Sunday, March 17, 2019

More Brexit

Stoat has called for another Brexit comment. I actually don't have a whole lot to add to what I said last time. It is clearly a mug's game to try to predict the day to day rollercoaster - it has been amusing to listen to podcasts which are hopelessly out of date within 24h as some previously unimaginable option is proposed or the Govt reneges on yet another promise. It has on occasion been headline news when the Govt merely reaffirms something it has already announced. And the Parliament channel has probably never before had such a large audience.

The basic reason for the short-term unpredictability is that there are 650 MPs and any number of SPADs etc forming their own alliances and opinions and making tactical decisions based on what they think may is voting on the direct basis of a rational preference ordering but maybe on the basis of what they think may increase the ultimate chances of the outcome they prefer, or perhaps just what will curry favour with their pals. And in some cases this may have more to do with seeing May win/lose than in anything to do with Brexit itself. Brexiters aren't even trying to be honest any more, whether in media interviews or even the House of Commons - perhaps the most impressive example (at time of writing!) of which was Brexit Secretary Steven Barclay closing Thursday's debate by imploring the House to vote for the Govt motion "in the national interest" before walking straight into the Noes lobby to vote against it. So trying to predict the short-term tactics, when motions are being won and lost by as few as 2 votes, and amendments are tricksily worded and edited and withdrawn on backroom discussions, is a bit futile.

There are lots of analogies with climate change which can be useful - we can't predict the detailed weather (though we can for about a week which is rather longer than parliament right now) but we can predict that summer will be warmer than winter and the 2050s will be hotter than the current decade. There are also lots of lying liars in the climate change debate, and most of them are on the brexit side too, which could be helpful if it wasn't obvious enough already. But there are also underlying truths that are not affected by what people say. We are warming the climate, and it still remains the case that there is no brexit that has majority support, in fact quite probably none of the brexit options would even have substantial minority support if all the potential brexits were to be considered in a multi-way vote. Debatably, remaining in the EU just about has majority support overall, it's certainly the most popular single option and quite likely more popular than any other single choice in a head-to-head vote. It seems quite plausible that we will be testing that proposition in the future. 

Parliament revoking A50 immediately is of course the best action, but on that basis it's unlikely to happen any time soon. Of the options under regular discussion, a long delay would be my pref as it gives more time for people to come round to #nobrexitatall which remains the only sensible final state of the Galton board we are currently rattling our way down. That said, another lesson to be drawn from climate change is that few people ever change their minds due to evidence. While I'm not a fan of another ref ratifying May's deal I do think it's a plausible compromise and while I've already said it's a bit pointless to predict what will happen, it does seem (today!) to be a reasonably likely pathway. I'm not very confident about which way a referendum would go - I'm sure that many people will think that May's withdrawal agreement is "getting it over with" rather than in reality just starting an indefinite period of negotiation over a future trade deal, all the while being subject to EU rules while losing all influence over them. On the other hand, so many have sworn to oppose May's deal, for all sorts of reasons, that it would be the mother of all u-turns for them to vote for it.

One advantage a referendum does have is that it would force the "I voted brexit but not for this brexit" crowd to take ownership of their decision. Also the "oh of course I voted remain but think we should leave" group would no longer be able to hide behind someone else's decision. You brexit, you own it. We'll get to see how many people actually want to leave the EU, rather than just live off the betrayal narrative. 

One of the highlights of recent days has been the abject failure of Farage's Gammonball Run aka "March to Leave".
It's truly remarkable that anyone with Farage's supposed politics skills could come up with such a guaranteed stinker of a plan. Whoever thought there would be mass support for trudging down the east coast of England for 10-20 miles per day in March, paying 50 quid for the dubious privilege of watching Farage say a few words before driving away in his bus, needs their head examined. If you want a short-term prediction from my blog, it is that this march is called off for some hastily-made-up and implausible reason before it gets to London. The optics of a small rabble of shouty old men yelling abuse at everyone they encounter, versus the good-humoured million person march of all types who will be in London next Saturday, could prove more than a little damaging to their image. Quite why the media is still in thrall to this rump of angry ignorant bigots remains a mystery to me. The BBC actually sent a reporter and cameraman for the start of the march, and put it on national TV. Perhaps they were doing auditions for the Question Time audience next week.

