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“CO2 levels are now comparable to the Pliocene Climatic Optimum, between 4.1 and 4.5 million years ago, when they were close to, or above 400 ppm. During that

“CO2 levels are now comparable to the Pliocene Climatic Optimum, between 4.1 and 4.5 million years ago, when they were close to, or above 400 ppm. During that time, sea levels were between 5 and 25 meters higher than today offsite, high enough to drown many of the world’s largest modern cities. “ Oh boy, that’s not good. I mean it’s going to take a while for it to raise up, but so long Florida.

oneoff786 4y ago
Where has this water gone exactly? Freezing wouldn’t explain it. Is it lagged thermal expansion of the ocean water as it catches up to the air in heat?
- kuu 4y ago
  Frozen in glaciers and poles, I would assume...
- arethuza 4y ago
  It's a combination of melting of glaciers and ice-caps and thermal expansion of water as it warms: https://oceanservice.noaa.gov/facts/sealevel.html https://oceanservice.noaa.gov/facts/sealevel.html
- zamfi 4y ago
  > Freezing wouldn’t explain it. Pretty sure freezing is exactly it — Greenland and Antarctica contain lots of water stored well above sea level. These fluctuated a lot worth sea levels.
  - oneoff786 4y ago
    Several people are saying this so I’ll reply to just this one. It wouldn’t make sense for water to freeze up over Antarctica over time as a way to reduce sea level. Water freezing on top of water doesn’t affect water height. And water freezing on top of submerged land would just raise the water levels because it’s more voluminous. There needs to be a mechanism for the ice to accumulate on top of itself far above sea level for sea level to go down beyond just water freezing. As another poster explained, it’s snowfall accumulating semi-permanently in the same spots that moves water to these areas. Excuse my pedantry.
    - marginalia_nu 4y ago
      > There needs to be a mechanism for the ice to accumulate on top of itself far above sea level for sea level to go down beyond just water freezing. It's pretty common in the arctic regions that water forms ice crystals and falls out of the sky, landing on the ground. Snow, I believe they call it.
      - oneoff786 4y ago
        I literally acknowledged it was snow it the following sentence
    - zamfi 4y ago
      Not pedantic, I think people just didn't realize you were narrowly thinking of seawater freezing directly when you said "freezing wouldn't explain it".
- tlb 4y ago
  A lot of it is in the glaciers of Antartica, which cover the whole continent with around 1900m of ice. They weren't created from seawater freezing, but from snow getting packed down. But the water will go into the ocean if they melt.
  - oneoff786 4y ago
    Ah ok that makes sense
    - dhzhzjsbevs 4y ago
      There isn't that much water on earth, this image does an amazing job of explaing the scale in the quickest way. It also sort of explains how easy it would be for earth's water to have come from asteroid impacts. https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/thumbnails/image/all-the-worlds-water.jpg https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/...
      - oneoff786 4y ago
        I’m not saying it’s wrong, but this graphic is very difficult for me to understand. Is there any geographical significance to the location of the water blobs? No, right? But they also don’t include saltwater which is most of it. Right?
        dhzhzjsbevs 4y ago
        The big bubble is all water, frozen, sea, etc. The small bubble is all fresh (rain clouds etc), rivers, lakes. The smaller is lakes and rivers only. Here's an article showing comparisons to various moon ice. https://www.businessinsider.com/earth-water-ice-volume-versus-planets-moons-2018-5 https://www.businessinsider.com/earth-water-ice-volume-versu...
        oneoff786 4y ago
        It says liquid fresh water. I don’t think the big bubble includes the ocean.
- masklinn 4y ago
  Antartica is nearly 10% of total land (it's larger than europe, and half the surface of africa), and the ice depth averages more than 2km over land. It stores enough ice to raise sea levels by nearly 60m if / when that melts entirely. It currently loses more than 250Gt/year of ice, up from 40Gt during the 80s. But it holds an estimated 26500000Gt (26.5Pt) of ice.
- DalasNoin 4y ago
  Additionally to what others have mentioned, there is also the effect of the gravitational pull of ice shields. https://www.antarcticglaciers.org/question/antarctic-ice-sheet-gravitational-effect-sea-level/ https://www.antarcticglaciers.org/question/antarctic-ice-she... There was a discussion about this effect on hn years ago, the original link send to be dead now. But this is the thread on hn: https://news.ycombinator.com/item?id=23389690 https://news.ycombinator.com/item?id=23389690
- m0llusk 4y ago
  Rigorous explanation of bodies of water on the planet requires accounting for how water and ice deform the crust with their mass.
- AbrahamParangi 4y ago
  Glaciers also compress the earth underneath them, which rises back up when they melt in a process called isostatic rebound.
- guerrilla 4y ago
  > Is it lagged thermal expansion of the ocean water as it catches up to the air in heat? I've read that this will be the primary contributor. Might want to double check the answers you're getting here.
paganel 4y ago
The sea-levels have always fluctuated, no need to worry for Florida, if it happens, it happens. Also, no need to look 4 million years back for similar events, Doggerland [1] was still a thing with actual humans living on it only ~8,000 years ago. [1] https://en.wikipedia.org/wiki/Doggerland https://en.wikipedia.org/wiki/Doggerland
gadders 4y ago
>> During that time, sea levels were between 5 and 25 meters higher than today offsite, high enough to drown many of the world’s largest modern cities. That makes for a great headline, but a large part of the Netherlands' coastal areas are currently below sea level, and yet are not "drowned".
meatsauce 4y ago
It is clearly a real threat, that's why we have advocates for strict "climate regulations" buying multiple beach-front homes, their own islands, and private jets...
Yizahi 4y ago
Also it is probable that we will see a big extinction event even before +1m sea level mark. Imagine climate changes enough and staple crops start to fail en masse - wheat, rice etc. The hunger and rising costs will likely case a world war, or several.
macinjosh 4y ago
Hopefully, this will fix the US's coastal elites problem.
tim333 4y ago
Gonna take a while to rise 5 to 25 meters though. I think it's currently rising at like 0.8m per century.

