Editor’s Note—This article is one in a series about how NASA and other science institutions measure and monitor sea level rise. They estimate that over the past 140 years, global mean sea level has risen 21 to 24 centimeters (8 to 9 inches). Find more stories about our changing oceans and coasts in Earth Observatory’s sea level rise collection. Looking for data related to sea level rise? The Sea Level Change Data Pathfinder on NASA’s Earthdata site highlights tools used by researchers to study ocean altimetry, including the Integrated Multi-Mission Ocean Altimeter Data for Climate Research.