# How much do ocean currents alone slow Earth's rotation?

Tidal friction is commonly spoken of as the reason for the slowing of Earth's rotation. What if the moon didn't exist? We would still have ocean currents and wind due to the Coriolis effect and the resulting friction certainly must be significant. Is it possible to quantify the contribution of each source of friction?

## 2 Answers

Tidal friction is referring to the entire planet changing shape, not just the meager 1 TW of wind driven friction (https://earthobservatory.nasa.gov/images/654/dissipation-of-tidal-energy).

The rotational energy of the Earth is about $$2\times 10^{29}\,$$J, so a terawatt is tiny; moreover, that is dissipating wind energy, provided by the Sun continuously.

• I was referring more to the friction due to ocean currents. Tidal motion is only one component of the overall ocean water movement, all of which causes friction. And now that you mention it, is is possible also to parse out ocean tidal friction from the flexure of the planet as a whole? – Scott Ewart Jul 21 at 21:09

As explained in Wikipedia,

the tidal bulge is pushed ahead by Earth's rotation. This offset bulge exerts a net torque on the Moon, boosting it while slowing Earth's rotation. ... energy and angular momentum are transferred from the rotation of Earth to the orbital motion of the Moon

Without the Moon there can be no torque or angular momentum transfer. (Ignoring the Sun, which also has a tidal effect about 20% of that of the Moon.)