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?
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.
By far most of the water is in the oceans, which have an average depth of 3688m. 2% of the water is currently frozen, so one can easily estimate how much would the sea level raise, had it all melt.
EDIT: Corrected km to meters, as comment below points out.
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?
It's not the volume of the ocean that matters for sea level rise but the surface area, right? Ocean surface area is 140M square miles, so 6.4M cubic miles of water would naively be like a 241 foot rise -- each cubic mile gets split into 140/6.4 slices.
I'm a bit stupid, but I understand if we are dropping 6.4M cubic miles from space, there will be an increase in water level, but if the 6.4M cubic miles of water was already present in the system, just frozen, how does it increase the total sea level? There is no net change in volume right?
Sea ice floats in the sea. When melted ... it's still floating in the sea, as water. There's no net sea-level change, at least not from contributed ice.[1]
Land ice sits on land. When it melts, most of it flows to the sea.[2] That increases the total amount of water in the oceans, and hence, sea level. The total rise if all Antarctic and Greenland ice melted would be about 60-70m (200-230ft).[3]
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Notes:
1. There are other effects, including thermal expansion (water expands slightly as it warms), and centripetal effects (water can flow more than continental crust does, and would spread out slightly more at the equator than the poles with more liquid water in the oceans). Those effects are comparatively small, though not fully negligible.
2. The exception would be enteric basins which have no outlet to the oceans, in which case melted ice flowing into these would form lakes. Examples of enteric basins include the Great Salt Lake and surrounding former Lake Bonneville, the Dead Sea, and Death Valley. Note that as glaciers melt, there's a rebound effect in continental crust, and regions presently below sea level or which would otherwise form enteric basins might not after that rebound effect is taken into account.
Additionally the crust is elastic and will move around a bit (especially lifting) with the ice weight off. This is still occurring in many places that were glaciated previously.
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.
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.
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".
