20 January 2010

Theory of Climate -- Philosophy

Is there a theory of climate, and if so, what is it?  That turns out to be a harder question than you might think.  It's my slight rephrase of a question asked in this month's question place.  The difficulty lies in the fact that 'theory' has several different meanings.

We can dismiss the most common daily life sort of usage -- a theory is something that is false.  It's used in comments like 'That may work in theory, but it doesn't work in practice.'  If we're talking about what happens in practice, we're talking about what happens in the real world.  Scientific theories have to apply to the real world.  If your idea makes false predictions about the real world, then the idea is (at least partly) false.  And, if your idea consistently makes false statements about the world, then it is not a theory, or even a hypothesis.  If there is a scientific theory of climate, it must be making true statements.

We can also dismiss the next most common daily life usage -- a theory is a WAG (wild guess).  A common sort of theory of this type is where I, for instance, theorize that since the last time I took my car to the shop, it got good service, that the next time I go, it will as well.  There's really very little data behind that thought, and very little analysis.  But it seems like a reasonable sort of statement.  Or the 'lucky socks' theory sports fans or athletes might have.  Their team won the last time they wore a particular pair of socks, so they theorize that the team will win again (or at least have a better chance of winning) if they wear the same socks for today's game.  Again, it seems reasonable to the person making the statement, but there's little data behind it and little analysis.

Now to consider the more difficult waters, where I hope that the two philosophers I know sometimes read will comment with appropriate corrections and elaborations.

One part of math/engineering/science usage is that, in contrast to common usages, a theory is a very good thing indeed.  Actually the best you can get.  Some other terms you'll hear are conjecture, hypothesis, and law.  The 'good service' or 'lucky socks' theories, as we'd term it in common conversation, are really more in the nature of a conjecture.  We've got very little data, and very weak chains of reasoning.  But, hey, it looks ok.  After you collect more data and get stronger lines of reasoning, you have a hypothesis.  It's also better if the hypothesis covers more situations than the conjecture.  Get to the point of covering many situations, with very strong evidence and very strong lines of reasoning, and you finally have a theory.

Law is a different kettle of fish entirely.  In terms of how we do science any more, it's also an anachronistic term -- something that used to be used, but now is uncommon.  Laws, in my areas at least, are simple mathematical relations between a couple of things.  Newton's Law of Gravitation, for instance, says that the gravitational force between two bodies is proportional to the product of their masses divided by the square of their distance.  Simple relation and it's even reasonably correct.  Hard for you to test for yourself, so I'll mention another one.  Hooke's law of elasticity.  This says: take a spring (or rubber band, or piece of elastic, or bungee cord, ...) and hang it up.  Measure where the end is.  Now put a small known weight at the end and measure how much longer the spring gets.  Add a second weight, equal to the first.  You'll see (says the law)  the spring lengthen by exactly the same amount as before.  This is reasonably correct as well.  But as you keep increasing the weight, you'll eventually see the distance the spring lengthens start to change, and eventually it changes quite dramatically -- if you put enough weight on the spring, it will break.  Laws in this sense are convenient expressions of relations.  You can use them, within limits.  But there definitely are limits and, often, even the proposers knew about the limits (I think Hooke did).

One place you can see the change in how scientists think/thought about Law versus Theory is that Newton's Law of Gravitation (1600s) was replaced by Einstein's Theory of General Relativity (1910s).

Within the realm of scientific theories, though, there are two different sorts.  I'll call them the elegant and the complex.  We mostly think about the elegant theories when we think about scientific theories.  The theory of evolution, for instance, is an elegant theory.  Its elegance lies in the fact that it covers an enormous range of observations, can be used to make a large number of predictions, and, yet, can be stated in a page.

I don't believe there is an elegant theory of climate.  It is of the complex theory sort.  I have in my library, for instance, a book on Number Theory, and one on Theory of Flight.  In neither will you find a one page description of the Theory of Numbers, or the Theory of Flight.  The sense of theory involved is 'a body of principles and understandings that apply to a given subject'.  It's an elegant theory when the number of principles or understandings is small.  And, for something like flight, or numbers, and on for many areas, you have quite a few principles to work with.

In climate, some of our principles, or statements of theory, would include:
  • Conservation of mass applies to the climate system
  • Conservation of momentum applies 
  • The laws of thermodynamics apply
  • The general theory of relativity applies
  • Quantum theory applies
  • Tectonic theory 
I'll take up illustrating how these apply to Theory of Climate tomorrow. In the mean time, I'll invite discussion of the philosophy and additional examples of theories or laws that are part of a Theory of Climate.

    16 comments:

    carrot eater said...

    Maybe it's covered by thermodynamics or quantum, but there's reaction chemistry in there as well. One has to appreciate the reactivity of methane and CO2 in order to assess their atmospheric lifetimes.

    I'm surprised to see general relativity in there. I'd have thought classical mechanics was good enough to describe what's needed here.

