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turchin comments on Levels of global catastrophes: from mild to extinction - Less Wrong

3 Post author: turchin 27 December 2015 05:26PM

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Comment author: turchin 29 December 2015 10:46:10AM *  1 point [-]

While I don't agree with everything arctic news say and I see that they overhype some recent small changes in methane concentration, I heard the idea of runaway global warming before. I also think that artificial runaway global warming is possible if nukes will be used to destabilize methane of ocean floor. While answering previous comment I was surprised to find in wiki that if median earth temperature once rise to 47C, than water vapor greenhouse effect will push it until new stable state at 900 C. I still think that we should be more afraid of small probability (I estimate it in 1 per cent) of runaway global warming than of high probability conventional global warming (2-4 C).

The main thing about it is, in my opinion, connected with your notion in the second period in your post that we don't observe past runaway global warming. (Except small scale one like 55 mln. years ago.) One of the reason for that may be observation selection: there is no life on all planets with runaway global warming (Venus).

But more serious consequence of it may be that runaway global warming is long overdue and our atmosphere is in metastable condition where small influence may flip-flop it. I wrote an article about in before "Why anthropic principle stopped to defend us"? https://www.scribd.com/doc/8729933/Why-anthropic-principle-stopped-to-defend-us-Observation-selection-and-fragility-of-our-environment (It needs to be rewritten).

Comment author: CellBioGuy 30 December 2015 09:50:46PM *  0 points [-]

Points taken. Still, the PETM was as recent as 50 million years ago, when the sun was on the order of 99.5% as bright as it is now and the base state from which the temperature and atmospheric carbon rose (as quickly as we have measurements able to say - as in, it took less than 15k years and they cant be more specific than that and there's evidence that at least some places warmed ifaster) was one in which there were fewer eroding mountain belts to suck up carbon and more subduction zones to produce it and a geological equilibrium CO2 concentration on the order of 3-4x that of today with an average global temperature of about 8 C warmer than today, before the pulse even happened. I find it unlikely the solar and geochemical situation has changed considerably over that ultimately not terribly long timeframe,

Comment author: turchin 31 December 2015 12:01:55AM 0 points [-]

I have read somewhere that the main difference is that now we have 10 times more accumulated methane in the form of methane hydrates on ocean floor and permafrost. Methane is strong green house gas, like 100 times stronger than CO2. But as it lives only 6 years in atmosphere, the main difference would be not its amount, but the speed which which it could be realised from permafrost. This depends of speed of CO2 accumulation (which is now very high, while the total level is still low). The last thought is mine conclusion from what I read.

Geochemical situation also changed as we had several ice ages which are very good for methane hydrates accumulation and also because geography of Arctic ocean changed.

Anyway, I think that we runaway global warming may be easily prevented by artificial nuclear winter or some cloud seeding, if situation will be urgent. But AI situation is more complex.