Halstead's Comments

Pangea: The Worst of Times

Ah yes - that's a good point, cheers!

What is a good donor advised fund for small UK donors?

One option I had thought about was - until there is an option for UK people, put the money in a CAF bank account and then get the gift aid, and wait until a suitable product becomes available. However, I think this is inferior to just putting the money in a Vanguard account - after 5 years 4% fees from CAF and no investment returns eats up all the gift aid benefits.

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What is a good donor advised fund for small UK donors?

The enterprising Phil Trammell says in an FB message

"I just got off the phone with Vanguard Charitable, and they say that there's no issue with setting up an account from overseas. The catch is that contributions have to come from a US-based bank or investment account...! Since anyone can contribute to anyone's DAF, this doesn't seem too hard in principle; you can just contribute by sending money to a US-based friend, or that rethink charity donor-swap org or something, and they deposit it in the account you manage online. (It could always be done in small batches, if you don't fully trust them.) The initial contributions wouldn't be tax-deductible (or maybe they would be for the friend you're initially sending the money to?), but at any rate the interest still wouldn't be taxed.

Maybe this too much of a hassle for any individual to bother sorting out, but if there's interest from enough other people, and someone's willing to set some arrangement like this up, would you want to use it?"

How hot will it get?

2a. On China, I don't think population size matters for the carbon intensity of gdp - that should mostly be accounted for in the population parameter. agree that gas and reneawables are cheaper and that might be a reason that emerging economies won't use as much coal.

b. It doesn't seem to matter that much that strong climate policy exists in some places, e.g. Sweden. What seems to matter is whether there has been a notable change in global climate policy over the last 5 years that renders just extrapolating from the last 30 years especially unreliable. I don't see anything that would justify that.

c. Yeah that's fair. renewables a re a reason to think that intensity might decline below trend.

d. The places where we might get $50 per tonne carbon prices are less than 10% of global emissions to 2050, on current trends. historical experience suggests that some extremely wealthy left wing countries might impose high carbon prices in the next 30 years. Unfortunately, this won't have much of an effect on global emissions. there might be some places that impose high carbon prices, but they will cover a small fraction of emissions, just following the trend of the last 5, 10 or 30 years.

e. I don't think they assume zero political coordination. Political coordination would increase on the trend it has been doing over the last 5, 10 or 30 years.

4. It might be that there is cheap negative emissions, but this doesn't seem to me in the most likely range of scenarios (barring ocean fertilisation or something being good, which I don't know much about). It's worth pointing out that median carbon intensity ends up being pretty low on the estimate I give - it is a quarter of carbon intensity today, and the the upper end of the 95th percentile is a tenth of carbon intensity today. This is with climate action proceeding at the same dismal pace as it has over the last 30 years.

5. It would be weird to model geoengineering in this model. It seems to make much more sense to think about geoengineering as one of the solution tools you could use given where emissions might go. If you start thinking about the probability of solar geo in this model, the emissions wouldn't matter anyway, the temperature would. If you think there is a 10% chance of solar geo, then you would have to model at 10% chance of there being 2 degrees of warming. I think it is much easier to think about solar geo separately from this model.

How hot will it get?

right, that's bad news.

How hot will it get?

Hi Johannes, thanks for this.

1. By extra effort, I have in mind that we are on a trend line of effort on climate change, and extra effort would be a diversion from this historical trend. One rough proxy for this would be the global average marginal carbon price, which has crept up from about $0 to about $2 per tonne over the last 15 years. If in the next 10 years the global average marginal carbon price were to increase to $40, that would be a diversion from the trend line of climate effort.

