Studies and Numbers on Population Decline Linked to Temperature Rise

[Burnrate]

Has there been any papers published on this?  Anything looking at the expected loss of life for specific temperature rises (such as 2.5°C means 5 Billion people left, 5°C means 1 Billion people left)?

Everything I have read is either a general 'Humans might not make it at all' or they dance around saying anyone will die and just talk about cities flooding and crops burning.

I know with our current 1°C we are already having food shortages, more fires, floods, hurricanes, etc.  Lots of people dying from disasters and the long term carrying capacity of the Earth has probably been reduced, and we are possibly already above what it is.  I have even read that global warming caused the cessation of the monsoon/rainy season in large parts of Africa which has been a huge contribution to strife and starvation there.

[Paddy]

Population prediction is a messy game. I don't think any such studues exist, and if they did, I wouldn't take them too seriously.

[bbr2314]

The UN only ever predicts continued growth. They show 10 billion and counting by 2050. About as useful as the RCP predictions on temperatures (aka, useless).

[anthropocene]

The UN only ever predicts continued growth. They show 10 billion and counting by 2050. About as useful as the RCP predictions on temperatures (aka, useless).

I don't usually react to statements like this. The freezing/melting thread is mainly a bit of fun and a good introduction to the forum so wild statements are let go there but down here in the darker recesses of the forum if you make statements like the above you better be able to back them up. I see bbr that in typical fashion instead of making one accusation and backing it up with facts ore reasoned argument you double-down by equating it with another wild accusation about RCP, likely meaning that the thread diverts into a completely different direction. (Can you see how this could be annoying?) To stop this I'll make a new thread: 
See:
https://forum.arctic-sea-ice.net/index.php/topic,2374.0.html

Anyway to keep to this thread. Burnrate: You may want to look at the "Near Term Human extinction" thread: A different question I know but there are some useful posts on there to do with projected human population with different heating scenarios. It's quite old now but Mark Lynas "Six degrees" book most probably has some useful references in it and goes into some detail on impacts on human civilisation.
My thoughts:
1) Unlikely to get scientific papers on this subject because it is so dependent on social and political choices and technological development which cannot be predicted
2) Can we sustain the future population levels predicted by the UN? Yes (in the medium term - say 80 years) but most probably only by remaining above the carrying capacity of the earth and by NOT doing what is required to reduce concentration of GHGs in the atmosphere (e.g. reversing deforestation. increasing soil carbon content etc). Up to this point with a choice between business as usual development and population increase and on the otherhand being more sustainable we've always chosen the first option;  This is self defeating because it makes the situation worse when the debts have to be paid but I don't see any reason why this will change in the future. 

[bbr2314]

The UN only ever predicts continued growth. They show 10 billion and counting by 2050. About as useful as the RCP predictions on temperatures (aka, useless).

I don't usually react to statements like this. The freezing/melting thread is mainly a bit of fun and a good introduction to the forum so wild statements are let go there but down here in the darker recesses of the forum if you make statements like the above you better be able to back them up. I see bbr that in typical fashion instead of making one accusation and backing it up with facts ore reasoned argument you double-down by equating it with another wild accusation about RCP, likely meaning that the thread diverts into a completely different direction. (Can you see how this could be annoying?) To stop this I'll make a new thread: 
See:
https://forum.arctic-sea-ice.net/index.php/topic,2374.0.html

Anyway to keep to this thread. Burnrate: You may want to look at the "Near Term Human extinction" thread: A different question I know but there are some useful posts on there to do with projected human population with different heating scenarios. It's quite old now but Mark Lynas "Six degrees" book most probably has some useful references in it and goes into some detail on impacts on human civilisation.
My thoughts:
1) Unlikely to get scientific papers on this subject because it is so dependent on social and political choices and technological development which cannot be predicted
2) Can we sustain the future population levels predicted by the UN? Yes (in the medium term - say 80 years) but most probably only by remaining above the carrying capacity of the earth and by NOT doing what is required to reduce concentration of GHGs in the atmosphere (e.g. reversing deforestation. increasing soil carbon content etc). Up to this point with a choice between business as usual development and population increase and on the otherhand being more sustainable we've always chosen the first option;  This is self defeating because it makes the situation worse when the debts have to be paid but I don't see any reason why this will change in the future.

