Sunday, March 25, 2007

There is no such thing as a global temperature

...so how can there be an increase or a decrease in its average?

You might as well say that there is a global average telephone number.

The thesis is argued convincingly at this link by two very persistent and insightful Canadian authors and their Scandinavian colleague.

Key points:
(Those who glaze over easily when confronted by mathematics can skip to numbers 5, 6 and 7)
  1. Sums or averages over the individual temperatures in the field are not temperatures. Neither are they proxies for internal energy.
  2. Temperatures from a field (individually or averaged) neither drive dynamics nor thermodynamics. Instead dynamics are driven by gradients and differences, in temperatures and other variables.
  3. A global spatial average cannot be an index for local conditions, otherwise nonlocal dependence (i.e ”thermodynamics at a distance”) for local conditions would be required.
  4. The utility of any global spatial average of the temperature field as an index for global conditions has been presumed but not demonstrated.
  5. It is easily demonstrated that different spatial averaging rules over temperatures can have contrary trends in time (i.e. some increase while others decrease in time) when the two fields being compared have range-overlap, as they do in this context. This is demonstrated here in a basic example and subsequently with actual atmospheric temperature-field observations.
  6. No ground has been provided for choosing any one such statistic over the rest as the one proper index for global climate.
  7. If there are no physical or pragmatic grounds for choosing one over another, and one increases while the other decreases, there is no basis for concluding that the atmosphere as a whole is either warming or cooling.

8 comments:

Bill said...

Excellent points all. Many of these were also outlined in the excellent book Taken by Storm by Essex & McKitrick (2002).

Halfwise said...

Thank you Bill for visiting and for leaving a comment. I found 'Taken by Storm' fascinating and completely convincing.

So much of the AGW argument seems to be a series of extrapolations from a basic hypothesis that does not stand up to close examination. Essex and McKitrick have made that examination their business, and we should all be grateful for what they have revealed.

Exile said...

I am interested in finding out more by reading taken by storm, but in the meantime, I would like to know why glacial melting is not a basis to argue for atmospheric warming?

Halfwise said...

Exile,
Thanks for visiting. Glaciers (specifically alpine glaciers) grow when there is more snow accumulation during the winter than snowpack loss in summer. A glacier will retreat when snowpack loss exceeds snowfall. So what you see with glaciers is a reflection of the timing of precipitation and evaporation, as much as it is a reflection of average temperature.

We would both agree that the earth has warmed, compared to the temperatures of (say) 1980. I would say that it is undeniable that the earth is warmer than it was in 1650 when all those Dutch and English artists were painting skaters on frozen canals and rivers. And compared to 11000 years ago during the Ice Age, it is quite pleasant even though spring is rather late this year.

But temperatures are cooler in my area than they were 70 years ago. 700 years ago Europe was warmer than it is today. So a lot depends on the timeframe that you pick.

Climate changes relentlessly, and it changes for reasons which we are still seeking to properly understand. The world needs vigorous debate about every scientific theory, so that our understanding can be tested and can grow. Environmental pressures and industrial inertia find an equilibrium point that benefits society greatly; were either side to prevail on its own we would be in a very sorry state indeed.

John M Reynolds said...

Robert Aterman of the http://myconservativedreamworld.blogspot.com/ blog left a message on my http://greycanada.blogspot.com/2007/08/temperature-trends.html post with a link to this post of yours.

Sorry if I you don't like me commenting to an old post, but I do notice some things that are wrong. Of course, you may already agree with me in light of your last comment, but here it goes.

There is a global average temperature; otherwise, we would not have ice ages followed by interglacial periods. The problem is with measuring it. One obvious indication that it is difficult to measure is that El Nino should never cause a huge climb in the global average. It is causes North America to warm, but it also causes Asia to cool. There should be no huge affect on the global average temperature.

For a single more scientific point, your number 3 is wrong. Wind from non-local areas will dramatically warm or cool the local area.

Of course there are problems with the measuring. They are relying on "rural" weather stations to provide the most "consistant" data. Those data are skewed by local conditions such as having an air conditioner a few meters from the thermometer or it being set beside pavement that is baked in the sun, or is place in the shade. As well, several "adjustments" are applied that are questionable. Finally, the proxy temperature indicators show a divergence between their data and that of direct measurement.

Several of you points (2, 4, and 5), while not specifically indicating that there is no global average, do indeed show that it is quite difficult to estimate or measure.

Anonymous said...

@John M Reynolds
You miss the point - an "average of temperatures" is not a temperature. The "global average temperature" is not an actual temperature - it is merely a statistic. The planet would have to be in thermodynamic equilibrium for there to be a single temperature - and it is not.
Consider the fact you cannot tell what reality is by averages: If I give you an average of 50 degrees for a given day, you cannot tell me what the high and low were. Furthermore, "If temperature decreases at one point and it increases at another, the average will remain the same as before, but it will give rise to an entirely different thermodynamics and thus a different climate. If, for example, it is 10 degrees at one point and 40 degrees at another, the average is 25 degrees. But if instead there is 25 degrees both places, the average is still 25 degrees." Bjarne Andresen
Do you see the problem with averages yet?

Halfwise said...

Old post, but the points made are still debated so I suppose there is still some educating to be done. As Anonymous says, the average of temperatures is a statistic not a temperature.

JMR's comment that rural weather stations are not reliable because of local anomalies would lead me to wonder how he views the effect of runways, jet engines or parking lots associated with the rest of the station population.

4TimesAYear said...
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