In Which I Disagree with XKCD
The latest XKCD What-If discusses how to spin up the Earth:
That isn't the only solution.
If we wanted to get rid of leap seconds, we’d need to keep the Earth spinning at a more constant rate. This means speeding up the Earth and shortening each day by about 0.8 milliseconds.
In the end, there’s only one solution: Hitting the Earth with asteroids.
The Earth is slowing down as a result of tidal drag. As is well known, the rate at which the Earth is slowing can increase as a result of extracting energy from the tides (see The Last Judgment by J. B. S. Haldane). In the other direction, the slowing can decline or even reverse if energy is put into the tides. This will require enormous amounts of power … but far less than that present in the sunlight hitting the Earth.
The basic physics of this is simple enough. Pump enough water around the Earth's oceans to cause the tidal bulge to be ahead of the Moon instead of behind. The trivial engineering details can be left as an exercise for the reader.
In other news, I'm celebrating Isaac Asimov's birthday by posting something extremely nerdy on my blog.