What are you talking about? All the UN ever does is show rosy numbers and growth re: population, just like they did in Oil for Food when they were secretly channeling billions to Saddam. The UN is a corporatist sham that only exists to maintain and perpetuate the status quo, hence why their #s are always ridiculously optimistic.

Business as usual will continue and at a certain point billions will start dying when the US, Russia, and Europe are no longer able to export food to the developing world. This will happen when AMOC shutdown and freshwater hosing reach the point of no return (or, are severe enough to impact agriculture for a year or two). RCP completely ignores AMOC shutdown and any feedbacks, it is literally a collection of unintuitive lines produced by computer models, and completely misses what is actually happening on the ground.

Much of America's heartland saw its coldest April in recorded history this year, with snows falling through much of the month. RCP scenarios say snows should be disappearing and warming should be everywhere yet here we are in 2018 with records for cold being broken stretching back to 1895, in spite of +50% GHG forcing since then. The worst of BOTH worlds (both record heat AND cold) is severely more damaging than record heat alone, which is why this will go completely unacknowledged by the bureaucrats in the UN whose only mission is maintain the status quo of producing ++++surplus wage slaves in developing regions to cater to the consumption needs of the global middle class.

[Burnrate]

Population prediction is a messy game. I don't think any such studues exist, and if they did, I wouldn't take them too seriously.

Yeah I wouldn't think there would be something reliably accurate but it would be interesting to see all the factors being considered.  You could probably draw a lot of conclusions from smaller scale events up to a certain point and then it's all really speculation but the speculation could be very educational.

[anthropocene]

What are you talking about? All the UN ever does is show rosy numbers and growth re: population, just like they did in Oil for Food when they were secretly channeling billions to Saddam. The UN is a corporatist sham that only exists to maintain and perpetuate the status quo, hence why their #s are always ridiculously optimistic.

Again, instead of keeping to the main point -  throwing out another statement - presumably to distract and act as another argument which it takes the other side time and effort to shoot down. This is a Trump tactic. Enough of it - I won't go down that road.

Latest UN population predictions are here:
https://esa.un.org/unpd/wpp/Publications/

I can't see any mention of climate change so either it is not seen as anything like as big a factor as fertility rates or there is so much uncertainty it cannot be modeled onto population predictions. Just some points:
1) Can't see any recent reviews of population predictions but historically they seem pretty good; if anything tending too high (up to 5%) due to lower than expected fertility rates
2) In the past (assume it is still the case) most of the data and projections for population are simply an amalgamation of data from individual countries
3) I'm not sure what you think the UN does but I think you're massively over-estimating its power and what it has control over.  The UN shouldn't be blamed for all the actions its member countries do - that's a completely different story.

So you agree that 2018 has been a pretty exceptional year? What effect has this had on food production in the US and Canada? From here - not much: https://www.usda.gov/oce/commodity/wasde/Secretary_Briefing.pdf 

Interestingly I see in 2018 that Brazil has overtaken USA as largest soya producer. This has been achieved by increasing acreage into pasture and I would guess rainforest as well. Unless it is stopped, increasing food production can continue like this for the foreseeable future=> supporting predicted population growth.

So it seems population predictions will only dramatically change if global climate (and regional climate) predictions show conditions severely impacting food production and (regional) survivability.
Again the IPCC ( and therefore the RCPs) are simply a summary of current available scientific literature. I completely agree that one criticism of the RCPs is they don't contain many feedback loops that COULD happen. The problem is, in the RCP graphs where do you put them and what effect do they have? Go on - do it: Produce an updated RCP graph with impact of AMOC shutdown on it. Is that graph backed up with scientific literature or is it backed up with hand-waving? If it's hand-waving - good luck with anybody else taking it seriously. Also, AFAIK the latest scientific discussion is still trying to work out exactly what the impacts of a shutdown of the AMOC would be.
Let me be clear of my position here:
1) Do I think the RCPs are 100% right? No, almost certain to be out a bit. The optimistic pathways are most probably so optimistic to be unattainable (There is currently no practical BECCs technology for example).
2) Are there reasonable risks that feedbacks may kick in and send global temperature higher (and have maybe more severe regional impacts)? Yes
3) When will they happen? Almost 0% chance in the next 15 years, steadily increasing after that.
4) Do I think we'll be majorly f*cked later in the century? You betcha, unless we make some major changes PDQ

But don't say the population predictions and RCPs are useless. At the moment they're the best there is and many decisions and plans will be being made based on them. 

