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Comment by kerkeslager | Hacker News Reader

Earth is just a ball of rock hurtling through space. Earth is going to be okay at any temperature because it doesn't even make sense for a ball of rock hurtling through space to not be okay. It's not Earth we have to worry about, it's humans.

1. We know is that there's a range of temperatures where humans have thrived for hundreds of thousands of years, and life has thrived for millions of years.

2. We also know that there's a range of temperatures where it will be too hot for humans to survive.

3. We also know that global temperature is changing from the former to the latter.

Given these three facts I don't think we need to know what the ideal temperature of the earth is to be concerned.

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“All humans are going to die because the temperature gets too hot for our biology” is fallacious. Do you think we’ll gain 30C and Siberia will become unlivable? Does everyone die when the summer temperature is 30C higher than winter? We are literally planning Martian colonies, do you think we can’t figure out how to survive on Earth?

The issue is the effects of moderate temperature increases, rising sea levels, changing farming, etc. so it’s a mass disruption to our civilization (migration, resource wars, etc.) Not that we’ll literally be too hot and can’t somehow survive that as a species.

Humans live in Australian Outback and Alaska. We are adaptable, but the growing pains are not pleasant, hence the problem to civilization.

There are a lot of periods in Earth's own geological history that humans would not have survived. There are also a lot of other rocks in our solar system that humans would not survive on. Whether or not we can survive climate change depends on the bounds of how much change happens and how quickly, especially in terms of feedback mechanisms (clathrate gun, H2S from an anaerobic sea, etc).

There was a temperature in recent times (hundreds of millions of years) where humans would not have survived, anywhere on Earth? Yet giant dinosaurs with the wrong ratio of mass to surface area did?

Really, when? How much hotter was it in the past?

I’m not saying we shouldn’t fix the issue. I’m saying the argument that the average temperature will be unlivable is bad. It’s like saying bullets kill people because of the lead content, not the process of getting injected. The process of climate change will impact us most, not the impact of the temperature on our biology.

https://en.m.wikipedia.org/wiki/Permian%E2%80%93Triassic_ext...

We do have to be careful playing with the chemistry of the atmosphere of the only habitable planet we have.

You do realize the chemistry of the atmosphere has changed far more than a few ppm of carbon, right? Like oxygen varying from 15% to 35%?

https://upload.wikimedia.org/wikipedia/commons/thumb/f/f3/Sa...

The argument that extra CO2 or a few degrees C will be unlivable for humans is laughable. The changes to our civilization from this is not (farming, weather patterns, mass migrations).

Yes, and that history of chemical changes is punctuated by global mass extinction events!

Just saying, it's not like there's a law of nature that keeps Earth habitable for humans. We should be aware of that. I think you're shifting the goalposts -- earlier you seemed quite confident that there wasn't a period within hundreds of millions of years that wouldn't have been habitable by humans. Have I changed your mind about that?

I don't think anyone who worries about climate change as an existential threat is thinking of sea level rise, a few degrees C and a few hundred ppm of carbon doing us in. Those could make life quote difficult at most. But it's the feedbacks that might run away from there, which are very hard to bound. How quickly might a few hundred ppm become a few thousand, if methane hydrates start to off-gas? Etc.

How confident can you be that it won't happen, when the Earth has carried itself away before?

Sorry, not convinced that the earth has been uninhabitable for humans in the past few hundred million years. What conditions made it uninhabitable everywhere on the planet?

Earlier posters made it seem like the problem with climate change was that earth was moving out of a narrow temperature band that supported human life. We live in the arctic, jungles, deserts, ice ages, mountaintops. We will be fine. The problem is the transition’s impact on our existing civilization (sea level change, new weather patterns), not the final temperature.

Let me put it this way: if we discovered earth 100 years in the future, even with our current climate change rate, we would rejoice about how easily it could be colonized (vs Mars, the moon, etc).

The climate will get hotter, and it’ll still be quite livable in places. This is the equivalent of people who think earth is in the “just right” orbit, if it were 10 feet off in either direction the planet would freeze or burn. And yet the elliptical orbit of the earth around the sun varies by millions of miles, and we don’t light on fire when climbing a ladder. We don’t die because someone left the AC 5 degrees too hot or cold.

Thanks, I appreciate your thoughtful responses so far.

http://burro.case.edu/Academics/USNA229/impactfromthedeep.pd...

If you can, please let me know what you think of the image on page 6. Mind you this is an unproven theory about the end permian mass extinction. But it's an interesting perspective on what could cause the whole planet to become uninhabitable, rather than just shifting the comfortable zone farther to the poles. I'm curious about your thoughts on, if it did happen that way, how long humans would last in such conditions.

Humans are hardy and adaptable, but so are insects, birds, rats, and many other species. Somehow the end permian extinction killed up to 96% of all species, including even insects and the formerly ubiquitous trilobite, and apparently nowhere on Earth was spared. Land vertebrates were almost wiped out.

I also appreciate the optimism about mars colonies, but we actually haven't demonstrated the technology or robustness to even sustain a colony on Antarctica without outside support. If we did set up a mars colony, I'm skeptical that it could last even a hundred years on its own. Technology is a powerful tool but supporting cement factories, steel mills, silicon fabs, power plants, farms, and everything else, in a self-sustaining way, really requires a habitable planet. I don't think it would be possible to sustain in an underground bunker for very long.

Thanks for the reference, that is interesting. I think that's what I was looking for in a theory of why things will be bad: it's not the temperature change itself (a few degrees is fine), or the atmospheric CO2 levels (still far less than 1%), or even the water levels (we can move, if painful economically), but the release of H2S, which kicks off a chain reaction of extinction, which may impact food supply etc.

I hardly know enough to comment on whether that is likely. But I think it's a much better argument about why the Earth will be uninhabitable for us specifically.

(That said, it doesn't really matter if the earth eventually becomes uninhabitable or not, we want to avoid the cost of having to move everyone for even minor sea level rises.)

Thanks for replying. Yeah I fully agree with you. The more probable impacts of climate change are bad enough that they should be the motivation. I think as an existential threat, it's an unlikely outcome but not one that we can totally rule out... Like other existential threats.

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