Dust flux, Vostok ice core

Dust flux, Vostok ice core
Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).

Monday, June 6, 2011

Modeling and the axiomatic approach to science

I have previously written on the problems that arise from taking an axiomatic approach to science.

To review once again--science proceeds through the testing of falsifiable hypotheses, which, if falisified, are rejected. If numerous attempts to falsify an hypothesis fail, we begin to accept that the hypothesis explains some set of observations, and this explicatory power moves into the scientific pantheon as a theory.

The axiomatic approach is quite different than the normal scientific approach of testing hypotheses. The question today is whether the modeling approach lends itself to hypothesis-testing or is purely deduction from axioms. My interest in this question stems from the recent GAC symposium on "Earth climate: past, present, and future", moderated by Dr. Andrew Miall.

Our question today concerns climate modeling. Is it inherently axiomatic (i.e., based on non-falsifiable non-reducible logical statements)? Arguments in favour of this view include: 1) whereas an inductive scientist may admit a relationship between a pair of parameters, once the relationship is included in a deterministic model, that relationship is quantified; 2) once the relationship between two parameters is quantified, that quantification tends not to change unless challenged by specific observations compared to the model; 3) specific comparisons usually cannot be used to test any one particular quantified relationship in a complex model--there are ambiguities; 4) the models (here I am specifically looking at GCM models) tend to be very difficult to test, as the required simultaneous observations are difficult to come by.

The Thursday morning session was contentious, with talks by Ian Plimer, Jan Veizer, Hans Svensmark (pre-recorded, unfortunately), each of which could be construed as "climate denying". These talks focussed on points or particular weakness in the climate warming arguments, particularly the effects of solar and cosmic effects on climate. Interestingly, the Svensmark talk dealt with very long-term effects (140 my time-scale), which may be reflected in the 28 My cyclicity in mass extinctions Raup and Sepkoski's work on mass extinctions.

[If the extinctions are instead related to the passage of the solar system through relatively denser portions of the galactic arms (140 my cyclicity), and if extinctions were related to this event (instead of Nemesis), the spectral power observed in the 28-my periodicity could be explained as a harmonic of 140-my cyclicity.]

Norman Kalmanovitch discussed observations of the blackbody radiation escaping from the Earth increasing in tandem with warming, suggesingt that warming is externally driven rather than due to enhanced trapping of heat by greenhouse gases (whereupon one would expect escaping radiation to decrease with warming).

The theme of solar influence on climate continued in the afternoon session. Important points of the afternoon session were that the Little Ice Age was not entirely a European phenomena, but appears in paleoclimatic records of other disparate areas around the world; and climate models tend to overestimate the variation in temperature.

The audience was much smaller for the Friday morning session, which dealt mainly with paleoclimatic records.

The first two talks of the session showed the importance of realistic understanding of future climate change, as accurate predictions of future thickness of the ice roads that service several diamond mines in the Northwest Territories of Canada has a clear economic impact.

My talk was largely a reiteration of previous posts.

The last talks dealt with earlier portions of the global record.

The debate which followed was enjoyable but one-sided. As commonly happens, potential participants to these conferences draw their cues from the moderator and the list of talks, and those with a pro-IPCC viewpoint basically stayed away from this session.

On the basis of the geological record, it is reasonable to conclude that increasing atmospheric CO2 will lead to increased global temperature. How much of an increase is the question.

Even as you construct a climate model, you may be aware that there is a large range of possible values expressing this correlation. But when you create a model, you must select a value, even if you don't really believe it. You may not strongly defend your choice of parameter. But if your model becomes famous, and a lot of other people begin to use it, then you defend the model vigorously, not so much because your own reputation is at stake, but rather the reputations of all of your followers. This is the influence of the human condition on the scientific method.

No comments:

Post a Comment