[bbr2314]

But don't say the population predictions and RCPs are useless. At the moment they're the best there is and many decisions and plans will be being made based on them. 


They ARE useless and the fact that decisions and plans will be made using them is precisely why we are supremely screwed. You just admitted in your post that the climate is screwed yet you still give credence to notions that the UN projections have some value EVEN THOUGH THEY IGNORE CLIMATE CHANGE IMPACTS.

[dnem]

If I had to guess, I'd say the human population will peak and begin its inexorable decline toward a sustainable number - 1 to 2 billion? - during the 2030s.  Extreme economic disruption, food scarcity, unmanageable costs of climate impacts , etc. will all be well underway and fertility rates will plummet as death rates soar.  Obviously a total guess, but that's where I'd put my money.

[oren]

My personal guess is a decline beginning mid-century (2040s?) and ending in much less than the carrying capacity of 1-2 billion, a classic overshoot-undershoot. Eventually the main killer will not be climate change in and of itself, but the resulting civilizational collapse.
The 1 billion humans of the year 1800 were much more resilient to collapse, most having the knowledge and experience of how to grow their own food, and how to make do under conditions of scarcity, while the surviving 1 billion of a collapsed globalized economy, mostly living in urban centers, will have a much harder time, especially with collapsed distribution networks and wars causing closed borders and embargoes.
Regarding UN population studies and RCPs, I think they are quite useful in describing the expected BAU trajectory - until it fails. To use an analogy, you can't estimate the outcome of an impact until you know how fast the car is going into the wall.

[Burnrate]

...
2) Are there reasonable risks that feedbacks may kick in and send global temperature higher (and have maybe more severe regional impacts)? Yes
3) When will they happen? Almost 0% chance in the next 15 years, steadily increasing after that.
...

Anything to point to for this prediction (more than hand waving ;P)

It seems that some feedbacks are already 'kicking in.'  Methane release from the permafrost is already quite measurable and impactful.  The Atlantic Ocean current is already slowing down.  Arctic sea ice loss is already so far along the decrease in albedo is causing more melting

As far as regional impacts it is my understanding that climate change in the 1900's caused a large change in the amount of rainfall received in parts of Africa which is a major cause for a lot of their famine and war (I'm not an expert on this).  Not to mention more severe fires, flooding, and storms all over the world.

[Burnrate]

If I had to guess, I'd say the human population will peak and begin its inexorable decline toward a sustainable number - 1 to 2 billion? - during the 2030s.  ...

My personal guess is a decline beginning mid-century (2040s?) and ending in much less than the carrying capacity of 1-2 billion, ...

I see that 1 billion number being used a lot.  I wonder if it is because it's a pre-industrial population number or it came from somewhere else.

From everything I've read and the possibilities of feedbacks I have the feeling that things will start going downhill rapidly in the 2030's but it would probably take a few decades to reach a new equilibrium population.

From what everyone has said it is very hard to predict because so much depends on decisions made.  People could live in giant domes with greenhouses and solar power.  We have the technology but maybe people will just fight and move north.

I guess it would be nice to read some detailed scenarios based on sets of assumptions and describing events throughout.

[bbr2314]

The global elite will maintain power, accumulated capital will not vanish. We will return to some type of Neo-feudalism (it's already happening in the developed world, where real estate is gouging increasingly massive portions of disposable income as consumption otherwise has begun to drop precipitously amongst the younger generations).

Even though 6-7 billion will die, some semblance of order will likely remain where redoubts of capital remain strong. The one plus side of globalism is that the "global elite" are fully aware their struggle is with the 7 billion wage slaves and not with one another. If the Chinese Politburo and Putin's government have to sacrifice 90% of their populations through mutual continuous warfare for their own continued survival, that is just business as usual, and they will not blink an eye.

Western "democracies" may face more problems initially but the US and others are also rapidly hurtling towards totalitarianism as well, and this will not reverse, if anything it will accelerate as climate change worsens. There is no alternative. But the relative lack of density in the US / Americas means that the sooner totalitarianism is embraced (alongside top-down planning), the easier it will be for society OVERALL to deal with the damage of climate change. And with only 700-800 million people in the Americas, the culling on these continents need be far less severe to get to baseline vs. Eurasia, where China and India each need to lose a billion apiece ALONE.

