[pmontra]

Your observation seems to make sense.

Intuitively, if we extract energy from the tides, tides will be less tall and the speed of water will be smaller. Ocean currents will slow down too.

What I don't know is, less friction on the seafloor means that we would actually make Earth slow down less faster than it would do if left alone?

[Interloper2099]

It’s a bit odd to extrapolate to this level. It’s like thinking, yes, I can set one tree on fire and release energy, but look how crazy it is if all the trees in North America burn at once!!

And currents are also affected by the rotation of the Earth, temp differences, and salinity differences so they might not change dramatically.