Waterworld and Other Worst Case Scenarios

I learned some interesting things in the aftermath of the Rule of Cool post. In particular, did you know the underwater future of Waterworld can never happen? Shocking, considering one of the main messages of that (stupidly expensive) film was: "If we don't take better care of our planet, this is what will happen."

In order for the world to be entirely, or even mostly, covered with water, sea levels would have to rise over 8 kilometers.* But if all of the ice in the entire world melted, sea levels would only rise about 80 m. At worst, the Earth would go from this:

To this:**

Interesting. Devastating. But not world-destroying, which, really, is what I was hoping for.

So what's an inspiring author (who wants a world covered entirely in water) to do? Here are some possibilities:

• Fantasy World. It's not Earth, so who's to say how much ice may or may not have melted to drown the civilization underneath?
• Ice Meteor. An asteroid made entirely of frozen water crashes into the planet, and then melts. Such a meteor would have to have a radius of 900 km (about a seventh the size of the moon) to contain enough water, and that kind of meteor collision would have other consequences. But we're talking thousands of years in the future anyway, right? A crater the size of Australia wouldn't be a big deal by then.
• Shrink the Earth. Theoretically, if enough internal pressure were released such that the Earth shrank, the existing water would be enough to cover the globe. Of course the very act of releasing that pressure, combined with whatever catastrophic event triggered the release, would probably wipe out life on Earth anyway.
• Science Is Wrong. This is my favorite one to fall back to. Science is not often wrong, but considering how much we don't know and those times science has been wrong before, it's always possible. Maybe the Earth is filled with water that comes to the surface. Maybe there's more ice underneath Antarctica than we thought. Who knows?

I'm not saying I'm going to do any of these to my world, but it's fun to think of the possibilities. Speaking of which, this list of risks to civilization is all kinds of awesome, especially for those of you considering post-apocalyptic scenarios that are scientifically possible.


* The metric system is just better, sorry. Do your own conversions.

** The map isn't entirely accurate. The program that generated it just uses altitudes, so places like the Caspian Sea wouldn't actually get bigger like they do in the picture.