Global Sea-Level Rise is Accelerating Faster Than Previously Estimated

Global sea levels continue to rise. In fact, there's been an acceleration in this rise from the 20^th century to the last two decades and now, scientists have found this increase has been far larger than previously estimated.

Previous estimates of sea-level rise have placed levels between 1.5 and 1.8 millimeters annually over the 20^th century. Yet now, scientists suggest that from 1901 until 1990, this figure was closer to 1.2 millimeters per year. However, everyone agrees that since then, global sea levels have risen about 3 millimeters annually. This, in turn, shows that there's a marked acceleration in global sea-level rise.

"What this paper shows is that sea-level acceleration over the past century has been greater than has been estimated by others," said Eric Morrow, one of the researchers, in a news release. "It's a larger problem than we initially thought."

Usually, researchers estimate sea-level rise by dividing the world's oceans into sub-regions, and then gathering records from tide gauges. Using records containing the most complete data, scientists then average them together to create estimates of sea level for each region, and then average these rates together to create a global estimate.

"But these simple averages aren't representative of the true global mean value," said Carling Hay, one of the researchers. "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."

In order to get past these issues, the scientists aimed at modeling the physics that underpin sea-level "fingerprints." Using a global set of observations, they created a model that accounted for ice age signals and how ocean circulation patterns are changing and how thermal expansion is contributing to both regional patterns and the global mean. In the end, they found that estimates of sea-level ris over most of the 20^th century were too high. Instead, there's been an acceleration in recent years.

"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," said Hay. "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 are published in the journal Nature.

For more great science stories and general news, please visit our sister site, Headlines and Global News (HNGN).