Near-term human extinction scenarios from environmental degradation?

[caraher]

I hear people toss around the notion that humans may go extinct as a result of climate change, but it's never been clear to me that this is even a plausible, let alone likely, outcome. The person who seems to push the idea the hardest is Guy McPherson... and I certainly share his concern for things like positive feedbacks. While he does outline multiple scenarios he considered human extinction events based on climate change, these seemed to vary widely in plausibility, with the plausibility level lowest for the ones I understand best.

So if you think climate change suggests we may face extinction as a species (and not a "mere" hard population collapse and the end of civilization as we know it), how exactly does this come about? And more importantly, what research backs up your extinction scenarios?

Most of my idle Googling on this just loops back to McPherson...

[madrchsod]

1. we have come very close to the edge but we are still here.

i think if a rather large rock hit us we`d probably go extinct.

[snot]

2. Pardon me if this is off-topic; but

does nothing short of total extinction matter? (E.g., millions or more are displaced or die . . . . )

Ok, you're asking a theoretical but legitimate question . . . .

[NoOneMan]

4. To the 99% that may go...

I don't think they give a fuck if its total or not, as its as bad as it could be to them.

[caraher]

8. For the purposes of my question, no

For me personally, of course something less than extinction matters. We've already seen disasters I'd deem unacceptable and I expect they will become more frequent and worse, unfortunately.

But I'm asking a fairly narrow question about a specific claim. My "gut" feeling has been that trashing "civilization" is likely but extinction as a species far less so, but if I'm wrong about the second part I'd like to know why.

[NoOneMan]

3. Oy, the rich will make it in their platinum bunkers

So Guy is just a big fat baseless liar.

I also think their hired mercenaries will survive

[theHandpuppet]

10. Funny, I think it will be just the opposite

That is, those who will survive will be small communities of existing hunter-gatherers in remote areas.

[hatrack]

17. Yeah, but everybody else not in said platinum bunkers will know where the bunkers are . . .

And there will be many more of them, even under post-catastrophic circumstances, than of the rich guys and their bodyguards.

If anything, it's more likely that the bodyguards survive - after all, they know how to use the guns better than the rich guys, so why keep around a bunch of Pet Kochs?

[SheilaT]

5. As bad as environmental degradation is probably going to be

in the next century, total extinction strikes me as unlikely. There may well be an enormous die-off of humans, but extinction? I honestly don't think so.

As if my opinion actually matters in what happens.

[wundermaus]

6. Positive feedback (when it comes to climate stability) is a bitch...

Last edited Thu Oct 24, 2013, 03:07 AM - Edit history (1)

and then we die.
It may be too late... or
It may not be too late.
So, is inaction an option?

http://rsta.royalsocietypublishing.org/content/371/2001/20120294.full

[caraher]

9. Thanks for the link

That's the sort of thing I'm looking for, especially toward the end. It stops just short of an extinction prediction but certainly makes a case for heedless fossil fuel burning putting us in the ballpark on a few-centuries time scale.

[stuntcat]

12. wow thank you, never seen that

And it's about 5 years old.. even before co2 passed 350 ppm

[GliderGuider]

7. IMO not before the first half of the 22nd century.

I do expect things to begin to fall apart big-time within 25 years. Polar amplification leads to weather disruptions and declining food production due to the increasing disorganization of the polar jet stream, as well as to accelerating Arctic methane feedbacks. Early signals of the dieback could appear around 2030, withe the dieoff starting in earnest around 2050. A drop to under two billion people by 2100, with extinction a possibility within the following century. It's only a possibility though, not a certainty - unless methane feedbacks raise the CO2e to over 1000 ppm by 2100. We made it through Toba after all, with perhaps fewer than 25,000 surviving individuals.

But even if humans do make it through, this is our only kick at the can for creating a global industrial civilization. We won't get a second chance. We're too clever, we've been too deep into overshoot for too long, we've been too good at degrading the stored, concentrated energy resources of the planet. We've just about sawed off the branch we're sitting on.

