Hacker News Reader

Comment by lelanthran | Hacker News Reader

> For example, 8 degrees of warming would be much worse than 4 degrees of warming, and could mean the difference between human extinction and the mere collapse of our civilization.

I'm assuming celsius, not farenheit.

I'm curious why a mere 8 degrees increase leads to human extinction.

Is that "8 degrees evenly over the globe"? If so, that most certainly would leave the majority of land arable and comfortably livable.

Is that "8 degrees average with such a high deviation that no land is left with a year-round range of 0 degrees to 30 degrees"? If that is the case, where can I read/view/see the model that produces such an extreme outcome?

View on HN

This guy Mark Lynas studied the models and wrote a book about it, but then he wrote it again based on newer models, so make sure to find the latest one called "Our Final Warning: Six Degrees of Climate Emergency" for a grizzly drilldown into the centigrades towards extinction. Few models deal with warming beyond three degress, in itself a point of some consideration, but the references are all there and here's the synopsis for the book.

> At one degree - the world we are already living in - vast wildfires scorch California and Australia, while monster hurricanes devastate coastal cities. At two degrees the Arctic ice cap melts away and coral reefs disappear from the tropics. At three, the world begins to run out of food, threatening millions with starvation. At four, large areas of the globe are too hot for human habitation, erasing entire nations and turning billions into climate refugees. At five, the planet is warmer than for 55 million years, while at six degrees a mass extinction of unparalleled proportions sweeps the planet, even raising the threat of the end of all life on Earth.

Actually I was kinda hoping for just a model or some peer reviewed conclusions.

I'm just not in the mood to devote a lot of time to what sounds (to me) like hyperbole: If the earth stabilised at +8 degrees celcius I find it hard to understand why the entire earth becomes literally uninhabitable.

It doesn’t. It’s an extrapolation based on the limited insights of a PhD who by any reasonable definition spends too much time with simulations.

If you want to think of a way it could be possible, though, think of those areas that would be habitable, realize that they would be highly contested, are mostly presently permafrost, and consider your own ability to both protect and survive on melted tundra and reproduce there, given you will starve in a single season without food.

> If you want to think of a way it could be possible, though, think of those areas that would be habitable, realize that they would be highly contested, are mostly presently permafrost, and consider your own ability to both protect and survive on melted tundra and reproduce there, given you will starve in a single season without food.

I actually did consider that first - that maybe at +8c humans will kill each other, but that's just pure speculation.

And, sure, food is necessary daily and constantly, but the situation you outline isn't an overnight thing. Hell, it isn't even a 100-year change, +8c is a lot longer.

That gives you plenty of time to move, and at +8c, as long as it is stable at +8c, you'd still have enough arable and livable land to ensure that humanity is nowhere close to extinction.

So if it isn't lack of land, and it isn't the temperature range that causes human extinction, what does?

I think it is incredibly unlikely personally. We have evolved nearly beyond environmental dependence, certainly beyond local environmental problems, and it is difficult to imagine our extinction as long as there are some plants and insects that survive. Possibly we could even persist on algae farming.

But if you add the fact that antibiotics will be in short supply, novel zoonotic diseases will ramp up, and most knowledge of how to survive in the wild has been lost and probably can’t be reconstituted in a couple of violent generations, I can see how it could come about.

There is also the social and psychological impacts of that scale of loss, and there are some other sort of scary indicators you could lean on (Calhoun rat experiments) to indicate that there are limits to what animal populations will reproduce through.

I’m not worried about it — we seem like a pretty robust system from my perspective. But it is interesting to think about abstractly.

https://www.quantamagazine.org/cloud-loss-could-add-8-degree...

Here is a well-written article (shared by another HNer here) on one plausible run-away event. But the same way as upon exerting more and more force to a branch it will first have linear changes going on, there will come a point where it will break.

Some possible runaway events include the aforementioned loss of clouds which in turn won’t reflect back that much sunlight (which currently can account for 30-70% of sun light not hitting the ocean water), melting ice will free lots of trapped CO2, changing climates may alter currents and winds causing very large-scale changes to certain areas (and might also affect cloud formation), etc. We are in a big, closed jar and that 8C change may not be a problem locally, it is that much more heat trapped globally.

But one should add that life is unlikely to die out in even the worst predictions (life, finds a way), but you still don’t want to find yourself in the situation where you will have to literally hunt down other humans because they may have food, or try to migrate with 100s of millions of other agitated, hungry people to nations which won’t be friendly to you because they themselves have enough problems to begin with.

Reply on news.ycombinator.com