En antagelse er bevis i klimavidenskab

Akademia, Diverse, IPCC, Klima, Michael Mann, Videnskab — Drokles on April 2, 2014 at 11:44 am

Bloggen Realclimate er det nærmste man kommer et uofficielt talsrør for FNs Klimapanel. Dens formål er at forklare klimavidenskab for en apatisk offentlighed og er stiftet af og består af nogle af klimapanelets mest centrale klimaforskere og de mest advokerende for menneskets uheldige indflydelse på klimaet som ishockeystavgrafens skaber Michael Mann og klimamodeløren Gavin A Schmidt. Så niveauet er derefter

Does global warming make extreme weather events worse? Here is the #1 flawed reasoning you will have seen about this question: it is the classic confusion between absence of evidence and evidence for absence of an effect of global warming on extreme weather events. Sounds complicated? It isn’t. I’ll first explain it in simple terms and then give some real-life examples.

The two most fundamental properties of extreme events are that they are rare (by definition) and highly random. These two aspects (together with limitations in the data we have) make it very hard to demonstrate any significant changes. And they make it very easy to find all sorts of statistics that do not show an effect of global warming – even if it exists and is quite large.

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While statistical studies on extremes are plagued by signal-to-noise issues and only give unequivocal results in a few cases with good data (like for temperature extremes), we have another, more useful source of information: physics. For example, basic physics means that rising temperatures will drive sea levels up, as is in fact observed. Higher sea level to start from will clearly make a storm surge (like that of the storms Sandy and Haiyan) run up higher. By adding 1+1 we therefore know that sea-level rise is increasing the damage from storm surges – probably decades before this can be statistically proven with observational data.

Så altså, hvis vi antager at klimaet ikke opfører sig som et komplekst og dynamisk system så behøver vi slet ikke empiri for at bevise vores teorier. Teorierne står i deres egen ret og er deres eget bevis. Det kunne de jo godt have sagt inden de hævede deres løn for at beskære træer og programmere dyre computermodeller. Som illustration på deres cirkellogik kommer de med dette fornemme eksempel

Imagine you’re in a sleazy, smoky pub and a stranger offers you a game of dice, for serious money. You’ve been warned and have reason to suspect they’re using a loaded dice here that rolls a six twice as often as normal. But the stranger says: “Look here, I’ll show you: this is a perfectly normal dice!” And he rolls it a dozen times. There are two sixes in those twelve trials – as you’d expect on average in a normal dice. Are you convinced all is normal?

You shouldn’t be, because this experiment is simply inconclusive. It shows no evidence for the dice being loaded, but neither does it provide real evidence against your prior suspicion that the dice is loaded. There is a good chance for this outcome even if the dice is massively loaded (i.e. with 1 in 3 chance to roll a six). On average you’d expect 4 sixes then, but 2 is not uncommon either. With normal dice, the chance to get exactly two sixes in this experiment is 30%, with the loaded dice it is 13%[i]. From twelve tries you simply don’t have enough data to tell.

Så altså, den videnskabelige tilgang er at stole på en blanding af rygter og ens instinkter frem for eksperimenter. Problemet med klimaet, som et eksperiment, er, at man kun har det ene og intet at sammenligne med. Hvis denne beværtning er symbolet på verden, hvorfor opfatter man den så som snudsket fremfor normal? Åh, det er antagelsen om virkelighedens korrumperede ulidelighed og den bliver kun bekræftet af empiriens afkræftelse.

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