2&3. These are all specific factors that a more precise estimate might take into account. It would be worth playing around with the estimate to see what effect this was on predicted emissions. It's worth noting that the rough 'follow the last 30 years' approach does produce the same median as other much more sophisticated models. Also note that if you play around with the model and put in much higher projected reductions, you do get a median that is more like RCP4.5, but the tail risk of much higher than expected emissions remains

Reasons to think carbon intensity might reduce beyond trend

  • a. China is anomalous both in terms of growth and reliance on coal. (This doesn't update me that much. The growth factor should be accounted for in the other parameter, and as long as coal is the cheapest energy source, our default assumptions should be that poor countries will rely on it to escape poverty. This is worsened by general equilibrium effects - declines in demand for coal in the West will reduce the cost for everyone else.)
  • b. Climate policy is kicking off. (I don't put much weight on this. Climate action is still very weak across the world and there are horrible political factors that push against strong changes in the trend)
  • c. Technologies in store that should help with carbon intensity. The most obvious ones are solar and wind, which follow an exponential cost reduction curve. If these start to play the role that some people predict, then we might see carbon intensity reduce below the trend line. (I personally would be surprised if these ever get to more than 30% of electricity worldwide, which is still a big deal. The super-pro-renewables people might expect more like 80% of electricity. But perhaps our default should be something like what we're witnessing in Germany, where they are trying very hard to push solar and wind but it's not having much of an effect on carbon intensity of gdp.)
  • d. I doubt large-scale CCS would happen on large enough scale without significant diversions from the trend in climate effort since it costs >$30 per tonne. This is less true but still true for advanced nuclear. The only countries that have pushed nuclear to a significant extent have done so for reasons of energy security. So, the reference class isn't that promising.
  • e. Yeah I agree with these points about assumed independence. The main caveat I would have is that political coordination is much harder than expected.
  • f. I agree that we have time to learn about high climate sensitivity so there is also an interaction there which reduces overall tail risk.

Reasons to think carbon intensity might increase beyond trend

  • g. Maybe political coordination is much harder than we expect. Maybe there is an arms race and people give up on climate.

All of this suggests that the estimates of carbon intensity decline might be biased a bit upwards. The most important factors seem to be decline in costs of renewables, electric cars and potentially advanced nuclear, as well as factors e and f.

4. I don't put much weight on the absence of negative emissions (unless we discover a very cheap form of it). If negative emissions remains at >$50/tonne, I don't see it having much of a role in the 'no extra effort' scenario.

Yeah I think it's most useful to think about what will happen if solar geoengineering is not an option, as this will allow us to figure out the potential benefits of solar geo from an ex risk pov. I agree that solar geo could be a useful backstop, though I don't see it getting deployed unless something quite extreme happens and I would view the governance challenges of deployed solar geo as a major way in which climate change contributes to GCRs.

How hot will it get?

Hi Arden,

1. Yes that's right. (Which scenario is better calibrated is up in the air. The Christensen et al one is an expert estimate but economists are very bad at predicting growth next year, so it's not clear that an expert survey is better than just extrapolating from the last 30 years.)

2. Yes, that is what the second model is *trying* to do but note that qualification that it is mainly trying to estimate the tail risk, so to get the 95% confidence interval right. In guesstimate, the median concentration isn't right (given the first model), but the 95% CI is. However, it would be quite easy to make a model estimating the chance of a certain level of warming conditional on a particular level of CO2 concentrations. I have added an example of this to the bottom of the second guesstimate model. If you think, following Rogelj et al, that the most likely current policy scenario is 700ppm, then the 95% confidence interval for warming is 1.6 to 5 degrees, with a median of 2.9 degrees. The chance of more than 6 degrees is about 1%. This shows the effect of priors - on Wagner and Weitzman's estimate, the chance of >6 degrees is more like 10%

How hot will it get?

Ah, I didn't know that, thanks, I haven't followed the literature that closely over the last year. I'll put that into the model.

On a side note, that does seem high, and doesn't seem like it would fit with the observational data for the last 200 years very well.

How hot will it get?

haha yes thanks matthew, that's a good spot!

So, the thought is that we would have some non-trivial probability mass on burning all the fossil fuels if there is an AI explosion. My best guess would be that this makes working on AI better than working on marginal climate stuff but I'm not sure how to think about this yet

How hot will it get?

Yeah, i think the AI explosion scenario should be taken with several piles of salt. It gets to the point that we need to be consistent about our expectations about AI timelines and about climate change. As you suggest, AI-driven progress could drive down carbon intensity, but climate change remains a horrible coordination problem, so it's not clear that all AI progress overcomes that

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