“Transition to a Moist Greenhouse with CO2 and solar forcing” https://www.nature.com/articles/ncomms10627
turchin
Karma: 620
I think that the difference between tipping point and existential temperature should be clarified. Tipping point is the temperature after which self-sustaining loop of positive feedback starts. In the moisture greenhouse paper it is estimated to be at +4C, after which the temperature jumps to +40C in a few years. If we take +4 C above preindustrial level, it will be 1-3 above current level.
I didn’t try to make any metaphysical claims. I just pointed on conditional probability: if someone is writing comments on LW, (s)he is (with very high probability) not an animal. Therefore LW-commentators are special non-random subset from all animals.
I think that here are presented two different conjectures:
“I am animal”—therefore liquid water on the planets etc.
“I am randomly selected from all animals”.
The first is true and the second is false.
From climate point of view, we need to estimate not only the warming, but also the speed of warming, as higher speed gives high concentration of methane (and this differential equation has exponential solution). Anthropogenic global warming is special as it has very high speed of CO2 emission never happened before. We also have highest ever accumulation of methane hydrates. We could be past tipping point but do not know it yet, as exponential growth is slow in the beginning.
From SIA counteragrument follows that anthropic shadow can’t be very strong: we are unlikely to observe the world with a very strong anthropic shadow. However, some anthropic effects on climate likely to exist as we observe the preservation of habitability of the Earth despite changes а Sun luminosity. This gives us some range of values there anthropic shadow can be, and 0.1 per cent seems to be a reasonable estimate inside it. Though exact number or range is difficult to estimate. May be Sandberg’s work on near-misses in nuclear war would help—when we will have a chance to see it.
I feel that I didn’t answer the whole your question, so can you point what exactly is your point of disagreement.
I use exponential prior to illustrate the example with a car. For other catastrophes, I take the tail of normal distribution, there the probability declines very quickly, even hyperexponentially. The math there is more complicated. But it does not affect the main result: if we have anthropic shadow, the expected survival time is around 0.1 of the past time in the wide range of initial parameters.
And in the situation of anthropic shadow we have very limited information about the type of distribution. Exponential and normal seems to be two most plausible types for catastrophes. There is also semi-periodic ones, but they could be described as a sum of periodic plus normal.But obviously there is more to dig here.
If you were random animal, you will be an ant with 99.999999 probability. So either anthropic is totally wrong, or animals is wrong reference class.
Do you regard animals as observers?
Do you regard animals as observers?
Sanberg recently published its summary in twitter. he said that he uses the frequency of near-misses to estimate the power of anthropic shadow and found that near misses was not suppressed during the period of large nuclear stockpiles and it is evidence against anthropic shadow. I am not sure that it is true, as in early times the policy was more risky.
We don’t know where is the tipping point, so uninformed prior gives equal chances for any T between 0 and, say, 20 C additional temperature increase. In that case 2C is 2 times more likely.
But the idea of anthorpic shadow tells us that tipining point is likely to be 10 per cent of the whole interval. And for 40C before moisture greenhouse it is 4C. But, interestingly, anthropic shadow tells us that smaller intervals are increasingly unlikely. So 1C increase is orders of magnitude less likely to cause a catastrophe than 4 C increase.
I will illustrate this as following example:
Imagine you are buying a used car which had run 300K miles. It is a unique survivor for its age.
If the car had 1 in 1000 chance to survive until its age, then doubling period of the probability of death (aka half-life) for it is 30K miles (10 doublings); if it had 1 in 1 000 000 chances to survive until current age, it has 20 doubling or 15K miles. The 1000 times growth of anthropic shadow lower car’s life expectancy only 2 times.
Future survival declines very slowly:
Anthropic shadow power 1 in 1000 = survival 10 per cent more
Anthropic shadow power 1 in 1000 000 = survival 5 per cent more.
Anthropic shadow applies not to humanity, but to underlying conditions on which we can survive.
For example, the waves of asteroid bombardment are every 30 million years, but not exactly 30 mln.
The next wave is normally distributed around 30 with mean deviation, say, 1 mln years. If 33 mln years have gone without it, it means that we are 3 sigmas after the mean.
Image as a toy example a tense spring which is described by Hooke’s law. Fs = kx.
Imagine also that we can observe only those springs that are tensed far beyond their normal breaking point = it is a model of anthropic shadow.
From logarithmic nature of the relation between remaining life expectancy and the power (probability of past survival) of anthropic shadow follows that for almost any anthropic shadow the remaining life expectancy is between 5-20 per cent of past survival time, lets call it dA.
For a tensed spring it means that its additional length beyond the breaking point is around 5-20 percent of total length (with several linearity assumptions which will not list here for simplicity).
Now, the fragility of the spring could also be measured in its additional length increase which will cause its breakdown, dL.
dL can’t be more than the dA, as dA is already improbable event, and dA is less than 5-20 per cent of total length of the spring. Therefore, dLis less than 0.05-0.2 of L.
This seems to work only for the situation when the relation of the main parameter L is linear with the force of tension. But even for non-linear parameters they could be approximated by linear ones near the point.
TL;DR: Fragility is delta L (increase) of the main parameter of the system which causing its catastrophe. Fragility is proportional to anthropic shadow in a system similar to tensed spring or overinflated ballon, but in most cases of anthropic shadow it is independent of initial parameters an is around 10 per cent change. In the case of climate, it is not very clear what is main parameter, but likely it is means temperature.
Yes, agree. Two more points:
Not all population counts, but only those who can think about anthropic. A nuclear war will disproportionally destroy cities with universities, so the population of scientists could decline 10 times, while other population will be only halved.
Anthropic shadow means higher fragility: we underestimate how easy it is to trigger a nuclear war. Escalation is much easier. Accidents are more likely to be misinterpreted.
If there will obvious global runaway global warming, like +6C everywhere and growing month by month, people will demand “do something” about it and will accept attempts to use nuclear explosions to stop it.
I don’t have access now to the document “Nuclear war near misses and anthropic shadows”
If we create artificial nuclear winter—it could be created by one strong actor unilaterally. No coordination is needed.
Such nuclear winter may last few years and naturally resolve to normality. During this process two things could happen: either the tipping point conditions also stop, like methane leakage ends. Or we create more permanent solution to our problem like more stable form of geoengienering.
The artificial nuclear winter doesn’t need to be very strong (in −2-3 C range), so no major disruption of food production will happen.
I discuss different arguments against anthropic shadow in my new post, may be it would be interesting for you https://forum.effectivealtruism.org/posts/bdSpaB9xj67FPiewN/a-pin-and-a-balloon-anthropic-fragility-increases-chances-of
I think, yes. We need a completely new science of “urgent geoengineering”—that is something like creating artificial nuclear winter by controlled fires in forests which will give us a few years of time to develop better methods or to reverse the dangerous trend.
I tried 6 years ago to create a more detailed plan (it may obsolete, but that is what I have) here
http://immortality-roadmap.com/warming3.pdf it is a chart
and it is its explanation https://forum.effectivealtruism.org/posts/C3F87C8r6QFXwnwqp/the-map-of-global-warming-prevention
The relation between warming and CO2 is exponential, s we need to count the number of doublings of CO2. Every doubling gives a constant increase of the temperature. Assuming that each doubling gives 2C and 22= 2exp4.5, we get around 9C above preindustrial level before we reach tipping point.
In the article the tipping point is above 4C (in the chart) plus 6C from warmer world = 10C, which gives us approximately the same result as I calculated above.