Someone recently pointed out that the surface of the Earth is not flat. Also the surface of the ocean is not flat. Sea level along the West Coast is higher than along the East Coast, science says, by about 20 cm, depending on local conditions.
Why does that matter?
Mt. Whitney in California is listed as having an elevation of 14,505 feet above sea level. Should that be 14,505 feet plus 20 cm?
Perhaps not. I don't know how mountains are measured. There is something called "mean sea level," a useful average. Meanwhile the many sea levels keep rising.
And the seas are rising steadily. As the planet warms, will Whitney lose elevation?