I’m working (very slowly) on a SF story set in the not too distant future, and I want a global catastrophe to get out of having to correctly predict the next 100-200 years of climate change.
What I’d like is just 10-50 meters of sea level rise due to something outside our climate models, like a comet impact on Antarctica. But I’d like the size and other consequences to be realistic and preferably not be extinction level, although I’m fine with some super tsunamis killing hundreds of millions.
Does that Goldilocks spot exist?
I could have posted this in GQ, but I based on the purpose and the vagueness of the question I put it here instead.
One thing that’ll help you is that atmospheric effects tend not to cross the Equator. So debris from your Antarctic impact might cause an “asteroid winter” in the Southern Hemisphere, but not the Northern.
That said, 10-50 meters of sea level rise is a heck of a lot. I don’t think you could get that even by dumping all of the land-based ice into the ocean.
If every bit of ice melted - Antarctica, Greenland, mountain glaciers, etc. - sea levels would rise ~70 m. Antarctica alone would be about 60 m. So it’s within the realm of possibilities.
The volume of the moon is about 1.8% that of Earth. Just have the moon smash into the Arctic Ocean and the resulting displacement should take care of at least low-lying coastal areas.
OK, so you’re still talking about knocking at least a sixth of the Antarctic land ice into the ocean. That’s going to take a very, very big impact, big enough that the effects probably would be significant even in the other hemisphere.
Yeah, anything that melts that much ice is going to be a planet killer. Bigger than the biggest thing to hit the Earth since the Late Heavy Bombardment.
If my calculations are right, the energy released by the Chicxulub meteor would theoretically be more than enough to melt that volume of ice by a factor of 5-10. A lot of the energy would go toward things other than melting ice, so you’re probably looking at something comparable. Not exactly a planet killer, but big enough to affect both hemispheres.
Would it have to melt it completely to cause it to float to the ocean and thus raise the sea level regardless? Would simply heating up most of it lubricate the ice flows to make them slide off a lot faster? And could that also be achieved by a combination of melting the ice shelves and eliminating their checks on ice flow, and raising the sea level a little bit by melting and thus exposing more of the flows to the water?
Probably not completely scientifically defensible, but how about a sudden massive upsurge of volcanic action in Antartica? A modern-day Deccan Traps (but much smaller and quicker). All the heat melts 20m-of-seal-level worth of ice, but wouldn’t directly catastrophically impact global weather patterns.
[And don’t tell me that the geology of Antarctica makes this impossible. Nothing is impossible if you can dream it!]
It’s not that the geology of Antarctica makes it impossible, it’s that to get a Deccan Traps-type flood basalt, it’s looking increasingly likely that you need a Chicxulub-level impact on the antipode i.e. the Arctic. Not so great for non-extinction-level event, is it? And certainly not just confined to the Southern Hemisphere.
You could use some experiment made to tap into deep water or geothermal energy that causes some unforeseen consequences. Or if looking for a more natural cause, a rising of the Pacific Plate.
What if Alpha Crucis went supernova? How bright would it shine? Could it theoretically melt some appreciable fraction of the Antarctic glacier in the few days or weeks it lasted, without cooking the entire hemisphere?
To me that is not much better then “the neutrinos are mutating”. And plate tectonics is outside the timescale I want to work on.
I may just have to accept sea level rise of that magnitude is not plausible. The impact killing a lot of people and making our current climate projects irrelevant will work just fine for my purposes.
Well a 200m impact of porous rock asteroid into sedimentary rock produces a crater ~400m deep. I’d imagine doing the same into the Pine Island glaciar would both immediately release a large amount or ice and dump water vapour into the atmosphere. However, there is apparently volcanic activity under the glacier. A sudden impact and release of 100s of meters of ice might induce a massive outflow of lava. I suppose you could say it triggers a progressive loss of the entire West Antarctic ice sheet over a few years.
The impact is “small” enough to not trigger global notice but the resulting melt might be
Look at the most recent data about how Greenland is melting. The original model was that the ice would just gradually melt “all over”. What appears to actually be happening (at least, from my naive and not really well researched understanding) is that the ice is melting and forming small ponds, the water absorbs more solar energy (since it is darker than ice) and warms up, tunnels to the bottom of the ice and is pushed along the bottom of the ice and the land. This acts as a lubricant and speeds up the movement of the ice towards the ocean.
Your story could reasonably postulate something along these lines (though faster or more intense than in reality) for either or both Greenland or the Antarctic.
A “dirty” comet could spread soot-ish material over a large area and thereby accelerate melting quite a bit. But it would still take a while.
Well, how about magnets. They’re magic, right? Earth’s dipole magnetic field decreases dramatically. Now a lot of particles start hitting the poles. Mumble, mumble. Ice melts.
Googling: Well, there’s this paper that suggests the location of ice caps can get quite variable when the magnetic field weakens. So the regular ice caps melt and new ones start building up. High water ensues for a while.
Note that there was a brief magnetic reversal 41k years ago that lasted about 440 years. But it apparently didn’t make a big climate impact. (Other stuff happening around then did. Super-volcanoes are no fun at all.) And if it did, still we’re talking about centuries.
How about a small rogue star passing thru the Solar System? One of those magic things like Nibiru that either can’t be seen at all or are magically invisible since they are coming in from over the South Pole.
(Hey, Neal Stephenson wrote a whole book based on the premise that the Moon tore itself apart for no apparent reason.)
The Antarctic ice cap has been around for tens of millions of years. Polar reversals happen around 4 or 5 times per million years on average.
The “small rogue star” idea is pure Velikovskism. (Note–not a compliment.)
To raise the sea level 10 m, you need to melt 3.6x10[sup]19[/sup] kg of ice. That requires about 1x10[sup]25[/sup] Joules of energy to go from 0° C ice to 0° C water.
Ice is around 0.02% deuterium. If the deuterium in 6x10[sup]13[/sup] kg of ice were to somehow undergo fusion, it would provide the energy needed to melt enough ice to raise levels 10 m. In other words, you’d need about 1.7x10[sup]-6[/sup], or 0.00017% of the deuterium in the ice to undergo fusion.
So easy-peasy. The meteor somehow compresses the atoms enough to start a runaway fusion reaction. Or the rogue scientist at the McMurdo research station has a breakthrough in his cold fusion experiments, but it escapes containment. It happened to Dr. Octavius, so it’s not that far-fetched.
