What’s the likeliest doomsday scenario?

May 18, 2012

Dear Cecil:

I'd like your opinion on which is most likely in our lifetime: (1) The sun explodes. (2) Earth shatters, like that planet in the asteroid belt. (3) We get the Big Rip, where everything dissolves as Shakespeare predicted, "leaving not a wrack behind." (4) A gamma-ray burst hits us. (5) An unseen black hole swallows us. (6) We all die from nuclear winter. (7) The Cubs win the World Series. (OK, that ain't gonna happen.)

Cecil replies:

I appreciate your realistic attitude, Mark. A postseason-ending celebration at 1060 West Addison? The apocalypse will arrive first. Other possibilities we can’t be so sure about. The 2040s, for example, look to be trying times.

For brevity I’ll exclude events so unpredictable, remote, or unlikely there’s no use worrying about them, much less planning for them. Thus we’ll blow off supernovas (even including neighboring stars in addition to ours, the odds say we might get one every 110 million years), gamma-ray bursts (maybe one in 2 billion years), or solar flares (who knows?). And no matter how much time it turns out we have left, I'm not about to spend any of it sweating the Big Rip.

Increasing solar luminosity will torch the planet eventually, but not for 500 million years minimum. We’ve already experienced several mass extinctions, with the survivors mainly on the order of lichens, deep-sea tube worms, and small rodents. On the plus side, depending on definition, disasters on this scale have occurred just three to five times in the past half-billion years, so I myself am losing no sleep.

Comet strikes (once per 7.2 million years on average) and catastrophic asteroid impacts (once per 10 million years) are more of a concern, as are supervolcanoes, discussed here before. In recent history we’ve had a cataclysmic eruption every 2.8 million years on average. A major eruption happens at the Yellowstone caldera about every 600,000 years, and the last one was about 600,000 years ago, so do the math. How serious might a supervolcanic eruption be? One theory is that the eruption of the Toba volcano in Indonesia circa 72,000 BC caused so much global cooling — as much as 30 degrees Fahrenheit worldwide — that humankind came within a hair’s breadth of annihilation, with possibly 1,000 or fewer women of childbearing age left alive.

But that was then. More urgent concerns face us now:

  • Nuclear holocaust hasn’t been on most people’s minds since before the era of George H.W. Bush (you know, the mostly harmless one), but don’t tell that to the Bulletin of the Atomic Scientists, whose Doomsday Clock is currently set at five minutes till midnight. Bear in mind that since 1947 the furthest the Doomsday Clock has been from midnight is 17 minutes. Granted, few still expect all-out thermonuclear war. But we could see a big hole in Iran.
  • Global warming may go critical by midcentury, meaning at minimum we lose Bangladesh and worst case we see something akin to the methane-hydrate-release scenario adverted to here in 2007. Quickly: frozen ocean methane melts due to rising temps, leading to massive atmospheric buildup and your classic hockey-stick warming spike. Such an event may have tripped the Permian extinction 251 million years ago, when perhaps 95 percent of planetary species were wiped out. Early reports suggest elevated methane release may have already begun.
  • Closely related to global warming is the looming energy crisis, which may also reach an inflection point somewhere around 2050. Some think we’ve already passed peak oil and from here on out production will decline. Absent a breakthrough in solar power, it won’t be physically possible to meet the world’s power needs through alternative technologies. In itself this isn’t an insoluble problem, since we’ve got plenty of coal and nuclear resources. However, using the former will accelerate global warming, while the latter would require a balls-out nuclear plant construction program to be underway now, which it’s obviously not. Opposition will dissolve once energy prices soar, but safety standards will likely also be abandoned, and the result won’t be pretty. I’ve warned you before; you’ve paid no attention. Remember this 30 years hence.
  • We’re not done yet. Next up may be the watershed event certain tech types are calling the Singularity — the point when we invent computers so powerful they have consciousness, or else attain it on their own. One proponent of this notion, futurist Ray Kurzweil, thinks it’ll mean the end of the human race as we know it: either we’ll jack our brains into the cloud and become cyborgs, or the computers, now truly intelligent, will find they have no further use for thinking meat. The doomsday date? Kurzweil pegs it at 2045. Personally I consider this the rankest crackpottery, but many lines cross during that fateful decade, so why shouldn’t Kurzweil pile on?
  • Finally, some say, the Mayan calendar terminates this year, and therefore so will we. I see in today’s paper that 10 percent of the world believes this. Coincidentally, precisely the same number believes in the Cubs.
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References

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Chapman, Clark R. “The hazard of Near-Earth Asteroid Impacts on Earth” Earth and Planetary Science Letters 222 (2004) 1 –15.

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Hirsch, Robert L. et al. “Peaking of World Oil Production: Impacts, Mitigation, & Risk Management” SAIC, United States, February, 2005.

International Monetary Fund World Economic Outlook (WEO). “Tensions from the Two-Speed Recovery: Unemployment, Commodities, and Capital Flows”, April 2011 chapter 3: Oil scarcity, growth, and global imbalances.  

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“The Straight Dope: Are there deposits of methane under the sea? Will global warming release the methane to the atmosphere?” http://www.straightdope.com/columns/read/2719/are-there-deposits-of-methane-under-the-sea 

"The Straight Dope: Followup: Why don't we ditch nukes and coal?" http://www.straightdope.com/columns/read/3000/followup-why-dont-we-ditch-nukes-em-and-em-coal 

Weissman, Paul R. “The cometary impactor flux at the Earth” Near Earth Objects, our Celestial Neighbors: Opportunity and Risk Proceedings IAU Symposium No. 236, 2006. Pg. 441-450.

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