Posted: Apr 27, 2010 5:10 pm
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MODNOTE Split from earth-sciences/global-warming-science-discussion-t5951.html . - Mazille |
FACT-MAN-2 wrote:
The science is telling us, with 95% probability, that earth's mean annual temeperture will be standing at somewhere between 2 and 7 or 8C above where it stood in the preindustrial era come the year 2100, which is indeed 90 years from today.
One should ponder a moment about the 95% statement. What does it really mean? Does it mean that there is a 95% chance that such phenomenon will in fact occur within 2100? No, it does not mean that. It means that if you take for granted all the axioms and assumptions from where such numbers were produced (if they were), and by "granted" I mean take them as "absolute truths", 100% true representations of the world, then there's 95% chance of this occurring.
But there's a problem here. These assumptions are called "models". So for one to utter these statements one must profess a 100% trust unto climate models, which is obviously silly. These models, in turn, have hundreds of smaller assumptions, some very easy and definite, some very hard to pin down, some even, are just values to keep the models "sane", that is, visually appealing, retrofitting nicely with the past and so on, with very little physics knowledge involved.
So how much of trust should one impinge to these models? And is this trust even possible to define numerically? I don't think so.
Finally there's the issue of averaging multi-model runs, as if they were "all equally good", after dismissing others because they gave too much warming or too little!
After all of this, to still utter the silly proclamation of "95%" chance of this going to happen like X and Y without the multi-tonne weight of caveats annexed to it is disingenuous and misleading. Fortunately, science is catching up to this common sense basic notion. The next IPCC report will address this issue better than the one we have now, although I still think it won't address it fully honestly. If it did, we would be brought back to the early 90s conclusion, and that would be politically catastrophic, if we want to have any nation doing something "about it".