Will climate change decimate humans before 2050?
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2050
17%
chance

If climate-based disasters, including their chain reactions (drought -> famine; sea level rises -> migration -> disease; etc.), cause a 10% reduction ("decimation") of humans by the close date this resolves YES. Otherwise NO after close.

10% reduction might mean any one or mix of factors:

  • outright deaths

  • decrease in fertility causing population decline w/in timeframe

  • reduction in population replacement curves, over the global average

  • etc.

Our baseline for decrease in population not due to extraordinary deaths will be framed around the 2022 UN Projections (currently located here). This is not the defining point of truth if solid analysis and data comes to light, especially considering that the UN already takes some climate trends into account, but it's a great indicator of unexpected change, such as if life expectancy, fertility, or replacement rates drop precipitously in later versions of their projections. See also the OWID data linked in this comment.

Some 2050 numbers from the 2022 projections:

  • 9.7 billion humans

  • 16.4% aged 65+

  • Fertility (births per woman): 2.1

  • Life expectancy: 77.2; 74.8 (M), 79.8 (F)

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2050 (this): /Stralor/will-climate-change-decimate-humans

2070: /Stralor/will-climate-change-decimate-humans-9f63de4b27a2

2090: /Stralor/will-climate-change-decimate-humans-a6501c666cd9

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Maybe we need to clarify that climate migrants from the global south do count as humans

@JaimeSantaCruz I sure hope it's not implied anywhere that they don't

How would this resolve if e.g. superintelligent AI boils the oceans?

@adele I'd have to hear a very convincing argument that a specific intentional action like that is "climate change" when it happened. instinct says that's an easy NO

@Stralor To be clear, I'm not imagining boiling the ocean as the explicit goal of the ASI, but as a side-effect of massive amounts of power generation.

@adele ah, yeah that's fair! I don't see why that wouldn't count

Samuel NIHOULboughtṀ987YES
reposted

That’s a very high conviction bet, especially for a reasonable small account.

“The number of heatstroke victims hit record numbers in 2022 as global warming continues. In heat-induced injuries, circulatory shock is the most severe and deadly complication. This review aims to examine the mechanisms and potential approaches to heat-induced shock and the life-threatening complications of heatstroke.”

https://link.springer.com/article/10.1007/s00011-022-01687-8

@StephanHeijl "Both heat and cold can kill. But cold is far more deadly. For every death linked to heat, nine are tied to cold."

@StephanHeijl Extreme temperatures (both cold and hot) are exacerbated by climate change.

If climate change causes a lot of economic damage, then it might actually lead to increases in the human population, because countries getting richer generally leads to them having a lower birth rate and population growth rate (excluding immigration). I’m unsure if countries that become poorer, as might happen with devastating climate change, will increase their birth rate; it would probably take time, as it involves cultural changes. Climate change has, I think, slowed down the growth of some countries, which would lead to increased births relative to the counterfactual.

It might be that in rich countries that get poorer, people have fewer children, since they don’t have the money to raise them in sufficient comfort and have access to contraceptives. I don’t think that’s enough to decimate humanity when it’s countered by poor countries having less reduction in their birth rate.

The upshot here is that I think it’s unlikely climate change will decimate humans through decreased births from severe economic damage. It could by increasing deaths through economic damage, extreme weather, or maybe wars.

@Trifalcon I think hunger, extreme weather, loss of habitat and wars / border conflict caused by migration might well happen within the next 25 years. And I think it’s more than 10% likely it can decimate humanity, although I agree it’s an awful lot of people. Something like 800 million people?

bought Ṁ250 YES

@JaimeSantaCruz https://www.science.org/doi/10.1126/sciadv.1400253

Accelerated modern human–induced species losses: Entering the sixth mass extinction”

2015

@JaimeSantaCruz Yes, humans are having less children but that's not because of climate change.

@NiklasBergstrom Yes, I absolutely agree with you, I was answering a previous comment that suggested we were still growing.

If the world population drops by 12 percent from the trend in 2049 and there's not a clear consensus on what caused it (e.g. it is highly multivariate and messy), how do you plan to resolve?

@RobertCousineau an answer I gave to another question:

how do we ever do these things? If there's not associative data, this cannot resolve YES, but I expect plenty of scientists will go "these events resulted in this loss of human potential", just as we saw with COVID impact analyses

I would say "multivariate and messy" would prob include climate but doesn't wholly equal climate. Likely resolve NO.

bought Ṁ250 YES

I will be dead before I get payed for this, but has Manifold not been paying attention? 2.1 fertility rate is .2 below replacement rate.

Also:

https://www.theguardian.com/environment/2023/jul/25/gulf-stream-could-collapse-as-early-as-2025-study-suggests

https://news.stanford.edu/2023/09/18/human-driven-mass-extinction-eliminating-entire-genera/

https://www.nature.com/articles/nature09678 - “Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.”

Nature volume 471, pages 51–57 (2011)

@JaimeSantaCruz If your fertility figure was true, we weren't 8 gigapeople already.

@a2bb I’m not inventing it, but I’ll look for the source

@JaimeSantaCruz Might be a projection from this:

“As health has improved and the mortality in the population has declined, we’ve typically seen accelerated population growth. But the global average fertility rate has halved from around 5 in the 1960s to around 2.4 in 2021. Rapid population growth then comes to an end as the fertility rate declines.”

https://ourworldindata.org/fertility-rate

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