Global Temperature, Global Warming?

What is global warming? Most people would answer this seemingly simple question with something like the following (see the article at wikipedia.org):

Global warming is the observed increase in the average temperature of the Earth’s near-surface air and oceans in recent decades and its projected continuation. […]

One would think that all scientist agree on this definition. However, actually they don’t.

Some scientist would say that it does not even make sense. The June 2007 issue of the Journal of Non-equilibrium Thermodynamics includes a paper of Christopher Essex (U. of Western Ontario), Ross McKitrick (U. of Guelph) and Bjarne Andresen (Niels Bohr Institute), with the interesting title:

Does a Global Temperature Exist? [PDF]

In this paper it is argued that the concept of a “global temperature” is thermodynamically as well as mathematically meaningless. First of all, you cannot just add local temperatures on the Earth and then take the average to define a single “global” temperature of the Earth. Secondly, the average is not canonically defined. For example, taking a box of air with temperature 0 degrees and an identical one with temperature 100 degrees would lead to an arithmetic average of 50 degrees (add the two numbers and divide by two). However, the geometric average in this case, obtained by multiplying the two numbers (in degree Kelvin) and taking the square root is 46 degrees. Thus claims of distaster – or not – maybe a consequence of the averaging method used.

So, what is Global Warming? Can it be defined in a sound way, both from a physics and mathematics viewpoint?

Eli Rabett over at Rabett Run thinks that this paper is “a bowl of steaming crap”; I guess Lubos Motl thinks otherwise.

Update: The climate-friends at RealClimate.org thinks that this paper is irrelevant.

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3 Responses to Global Temperature, Global Warming?

  1. Luboš Motl says:

    I don’t think the paper is a new theory of relativity. 😉 But the general statements are clearly right.

    The main reason why certain people are interested in the “global temperature”, otherwise an uninteresting quantity whatever the definition is, is that they want to create a “global government”.

    There are all issues what weights and what pre-functions should be applied to the local temperatures before the average is computed, whether the ocean surface should be counted and how much of it, whether the weights should differ for land and ocean (and uninhabitable regions), and so forth.

    Whatever definition one accepts, the results won’t be terribly meaningful because the correlation of the small global changes to any interesting (local) phenomena is tiny.

    For example, the number of storms increases with the difference between tropical and polar temperatures. The global warming theory predicts that the poles warm up faster which means that the difference should decrease, together with the number of storms. That’s a basic conclusion of introductory chapters of meteorology, as Lindzen explained in a recent Swindle documentary, too.

    This conclusion doesn’t sound sexy enough, so some people randomly flip the orientation, relying that no one will notice. Indeed, no one notices because most people are just stupid. They say that the extremes, storms, and variations will increase, which is just the opposite of the conclusions of any sane science.

    There would be many examples like that. All of these things can happen simply because the global temperature is virtually uncorrelated to everything that is interesting for the society. Because the correlation is so tiny, it is very easy to pretend that the correlation is there, has an arbitrary sign (the politically convenient sign), and all these phony and unphysical correlations – analogous to homeopathy and astrology – are used by various advocacy groups to achieve their political goals.

    This has nothing to do with science. The very notion that the global temperature is one of the interesting quantities is a relic of pseudoscience because the global temperature doesn’t exist. Every physicist should agree that temperature can only be defined for objects in equilibrium which doesn’t exist on Earth. This quantity would only start to be interesting if the trends at the corresponding timescale became more important than local variations – and we’re orders of magnitude from such a state.

  2. global warming is becoming such a obvious problem that someone somewhere other than Al Gore needs to step up to help drive the bus!

  3. anoni says:

    From a physical standpoint, the average is meaningless. Nothing functions according to the “global average temperature”; everything functions according to the local temps and only local temps. Your furnace thermostat doesn’t work according to the average; you don’t decide to put on a coat according to the average; plants don’t grow according to the average. The average tells us nothing about what reality is. You can actually have 100 in Chicago and -100 in Antarctica on the same day and get an average of 0 or you can have both places reading 0 on the same day. In both cases, the average would be 0, which would tell you nothing about what the reality is/was.

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