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Comment by idoh | Hacker News Reader

The feedback loop peaks out at a global temperature increase of 5-8 degrees celsius, if the models and past events are to be believed: https://en.wikipedia.org/wiki/Paleocene–Eocene_Thermal_Maxim...

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There is a lot of ignorance regarding what 5-8 degree warming means. The worst case scenario (and that is the only one we should be concerned with!) is a global mass extinction event. We've already had 5 of them - one of which was due to runaway greenhouse warming - https://cosmosmagazine.com/palaeontology/big-five-extinction... We cannot be sure we'll stop at 5 degrees or 8 degrees. After that we will have a mass extinction event, and humans would most likely not survive it.

How would every last human die? I mean, sure, millions or even billions . . . but not one human surviving with all the resources and resourcefulness we have at our disposal?

Oxygen and nutrition; we can't even get self-sustaining bio domes working now, despite decades of attempts.

We could solve the problem, sure, but it's a race against time while society is crumbling, in this scenario.

You'd be surprised what we could get to work if the survival of humanity depended upon it. You'd better believe we'd get self sustaining bio domes working tout de suite if that were the only way to ensure our survival.

It could be difficult to see the forest for the trees. In this model the sea level rising would flood many of the largest cities on earth, resources would certainly be focused on managing the onslaught of climate refugees that result.

OTOH, the Manhattan Project occurred during a time of near-total war; so there's hope.

Fighting over the remaining resources of course.

There are more than enough nukes out there to do the job. Famines and massive numbers of refugees will almost inevitably lead to wars...

The recent Syrian refugee crisis, which has been thought to be among the first crisises partially induced by global warming (https://www.scientificamerican.com/article/ominous-story-of-...), has already ensured most of the EU has right extremism on the rise and sometimes already strongly influencing governments.

Previous instances of warming have seen all land mammals of greater than, IIRC, 10 kg, gone extinct.

Widespread ecosystemic impacts can be profound, and difficult to model.

The world is already going through a mass extinction event. By the destruction of habitat and direct hunting, species are going extinct at an alarming rate.

Isn't a 5 - 8 degree rise catastrophic though? Genuine question.

For any Americans paying attention, please keep in mind that that's 8C, not 8F.

8C ~= 14.4F for reference

Depends on what you consider catastrophic. 5-8C means you lose both the Greenland and Antarctic ice caps, so you get 60m (200 ft) sea-level rise, so you totally lose all the coastal cities, and the current round of civilization is almost certainly done for. But homo sapiens will probably survive, and so civilization will probably eventually be rebuilt. It won't be the end of life on earth under any circumstances.

Actually, the biggest danger is that political instability brought on by climate change will lead to nuclear war. That would be much worse than losing civilization to climate change because it would happen much faster, essentially instantaneously. That is not at all unlikely even under much more modest warming scenarios.

Why would civilization be over? The sea rise wouldn't happen over night and people would move or build walls.

That's a lot of people to move and things to rebuild. Op did say "the current round of civilization". I also agree that lots of things changing at once are likely to create instability, with negative economic and social impacts (unless governments massively intervene, which I suspect many in the US would not appreciate).

I'm sure walls are an option, but they will be expensive to maintain and it doesn't take much to have big consequences. https://en.wikipedia.org/wiki/Drainage_in_New_Orleans

And that was just on a city scale. Doing this country or continent wide is engineering on an entirely different level. NL has something like this but it's only 30 feet high and extrapolating from that experience to something able to withstand 60 meters of ocean (which is dynamic, an an average of 60 meters does not include storm surges and tides) is making me think this is infeasible.

>That's a lot of people to move and things to rebuild. Op did say "the current round of civilization".

If that's the bar for civilization ending, then civilization ended when people came to the US, ended again when they expanded out to the West, etc.

Just because people on the US coasts move means little to the 60 percent of citizens that don't live near the ocean.

And again, it's not going to happen overnight. A wall of water isn't coming in that will force everyone to put their things in a car and go. It will be slow build-up that slowly forces people out as they decide it's to expensive to mitigate.

"If that's the bar for civilization ending, then civilization ended when people came to the US, ended again when they expanded out to the West, etc."

Interesting that your example is literally true both times for the people who where there earlier.

We already have tremendous political instability in the US and Europe right now caused in part by a not-so-great-but-not-devastating economy and the Syrian refugee crisis. Imagine a worldwide crisis with tens or hundreds of millions of people losing their homes and livelihood, how is that going to play out?

40% of global population lives in coastal areas of lesser elevation than 50m.[1] That is more like 3 billion people. Syrian refugee crisis seems quite insignificant in comparison. Of course, only one of those is currently underway, and we don't really know how fast sea levels will rise.

[1] http://www.un.org/esa/sustdev/natlinfo/indicators/methodolog...

>We already have tremendous political instability in the US and Europe right now

This is definitely not true for the US. At least not by any global notion of political instability. The US government isn't near collapse, there is a very limited likelihood of any kind of coup, the economy is doing very well, and riots have been very rare.

There is a lot of political bickering, but it doesn't seem to be any more-so than during the last party-in-the-office changes (Clinton to Bush, Bush to Obama).

Florida is porous. You can build walls but they don't do much. The water will rise to cover the entire peninsula. Long before that tides and storm surge will destroy all of the surface roads to coastal cities. I wouldn't lend money there for longer than 30years.

http://geology.com/sea-level-rise/florida.shtml

Because a 60 meter high seawall around pretty much all of the country would be a bit problematic material wise alone (you'd have to chop down a couple of major mountains, assuming you have those), coupled with the slight problem of then having to get rid of all the water landing in your nice new bathtub by precipitation.

