[hn_throwaway_99]

> If we don't, we all die.

No, we don't. Even in the worse case scenarios, a runaway greenhouse effect a la Venus was never remotely part of the scientific consensus. Heck, the IPCC just retired the worst case RCP 8.5 scenario saying it is now scientifically implausible. Now a big reason it was deemed implausible is the transition to renewable energy is happening. But even if RCP 8.5 did happen, it was not a humanity ending scenario.

[waffletower]

Arguing over whether we all die or we all don't cheapens the risk of the death of millions if/when wet-bulb temperature limits (> 35C,95F at 100% humidity) become routine in populated geographies.

[Findecanor]

I would not take solace in IPCC retiring a scenario. Their predictions are based on conservative aggregates of existing science, and have always been considered by many in the climate science community to be underestimating climate change.

[hn_throwaway_99]

> have always been considered by many in the climate science community to be underestimating climate change.

This is exactly wrong as it relates to RCP 8.5. A number of research papers came out basically showing how 8.5 was completely implausible, and it was only after these papers were widely cited and reached consensus did the IPCC retire 8.5.

This article by some of the original authors of one of those papers explains the situation well: https://www.theclimatebrink.com/p/on-the-death-of-rcp85 . If you actually read their linked research paper, I don't think any unbiased observer could think 8.5 is plausible anymore (and, in fairness, 8.5 was always proposed as a worst case scenario, not a "business as usual scenario", as that climatebrink article explains very well).

[specialist]

Sure, some fraction of humanity will survive. Terrific.

[jcattle]

> But even if RCP 8.5 did happen, it was not a humanity ending scenario.

Can you do it like the IPCC report and assign a confidence to that claim?

Mine would be: RCP 8.5 ending humanity (very low likelihood, low confidence), based on absolutely nothing.

[CalRobert]

In what scenario does humanity not achieve net neutral emissions and survive?

[hn_throwaway_99]

This idea that climate change would lead to "ending humanity" just shows to me how a lot of the popular messaging outran the actual science on the issue.

Again, a "runaway Venus" was never really in the cards. As far as I am aware, basically all the carbon that is now locked in the ground in fossil fuels was once in the environment, and Earth still supported copious life at that time. E.g. at one point when dinosaurs roamed the Earth, there were no polar ice caps (Antarctica, even when it was near its current position over the South Pole, had lush green forests and lots of dinosaurs, even with many months of darkness), sea level was many meters higher, but life still flourished.

I'm not downplaying climate change. A significant, geologically fast rise in global temperatures would kill millions/billions of people, inundate coastal areas, result in major migrations and resource wars, etc. But "ending humanity" by making the entire planet unlivable was never supported by the science.

[CalRobert]

As far as I'm aware, until we get carbon emissions to zero (or net zero), temperatures will continue to rise.

[ndrh]

For another 50 years after we do stabilize them, yes.

The contrarian throwaway said: "A significant, geologically fast rise in global temperatures would kill millions/billions of people, inundate coastal areas, result in major migrations and resource wars, etc."

-- this sounds close enough to what I said, simply "We all die." I didn't say the oceans would evaporate. But with that amount of damage, global civilization and culture would probably not survive. Going carbon-neutral is not a "meh, let's do it later, or not" type of thing.

[hn_throwaway_99]

> this sounds close enough to what I said, simply "We all die."

This is not just arguing over semantics. There is a huge difference between what I wrote and "we all die". The global population is 8.3 billion. Climate change would be most catastrophic to poor populations in heat prone areas like Southeast Asia, parts of Africa, parts of Mexico, etc. where the wet bulb temp would exceed human survivability. Also, coastal cities would have to build defenses or move.

But we could lose one or two billion people and there is nothing that makes me believe that "global civilization and culture would probably not survive". I just done see how you make that leap. There would be huge change but plenty of places would be perfect for human habitation, some moreso than today.

[fallingfrog]

Yes, all this is my understanding also. I would add to that that think it's good to keep as a goal that we want to have the political ability to make prudent changes to avoid disasters even if those disasters are not totally world ending but merely catastrophic levels of suffering for a hundred years or so.

[hn_throwaway_99]

But there is not unlimited carbon to burn. All that carbon in the ground was in the air/water at one point in Earth's past, when Earth was teeming with life.