Picofluidicist

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Attribution of recent climate change

Please don't be silly on Attribution of recent climate change. Your recent edits there amount to vandalism. Its been pointed out to your that vl is indeed defined at 90%. See page 4 of [1] William M. Connolley 18:31, 25 June 2007 (UTC)

Hi William (and Stephan). I started at page 4 of [2] and was not satisfied. The term "very likely" was defined in terms of ">90% probability" which I then looked for at [3], where I failed to find any definition, only a couple of references (7 and 8 in [4]) to the psychology of defining uncertain terms. Help me out: where is a hard definition of the relevant probabilities in any of the IPCC output, one which is based on ensemble averages, error bars, etc, i.e., the standard tools of statistics, rather than wet-finger guesstimates? Help me put some clothes on this emperor. Best regards to you both. User:Picofluidicist

Please don't pretend that "very likely" has not been defined, since it clearly has been. You are entitled to go on and wonder how probabilities are assigned to various statements, but that is another matter. Doing so without external WP:RS would amount to WP:OR - your opinions on this are not wanted, and neither are mine William M. Connolley 18:54, 25 June 2007 (UTC)

C'mon, William. I said, not that "very likely" was not defined, but that it was defined in terms of an undefined ">90% probability." Looking at a report and pointing out what is not there is not original research, it's merely a keen grasp of the obvious. What you seem to be telling me is that you're at a loss as to how the probabilities are defined. Is that correct? User:Picofluidicist

May I recall your actual text? "However, the meaning of "90% probability" is nowhere defined in the report, and in the absence of a rigorous statistical definition...". The "meaning of 90% probability" is rigorously defined by the mathematical field of probability theory. It now seems that you do not question the definiton, but rather the method with which the IPCC arrived at that value. That is a totally different question, of course. --Stephan Schulz 19:38, 25 June 2007 (UTC)

Hi Stephan. Probability theory does indeed provide rigorous statistical definitions of probability, and that type of rigorous statistical definition is what I expected to see in browsing the latest IPCC output. However, I was disappointed in that expectation, and instead I see wet-finger guesstimates. Do you see something more rigorous in the report? Can you please show me where? Picofluidicist

You are still confusing the definition of a probability with the way it is estimated (which, by the way, for empirical sciences is the best we can do). --Stephan Schulz 20:13, 25 June 2007 (UTC)

Hi Stephan. It seems to me that I'm not the one who is confused. You might want to take a look at the Wikipedia article on probability. In scientific literature I look for a frequentist approach to probability, but the IPCC report seems unwittingly conflate a frequentist approach with a Bayseian approach, assigning a hard number to a subjective plausibility. And you seem to be fine with that, right? Picofluidicist 20:53, 25 June 2007 (UTC)Picofluidicist

Not entirely sure what you want here. They did say 90% probability, that's easily verifiable, and from an authoritative source. As to whether it's sensible to put hard numbers on things which are only estimated, well, what would you prefer? That they said "very likely"? Or did a poll of the scientists involved to see what they thought? Or would you have preferred that they said they had no idea (which wouldn't be true)? Do you prefer it on tv weather forecasts when they say there is a 70% chance of precipitation, or when they show a black raincloud? --Merlinme 12:37, 26 June 2007 (UTC)

Hi Merlinme. I started off with an edit that said that the IPCC report used the term "90% probability" without defining what "90% probability" means. What do you think it might mean? I don't watch TV weather forecasts any more, but I think the probabilities they compute (and I'm pretty sure they use a defined computation method) are based on past experiences with similar weather systems in the same area which have resulted in rain, for example 70% of the time. In contrast, the global climate models are all based in pretty much the same set of physical assumptions, and so they result in pretty much the same set of predictions, and if the assumptions are correct then the GCMs are in general correct, but if the assumptions are wrong then the GCMs are in general wrong, and there is no past history of ensemble averages of being right and wrong from which to compute a probability. So when a given modeller says he's 90% certain that his model is correct, that's a subjective WAG (wild-ass guess). And if 90% of modellers say they're 100% certain, while the rest say they're completely uncertain, you get an 90% probability defined as an ensemble average of WAGs, which is a Delphi approach, which is at least a defined methodology. I'll repeat that the definition of a methodology for computing probabilities is absent from the IPCC report, and I'd like that simple fact to be reflected in the Wikipedia articles on global warming. However, gatekeepers like Connolley and Schulz seem to feel that pointing out this lack in the IPCC report violates their religion, so they're not going to let it happen. Picofluidicist 05:30, 27 June 2007 (UTC)

Yes, but if you change the physical assumptions of the models, then you get results which match observed data worse than with the current set of assumptions; that's why modellers use the current set of assumptions. If you think those assumptions are wrong, you're very welcome to find a set which better match the observed data, but it would be Original Research, and not suitable for Wikipedia. Modern weather forecasts (as I understand them) don't attempt to find a close match for the current situation in some vast database and then assume the future will be similar; they start off with assumptions about what happens when wind speed, cloud cover etc. are as currently observed, and then after one iteration they recalculate with the new variables. There's no 'experience' involved as such, but the variables have been tweaked until they match observations as closely as possible. The "90% certainty" figure the IPCC use is a bit neat, but I support their attempt to try to explain how certain they are. I still don't really understand what you'd prefer them to say. --Merlinme 14:21, 27 June 2007 (UTC)

The IPCC report is a done deal. It is what it is, and I do not propose to change a word of it. However, a Wikipedia article which cites the IPCC report is a constantly evolving entity, and should comment upon the inherent limits of its cited sources, limits which are self-evident without original research. Perhaps such simple observations will help to stimulate a stronger approach to probability in the next IPCC report. Unless, that it, such observations are quashed by overzealous gatekeepers. As for GCM modeling assumptions, they may well be correct, but hey, if Eta Carinae blows this year and plunges us into an ice age that would argue a little more strongly for the cosmic ray shielding/solar activity hypothesis.Picofluidicist 19:45, 27 June 2007 (UTC)

90% probability

See probability theory or any reasonable book on statistics or probability theory.--Stephan Schulz 18:31, 25 June 2007 (UTC)

"may need clearing up afterwards"

I tend to shoot from the hip, entering rough edits which may need cleaning up afterwards by myself and others.

Ah, I see. My slight clean-up. Your response.

Please read this and comment there. Thank you. -- Hoary (talk) 00:34, 7 July 2010 (UTC)

14 March

Please do NOT add the non-sensical 'Steak and Blow-Job Day' to March 14: it WILL be reverted. Full stop. --CalendarWatcher (talk) 13:59, 3 February 2012 (UTC)

A kitten for you!

Nice work on Charlotte's Web, fellow xkcd reader ;o)

OwenBlacker (Talk) 13:55, 27 July 2012 (UTC)