lördag 18 december 2010
Definition vs Axiom and Consensus in Climate Science
In mathematics and physics it is essential to understand the difference between a definition
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?