton)

One of the defining traits of a chaotic system is 'sensitive dependence to initial conditions'. This means that even very small changes in the state of the system can quickly and radically change the way that the system develops over time. Edward Lorenz's landmark 1963 paper demonstrated this behavior in a simulation of fluid turbulence, and ended hopes for long-term weather forecasting.

However, climate is not weather, and modeling is not forecasting.

Although it is generally not possible to predict a specific future state of a chaotic system (there is no telling what temperature it will be in Oregon on December 21 2012), it is still possible to make statistical claims about the behavior of the system as a whole (it is very likely that Oregon's December 2012 temperatures will be colder than its July 2012 temperatures). There are chaotic components to the climate system, such as El Nino and fluid turbulence, but they all have much less long-term influence than the greenhouse effect.  It's a little like an airplane flying through stormy weather: It may be buffeted around from moment to moment, but it can still move from one airport to another.

Nor do climate models generally produce weather forecasts. Models often run a simulation multiple times with different starting conditions, and the ensemble of results are examined for common properties (one example: Easterling 2009). This is, incidentally, a technique used by mathematicians to study the Lorenz functions.

The chaotic nature of turbulence is no real obstacle to climate modeling, and it does not negate the existence or attribution of climate change.

Last updated on 8 September 2010 by chuckbot.

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Comments 51 to 63 out of 63:

  1. Aside from KR's answer, you might like to look at Realclimate here and here for comments from the people that do the modelling
  2. scaddenp - Agreed; those are well written, certainly better than I can do late on a Friday night.

    Ed Loretz was truly a genius.
  3. scaddenp @51 & KR @50

    Thanks. Those were interesting discussions to read. I believe they confirm, as I was trying to point out, that there is indeed chaotic behaviour in climate models themselves. When one takes long averages of climate model output it does not appear chaotic - by rather reflects the forced response of the system - I agree. That is why climate models have performed well at predicting the forced response to CO2 so far. This success does not discount the possibility that the climate system could "flip" into a totally separate equilibrium, given enough forcing. This is the idea of abrupt climate change, and although the chances of this may be very small - it certainly should not be ruled out as a possibility.

    This type of chaotic behaviour actually exists throughout a hierarchy of models: Stommel's classic analytical model of the thermohaline circulation is very simple, yet demonstrates mutiple equilibria are possible for the oceanic circulation. People in the field have sometimes questioned whether this behaviour would exist in a complex-model: The new results from the MITgcm team confirm that it does.
    The MIT experiments use a state-of-the-art fully coupled AO-GCM, including a dynamic-thermodynamic sea-ice model.
    The model is therefore similar to any AR4 model in terms of the ocean-atmosphere dynamics (it had a simplified representation of the continents though).
    (The MIT study by Ferreira et al. )

    I'm not trying to argue the predictability of the forced response to CO2 - its clear the models are capable of that. I'm suggesting that there are good reasons to carefully consider what uncertainties exist - because we may have underestimate the climate risks associated with our CO2 forcing.
  4. Completely stuffed that post... Trying again.

    That is an interesting paper Neil. Coincidentally, someone else I think has asked about at RealClimate
    I have posted the link to this paper. I would say stay tuned.Phil
  5. neil - Agreed, multiple equilibria are very possible. In fact, that was discussed here in the What would a CO2-free atmosphere look like thread.

    One important point about the dynamics, though - many times a particular equilibrium (a local minima in terms of the N-dimensional state space of the system) can be quite robust, stable through a fair amount of peturbation yet remaining in that region. Small perturbations shift the system a bit, but it tends to return to the local minima. Only upon a very large perturbation can such a system be moved over a ridge to another valley in the state space, another equilibrium, where it again will be stable until a large perturbation shifts valleys again.

    The thread I referenced shows that for a very simple model - there are three different equilibria for a single value of CO2, but the shift to a different valley of stability regarding CO2 concentrations takes a very large perturbation. I find it very interesting that this has now been shown for more complete models of the climate, although given state space behavior it's not entirely surprising.

    At the edges of the equilibria are the phase changes - glaciation, melt of the icecaps, severe thermohaline shifts, clathrate release, and so on. Large perturbations to watch out for...
  6. neil - Gah; all that typing and I forgot to include the main point.

