Scientists say in a new study that previous measurements of rising sea levels in the Northern Hemisphere in the 20th century were wrong—it's actually worse than we thought. They say we have been underestimating rising sea levels by 5 to 28 percent depending on the location in the world.
Crucial to the work was use of "ice melt fingerprints," a tool originally used in 2001 to help scientists determine why melting ice in say, Antarctica, is different from melting ice in Alaska. Using the fingerprints, scientists from NASA's Jet Propulsion Laboratory and the University of Hawai'i at Mānoa closely analyzed various ice centers of the planet for a look at how they've been melting. Greenland was estimated to have been wrong by 28 percent off, while the melting Alps were off by 5 percent. The variations in individual ice centers give scientists reason to ratchet up the amount sea levels on the whole actually rose in the 20th century.
"The investigation concludes that it is highly unlikely that global average sea level rose less than" 5.5 inches, the previously widely accepted number, says the discovery's lead author Phillip Thompson of the University of Hawai'i in a statement. The most likely amount was closer to 6.7 inches, they say.
"This is the frontier in sea level science right now," Thompson said. "We care about human timescale planning, decisions we're going to make in the next 10 to 20 or 30 years."