This graph shows the change in sea level since 1880 with a rise in sea level of about 18.5 centimeters during the 20th Century. The data used to make this graph come from 23 tide gauge stations that are on land that is geologically stable. The tide gauge data for each year was averaged. The thick black line is an average that shows the trend.
Courtesy of Robert A. Rohde/Global Warming Art Project