A seawall isn't just a wall, it's more like a dike if it is to survive and that means it has a width many times larger than it's height.

And then there is seepage to contend with. This is anything but a trivial problem and we have never done engineering on that scale before.

The easiest solution would be to move to higher ground.

Right, you get 5-8 C (9-14 F) increase in global mean temperature. That mostly translates, I think, to temperature increases during winter, and at higher latitudes. Biomes will both be shifted poleward and warped, and that will happen faster than some component species can adapt.

The good news is that runaway greenhouse warming won't evaporate oceans and bake out CO2 from surface rocks :)

  But homo sapiens will probably survive, and so civilization will probably eventually be rebuilt

This is a very arrogant assumption. Our species is one component of a little-understood web of interconnected dependencies. Just because humans are slightly more clever than past dominant species doesn't make us any less extinction-proof.

  Just because humans are slightly more clever than past dominant species doesn't make us any less extinction-proof.

Homo sapiens: the Dunning-Kruger hominid.

I've suggested: the anti-ant.

Ants, individually, are stupid. Collectively, they're intelligent, and solve complex problems.

Humans, individually, are brilliant (by animal standards). Collectively, not so much.

I'm guess you meant that cleverness doesn't make us any more extinction-proof. But actually it does. Cleverness is a huge advantage in the survival game.

The relation might not be linear though.

Thanks for the correction re: more versus less. But I'll still posit that this is an arrogant line of thinking:

  Cleverness is a huge advantage in the survival game.

Cleverness won't be much help when underlying dependencies disappear.

Edit: one way humans will extinctionize our species:

https://phys.org/news/2017-02-scientists-categorize-earth-to...

We're basically driving this car full speed towards the cliff. No amount of cleverness will stop this.

> Actually, the biggest danger is that political instability brought on by climate change will lead to nuclear war

Can you please elaborate on this point?

Elaborate how?

The dipshits in Russia, China and US will push buttons in their briefcases and we are all going to burn (or die of starvation soon after).

I don't think they had coastal cities or farming back then.

5-8C would lead to mass starvation. Our agricultural systems are built on extremely well adapted crop varieties for the regions they grow in. The lead-in time for generation of new crop varieties is very long (even with genetic modification). Rapid catastrophic climate change, with major associated changes in pest and disease prevelence, would simply overwhelm our ability to generate adapted crop varieties to maintain yield. Add to that more extreme weather events. Then on top of all this, investment on agricultural science has been declining for years, precisely at the time when plant breeders should be focusing on what is happening 20-30 years from now.

Don't we pretty much already have a massive oversupply of calories?

In a perfect world where food distribution isn't affected by things like spoilage, lack of transport infrastructure, politics, trade barriers, diversion of food crops to biofuels, monopolies, war etc. etc., we may have an oversupply. In reality, it's not even close, given that yield increases in staple crops like wheat are beginning to flat-line, and population growth marches ever onwards (and millions are lifted out of poverty to the middle class).

The Green Revolution was through picking all the low-hanging fruit - hybrid crops and synthetic fertilizers. Increasing yield to match demand is already looking like an issue without the effect of catastrophic climate change. Other issues occurring in the next 20-30 years include encroachment of cities into prime arable land, land degradation, and increased cost/reduced availability of phosphorous fertilizers.

It's a massive issue that barely registers on the public conscience, and we may hit the perfect storm soon, particularly if a new nasty rust or plant virus pops up on the scene at the same time.

Yes, it's not the temperature (though that would already cause lots of problems) it's the secondary effects such as oceans rising, likely a change in the gulfstream and so on.

2c seems pretty bad. I guess 5 means no coral reefs, smaller rivers, smaller Antarctica. Permanent northwest passage is a consolation prize, I guess.

6 degrees renders large areas of the topics uninhabitable by humans. As in: extended periods where 100% humidity + outside temperature above human body temperature.

On any given day, absent technology, this will kill you in a matter of hours.

Indonesia (100+ million people) is a climate area that would experience this).

I'm sorry, but I need to question the validity of this claim. People have been living in very warm climates for a very long time.

I myself have been camping in the Mojave for several days at a time with temperatures high above 100 degrees Fahrenheit.

Are you implying that the combination of heat and humidity is the deadly combination? If so, can you provide some evidence?

High ambient humidity means no net evaporation of your sweat so no cooling effect of sweating. If the ambient temperature is above body temperature and humidity is high, you won't be able to cool yourself and will quickly overheat (keep in mind that you already generate 100 W resting). Your experience in the hot desert was different because it was very dry.

if that feedback loop is in addition to the warming we do on our own, that would plausibly put it us kind of close to the cretaceous hot house side of this plot https://xkcd.com/1379/

5-8c is massive.

If you live in a temperate climate,

20c is quite pleasant and warm.

28c is getting into the range of a really hot day.

Remember the sun wasn't so bright then either.

If you're talking about when all the coal was buried, that was about 350 million years ago in the Carboniferous Period (so named because that's when the plant matter that became our coal was laid down). And yeah, it does appear the Sun was about 2-3% less intense, corresponding to roughly 2-3 degrees Celsius in the case of a blackbody at equilibrium in space. http://phenomena.nationalgeographic.com/files/2013/01/sun-gr...

That's a pretty neat fact, I didn't know the sun was measurably brightening over that timespan.

So the obvious solution is we just need to darken the sun a bit. </s>

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