If May's withdrawal agreement does get through at the 3rd or 4th time of asking (because hey, MPs are allowed to change their minds on a daily basis, but the common people should know their place even if they were too young to vote back in 2016) then we will of course have a longer-term future of internecine warring within the Tories as they bicker firstly over their new leader and then in subsequent years (as the "transition" gets extended over and over again) over what sort of relationship we should have with the EU. That should take us up to, oooh, about 2030 or thereabouts, by which time most of those still around will be wondering what on earth this was all about and hopefully by then (maybe sooner with luck) we'll be ready to apply for proper EU membership, as a poorer and smaller nation, and under substantially worse conditions.

And all those who voted for this shitshow will blame someone else.

Monday, January 28, 2019 Costs of delaying action on climate change

This post was prompted by a silly twitter argument, about which probably the least said the better. Someone who has set themselves up as some sort of “climate communicator” had asserted that if we don’t halve our emissions in 12 years then the world as we know it will end. Moreover, anyone who even thought this assertion was controversial was, in their eyes, a denier. Well, I thought it was not so much controversial as simply false. But I did wonder, what is the actual effect of delaying decarbonisation of the global economy? In the sense of, let’s hypothesise that we actually can take policy action that decreases carbon emissions, what difference does it make when we start?

I’m sure people must have done (and published) these sort of calcs but to be honest I don’t recall seeing them. Most of the research I’ve seen seems to be more along the lines of: if we delay action then how much more stringent will it have to be, in order to meet a particular target? This pic below shows that sort of thing:
screenshot 2019-01-27 09.42.12
I don’t think this sort of thing is really all that helpful as it gives no clue as to how realistic any of the pathways are. It seems that this sort of graph is basically motivated by a political assertion (“let’s not let warming exceed X degrees|”) rather than any plausible understanding of the world we live in. I also don’t think it is very realistic to think that the world will design and implement carbon emissions policies that credibly aim at a particular max temperature change, at least not within my lifetime. So, here’s an alternative question that although still rather simplistic is (IMO) more directly relevant to the real world. Let’s assume we are able decarbonise at some given rate. How much difference does it make how soon we start?

To answer this, we have to model (a) CO2 emissions and how they vary with policy delays (b) how atmospheric CO2 concentrations vary with emissions (c) how climate change depends on CO2 concentrations, and finally perhaps (d) the economic impacts of climate change.

For (a), I assume an exponential growth rate for historical and future emissions up to the initiation of decarbonisation, followed by an exponential decline. I use a historical (and near future) growth rate of 1.9% in these calcs. For decarbonisation, I use a rate of 2% which would halve our emissions in 35 years. This is less than half the rate that would be required to halve emissions in 12 years as hypothesised earlier. Atmospheric CO2 concentrations are then provided from emissions by the equation of Myhrvold and Caldeira (2012). I could have used real historical emissions for the historical period of my simulation, but actually I get a marginally closer fit to historical CO2 concs when just using the exponential growth with my chosen rate. Three decarbonisation dates tested are 2020, 2030 and 2070. Ie starting now(ish), or alternatively after a delay of 10 or 50 years respectively.
screenshot 2019-01-27 13.31.02
Current CO2 concentration is about 410ppm, increasing by 2.5ppm per year. I didn’t bother distinguishing or labelling the three lines on each graph as it’s obvious which relates to which scenario. I have marked the date at which decarbonisation starts, so you can see how the concentration increases for quite a while after we start to cut emissions.

