It would have been easier to understand had they simply stated that liquids apply resistance to the rotational force. While I am grounded in Earth
Science I never ever got beyond algebra, so physics are pretty much an unknown quantity to me. Thanks for the clarification.
It doesn't have anything to do with liquids applying some kind of resistance or drag, it just has to do with transporting mass away from the Earth's
axis of rotation (the poles) and conserving momentum in that process.
Think about it in terms of torque: if you want to change the tire on your car, it's a lot easier to do with a nice long tire iron, because it allows
you to leverage the force you apply from a distance. Now imagine choking your hands up on that tire iron closer to the axis of rotation of the nut:
you need to apply more force to get the same torque, right?
In this case, it's kind of analogous, but inverted. When you have a bunch of mass at the poles, near the axis of rotation, you can think of it like it
has a certain amount of torque as it's spinning. Now if you move that mass away from the axis of rotation (by melting it and letting it flow out
towards the equator), you magically added more torque. But you didn't actually add any extra energy into the system, you just rearranged some stuff
The laws of physics say momentum must be conserved – so what this effectively means is the Earth must therefore spin slower to maintain the same
“torque” as it had before.
For those people who seem to find this principle so incredulous, or secretly suspect it's part of “the global warming agenda” somehow, figures
skaters use it all the time:
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