[pscot]

11. We have less than 100 years left

I read it in the Daily Mail. The comments following the article are, as always, invaluable.

http://www.dailymail.co.uk/sciencetech/article-1287643/Human-race-extinct-100-years-population-explosion.html

[CRH]

13. Total extinction, not soon but maybe, ...

depends on the CO2 concentrations after the frozen carbon sinks release. Some humans will probably survive well into the 22nd century, but agriculture will not exist. That means gathering and traveling and trying to find an area that can support the water and nutritional needs of higher order mammals. It will also mean adapting to very different foods than those that have allowed humans to flourish over the last ten thousand years.

But if the planet hasn't found a plateau by 6-8*C mean rise, and continues heating to levels it has in the past, the time span of return to a food producing environment for higher order mammals, will be at minimum many thousands of years. In this scenario, extinction is most likely.

I personally feel without a plateau at 6*C mean, it is just a matter of time. And in a few generations, humans would not be the same.

56 million years ago during PETM the first ancestors of the horse reduced in size 30% to about the size of a house cat. After many thousands of years of cooling they then increased 70% in size. As millions of years of cooling occurred, evolution eventually produced the much larger present equine family. However the ancestors of horses were mammals, and did survive 5.5*C mean rise albeit smaller and in select locations. At what point do mammals become extinct is a good question. The bat is a mammal and is nocturnal and lives from eating insects. They will make it quite a bit further into a global heating episode, than more delicate species, like humans.

[kristopher]

14. What consequences if 96% of marine and 70% of terrestrial vertebrate species disappear?

Permian–Triassic extinction event
From Wikipedia, the free encyclopedia



The Permian–Triassic (P–Tr) extinction event, informally known as the Great Dying,[2] was an extinction event that occurred 252.28 Ma (million years) ago,[3] forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with up to 96% of all marine species[4] and 70% of terrestrial vertebrate species becoming extinct.[5] It is the only known mass extinction of insects.[6][7] Some 57% of all families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event,[4] possibly up to 10 million years.[8]

Researchers have variously suggested that there were from one to three distinct pulses, or phases, of extinction.[5][9][10][11] There are several proposed mechanisms for the extinctions; the earlier phase was probably due to gradual environmental change, while the latter phase has been argued to be due to a catastrophic event. Suggested mechanisms for the latter include large or multiple bolide impact events, increased volcanism, coal/gas fires and explosions from the Siberian Traps,[12] and sudden release of methane clathrate from the sea floor; gradual changes include sea-level change, anoxia, increasing aridity, and a shift in ocean circulation driven by climate change....

http://en.wikipedia.org/wiki/Permian–Triassic_extinction_event

[NickB79]

15. IF we go extinct, it will be from the resource wars brought by AGW

I don't seriously think that humanity will be directly wiped out by climate change in the next few centuries. Even with massive warming, crop failures, disease migration, and sea rises, I'd expect some populations of humans would survive near the poles as hunter/gatherers.

The most likely chance that we'd face extinction, IMO, is if the world's superpowers decide to go toe-to-toe for the last concentrations of resources this planet has to offer (fossil fuels, mineral resources, fertile farmland, forests, etc).

A bunch of nations, desperately clinging to their old ways in a rapidly changing world, while armed with chemical, biological and nuclear weapons, and you have the recipe for WWIII.

[GliderGuider]

16. I've never thought that WWIII would have the necessary lifting power.

If we accept that the species can keep on trucking (in some manner) with 20,000 survivors, then extinction through warfare is highly unlikely IMO. The only caveat would be if a persistent, genetically-targeted, live-organism bioweapon was used, and the pathogen subsequently mutated to attack all humans. Even more than nuclear weapons or 400 Fukushimas, that's my nightmare scenario.

I still think it's a low runner, though. Compared to that, a massive dieback due to food and habitat limits stemming from CO2/methane releases is virtually a certainty over the next century or two. IMHO.