oneoff786 4y ago

Where has this water gone exactly? Freezing wouldn’t explain it. Is it lagged thermal expansion of the ocean water as it catches up to the air in heat?

kuu 4y ago
Frozen in glaciers and poles, I would assume...
arethuza 4y ago
It's a combination of melting of glaciers and ice-caps and thermal expansion of water as it warms: https://oceanservice.noaa.gov/facts/sealevel.html https://oceanservice.noaa.gov/facts/sealevel.html
zamfi 4y ago
> Freezing wouldn’t explain it. Pretty sure freezing is exactly it — Greenland and Antarctica contain lots of water stored well above sea level. These fluctuated a lot worth sea levels.
- oneoff786 4y ago
  Several people are saying this so I’ll reply to just this one. It wouldn’t make sense for water to freeze up over Antarctica over time as a way to reduce sea level. Water freezing on top of water doesn’t affect water height. And water freezing on top of submerged land would just raise the water levels because it’s more voluminous. There needs to be a mechanism for the ice to accumulate on top of itself far above sea level for sea level to go down beyond just water freezing. As another poster explained, it’s snowfall accumulating semi-permanently in the same spots that moves water to these areas. Excuse my pedantry.
  - marginalia_nu 4y ago
    > There needs to be a mechanism for the ice to accumulate on top of itself far above sea level for sea level to go down beyond just water freezing. It's pretty common in the arctic regions that water forms ice crystals and falls out of the sky, landing on the ground. Snow, I believe they call it.
    - oneoff786 4y ago
      I literally acknowledged it was snow it the following sentence
  - zamfi 4y ago
    Not pedantic, I think people just didn't realize you were narrowly thinking of seawater freezing directly when you said "freezing wouldn't explain it".
tlb 4y ago
A lot of it is in the glaciers of Antartica, which cover the whole continent with around 1900m of ice. They weren't created from seawater freezing, but from snow getting packed down. But the water will go into the ocean if they melt.
- oneoff786 4y ago
  Ah ok that makes sense
  - dhzhzjsbevs 4y ago
    There isn't that much water on earth, this image does an amazing job of explaing the scale in the quickest way. It also sort of explains how easy it would be for earth's water to have come from asteroid impacts. https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/thumbnails/image/all-the-worlds-water.jpg https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/...
    - oneoff786 4y ago
      I’m not saying it’s wrong, but this graphic is very difficult for me to understand. Is there any geographical significance to the location of the water blobs? No, right? But they also don’t include saltwater which is most of it. Right?
      - dhzhzjsbevs 4y ago
        The big bubble is all water, frozen, sea, etc. The small bubble is all fresh (rain clouds etc), rivers, lakes. The smaller is lakes and rivers only. Here's an article showing comparisons to various moon ice. https://www.businessinsider.com/earth-water-ice-volume-versus-planets-moons-2018-5 https://www.businessinsider.com/earth-water-ice-volume-versu...
        oneoff786 4y ago
        It says liquid fresh water. I don’t think the big bubble includes the ocean.
masklinn 4y ago
Antartica is nearly 10% of total land (it's larger than europe, and half the surface of africa), and the ice depth averages more than 2km over land. It stores enough ice to raise sea levels by nearly 60m if / when that melts entirely. It currently loses more than 250Gt/year of ice, up from 40Gt during the 80s. But it holds an estimated 26500000Gt (26.5Pt) of ice.
DalasNoin 4y ago
Additionally to what others have mentioned, there is also the effect of the gravitational pull of ice shields. https://www.antarcticglaciers.org/question/antarctic-ice-sheet-gravitational-effect-sea-level/ https://www.antarcticglaciers.org/question/antarctic-ice-she... There was a discussion about this effect on hn years ago, the original link send to be dead now. But this is the thread on hn: https://news.ycombinator.com/item?id=23389690 https://news.ycombinator.com/item?id=23389690
m0llusk 4y ago
Rigorous explanation of bodies of water on the planet requires accounting for how water and ice deform the crust with their mass.
AbrahamParangi 4y ago
Glaciers also compress the earth underneath them, which rises back up when they melt in a process called isostatic rebound.
guerrilla 4y ago
> Is it lagged thermal expansion of the ocean water as it catches up to the air in heat? I've read that this will be the primary contributor. Might want to double check the answers you're getting here.

paganel 4y ago

The sea-levels have always fluctuated, no need to worry for Florida, if it happens, it happens. Also, no need to look 4 million years back for similar events, Doggerland [1] was still a thing with actual humans living on it only ~8,000 years ago. [1] https://en.wikipedia.org/wiki/Doggerland https://en.wikipedia.org/wiki/Doggerland

gadders 4y ago

>> During that time, sea levels were between 5 and 25 meters higher than today offsite, high enough to drown many of the world’s largest modern cities. That makes for a great headline, but a large part of the Netherlands' coastal areas are currently below sea level, and yet are not "drowned".

meatsauce 4y ago

It is clearly a real threat, that's why we have advocates for strict "climate regulations" buying multiple beach-front homes, their own islands, and private jets...

Yizahi 4y ago

Also it is probable that we will see a big extinction event even before +1m sea level mark. Imagine climate changes enough and staple crops start to fail en masse - wheat, rice etc. The hunger and rising costs will likely case a world war, or several.

macinjosh 4y ago

Hopefully, this will fix the US's coastal elites problem.

tim333 4y ago

Gonna take a while to rise 5 to 25 meters though. I think it's currently rising at like 0.8m per century.