Treating the outcome of scenarios as a sample from the probability distribution function of what the real world actually is, Harvard economist Weitzman showed last year that the post hoc pdf would be a student-T distribution having a 'fat tail' that gives far greater weight to extreme events than an ex ante thin tailed normal distribution (a result that is far from being absorbed into the thinking of the policy community which, if it woke up, would focus on precautionary measures against such extreme events instead of frigging around with intergenerational consumption smoothing, passing the burden on to our grandchildren who, if they are not starving, will most likely be engaged in fighting the Climate Wars predicted by Gwynne Dyer) .
Of course global scenario outcomes are not the same thing as polar ice outcomes but maybe some clever statistician can do a Bayesian study of the extent to which the data support a normal distribution ex ante assumption Peter ----- Original Message ----- From: "dsw_s" <[email protected]> To: "geoengineering" <[email protected]> Sent: Thursday, July 30, 2009 12:43 AM Subject: [geo] Re: NSIDC GIVES UP '2-STANDARD DEVIATION RULE' AS - "MEANINGLESS" That connection between standard deviation and percentage of events isn't a universal law. It's a feature of the normal distribution, i.e. of distributions that are the sum of a large number of small independent components. I see no reason to expect that to be the case for sea ice extent or area. On Jul 23, 4:11 pm, Veli Albert Kallio <[email protected]> wrote: > Hi All, > > I think that we all should call the Arctic Ocean melting by its rightful > name: "melt-away of the North Pole Floating Sea Ice Cap" to make people > understand the gravity of situation. > > Two events that stuck me: > > 1) > > Yesterday 22.07.2009 National Snow and Ice Data Centre (NSIDC), University > of Colorado, Boulder, removed the two standard deviation markers as > meaningless and of no useful further reference leaving the mean annual > 1979-2000 average against 2007 melting as references. One standard > deviation indicates variability of a stable system to 68% of occurrences, > two standard deviations incorporates occurrences to 95% of events. > Usually, two standard deviations that cover 19/20 cases are the cut-off > point considered a stable system. As there are, furthermore now three > consequtive occurrences of the sea ice melting falling outside this limit > (2007, 2008 and now 2009) there are even less reasons to believe that > 1979-2000 average can be used as a reference. In other words, NSIDC admits > a passage of tipping point, a move away from system prevailing 1979-2000. > > 2) The sea ice has had all this season very strong peripherial melting as > well as some of the strongest ice has been drained out through the Fram > Straight, losses have been high as sunlight and insolation on the long > exposed periphery is much more efficient to mop up suns heat than holes > appearing in the centre. A split has occurred from the vicinity of Peary > Land to Komsomoletski Island today, it needs to be seen wheter the > currents keep pulling these apart further and further. This channel was > readily weakened by melting north-west of Laptev Sea, today's images > suggest the front part is 'falling' to Atlantic. However, last year the > re-freezing on the North Pole began on 25.07.2009 - that may re-seal, > unless the melting has advanced far enough and ice thinned by previous > stretchings too much. The tiny split on the last remaining section, off > Peary Land, occurring today. > > Thank God, we have such a good satellites and data to see these things in > real-time!! > > Kind regards, > > Albert > > _________________________________________________________________ > Celebrate a decade of Messenger with free winks, emoticons, display pics, > and more.http://clk.atdmt.com/UKM/go/157562755/direct/01/ -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.35/2269 - Release Date: 07/28/09 17:58:00 --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
