[rwh86]

Part of the reason is gravitational effects. When a large amount of ice melts, the Earth's gravity is shifted away from that region.

This gives you a sense of the absolutely huge amount of ice we're talking about. For example, if the West Antarctic Ice Shelf collapses we'll see about 10 metres of sea level rise, but mostly in the northern hemisphere. To underline just how much ice this is, this effect will slowly be counteracted as the ground below slowly rebounds (as it no longer has a huge amount of ice crushing it down from above).

[unavoidable]

Potentially related is the centrifugal effect - the Earth bulges at the equator slightly because of spin. Logically, melted ice would tend to cause water to "rise" more at the equators (further from the ice caps) than near the poles.

[droopyEyelids]

...and that would slow the rotation of the earth.

I'd love to see a calculation of how much ice would have to melt for us to add another leap second.

Or to back it up, how would timekeeping bodies deal with that?

Would we actually remove a second because there would technically be less "time" (measured in days, meaning axial revolutions of the Earth) per year?

[Johnythree]

It's been done. I can't find the reference, but apparently the extreme accuracy of atomic clocks has proven that the mass of water moving from the poles to the equator has slowed the earth's rotation as predicted.

[leephillips]

There's a reference and some discussion at http://arstechnica.com/science/2016/04/the-leap-second-becau...

[elorant]

This makes me wonder. Could it affect seismic activity?

[deftnerd]

Indeed it can!

"rapid deglaciation promotes earthquakes ... rebound stress that is available to trigger earthquakes today is of the order of 1 MPa. This stress level is not large enough to rupture intact rocks but is large enough to reactivate pre-existing faults that are close to failure."

- https://en.wikipedia.org/wiki/Post-glacial_rebound#State_of_...

[spdionis]

I wonder if this is related to the streak of big earthquakes happening currently in Italy.