The resulting climate change is modelled by the widely-used two-layer model of Winton, Takahashi and Held (2010) discussed in several papers by Held, Winton and others (2010 ish). Parameter values can be changed in this model, but the only one that really matters here is the equilibrium climate sensitivity (ECS) to a doubling of CO2. For non-CO2 forcings (aerosols, volcanoes, methane etc) I use historical estimates for the historical era and just hold these fixed at their current values indefinitely into the future. The model simulation matches historical data pretty reasonably as shown below. The max temp rises (up to the year 2350) for the three scenarios are indicated on the graph, ie you get a 0.25C increase in max temp for a 10 year delay, and 1.6C for 50 years. In other words, each year of delay initially leads to an increase in ultimate warming of about 0.025C, and this number rises steadily to around 0.04C per year in the middle of the century. The differences in temperature seen by the year 2100 are a little less than this, eg at this time there is just under 0.2C difference between the 2020 and 2030 scenarios.
screenshot 2019-01-27 13.31.36
Raising the sensitivity of the model increases the ultimate temperature rise of course, and also increases the difference between the scenarios. For a sensitivity of 5C (hard to reconcile with what we believe) the 10y delay leads to an additional ultimate warming of almost 0.4C, though in this case significant warming is continuing beyond the end of the simulations in 2350 and the long-term differences will also grow gradually beyond this time. For sensitivity of 2C, the decadal delay leads to an ultimate difference of just under 0.2C, and is only 0.15C at 2100.

So this is the cost, in climate terms, of delaying decarbonisation. I don’t think the underlying assumptions are unreasonable, though no doubt some could be changed. The growth rate of emissions at 1.9% per year is probably debatable but (when fed through the Myhrvold and Caldeira equation) gives reasonable historical results. My decarbonisation rate is a guess, but results are not very sensitive to this. Eg if we can achieve 5% decarbonisation rate, then the cost of a 10-year delay is reduced slightly to just under 0.2C rather than the 0.25C I've calculated. Note that the starting point for this post was an assumption (assertion?) that we can decarbonise at 5% per year, otherwise the world is going to end anyway.

Evaluating the economic impact of the warming may be the most contentious part. Here I’ve just used an estimate based on a version of the (Nobel-winning) Nordhaus DICE model, which I also used in this paper. Other estimates are available, and I wouldn't be surprised if these impacts have nudged up slightly but I don't expect they would be radically different. I’ve also used a simple 2% per annum growth rate for past and future GDP which some may disagree with, especially when extrapolated out to 2350. But what else should I have done?
screenshot 2019-01-27 13.31.19
There are indeed three lines on this graph, but they aren’t very clearly separated! The 2%(ish) cost of modest climate change just isn’t very visible against the background of several orders of magnitude of economic growth. To be clear, I don’t think that everything can be readily boiled down to money – recent events show, many millions are apparently willing to squander untold billions (of other peoples’ money, of course) on the hypothetical benefits of "sovereignty". Yes, I’m talking about brexit, the costs of which will undoubtedly dwarf any plausible impact of climate change on the UK, for many decades to come. But even if we aren’t trying to maximise economic benefit, it’s still an interesting context for the impact of climate change policies.

At this point I will refrain from making any more rhetorical flourishes but will instead leave the reader to decide whether this analysis indicates an end to the world.

Wednesday, January 02, 2019


Tim Harford says that the act of making predictions makes for better people (based on this paper). I've always enjoyed making predictions so I suppose I should be pretty wonderful by now. Hmmm...well in fairness he was only suggesting an association not a guarantee. In the hope of improving myself a little further, I offer the following:

  1. Brexit won't happen (p=0.95).
  2. I will run a time (just!) under 2:45 at Manchester marathon (p=0.6).
  3. Jules and I will finish off the rather delayed work with Thorsten and Bjorn (p=0.95).
  4. We will also submit a highly impactful paper in collaboration with many others (p=0.85).
  5. 2019 will be warmer than most years this century so far (p=0.75 - not the result of any real analysis).
  6. The level of CO2 in the atmosphere will increase (p=0.999).