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This is inspired by What single element could destroy the world?.

Injecting sulfur dioxide into the atmosphere has been proposed as a mechanism to relieve the symptoms of global warming by creating a "stratoshield" (a la Mount Pinatubo), reflecting more of the sun's light away from earth. Large amounts of sulfur would be burned and injected high into the atmosphere using tubing suspended from weather balloons.

  1. About how cold does it have to get to be relatively certain all vertebrate life goes extinct?
  2. How much sulfur dioxide is needed to get to that temperature?
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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

  • $\begingroup$ I'm voting to close this question as off-topic because it is actually an answer to another question. $\endgroup$ – James Jan 14 '16 at 19:37
  • $\begingroup$ Welcome to the site browly. This (while interesting) shouldn't be posted as its own question. It does not take much rep for you to be able to post on protected questions. Feel free to save this and post it as an answer to the question (which is mine coincidentally) once you gain the needed rep. Let us know if you have any questions. $\endgroup$ – James Jan 14 '16 at 19:40
  • $\begingroup$ @James No, it is a question. I'm posting it as a question because I don't have enough expertise, not just reputation. I need help with the sulfur dioxide cooling calculations. Would you still have voted to close it if I hadn't linked to the other question? $\endgroup$ – browly Jan 14 '16 at 19:40
  • $\begingroup$ I'm voting to close this question as off-topic because it would be better suited for a different Stack Exchange site. $\endgroup$ – AndreiROM Jan 14 '16 at 21:32
  • $\begingroup$ I actually feel like this could be a good question, but I'm voting to close it as Too Broad. While some of the sub-questions are related, many are not. $\endgroup$ – HDE 226868 Jan 14 '16 at 21:43
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  1. Maybe -20?
  2. If so, about $10^{11}$ kg.

For question 1, I’m going to guess that changing the average temperature from 16 degrees Celcius to -20 degrees will cause enough havok to create mass extinctions. The average temperature during the last ice age was about 10 degrees. If the temperature near the equator ranges from 10-30 above the average, -20 globally would get the equatorial temperature dipping below freezing regularly.

For the hose-to-the-sky cooling scheme, I’m getting all of my information from Levitt and Dubner’s SuperFreakonomics. This is just a rough estimate, so hopefully that will be good enough.

Intellectual Venture’s plan to completely reverse global warming requires 5 base stations, located around the globe, each with 3 hoses (p. 196) spraying liquified sulfur dioxide into the stratosphere, 7 miles up (p. 189). Each hose sprays at 34 gal/min (p. 192), or 190 kg/min, so 2800 kg/min for all 15 hoses. Since they say this will “effectively reverse global warming” (p. 196), let’s assume that 2800 kg/min will decrease the average temperature of the earth by 2 degrees Celcius.

I’m guessing that sulfur dioxide injection would be affected by the law of diminishing returns, but I’m going to assume a linear relationship because I lack the skill to do anything else. With that assumption, decreasing the average global temperature 36 degrees would require pumping about 100,000 kg of sulfur dioxide per minute. To cause mass extinction, let’s say we have to run this for two years, to make sure that artic and antarctic animals don’t get a chance to stock up on more food in the “summer”. That will take $10^{11}$ kg of sulfur dioxide, or $5\times 10^{10}$ kg of sulfur (1 kg of sulfur yields 2 kg of sulfur dioxide). Do we have that much sulfur handy?

It looks like it. The Athabasca Oil Sands in Alberta, Canada have pyramids of sulfur as a waste product of oil extraction. The book describes pyramids “a hundred meters high by a thousand meters wide” (p. 195), or 30 million cubic meters = $6\times 10^{10}$ kg S in each pyramid.

How many hoses do our five pumping stations need? Each station needs to output 20,000 kg/min, which would require about 100 hoses at each site, or maybe bigger hoses.

If we assume just two giant pumping stations, at the Athabasca site and at a similar site somewhere in the southern hemisphere, the sulfur dioxide "stratoshield" would shade the earth's surface in about 10 days (P. 194). Each station has enough sulfur to run for at least two years, so together, they can freeze the earth for more than four years (assuming the earth cools off quickly once it can’t receive as much energy from the sun).

The sulfur dioxide would settle out of the atmosphere “within a few years” (p. 197).

If my arithmetic is correct, this scenario is too close to plausibility for my comfort.

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  • $\begingroup$ It would be easy to detect and shut down though, so not really an existential threat. $\endgroup$ – Tim B Feb 16 '16 at 17:05

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