# If the moon wasn't receding from Earth, what would be the impact on the weather and tides?

Moon is slowly receding from Earth, which means that after its formation it was much closer to the Earth than now. How would weather look like if it wasn't receding at it would be now as close as at the beginning?

Surely, the tides would be much higher, but how big would be the difference? I've also watched document stating that the hurricanes would be much stronger. Was there any simulations, how much stronger they would be?

Tidal amplitudes roughly scale inversely with distance to the fourth power (this comes from the tidal force scaling as $r^{-3}$ and the Earth's potential scaling as $r^{-1}$). At its formation, the Moon was approximately seven Earth radii away from Earth, or about ten times closer than it is today. Thus, the amplitude of the tide on Earth would have been approximately $10^4$ times larger than it is today. As the typical ocean tide is 1 m, this means ocean tides would have been 10 km high on Earth! Of course, the collision that formed the moon turned the surface of the Earth molten, so really we're talking about a 10 km tall molten tide, which is far less scary...(kidding).

Imagine all the noise the ocean makes when it crashes on a beach. That noise requires energy to produce, and is partially driven by the action of raising/lowering the ocean via tides. Now imagine how loud a 10 km wave crashing would be. This is why the Moon receded quite quickly from the Earth shortly after forming, the tides enable the dissipation of a lot of orbital energy.

As for the hypothetical effect of this supertide on the present-day Earth's weather, the Earth's troposphere (which contains pretty much all of the Earth's weather phenomena) extends 10–20 km from the ground. Considering the height of the ground is changing by a similar amount due to the tide, I would imagine the effects on the weather would be quite dramatic.

• 10km tide? It's hard to imagine, wouldn't such tide be drawn by moon gravity deep into land? Sep 30, 2013 at 18:29
• The energy of the sound of waves crashing comes from the moon. I am going to mention this to my daughters next time we are at the beach with the moon visible. Thank you for this wonderful insight. Dec 20, 2014 at 10:02
• @dotancohen, most of the wave energy comes from the Sun: heat from the Sun warms air, which causes winds, which drives the waves across the ocean. It's the energy of the tides which mostly comes from the Moon, and isn't as dramatic these days. (Well, outside of places like the Bay of Fundy.)
– Mark
Dec 27, 2018 at 10:06