Seeing that more and more dams are being built since they are environmentally friendly (more or less), I was wondering if the weight mass of the water from these dams might have an impact on the rotation and angle of the earth? And if so, how would it affect the rotation and climate longterm?
In: Earth Science
Yes; any time you do something to transfer mass to a higher elevation, you are inherently going to change the rate of Earth’s rotation due to the conservation of angular momentum. Simply walking uphill is sufficient.
The trick with the dams (and particularly the Three Gorges Dam, which this factoid is about) is that the amount of water held up at higher altitudes is so massive that it actually produces a *measurable* change, although it’s still relatively insignificant.
To start with there are things that have a way bigger impact on the Earths rotation then humans building dams. Glaciers are melting and entire tectonic plates are moving in all directions. Some of these are big and sudden enough that we can actually measure them. However we have yet to be able to measure the impact any dam have on the Earths rotation, at least not been able to distinguish it from the background noise from all the other things changing the rotation of the Earth.
That being said storing vast quantities of water higher in the mountains does theoretically slow down the rotation of the Earth by a tiny bit. It can also have a small impact on the tilt but this is similarly very little and impossible to measure.
Not enough weight. A lot of images of the Earth and it’s core are misleading because of the scale differences between the crust and the mantle and core. Think of a peach. The skin would be the crust of the Earth. All of the water and rock that supports life is in that super thin part. Also the magma and stuff that make up the mantle and cores is significantly denser and more heavy than water.
So the collection of mass does effect Earths rotation. However this effect is absolutely tiny, and completely inconsequential in the grand scheme of things, there are many factors that outweigh water dams
Of course.
It’s a pretty famous fun fact that the biggest dam in the world, the Three Gorges Dam in China increased the length of a day across the world by 0.06 microseconds. The primary reason for this was that water that would usually end up being stored in the oceans was stored at a higher elevation, increasing the earth’s moment of inertia a little bit.
0.06 microseconds isn’t at all significant in all other respects though, no climate impact expected.
The water that exists behind dams exists even if the dams are not there. All water on earth has been here from the beginning and the amount never changes (other than the tiny tiny fraction that is separated into hydrogen and oxygen by human intervention). Water just moves around.
I did actually see a program on the science channel about the excessive use of cement in China. They said the population growth and building with concrete has increased the weight and the only answer would be building opposite China on the globe to balance the excessive weight. They even have a sand shortage and the mob is into sand theft.
Dams slow the earth’s rotation by fractions of microseconds. We are solving the problem by melting glaciers, which has the opposite effect.
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