Physicists say cosmic rays affect the length of day

I’d like to add a warning to this (along the lines of the Journalism Warning Labels by Tom Scott): Article title implies much more certainty than the article; the article is more restrained than the title would indicate, and the paper (at least the abstract) even more so. Changing the angular momentum of the earth would affect the moment of inertia, but the correlation here is with the sunspot cycle — the connection to cosmic rays is more tenuous.

The abstract actually says

We conclude that variations in mean zonal winds are modulated by the solar activity cycle through variations in irradiance, solar wind or cosmic ray intensity.

I’ll have to consult my local experts on earth rotation and get their opinion on this.