and an axiom or assumption. The statement that 100 centimeters equals 1 meter, is a definition
which is true by its own inner logic, and which cannot be disputed. The statement that a certain stick is 100 cm may be true or not true, depending on the actual length of the stick in question.
An assumption may be true or false, while a definition always is true. Full consensus can only
be reached for definitions.
However, to confuse definition and axiom is a trick that is sometimes used to confuse opponents in a discussion. The more stupid your opponents are, the better it works if you decide to use this trick.
An example: No Feedback Climate Sensitivity, as the rise of global temperature upon doubling of atmospheric CO2, is claimed to be 0.25. This mean that the warming would be 1 C upon radiative forcing of 4 W/m2 associated with doubled CO2. This is well described by Judith Curry in threads on CO2 no-feedback sensitivity.
Is this a definition or a fact? Well, it is a definition because the number 0.25 comes from Stefan-Boltzmann's Law and it is assumed that this law is to be used and this gives 0.25.
This explains why also skeptics like Lindzen and Spencer agree on a No Feedback Climate Sensitivity of 0.25. In fact everybody agrees on this in complete consensus, because it is a definition. It is pointless to argue about a definition, but one should remember that a definition does not say anything about reality, about the length of specific stick for example. A definition
is always true, cannot be false by its construction, and thus is empty of content.
But now comes the trick: Since there is (complete) consensus about a Climate Sensitivity of 0.25, one can fool people to believe that this says something about real global climate, which can be taken as a starting point when adding various feedbacks to get an IPCC best estimate
of climate sensitivity of the size 1 sending an alarm of a global warming of up 4 C.
So by twisting a definition into a physical fact, one can obtain what seems to be a statement about physical reality, which cannot be denied. Clever, but it is a "trick", which you see through if you do not want to fool yourself.
The master of twisting a definition into a physical fact was Einstein, who based (special) relativity on the constancy of the speed of light (in vaccum), without ever telling if he meant it to be a definition or a statement about physics, something which physicists still don't know for sure, and which is still causing a lot of confusion.
So remember, if there is complete consensus about a statement expressed in physical terms, as IPCC claims to be the case as concerns a No Feedback Climate Sensitivity of 0.25, then the statement is a definition which says nothing about physics. It is not to be expected that IPCC will be able to understand this, but what about Lindzen and Spencer?
Recall:
that the speed of light is constant is an experimental fact
SvaraRaderaYou see, as I Said you think it is both an exp fact and a definition because the modern length scale is lightsecond. Confusion.
SvaraRaderano, you're wrong.
SvaraRaderafirst it was _measured_ (not postulated) that the speed of light is constant then the speed of light is used to define the unit of length.
nobody used the lightsecond to measure the speed of light. ever!
no confusion at all.
if you make an experiment in which you find out that the speed of light is not c the definition of the unit of length will be changed.
(furthermore note that the length of 1 m has not changed when we decided to adopt light instead of a bar of platinum iridium).
As I said, the confusion is complete. But with lightsecond as length scale
SvaraRaderaas the standard today, then the speed of light is 1 lightsecond per second, by definition. And a definition says nothing about reality.
yes, you said that the confusion is complete.
SvaraRaderaand you appear to treat your statement as a definition.
i conclude there's no use in discussing that.
Yes, about a definition the consensus can be complete.
SvaraRaderaone definition you seem to particularly like is: claes is right
SvaraRaderaThis is not a definition: I may very well be wrong.
SvaraRaderaYes, you may be wrong, and you most certainly are wrong. like most of us. Nevertheless, you may have a point.
SvaraRaderaIt goes without saying that you can never argue on the truth value of a definition. A definition is just an explanation of what, exactly, we mean by a certain term than is used to describe a concept a or notion.
But in your argument above, which is somewhat vague, it seems that the problem is not that people are confusing assumptions with definitions. The problem is rather that people confuse assumptions with facts. Which is not the same type of error. The first one is a logical error; the second one is to confuse the model with the reality.
Are your bright enough to rise to this challange: to axiomatize the climate theory... :-)
i do not like the fact that you moderate the discussion by omitting comments.
SvaraRaderamy comment: "yes, of course, definitions have nothing to do with reality."
is quite important in this discussion. since you want to make such a fuzz about differentiating between definitions and reality it seems odd that a champ of logic like you uses the argument of not being true for discarding a definition.
@Anonym:
SvaraRaderathe argument is not vague, is plain wrong.
claes calls the fact that the speed of light is constant a definition. then to defend this argument he claims that the lightsecond is a definition.
(the latter is correct, the former is not correct). he then tries to imply (or worse he believes) that light has been measured as constant _after_ (and with the help of) the lightsecond.
claes pretends to believe that the definition of a meter (which is totally arbitrary) and the postulate that c is constant in special relativity (that comes from experimental observations) are exactly the same.
the last point opens to scenarios:
1. claes is intellectually dishonest and uses tricks to "win" a point
2. claes does not know what he's talking about
My point is that there is a lot of confusion and this is what the discussion shows.
SvaraRaderasorry claes, but the above discussion can at its best show that i am confused.
SvaraRaderaor that you are wrong.
there's no way that the above discussion can prove that there is a lot of confusion.
In my view Claes has many useful calculations and considerations of outcomes from calculations but that does not mean everything is correct. In all calculations there are assumptions. The assumptions maybe correct and defensible within the boundaries of consideration. Unfortunately the boundaries are often implied and not clearly stated. This particularly applies to Climatology where some individuals are deliberately withholding information about assumptions, particularly in models.
SvaraRaderaTake the Stefan-Boltzmann equation. This only applies to black bodies. To calculate energy transfer an emissivity factor, which is the ratio of actual energy to black body energy, has to be included. This factor covers the entire wavelength range and can vary with temperature, composition and physical state. Molecules of CO2 and the atmosphere are not black bodies. The radiation absorptivity (which is equal to the emissivity at a single wavelength) will vary with amount and density of clouds in the atmosphere.
Next calculation of heat transfer by radiation between two surfaces using the Stefan-Boltzman equation (corrected for emissivity of emitting and receiving bodies) only works in a vacuum. In a fluid (liquid or gas) there is a boundary layer over a surface. This boundary layer has different properties (including temperature) than the surface. Heat transfer occurs in the boundary layer by conduction, convection and phase change. Most non-technical persons will be aware that evaporation increases with wind (drying of clothes), wind chill factors, cooling of your soup by blowing. In closed systems such as heat exchangers it is possible to measure the heat transfer and determine the contribution by radiation and convection but the same is not true for systems open to the atmosphere. The following is an interesting article about about pan evaporation measurements http://www.rsbs.anu.edu.au/Profiles/Graham_Farquhar/documents/271RodericketalPanreviewIGeogCompass2009_000.pdf
Estimates of climate sensivity are just estimates often based unrealistic assumptions. If one considers Prof. Hoyt Hotel's equation (5-154 in Perry's Chemical Engineering Handbook based on actual measurements)the role of CO2 in the atmosphere is insignificant.
All the best for the festive season and a better new year.
Cementafriend