What is the definition sea level rise?

Answer 1

Sea level rises when the mean high tide level increases year after year. (If you took the level of the high tide for every high tide for every day for the last 10 years and compared the average for each year, you could come close to the comparison. To get the mean instead of the average, you would to multiply them out and then take the root. You would probably come within a few millimeters of the average.)