How far would average sea level rise from a 25% increase in total ocean volume? What amount of average sea level rise (in meters above 2020 levels) would be associated with a 25% increase in total ocean volume?
The reason I ask is because of this study that indicates Earth has lost appx. 25% of its water to space via methanogenesis process splitting the hydrogen molecules off of H2O, then the hydrogen escaping into space.
Regardless of whether this study is accurate, it has made me wonder what the Earth would have looked like with 25% more water. How much of a sea-level rise would that represent?
Obviously this would be a fairly complex equation since terrain is not uniform in contour. Less land is displacing every new layer of water you ade, compared to a lower layer of water. So (in addition to any changes from the radius of the sphere increasing) there should be a decreasing amount of average sea level increase per unit of water volume, until all land is covered.
I've looked to FloodMap.net for an answer, but they don't seem to provide the amount of water volume, at least, not to free users.
Curious if there is an open source code library that can handle this kind of calculation, or if there is a simple formula that would get us within a reasonable margin of error (i.e. it would provide a sea level that could be plugged into FloodMap to show what shorelines would look like under 25% more water, given today's continents).
It is not hard to do this calculation if you have global topography. Using a version with $\frac{1}{6}$- degree resolution and a sea level rise of 1027 m, the result is @Erik's value of 445 million cubic km. Here's the bit of MATLAB code:
H = 1027;   % sea level rise (m)
topo(topo&lt;0) = 0;   % change all ocean depths to zero
topo(topo&gt;H) = H;   % level off all land at a height of H
topo = topo.*(cosd(lat')*ones(1,2160)); % land volume per grid cell
land = sum(topo(:))*18.5^2/1000; % total land volume in km^3
water = sum(cosd(lat))*2160*18.5^2*H/1000 - land; % added water volume

Greenland and Antarctica fare ok, but Europe and Australia are basically gone: