New research suggests the acceleration of global sea level rise from the 20th century to the last two decades has been more dramatic than was previously estimated by scientists.
Scientists found previous analyses of global sea-level rise had overestimated by as much as 30 percent, but the rate of sea-level change is increasing more quickly than we thought it was, Harvard University reported.
"Scientists now believe that most of the world's ice sheets and mountain glaciers are melting in response to rising temperatures," said Carling Hay, a post-doctoral fellow in the Department of Earth and Planetary Sciences (EPS). "Melting ice sheets cause global mean sea level to rise. Understanding this contribution is critical in a warming world."
Past estimates have concluded sea-level rise was at between 1.5 and 1.8 millimeters annually over the 20th century, but this new research suggests between 1901 and 1990 that number was closer to 1.2 millimeters per year. It is a widespread belief the global sea level has risen about three millimeters since measurement first began, suggesting acceleration is greater than previously estimated.
To make these improved estimates, the researchers used a new perspective. In the past, scientists have made their models by dividing the oceans up into sub-regions and using records from tide gauges, averaging the measurements together to determine approximate rise in each area.
"But these simple averages aren't representative of a true global mean value," Hay said. "Tide gauges are located along coasts, therefore large areas of the ocean aren't being included in these estimates. And the records that do exist commonly have large gaps."
The team looked at sea-level "fingerprints" predicted in computer simulations in sea-level records.
"Using a global set of observations, our goal has been to infer how individual ice sheets are contributing to global sea-level rise," said Eric Morrow, a recent PhD graduate of EPS.
They accounted for ice-age signals to determine how circulation patterns are changing and thermal expansion is contributing to these patterns. They looked at every available sea record possible and summed up the information, adding in the rate of change in oceans as a result of thermal exposure.
"We expected that we would estimate the individual contributions, and that their sum would get us back to the 1.5 to 1.8 mm per year that other people had predicted," Hay said. "But the math doesn't work out that way. Unfortunately, our new lower rate of sea-level rise prior to 1990 means that the sea-level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought."
The findings were published in a recent edition of the journal Nature.