    I think some of the confusion over 'theory' and 'law' comes from middle-school science classes, where students get the idea that an idea progresses from hypothesis to theory to law, based on how strong it is. Is it still being taught in a way that leads to this confusion?

    yea-mon said...

    Not 'Theories' in name, but the 'Gas Laws' and those covering diffusion ans solubility certainly apply - might be too fine-grained for your treatment.

    I'm surprised at the inclusion of GR too, and looking forward to seeing it tied-in.

    As to confusion about 'theories' and 'laws', I never was very clear about that myself, and I did a degree in Pure Physics in the UK. I think a lot of the defining of such terms is more the purview of 'History & Philosophy of Science' for us - and more to the fore in the US due to strict definitions being pushed in Science Fairs. I took a look at the Feynmann Lectures and there's not much in the way of definition, at least in a dogmatic sense, of laws, theories and hypotheses.

    carrot eater said...

    Come to think of it, there are aspects of biology in the carbon cycle as well. Terrestrial vegetation and marine life are in the picture. And then geology/chemistry, in the weathering of rocks. Climate is a multi-disciplinary field where many can contribute.

    yea-mon: I don't think there are hard rules, but I've always understand it as Penguin states: almost every law I can think of is a mathematical relation. The theory is the surrounding framework and context.

    Penguindreams said...

    The more notions the merrier. Reaction chemistry, ecosystem evolution, gas laws, henry's law, ... keep them coming.

    I wouldn't worry terribly much about law vs. theory in terms of what you mention. For instance, although one can derive the ideal gas law from more elementary principles, for doing climate you just pull the gas law off the shelf. So it makes sense to list it in its own right.

    carrot: I can think of some exceptions to the law = mathematical relationship, that's why I specified 'in my field'. From paleontology, there is Cope's Law, which says that in an evolutionary lineage, organisms tend to get larger over time.

    Lou Grinzo said...

    Fascinating post, which I will point my readers to as soon as I post this.

    Perhaps this is the wrong level of abstraction for the immediate discussion, but I would also expect to see systems theory (dynamical systems?) come into play eventually. For the average science geeks sans formal science training (like me) the perverse degree of interplay between various parts of the Earth System is one of the most interesting, challenging, and unsettling aspects of climate. I'm thinking of things like methane feedbacks, how fixing the ozone hole will make warming worse in the southern hemisphere, and how reducing coal burning will trigger an increase in warming because of the virtually instant drop in sulfur aerosols, while the already emitted CO2 will be with us for a very long time.

    Duae Quartunciae said...

    I was thinking about this recently, but took a slightly different tack. You are, effectively, looking at all the theories which bear upon climate science in some way.

    I think there is one central unifying idea: balanced energy flows. Climate is all about how Earth sheds the energy it receives from the Sun. Energy flows vertically from space down and from the surface up, and also horizontally around the globe, and also the exchange with the ocean heat sink. Pretty much everything that affects climate does so by modulating flows; by changing albedo, by altering the transmission of radiant flow through the atmosphere, and with regional climate, by altering the way energy circulates.

    Certainly, you apply all kinds of theories in climate science; but invariably it is in order to sort out an energy flow in some way.

    jyyh said...

    Ecology only has relevance by the albedo effect of various types of vegetation, and the mass relation between autotrophs and heterotrophs (lets forget the green sea snail that was reported to exist), and the physical requirements for those to occupy an area, so it's quite limited. Unfortunately no one has come up with a simple way of estimating the GHG-exchange of an ecosystem on the scale the climate grid boxes are. Add to that, the human impact on several areas of the globe has lead to change in the ecosystem, and this in turn changes the amounts of soil/vegetation carbon compared to the wild areas (I'm assuming they are in sort of equilibrium relation to physical parameters).

    Hank Roberts said...

    > Ecology only has relevance by
    > the albedo effect

    Whoah. The "look, shiny" theory of biogeochemical cycling, eh?

    carrot eater said...

    Upon reflection, some people call the concept of the rate-limiting step as Liebig's Law, and this can't just be expressed as a single formula, though it's a simple concept.

    So I guess the statement that laws tend to be mathematical relations is weaker than I thought.

    steve said...

    The distinction I normally use with my students is that a law states a relationship (and hence the emphasis is on good predictive power), while a theory explains a relationship (i.e. the emphasis is on explanatory power). So we can have areas of science where we have laws but not theories (because we can describe a relationship precisely and robustly but don't have a good explanation of the underlying cause), and areas where we have theories but no laws (where we understand the underlying causal mechanisms, but cannot precisely predict future outcomes)

    Penguindreams said...

    Lou:
    Thank you. Not sure I agree about systems theory. I'll have to think about it some more. Definitely need to add it to the list of candidates. We certainly do deal with messy systems, so that part fits. But I can't think of any papers that concluded 'thanks to systems theory, we now see that permafrost methane release is a serious problem' or the like. Folks usually reach those conclusions out of other directions 'thanks to knowing about both permafrost and biology, we see ...'. Still, maybe we should be doing more by way of systems theory.

