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Comment by radford-neal | Hacker News Reader

No. Informed people realize that there is no possibility that climate change will lead to human extinction (except possibly by some indirect means, such as leading to a war in which bioweapons are used, but then, drastic action to curtail climate change could also lead to war...).

Saying "existential risk" again and again does not make it true. Hearing it again and again does not make a rational person believe it.

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>No. Informed people realize that there is no possibility that climate change will lead to human extinction

Avoiding human extinction from climate change is very easy but with this attitude you're not doing a good job at avoiding that fate. Right now I don't have much faith that humanity won't try to burn every single last drop of oil or chunk of coal. Although it should be very difficult to reach insane targets like 9°C warming it is definitively possible with enough ignorance and dedication and as humanity has shown we have an unlimited supply of these two qualities.

How would a 9°C warming cause human extinction? There is plenty of currently cold land that would benefit from warming temperatures for farming and humans are massively adaptable in that we live in large populations in pretty much every climate. Even if things continue the way they are, it'll happen over such a long time that time that the rate of change won't be a real issue either.

I'm all for zero carbon emissions but the ridiculous "everyone is going to die due to climate change" is pure FUD.

A 9 degree difference will wipe out almost all phytoplankton biomass responsible for generating most of the oxygen in our planet. You will see a raise in multiple meters of sea level, causing mass migrations involving over 20% of the world population, will make most of the planet uninhabitable, and will reduce the oxygen levels of the oceans to the point that they will be mostly anoxic.

That is an extinction level event greater than the Permian mass extinction.

So what specifically in your list do you think will cause humans to go extinct?

Phytoplankton are also responsible for 50-80% of atmospheric oxygen, so in the parent poster's scenario I think the loss of a breathable atmosphere is the most likely nail in our species' coffin.

Probably won't happen, probably not a great idea to push things to see how far we can let things go before it's catastrophic, though.

I don't need to speculate on this. There is never anything "specific" as any one of these things individually and all things combined are a death sentence.

With a 9 degree temperature increase a large amount of the planet simply becomes uninhabitable during the summer, period.

You just said it yourself. It's irrelevant whether the mechanism of action is direct or indirect. Collapse of the ecosystems that sustain us will accelerate processes that dramatically increase the likelihood of catastrophic events.

The semantic game of whether it's "human extinction" or "the end of organized large-scale human civilization" is stupid and grasping at straws.

> It's irrelevant whether the mechanism of action is direct or indirect.

If you take that view, then practically everything is an "existential threat". Wars have been triggered by soccer games...

As for whether "existential threat" means "human extinction" - well what else would "existential" refer to other than human existence?

Again, if you broaden this, then practically anything could be an "existential threat" - to democracy, say. And it's pretty clear that the people screaming "existential threat" intend for people to take it as meaning human existinction - the naive people at least.

> no possibility that climate change will lead to human extinction

low, but existing, possibility*

> Saying "existential risk" again and again does not make it true.

Existential risk includes more than extinction, it could also mean society collapses and takes 100 years to recover to current level, or 1000, or 10,000, or _never_ recovers. Maybe some societies collapse but others just turn into deserts. Maybe there is a recovery, but we'll never have the global trade networks of today, maybe we'll never send a man to Mars. It might mean 90% of the population is lost.

I've said nothing about the probability of any of that, but it goes up the slower we act.

Collapse of civilization (human society with huge amount of specialization) with the simultaneous ecological collapse can IMHO lead to human extinction. Civilization gives us science and technology, which allows us to be, in theory, less dependent on nature. Conversely, if the civilization fails, we will have to rely much more on nature. If the nature undergoes mass extinction event when we strongly need to rely on it, we can easily get screwed. We can probably (as species) somewhat manage to handle one of these events, but not both at the same time.

just because you don't want to accept it doesn't make it not real

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