Monday, November 11, 2019 Mina olen Eesti e-resident! 🇪🇪

I believe the title of the post proclaims me to be an Estonian e-resident. jules likewise. This marks the culmination of a very straightforward on-line process which was remarkably painless right up to the moment that we had to attend the Estonian Embassy in London to pick up our identity cards in person, at which point we had to brave Britain’s creaking rail network.

The point of establishing e-residency is to be able to set up a business there, which will enable Blue Skies Research to remain seamlessly in the EU in the event of the UK ever managing to leave. Not that the latter looks very likely, but in order to collaborate on any long-term project based on EU funding we need to be able to prove that there’s a plan in place to cover the theoretical possibility. This must be one of these “Brexit bonus” things that the tories have been promising us for the past few years. Though “bonus” would usually imply some sort of gain rather than added costs and bureaucracy, not to mention the losses in corporation tax which will henceforth be paid in Estonia rather than the UK. Even for our part-time hobby business, that is likely to be several thousands, perhaps up to ten thousand pounds, per year lost to the UK indefinitely into the future. Our combined share of EU membership fees is probably under a hundred quid per year. Even the bare cost of health insurance for when we visit our colleagues there will cost more than that when we lose the EHIC. But we will apparently get blue passports and we may eventually get a new 50p piece too when they have worked out the design. Apparently they had almost finalised that a while back, but hadn't worked out what to do about the border. Boom tish. Of course they still haven't, so Bonson is just lying through his teeth every time he opens his mouth, and the same old tory voters will just lap it up cos he's such a cheeky chappy with those clever latin bons mots.

We did managed to arrange another couple of things during the two-day trip, so it wasn’t a total waste of time. And it was cheaper than expected too, due to three of the four train trips being significantly delayed to such an extent we can reclaim half of the travel costs.

Saturday, November 09, 2019 Marty Weitzman: Dismally Wrong.

De mortuis nil nisi bonum and all that, but I realise I only wrote this down in a very abbreviated and perhaps unclear form many years ago, in fact prior to publication of the paper it concerns. I was sad to hear of his untimely death and especially by suicide when he surely had much to offer. But like all innovative researchers, he made mistakes too, and his Dismal Theorem was surely one of them. Since it’s been repeatedly brought up again recently, I thought I should explain why it’s wrong, or perhaps to be more precise, why it isn’t applicable or relevant to climate science in the way he presented it.

His basic claim in this famous paper was that a “fat tail” (which can be rigorously defined) on a pdf of climate sensitivity is inevitable, and leads to the possibility of catastrophic outcomes dominating any rational economic analysis. The error in his reasoning is, I believe, rather simple once you’ve seen it, but the number of people sufficiently well-versed in statistics, climate science and economics (and sufficiently well-motivated to carefully examine the basis of his claim) is approximately zero so as far as I’m aware no-one else ever spotted the problem, or at least I haven’t seen it mentioned elsewhere.

The basic paradigm that underpins his analysis is that if we try to estimate the parameters of a distribution by taking random draws from it, then our estimate of the distribution is going to naturally take the form of a t-distribution which is fat-tailed. And importantly, this remains true even when we know the distribution to be Gaussian (thin-tailed), but we don’t know the width and can only estimate it from the data. The presentation of this paradigm is hidden beyond several pages of verbiage and economics which you have to read through first, but it’s clear enough on page 7 onwards (starting with “The point of departure here”).

The simple point that I have to make is to observe that this paradigm is not relevant to how we generate estimates of the equilibrium climate sensitivity. We are not trying to estimate parameters of “the distribution of climate sensitivity”, in fact to even talk of such a thing would be to commit a category error. Climate sensitivity is an unknown parameter, it does not have a distribution. Furthermore, we do not generate an uncertainty estimate by comparing a handful of different observationally-based point estimates and building a distribution around them. (Amusingly, if we were to do this, we would actually end up with a much lower uncertainty than usually stated at the 1-sigma level, though in this case it could indeed end up being fat-tailed in the Weitzman sense.) Instead, we have independent uncertainty estimates attached to each observational analysis, which are based on analysis of how the observations are made and processed in each specific case. There is no fundamental reason why these uncertainty estimates should necessarily be either  fat- or thin-tailed, they just are what they are and in many cases the uncertainties we attach to them are a matter of judgment rather than detailed mathematical analysis. It is easy to create artificial toy scenarios (where we can control all structural errors and other “black swans”) where the correct posterior pdf arising from the analysis can be of either form.

Hence, or otherwise, things are not necessarily quite as dismal as they may have seemed.