    Given a system with multiple equilibria, a wide variety of initialization points will almost certainly provide a sampling of the equilibria, with various initializations stabilizing to local minima in the state space.

    That doesn't mean it's easy to move from one equilibrium to another, just that they exist. That said, we look to be heading to an ice-free Arctic, and if we maintain high temperatures for a few millennia we may see significant loss of the Antarctic as well.

    Florida (and Bangladesh) are not great long term real-estate investments.
  7. Sadly, this skeptic meme has resurfaced at WUWT. The poster in the June 13th item, Dr. Andy Edwards (not a climate scientist, mind you - his background is in AI and chaotic systems) claims climate is unpredictable based on the chaotic behavior of weather.

  8. I posted a link back to this discussion on WUWT. It will be interesting to see if there's any response.
  9. The parts of chaos theory that worry me in the context of climate change involve phase shifts and Lorenz' "strange attractors." Heating a teapot full of water from 70 degrees (F) to 211 degrees (F) just means hotter water, but with just a little more heat making it one degree hotter, a phase change occurs and the water starts turning into steam. Strange attractors often occur in non-linear systems where huge numbers of observable data circle around one region of a graph, but then, either due to a slight pertubation or for no apparent cause, the data starts to circle around another portion of the graph. The implications for climate change could be profound, but not readily testable. While temperatures now are generally circle around a mean temperature with a range of about -10 degree (F) to 110 degree (F), these aspects of chaos theory suggest that it is conceivable that the next tiny increment of carbon dioxide in the air could cause a radical shift with mean temperatures and ranges far different up OR down. I'm not suggesting that this is true, but it is one possible explanation for another problem with climate models. Last I heard, we still don't have good models to explain either why the earth has entered ice ages or how it ever gets out of one. Chaos theory suggests that for some very minor reason or no particular reason other than the way the non-linear interactions operate, huge changes in climate could result.
  10. rgriffin42... With regards to chaos theory Tamino has a very good recent post on this explaining that this issue is basically the difference between weather and climate.

    And on the issue of glacial-interglacial cycles... yes, there are very good and clear explanations on how this happens. Several articles are located here on Skeptical Science. And you can just try googling Milankovitch cycles.
  11. rgriffin42 @59, the same thing concerns climate scientists and interested observers like me. That is what all the discussion of tipping points is about. It is very possible that at a certain rise in temperature, some natural feedback will kick in that is strong enough that will rapidly accelerate the rate of warming. Potential candidates are the the release of methane from clathrates, the release methane from formerly frozen tundra, and the deforestation of the amazon, two of which can individually release more CO2 equivalent of methane than has been released by humans since the industrial revolution.

    Another suggested tipping point is the possible shut down of the North Atlantic conveyor, with a consequent significant reduction in temperatures in Europe. However, as best understood at the moment, that is not likely for several centuries, at which time it may bring relief to Europe, but will not trigger an ice age.

    In fact, from geological studies, we know the possibility of a cooling tipping point is remote. If there was such a cooling mechanism, it would place a hard ceiling on global temperatures - but we know global temperatures have been significantly higher than they currently are. Hence the instability you mention may make things get a lot worse a lot faster than we are expecting, it is very likely that they will be our salvation.
  12. Dana69 (on another thread) wrote: "If climate is deterministic in nature you could have reasonable assurance of the outcomes. If more stochastic (governed by the laws of probability) it would be problematic. ... Seems most arguers here land on the deterministic side."

    Both weather and climate are deterministic. A chaotic system is one that is deterministic, but so sensitive to initial conditions that it is essentially unpredictable beyond a short prediction horizon.

    STochastic processes are not necessarily a problem either, the field of statistics (the mathematics of stochastic processes) is well developed and we have means of dealing with it. One of them is Monte Carlo simulation, which is the basis for both weather forecasting and climate projection (although used in different ways).

    "They do not specifically say so, but the reference to Lorenz and the use of “attractor” imply that chaos theory is being invoked here not determinism."

    If you knew anything about chaotic systems, you would know that they are deterministic. A little bit of knowledge can be a dangerous thing if one is not fully aware of the limits of ones knowledge. I suspect the scientists who wrote that section of the IPCC reports have a very sound grasp of chaos theory and understand very well what it implies for climate projection.
  13. Can I suggest linking to this superb visual metaphor in the article.

    I'm sure there are other posts where it could also be used effectively.

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