[melaniejs (OP)]

Aeddan wonders:

With all the dams in the world (I believe its a third of the rivers in the world), we have slowed down the speed the world spins around, only a tiny tiny tiny amount!

Will something similar happen with wind turbines?

What do you think?

[Halc]

With all the dams in the world (I believe its a third of the rivers in the world), we have slowed down the speed the world spins around, only a tiny tiny tiny amount!

Will something similar happen with wind turbines?

The supposed slowing of Earth's spin is theoretically due to the change in the rotational inertia of the planet by redistributing some of the mass of the water into the basins of these dams. That means that some dams must speed the rotation if this is true, which is questionable.

Nevertheless, windmills do not have any measurable effect on angular inertia of the planet since they don't work by hoarding all the air into a pressurized ball somewhere, so the argument put forth for the dams does not apply at all to the windmills.

[Aeddan]

Hmm  makes me wonder if we have moved enough mass (water,city building) to have an impact.

I suppose a better question would be
What theoretical impact could covering lets say 10% of the planets surface have?
Surly we would reduce global wind speeds. A wind farm by the coast would act as wave breakers.

[Halc]

Hmm  makes me wonder if we have moved enough mass (water,city building) to have an impact.

Well, by the logic they're using, if I clip my toenail and flick the clipping to my south, that will slow the Earth's spin, just not by much. Likewise, the windmill will affect spin mostly based on from which direction the materials used in it came.
My above logic is faulty, since the toenail claim assumes that the Earth's crust is not deformed by the redistribution of mass from my flicking it.  Scaled up to the dam, one can perhaps compute that the water held by it came from Greenland, which is surely losing water faster than their reservoir was filled, and that's a movement southward.  But in fact, Greenland losing mass causes earthquakes where the crust adjusts upward as the lower mass of Greenland buoys upward, and likewise the dam causes the crust to sink a bit in compensation, and all that adjustment cancels most of the effects to Earth's spin. I have no idea if the computations published took that into account.

I suppose a better question would be
What theoretical impact could covering lets say 10% of the planets surface have?
Surly we would reduce global wind speeds. A wind farm by the coast would act as wave breakers.

As for the spin of Earth, it would have pretty much zero impact since no redistribution of mass would likely result. The materials would be mined from here and there, and their placement would be here and there.  All cancels out as to changes in Earth's rotational inertia.

The impacts you mention would perhaps be perhaps measurable. We'd be mining a significant percentage of wind energy at the surface, which is turn is a tiny percentage of wind energy, For instance, the winds much higher up would be negligibly affected by the slight change in the friction index with the surface so I doubt the waves at the shore would be measurably less.
We've cut down far more trees than 10% of the Earth's surface, so the windmills would only replace part of the resistance to wind that used to exist.