EclecticLip

The Wilkins ice shelf in Antarctica is melting.

The good news: it won’t raise sea levels because it’s sea ice.

The bad news: it’s even further evidence that global warming is getting worse, even faster than the worst-case IPCC forecasts.

There was a related story in the Globe and Mail recently, noting that sea level rise from melting ice wouldn’t be equal, everywhere.  Basically, when the West Antarctic ice sheet melts — perhaps decades from now, hopefully centuries from now, and even more hopefully never — sea levels will eventually rise more in the rich global North than in the poorer global South.  This is because the current ice sheet is big enough to exert a measurable gravitational pull on the seas.  

Note: the south pole’s ice has a very small effect compared to the earth’s equatorial bulge (our planet’s equivalent of “abdominal belly fat”) which is responsible for sea levels at the equator being much higher than those at the poles.  As the aforementioned link notes, Ecuador’s Mount Chimborazo (elevation 6268 m) is actually farther from the center of the earth than Mount Everest (elevation 8848 m)… because sea level in Ecuador is higher than sea level in… well, wherever sea level relative to Everest is measured from.   

But I digress…

When the Antarctic ice sheet melts, there’ll be much less mass at the pole; water will feel less of a “pull” towards it.  This will cause sea levels in the far south to tend to drop, which will offset the increase in sea levels due to landlocked ice melting into sea water.  (A nice explanation from New Scientist is here.)  The result is that in the looooong run, sea levels in the far global south may not change appreciably, while sea levels in the north rise by tens of metres.  Fun stuff.

It’s important to note, however, that it will take awhile for that water to leave the “Southern ocean” due to the nature of the currents there, as noted in this New Scientist article*.  And it bears repeating that unlike the Wilkins ice shelf, the West Antarctic isn’t considered likely to melt for… well, hopefully a decade at least.

* basically, researchers used models of ice-melt from Greenland to show that if its ice were to disappear, the water would dawdle in the Atlantic for fifty years before appreciably reaching the Indian Ocean, and then only drift into the Pacific about thirty years after that.

So… while the end impact of the West Antarctic ice shelf melting might be unaffected sea levels in the global south… it would be a steady-state fallacy to think there wouldn’t be any effect in the middling decades, before that water has “emigrated” to the rest of the world.