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The Moon is moving away from the Earth at a rate of 38.08 ± 0.04 mm/year. This is caused by the tidal bulges being pushed ahead of the Moon as the Earth rotates and the landmasses interact with the bulges, pushing them ahead of the Moon. The gravitational interaction between the bulges and the Moon cause the Moon to move faster in its orbit than it should to remain in the same orbit, it moves away from the Earth as a result of this.

Now, sea level rise will affect the interaction of the tidal bulges with the coast lines. But it's not clear to me if the bulges will be pushed more ahead of the Moon causing the Moon to move away from the Earth at a faster rate or if the opposite will happen.

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  • $\begingroup$ I don't know the answer yet, but why did someone downvote it without showing reason? $\endgroup$ – curiousbrain Aug 17 '15 at 4:00
  • $\begingroup$ This is an interesting question, but probably a difficult one to answer. It's been suggested in the past that the movement of the continents has affected the rate of recession of the moon, mostly because vertically-oriented continents block the water from flowing with the tide. But the fluid mechanics are fiendishly hard to model. I would guess the effect of raised sea level would be extremely small, but I don't know. $\endgroup$ – Nathaniel Aug 17 '15 at 5:06
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As I understand it, a tide is basically a wave with a wave-length = 1/2 the circumference of the earth. The peak to trough is 1/4 the circumference, see pretty picture:

enter image description here

That's why lakes don't have measurable tides. The east to west distance isn't sufficient on lakes. Only oceans have significant tides. The Pacific is already large enough to have a complete peak to trough, so the increase in Pacific tide would be pretty small. The Atlantic and Indian ocean have, on average, a bit less than 1/4 latitudinal circumference, so those tides could increase, based on increased surface area, but the overall change would likely be quite small overall even with significant ocean rise. Based on the the IPCC prediction of about 2-3 feet of sea level rise by 2100 the effect would probably be teeny-tiny. Perhaps not even measurable, but the answer to your question is probably yes, just a very tiny bit.

That's kind of an intuitive answer. If someone wishes to tackle this mathematically, feel free.

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