The numbers are even worse for places like Yemen, where the UN says there will be something like 100 million people in 2100 (LOL). They have already massively overshot carrying capacity, with wars and cholera raging all around, yet babies continue to be made at a prolific rate. You cannot blame the humans responsible, as they do not know any better, but unfortunately, at a point sooner than later, 95%+ will either migrate (and most will then die in the process as it won't just be Yemenis migrating) or die in place.

I would say Europe is infinitely more screwed than the US/Canada as the land bridge with Asia and proximity to Africa means it is going to be destination #1 for millions of destitute migrants as things escalate. Either they militarize the border and deal with an enraged Turkey or the dilly-dallying of "nice" democracies allows their societies to be overwhelmed and obliterated by waves of people who are far too numerous to integrate successfully in so short a time.

[oren]

Well said bbr, I agree with all your points. To add, the biggest die-off in relative terms will surely be in sub-Saharan Africa, where population growth rates are the highest and development and accumulation of "hard capital" are the lowest.

[bbr2314]

Maybe a massive Coronal Mass Ejection event so strong it rips away the magnetosphere for a few days. Massive= No electricity for a couple of months should decrease global population. More death in developed countries because they are very dependent on refrigeration for fresh food and medical facilities.

In July of 2012, a massive CME ripped through Earth’s orbit and narrowly missed us. That event, which was picked up by NASA’s STEREO-A satellite, would have registered a Dst of -1200 nT — comparable to the Carrington event.
“If it had hit, we would still be picking up the pieces,” space weather scientist Daniel Baker of the University of Colorado

Developed countries export all their excess food to the "developing" countries... diabetics might have problems but the people starving wouldn't be the ones proximate to the food.

[anthropocene]

But don't say the population predictions and RCPs are useless. At the moment they're the best there is and many decisions and plans will be being made based on them. 


They ARE useless and the fact that decisions and plans will be made using them is precisely why we are supremely screwed. You just admitted in your post that the climate is screwed yet you still give credence to notions that the UN projections have some value EVEN THOUGH THEY IGNORE CLIMATE CHANGE IMPACTS.

A gross mis-representation of what I said: UN population estimates we were talking about were to 2050. The statement about climate was about later this century. If you believe that climate will have an impact on population by 2050 then to get a measure of how much that may be you need to know the baseline of estimated population without climate impacts. QED: UN population estimates are not useless.   Mis-representation of what other people say, constantly raising new extreme statements before the old extreme statements can be discussed in any detail and no data or scientific evidence to back up statements made. I'll let everybody else draw their own conclusions.

[anthropocene]

...
2) Are there reasonable risks that feedbacks may kick in and send global temperature higher (and have maybe more severe regional impacts)? Yes
3) When will they happen? Almost 0% chance in the next 15 years, steadily increasing after that.
...

Anything to point to for this prediction (more than hand waving ;P)

Must admit I was mainly thinking of AMOC when I wrote that but it most probably holds for all potential positive feedbacks. For the list of potential feedbacks may as well use this list:
https://www.skepticalscience.com/humans-pushing-earth-closer-to-climate-cliff.html

   Main thinking is:

1) In order to increase so quickly to have significant impact in 15 years or less the feedback will require a fast positive feedback on itself.
2) At global temperatures at or just below current temperature fast positive feedbacks are unlikely to exist because if they did then Holocene temperature wouldn't have been as stable a temperature range as it seems to have been.

(Push beyond 1.5degC above pre-industrial (2035 and later) and the above argument starts to fail).

As far as I am aware the only feedbacks out of the 15 which could have a quick acting feedback on themselves AND can possibly change in the next 15 years are:
a) Arctic sea ice
b) Thermohaline circulation reduction
c) Permafrost (Methane release)


a) could be damped by negative feedbacks kicking in (Cloudier summer weather, cold fresh water lens and ice which needs to melt is at higher latitude)
b) Not aware of a mechanism to positively feedback on itself
c) Seems most likely candidate - but there are some good arguments why permafrost will not go in the next couple of decades; See David Archer's arguments e.g https://www.washingtonpost.com/news/energy-environment/wp/2015/03/02/why-you-shouldnt-freak-out-about-those-mysterious-siberian-craters/?noredirect=on&utm_term=.83af48faa127

For AMOC in particular, we still don't have enough data to really know what the trend is, even what is driving the changes and what impacts those changes will have. See for example:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076350

It's not clear why the step-wise decrease in 2008 happened, if it'll happen again, how frequently and what size of decrease. With current data, making predictions of AMOC collapse in next 10 to 15 years are pure guess work (and partly most probably wishful thinking).