Gravity is not the same around the Globe, there is something called the Geoid <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Geoid" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Geoid</a>.<p>Also, sea level is determined by a number of factors including astronomical and predictable, like moon, sun and other planets gravity influence, or random meteorological events like winds, low or high pressure systems and land mass configuration. All these contribute to the tide cycle and the sea level anywhere in the globle.<p>For example, there are places in the world with huge tide amplitudes like 12 m or so and other with no tides at all (excluding meteorological events).<p>The problem is the &quot;mean sea level rise&quot;. The &quot;mean sea level&quot; is usually determined by and average of at least 19 years of measurements of the sea level, which is approximately the time it takes to complete a full moon cycle.