    Duae:
    Certainly conservation of energy is a very important principle to pay attention to in looking at climate. But I don't think I can give it quite as commanding a place as you do. My reason is this. For the commanding place, I think, we'd have to be in a position to say 'If I am given the energy balance for a region of the globe, I know (or can derive/predict/...) everything there is to know about its climate.' I'll grant that this is arguably true for atmospheric temperatures. I question it for the ocean (as far as I know, nobody can tell you what the deep ocean temperature will be given only atmospheric temperatures and winds). And I think it's simply not true for precipitation. Several different configurations of the atmosphere/ocean/land ... can be compatible with a given energy flow. This is one of the issues for rapid climate change by way of changes to the 'conveyor belt' -- it can happen rapidly because no change in total energy is needed.

    Still, it could be. I know that in ecosystems, people refer to the importance of 'energy flow' (somewhat different sense of energy than in physics/chemistry) as being an excellent organizing principle. So ... persuade me.

    jyyh:
    I think Hank answers you correctly, if a little briefly. In a little more length -- ecosystems are also important for changing the atmospheric methane and CO2 levels. The living part of the biosphere contains about as much carbon as the atmosphere. Anything that significantly affects the biosphere acts on that reservoir. The biosphere is also what mediates changes in soil carbon, a reservoir that's about 3 times the size of the atmosphere's. And the biosphere has a major role in mediating the air-sea partition of carbon. (The 'biological pump' -- kill off the upper ocean's plant life and atmospheric carbon would rise a lot, rapidly.)

    I'll invite the biologists to contribute some more ways ecosystems can affect climate.

    Duae Quartunciae said...

    Penguindreams gives me an invitation I cannot refuse: " So ... persuade me"

    I wouldn't say "conservation of energy" is the principle; but rather that the one most important question asked all the time in climate is: "where does the energy go?".

    This got front and center just recently, when Kevin Trenberth made this very point in a recent paper and in comments to his colleagues in a private email -- which was promptly ripped out of context and misinterpreted in the CRU email hack nonsense. This is the famous "travesty" remark. But what Trenberth was saying is spelt out in detail in the paper he cited in the same email:
    * Trenberth, K (2009) An imperative for climate change planning: tracking Earth’s global energy, in Current Opinion in Environmental Sustainability, 1 pp 19–27.

    You set the bar too high to say that a commanding role to this principles is only justified if "energy balance" in a region tells you "everything there is to know about its climate."

    I think it is enough to say the big picture of climate is best understood in terms of energy flows. To say absolutely everything goes too far. I am looking for the most important critical organizing principle; but not necessarily the only principle you ever need to get at every last bit of detail. But it does tell you nearly everything, I think.

    You mention the ocean, but this is actually my strongest point! To figure out the impact of the ocean is all about energy flows. There's no implication that wind and atmospheric temperature is all that matters. But it still all comes down to sorting out the energy flows within the ocean and across the surface boundary. There's currents (wind in the ocean) turbulence and eddies, latent heat flows, radiant energy, ocean turn over (driven by energy flows again) and so on.

    Precipitation is a stronger point. It stretches the principle to relate precipitation in terms of energy flows, but it is still pretty crucial even so. The importance of precipitation to other climate issues involves the latent heat flow, and the energy impacts of cloud; but in general I grant water flow of the water cycle is a second principle in its own right, albeit not as central.

    I still believe energy flow stands out as the most critical central organizing principle of climate science, though it is not the entire picture.

    Cheers -- sylas

    jyyh said...

    Hank, Penguin, yes, you're correct, I my book the sequestration and storing of the carbon by the living matter has been in pedology (soil study) or sedimentation (part of geology). As they deal partly with organic compounds such as organic acids in peat that are not easily reused by the living plants or animals I've ignored them in ecology, though of course they are a big part in f.e. biochar.

    jyyh said...

    And of course there are also the aerosols from plant pollen and fungi spores which may effect the cloud formation periodically during seasons.

    Hank Roberts said...

    The bad news about thoughtful explanations:

    "With statistics, the voters just hear a patronising policy wonk, and switch off....
    .... "It's like a French Revolution in reverse in which the workers come pouring down the street screaming more power to the aristocracy."

    As Mr Frank sees it, authenticity has replaced economics as the driving force of modern politics. The authentic politicians are the ones who sound like they are speaking from the gut, not the cerebral cortex. Of course, they might be faking it, but it is no joke to say that in contemporary politics, if you can fake sincerity, you have got it made."

    http://news.bbc.co.uk/2/hi/americas/8474611.stm

    Penguindreams said...

    Hank:
    Yes, I saw that article. But it depends on your situation. Clearly I would not fare well campaigning for political office, which is what their focus was. There's more to the world, though, than political campaigns. Or at least I keep hoping so.